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Informacje o czasopiśmie
Format
Czasopismo
eISSN
1899-7562
Pierwsze wydanie
13 Jan 2009
Częstotliwość wydawania
5 razy w roku
Języki
Angielski

Wyszukiwanie

Tom 68 (2019): Zeszyt 1 (August 2019)

Informacje o czasopiśmie
Format
Czasopismo
eISSN
1899-7562
Pierwsze wydanie
13 Jan 2009
Częstotliwość wydawania
5 razy w roku
Języki
Angielski

Wyszukiwanie

20 Artykułów

Strength & Power

Otwarty dostęp

Rest Redistribution Functions as a Free and Ad-Hoc Equivalent to Commonly Used Velocity-Based Training Thresholds During Clean Pulls at Different Loads

Data publikacji: 21 Aug 2019
Zakres stron: 5 - 16

Abstrakt

Abstract

This study determined whether redistributing total rest time into shorter, but more frequent rest periods could maintain velocity and power output during 3 traditional sets of 6 clean pulls using 80% (TS80), 100% (TS100) and 120% (TS120) of power clean 1RM with 180 seconds of inter-set rest and during 3 “rest redistribution” protocols of 9 sets of 2 clean pulls using 80% (RR80), 100% (RR100) and 120% (RR120) of power clean 1RM with 45 seconds of inter-set rest. The total number of repetitions performed above 10 and 20% velocity loss thresholds, mean and peak velocity maintenance (the average of all 18 repetitions relative to the best repetition; MVM, PVM), and decline (the worst repetition relative to the best repetition; MVD, PVD) were calculated. For MVM, PVM, MVD, and PVD, there were small-to-moderate effect sizes in favour of RR80 and RR100, but large effects favouring RR120, compared to their respective TS protocols. The number of repetitions within a 20% velocity loss threshold was 17.7 ± 0.6 during RR and 16.5 ± 2.4 during TS (effect size 0.69); and the number of repetitions within a 10% velocity loss threshold was about 13.1 ± 3.7 during RR and 10.7 ± 3.6 during TS (effect size 0.66). Therefore, RR generally allowed for a better overall maintenance of velocity and power, especially at heavy loads. Coaches who wish to implement velocity-based training, but who do not wish to purchase or use the associated equipment, may consider rest-redistribution to encourage similar training stimuli.

Key words

  • power
  • cluster sets
  • fatigue
  • weightlifting
  • resistance training
  • traditional sets
Otwarty dostęp

Genetic Markers Associated with Power Athlete Status

Data publikacji: 21 Aug 2019
Zakres stron: 17 - 36

Abstrakt

Abstract

Athletic performance is a multifactorial phenotype influenced by environmental factors as well as multiple genetic variants. Different genetic elements have a great influence over components of athletic performance such as endurance, strength, power, flexibility, neuromuscular coordination, psychological traits and other features important in sport. The current literature review revealed that to date more than 69 genetic markers have been associated with power athlete status. For the purpose of the present review we have assigned all genetic markers described with reference to power athletes status to seven main groups: 1) markers associated with skeletal muscle structure and function, 2) markers involved in the inflammatory and repair reactions in skeletal muscle during and after exercise, 3) markers involved in blood pressure control, 4) markers involved in modulation of oxygen uptake, 5) markers that are regulators of energy metabolism and cellular homeostasis, 6) markers encoding factors that control gene expression by rearrangement of chromatin fibers and mRNA stability, and 7) markers modulating cellular signaling pathways. All data presented in the current review provide evidence to support the notion that human physical performance may be influenced by genetic profiles, especially in power sports. The current studies still represent only the first steps towards a better understanding of the genetic factors that influence power-related traits, so further analyses are necessary before implementation of research findings into practice.

Key words

  • genetic markers
  • genetic polymorphism
  • power athletes
  • strength athletes
  • athletes status
Otwarty dostęp

Caffeine Supplementation for Powerlifting Competitions: an Evidence-Based Approach

Data publikacji: 21 Aug 2019
Zakres stron: 37 - 48

Abstrakt

Abstract

In this paper, we review the effects of caffeine on muscle strength and provide suggestions for caffeine supplementation in powerlifting competitions. The currently available studies indicate that caffeine ingestion may enhance strength in two powerlifting competition events, the squat and the bench press. For the deadlift, the same might be expected even though studies directly using this event are lacking. Optimal doses of caffeine are likely in the range from 2 to 6 mg·kg−1, and are highly individual. When using caffeine-containing capsules, 60 minutes pre-exercise seems to be a good timing of caffeine consumption. For other sources such as caffeinated chewing gum, a shorter period (5 to 10 min) from consumption to the start of the exercise seems to be effective. For shorter duration powerlifting competitions (e.g., 2 hours), one pre-competition dose of caffeine could be sufficient for acute performance-enhancing effects that might be maintained across all three events. For longer duration competitions (with longer rest periods between one repetition maximum attempts), there might be a benefit to repeated dosing with caffeine; for example, ingesting smaller doses of caffeine before each attempt or event. During training, powerlifters may consider ingesting caffeine only before the training sessions with the highest intensity. This approach might eliminate the attenuation of caffeine’s effects associated with chronic caffeine ingestion and would help in maximizing performance benefits from acute caffeine ingestion at the competition. Nonetheless, withdrawal from caffeine (e.g., no caffeine intake seven days before competition) does not seem necessary and may have some indirect negative effects.

Key words

  • ergogenic
  • performance-enhancing
  • supplements
  • strength sports
  • 1RM
Otwarty dostęp

The Influence of Grip Width on Training Volume During the Bench Press with Different Movement Tempos

Data publikacji: 21 Aug 2019
Zakres stron: 49 - 57

Abstrakt

Abstract

The aim of the study was to determine the effect of the wide-grip bench press (WGBP) and the close-grip bench press (CGBP) on the number of performed repetitions (REPs) and time under tension (TUT) using a variable tempo of movement. Twenty (20) women experienced in resistance training were enrolled in the study (1RM-CGBP = 55.2 ± 9.5 kg; 1RM-WGBP = 52.7 ± 8.5 kg). Participants performed 5 sets of the BP with a maximal number of REPs at 70%1RM. Different tempos of movement, i.e., slow (6/0/X/0) and fast (2/0/X/0), and grip widths, i.e., the CGBP and the WGBP, were employed. The following variables were registered: maximal number of repetitions in every set (REPSet1-5), total number of repetitions performed in 5 sets (TREP), maximal time under tension in every set (TUTSet1-5) and total time under tension in 5 sets (TTUT). The two-way ANOVA revealed statistically significant differences between the WGBPFAST and the WGBPSLOW in TUTSet1-5 (p < 0.05) and TTUT (p < 0.01), as well as between the CGBPFAST and the CGBPSLOW in TUTSet1-5 (p < 0.01) and TTUT (p < 0.01). Significant differences between the WGBPFAST and the WGBPSLOW were also observed in REPSet1-5 (p < 0.01) and TREP (p < 0.01) as well as between the CGBPFAST and the CGBPSLOW in REPSet1-5 (p < 0.01) and TREP (p < 0.01). No significant differences between the WGBPSLOW and the CGBPSLOW nor the WGBPFAST and the CGBPFAST were found. The study demonstrates that the tempo of movement, regardless of the width grip, has a significant effect on the volume of effort in resistance training.

Key words

  • resistance exercise
  • repetition
  • time under tension
  • close-grip
  • wide-grip
Otwarty dostęp

A Comparison Between The Recovery Responses Following an Eccentrically Loaded Bench Press Protocol Vs. Regular Loading in Highly Trained Men

Data publikacji: 21 Aug 2019
Zakres stron: 59 - 67

Abstrakt

Abstract

The purpose of this study was to compare the physiological responses of a single bout of an eccentric accentuated bench press protocol (120% of 1RM in the eccentric phase/80% in the concentric phase; [120/80]) versus a regular high-intensity exercise protocol (80%/80%; [80/80]) in resistance-trained men. Eleven men (age = 25.6 ± 3.9 y; body mass = 84.6 ± 11.2 kg; body height = 176.4 ± 3.9 cm) with 6.3 ± 3.4 y of resistance training experience performed each protocol in counterbalanced, randomized order. Isometric, isokinetic and ballistic tests were performed at the bench press (IBPF, ISOK and BTP, respectively) at baseline (BL), 15-min (15P), 24-h (24P), and 48-h (48P) post-exercise for each testing session. In addition, muscle thickness of the pectoralis major (PecMT) was measured at the same timepoints via ultrasound. Significantly greater reductions in BTP (p < 0.001), peak force during both ISOK (p = 0.005) and IBPF (p = 0.006) at 15P were detected in 120/80 compared to 80/80. BTP was still significantly (p = 0.009) impaired at 48P following the 120/80 protocol, while no differences were noted following 80/80. PecMt was significantly elevated following both 120/80 and 80/80 (p < 0.05) at 15P, but significant differences between the trials were present at 15P and 24P (p = 0.005 and p = 0.008, respectively). Results indicated that heavy eccentric loading during the bench press exercise caused greater performance deficits than a bout of traditionally loaded high intensity resistance exercise. Power performance appears to be more influenced by the 120/80 protocol than isometric peak force. Eccentrically loaded exercise sessions should be separated by at least 48 hours to obtain a complete recovery of the initial muscle morphology and performance.

Key words

  • eccentric
  • muscle architecture
  • strength
Otwarty dostęp

Biomechanical Analysis of Successful and Unsuccessful Snatch Lifts in Elite Female Weightlifters

Data publikacji: 21 Aug 2019
Zakres stron: 69 - 79

Abstrakt

Abstract

The aim of this study was to identify biomechanical factors affecting successful and unsuccessful snatch attempts in elite female weightlifters during the 2013 World Weightlifting Championships. Fourteen female competitors took part in this study. Their successful and unsuccessful snatch lifts with the same load were recorded with 2 camcorders (50 Hz), and selected points were digitized manually on to the body and the barbell using the Ariel Performance Analysis System. The kinetic and kinematic barbell movement as well as the athlete’s body movement variables during the liftoff phase were examined. The results of this study show statistical differences (p ≤ 0.05) between successful and unsuccessful attempts in relation to the angle values in the knee and hip joints in preparation for the aerial phase position. Similarly, the center of gravity velocity was significantly higher in successful attempts during the catch phase. Thus, coaches should pay particular attention to the accuracy of the execution in preparation for the aerial phase position and to the velocity of the center of gravity of the competitors during the catch phase.

Key words

  • weightlifting
  • barbell
  • technique
  • kinematics
Otwarty dostęp

Postactivation Potentiation of Bench Press Throw Performance Using Velocity-Based Conditioning Protocols with Low and Moderate Loads

Data publikacji: 21 Aug 2019
Zakres stron: 81 - 98

Abstrakt

Abstract

This study examined the acute effects of the bench press exercise with low and moderate loads as well as with two predetermined movement velocity loss percentages on bench press throw performance and surface electromyographic (sEMG) activity. Ten trained men completed 5 main trials in randomized and counterbalanced order one week apart. Mean propulsive velocity (MPV), peak velocity (PV) and sEMG activity of prime movers were evaluated before and periodically for 12 minutes of recovery under five conditions: using loads of 40 or 60% of 1 RM, until mean velocity dropped to 90 or 70%, as well as a control condition (CTRL). MPV and PV were increased 4-12 min into recovery by 4.5-6.8% only after the 60%1RM condition during which velocity dropped to 90% and total exercise volume was the lowest of all conditions (p < 0.01, Hedges’ g = 0.8-1.7). When peak individual responses were calculated irrespective of time, MPV was increased by 9.2 ± 4.4 (p < 0.001, Hedges’ g = 1.0) and 6.1 ± 3.6% (p < 0.001, Hedges’ g = 0.7) under the two conditions with the lowest total exercise volume irrespective of the load, i.e. under the conditions of 40 and 60% 1RM where velocity was allowed to drop to 90%. sEMG activity of the triceps was significantly greater when peak individual responses were taken into account only under the 60%1RM condition when velocity dropped to 90% (p < 0.05, Hedges’ g = 0.4). This study showed that potentiation may be maximized by taking into account individual fatigue profiles using velocity-based training.

Key words

  • velocity loss
  • mean propulsive velocity
  • peak velocity
  • EMG activity
Otwarty dostęp

Comparison of Peak Ground Reaction Force, Joint Kinetics and Kinematics, and Muscle Activity Between a Flexible and Steel Barbell During the Back Squat Exercise

Data publikacji: 21 Aug 2019
Zakres stron: 99 - 108

Abstrakt

Abstract

The flexible barbell is purported to improve training gains compared with an Olympic steel barbell (SB) during the back squat exercise with Division I collegiate American football programs. The two bars loaded at 30% 1-repetition maximum were compared with ten trained Division I American football players (n = 10; age = 19.5 years; body mass = 89.4 kg; body height = 182.0 cm) completing 10 repetitions of the back squat exercise. Analysis included integrated-peak values of electromyography of the rectus femoris, biceps femoris, rectus abdominis, erector spinae, external oblique, vastus lateralis, ground reaction forces, and joint kinematics and kinetics of the hip, knee, and ankle. The flexible bar elicited significant increases in peak joint kinetics (Hip Moment: 229 ± 54 Nm vs. 209 ± 52 Nm; Hip Power: 494 ± 151 W vs. 382 ± 134 W; Knee Power: 305 ± 108 W vs. 241 ± 63 W), peak vertical ground reaction forces (1195 ± 209 N vs. 1120 ± 203 N), and muscle activity (Vastus Lateralis: 75.7 vs. 66.5%, Rectus Abdominis: 190 vs. 115%, Rectus Femoris: 69.8 vs. 59.9%, External Oblique: 115 vs. 69.0%). Greater vertical ground reaction forces, hip moment, hip power, knee power, and muscle activity of the vastus lateralis, rectus abdominis, rectus femoris, and external oblique suggest the FB provides biomechanical and physiological mechanisms for training gains over the SB for 30% of 1-repetition maximum loads.

Key words

  • biomechanics
  • electromyography
  • joint power
Otwarty dostęp

The Effect of Load Placement on the Power Production Characteristics of Three Lower Extremity Jumping Exercises

Data publikacji: 21 Aug 2019
Zakres stron: 109 - 122

Abstrakt

Abstract

The purpose of this study was to compare the power production characteristics of the jump squat (JS), hexagonal barbell jump (HEXJ), and jump shrug (JShrug) across a spectrum of relative loads. Fifteen resistance-trained men completed three testing sessions where they performed repetitions of either the JS, HEXJ, or JShrug at body mass (BM) or with 20, 40, 60, 80, or 100% of their BM. Relative peak power (PPRel), relative force at PP (FPP), and velocity at PP (VPP) were compared between exercises and loads. In addition, power-time curves at each load were compared between exercises. Load-averaged HEXJ and JShrug PPRel were statistically greater than the JS (both p < 0.01), while no difference existed between the HEXJ and the JShrug (p = 1.000). Load-averaged JShrug FPP was statistically greater than both the JS and the HEXJ (both p < 0.001), while no statistical difference existed between the JS and the HEXJ (p = 0.111). Load-averaged JS and HEXJ VPP were statistically greater than the JShrug (both p < 0.01). In addition, HEXJ VPP was statistically greater than the JS (p = 0.009). PPRel was maximized at 40, 40, and 20% BM for the JS, HEXJ, and JShrug, respectively. The JShrug possessed statistically different power-time characteristics compared to both the JS and the HEXJ during the countermovement and propulsion phases. The HEXJ and the JShrug appear to be superior exercises for PPRel compared to the JS. The HEXJ may be considered a more velocity-dominant exercise, while the JShrug may be a more force-dominant one.

Key words

  • jump squat
  • hexagonal barbell jump
  • jump shrug
  • force-velocity curve
  • power-time curve
Otwarty dostęp

The Influence of the Menstrual Cycle on Muscle Strength and Power Performance

Data publikacji: 21 Aug 2019
Zakres stron: 123 - 133

Abstrakt

Abstract

This study aimed to investigate the fluctuations of muscle performance in the Smith machine half-squat exercise during three different phases of the menstrual cycle. Thirteen resistance-trained and eumenorrheic women volunteered to participate in the study (58.6 ± 7.8 kg, 31.1 ± 5.5 years). In a pre-experimental test, the half-squat one-repetition maximum (1RM) was measured. Body mass, tympanic temperature and urine concentration of the luteinizing hormone were estimated daily for ~30 days to determine the early follicular phase (EFP), the late follicular phase (LFP), and the mid-luteal phase (MLP) of the menstrual cycle. On the second day of each phase, performance of the Smith machine half-squats was assessed using 20, 40, 60 and 80% of one repetition maximum (1RM). In each load, force, velocity, and power output were measured during the concentric phase of the exercise by means of a rotatory encoder. The data were analyzed using one-way repeated measures ANOVA coupled with magnitude-based inferences. Overall, force, velocity and power output were very similar in all menstrual cycle phases with unclear differences in most of the pairwise comparisons and effect sizes >0.2. The results of this investigation suggest that eumenorrheic females have similar muscle strength and power performance in the Smith machine half-squat exercise during the EFP, LFP, and MLP phases of the menstrual cycle.

Key words

  • women
  • half-squat exercise
  • resistance training
  • periodization, velocity
Otwarty dostęp

Similar Muscular Adaptations in Resistance Training Performed Two Versus Three Days Per Week

Data publikacji: 21 Aug 2019
Zakres stron: 135 - 143

Abstrakt

Abstract

The purpose of the present study was to compare changes in muscle strength and hypertrophy between volume-equated resistance training (RT) performed 2 versus 3 times per week in trained men. Thirty-six resistance-trained men were randomly assigned to one of the two experimental groups: a split-body training routine (SPLIT) with muscle groups trained twice per week (n = 18) over four weekly sessions, or a total-body routine (TOTAL), with muscle groups being trained three times per week (n = 18) over three weekly sessions. The training intervention lasted 10 weeks. Testing was carried out pre- and post-study to assess maximal muscular strength in the back squat and bench press, and hypertrophic adaptations were assessed by measuring muscle thickness of the elbow flexors, elbow extensors, and quadriceps femoris. Twenty-eight subjects completed the study. Significant pre-to-post intervention increases in upper and lower-body muscular strength occurred in both groups with no significant between-group differences. Furthermore, significant pre-to-post intervention increases in muscle size of the elbow extensors and quadriceps femoris occurred in both groups with no significant between-group differences. No significant pre-to-post changes were observed for the muscle size of elbow flexors both in the SPLIT or TOTAL group. In conclusion, a training frequency of 2 versus 3 days per week produces similar increases in muscular adaptations in trained men over a 10-week training period. Nonetheless, effect size differences favored SPLIT for all hypertrophy measures, indicating a potential benefit for training two versus three days a week when the goal is to maximize gains in muscle mass.

Key words

  • frequency
  • strength training
  • hypertrophy
  • volume
Otwarty dostęp

Isokinetic Strength of Rotators, Flexors and Hip Extensors is Strongly Related to Front Kick Dynamics in Military Professionals

Data publikacji: 21 Aug 2019
Zakres stron: 145 - 155

Abstrakt

Abstract

Achieving the maximum possible impact force of the front kick can be related to the isokinetic lower limb muscle strength. Therefore, we aimed to determine the regression model between kicking performance and the isokinetic peak net moment of hip rotators, flexors, and hip extensors and flexors at various speeds of contraction. Twenty-five male soldiers (27.7 ± 7.2 yrs, 83.8 ± 6.1 kg, 180.5 ± 6.5 cm) performed six barefoot front kicks, where impact forces (N) and kick velocity (m∙s-1) were measured. The 3D kinematics and isokinetic dynamometry were used to estimate the kick velocity, isokinetic moment of kicking lower limb hip flexors and extensors (60, 120, 240, 300°∙s-1), and stance lower limb hip internal and external rotators (30, 90°∙s-1). Multiple regression showed that a separate component of the peak moment concentric hip flexion and extension of the kicking lower limb at 90°∙s-1 can explain 54% of the peak kicking impact force variance (R2 = 0.54; p < 0.001). When adding the other 3 components of eccentric and concentric hip internal and external rotations at 30°∙s-1, the internal and external hip rotation ratios at 30°∙s-1 on the stance limb and the concentric ratio of kicking limb flexion and extension at 300°∙s-1 that explained the variance of impact force were 75% (p = 0.003). The explosive strength of kicking limb hip flexors and extensors is the main condition constraint for kicking performance. The maximum strength of stance limb internal and external rotators and speed strength of kicking limb hip flexors and extensors are important constraints of kicking performance that should be considered to improve the front kick efficiency.

Key words

  • strike
  • self-defense
  • impact force
  • peak moment
  • resistance training
Otwarty dostęp

A Preliminary Analysis of Relationships between a 1RM Hexagonal Bar Load and Peak Power with the Tactical Task of a Body Drag

Data publikacji: 21 Aug 2019
Zakres stron: 157 - 166

Abstrakt

Abstract

A critical job task for law enforcement officers that should be influenced by strength is the body drag. This study analyzed relationships between absolute and relative strength measured by a one-repetition maximum hexagonal bar deadlift (1RM HBD), with body drags completed with 74.84 kg and 90.72 kg dummies. Twenty recreationally-trained individuals completed the 1RM HBD in one session, with peak power measured via a linear position transducer. Over two subsequent sessions, participants dragged the 74.84 kg and 90.72 kg dummies with two techniques. The first technique followed Californian standards, where participants wrapped their arms around the dummy and lifted it to standing before timing commenced. In the adapted technique, timing included the initial manipulation of the dummy. Participants dragged the dummy as quickly as possible over a 9.75 m distance. Partial correlations and linear regression (controlling for sex; p < 0.05) analyzed relationships between the HBD and body drags. The standard 74.84 kg body drag correlated with every HBD variable (r = -0.477 to -0.666), and was predicted by the absolute 1RM HBD (r2 = 0.467). The adapted 74.84 kg drag correlated with all HBD variables (r = -0.535 to - 0.754), and was predicted by peak power and the 1RM HBD (r2 = 0.758). Both 90.72 kg drags correlated with absolute and relative 1RM HBD (r = -0.517 to -0.670). Strength related to all body drags; peak power may be more important for drags with lighter loads. Strength training should be a focus in law enforcement to enhance drag performance.

Key words

  • casualty drag
  • lower-body strength
  • police
  • tactical athlete
  • victim drag
Otwarty dostęp

Influence of Strength and Power Capacity on Change of Direction Speed and Deficit in Elite Team-Sport Athletes

Data publikacji: 21 Aug 2019
Zakres stron: 167 - 176

Abstrakt

Abstract

The aim of the present study was to investigate the influence of maximum strength and power levels on change of direction (COD) ability and deficit in elite soccer and rugby players. Seventy-eight elite athletes (soccer, n = 46; rugby, n = 32) performed the following assessments: squat and countermovement jumps (SJ and CMJ), 1 repetition-maximum in the half-squat exercise (HS 1RM), peak power (PP) in the jump-squat exercise, and 20-m linear sprint and Zigzag COD tests. Utilizing the median split analysis, athletes were divided into two groups according to their HS 1RM and PP JS (e.g., higher and lower HS 1RM and higher and lower PP JS). The magnitude-based inference method was used to analyze the differences between groups in the physical performance tests. Athletes in the high strength and power groups outperformed their weaker and less powerful counterparts in all speed and power measurements (i.e., 5-, 10-, and 20-m sprint velocity, Zigzag COD speed, and CMJ and SJ height). In contrast, stronger and more powerful athletes displayed greater COD deficits. The present data indicate that players with superior strength-power capacity tend to be less efficient at changing direction, relative to maximum sprinting speed, despite being faster in linear trajectories. From these results, it appears that current strength and power training practices in team-sports are potentially not the “most appropriate” to increase the aptitude of a given athlete to efficiently utilize his/her neuromuscular abilities during COD maneuvers. Nevertheless, it remains unknown whether more multifaceted training programs are effective in decreasing COD deficits.

Key words

  • soccer
  • agility
  • sprint velocity
  • COD performance
  • cutting
Otwarty dostęp

Knee Forces During Landing in Men and Women

Data publikacji: 21 Aug 2019
Zakres stron: 177 - 192

Abstrakt

Abstract

Sex differences in biomechanics may provide one explanation for the greater incidence of knee injuries in women, but few studies have compared internal forces. In this study, a musculoskeletal model was used to compare male and female, bilateral and unilateral landings based on motion capture and force plate data. Participants were classified as landing medially or laterally loaded based upon the mediolateral load share at the knee (bilateral: p < 0.001, η2=0.452; unilateral: p < 0.001, η2 = 0.444). Knee kinematics and ground reaction forces were not different between the two groups (p > 0.05, η2 = 0.001 – 0.059), but there were differences in muscular recruitment. Landing strategy did not appear to be dependent on sex. However, for both medially and laterally loaded bilateral landings men had greater gluteal (p = 0.017, η2 = 0.085) and hamstrings forces (p < 0.001, η2 = 0.183), whereas women had greater quadriceps forces (p = 0.004, η2 = 0.116). This study demonstrates an association between muscular recruitment and medially loaded landings. Landing strategy seems to be a function of skill not sex; however, within a particular landing strategy there may be sex differences in muscular activation that contribute to the difference in injury rates.

Key words

  • sex characteristics
  • knee injuries
  • anterior cruciate ligaments
  • mediolateral load share
Otwarty dostęp

Effectiveness of Whey Protein Hydrolysate and Milk-Based Formulated Drinks on Recovery of Strength and Power Following Acute Resistance Exercise

Data publikacji: 21 Aug 2019
Zakres stron: 193 - 202

Abstrakt

Abstract

Intensive resistance exercise can result in exercise-induced-muscle-damage, which commonly leads to reductions in acute muscle function. Post-exercise ingestion of carbohydrate-protein mixtures intends to attenuate these effects. This study aimed to compare the effectiveness of whey protein hydrolysate and milk-based formulated drinks on recovery of muscle function following resistance exercise. Thirty resistance-trained males were randomly assigned to either whey hydrolysate and dextrose drink (WH), milk-based drink (MB) or flavored-dextrose (CHO), and performed baseline assessments of perceived-muscle-soreness, the countermovement jump, the seated-medicine-ball throw and isokinetic assessment of the knee extensors and flexors maximal strength. Subsequently, participants performed resistance exercise consisting of various multi-joint barbell exercises. Following resistance exercise participants then consumed either WH (533 Kcal, 32.6 g Protein, 98.3 g Carbohydrate, 1.1 g Fat), MB (532 Kcal, 32.8 g Protein, 98.4 g Carbohydrate, 0.6 g Fat) or CHO (531 Kcal, 0 g Protein, 132.7 g Carbohydrate, 0 g Fat). All assessments were repeated 24 and 48 h post-resistance exercise. Muscle soreness was markedly increased at 24 h and 48 h in all groups (p < 0.001). However, for dynamic power measures (countermovement jump, seated-medicine-ball throw), CHO experienced a decrease for the countermovement jump only at 48 h, whereas WH and MB experienced significant decreases across the countermovement jump and the seated-medicine-ball throw (p < 0.05). All groups experienced significant decreases in isokinetic-extension torque at both 24 h and 48 h; however, flexion torque was decreased for CHO only at these time points (p < 0.05). Consumption of WH or MB did not enhance recovery of dynamic power-producing ability or soreness compared to CHO. Based on within-group effects WH and MB ingestion had seemingly marginal to small positive effects on recovery of isokinetic strength, however, there were no between-group differences for these variables.

Key words

  • strength training
  • ergogenic aids
  • muscle function
  • muscle damage
Otwarty dostęp

Force and Electromyographic Responses of the Biceps Brachii after Eccentric Exercise in Athletes and non-Athletes

Data publikacji: 21 Aug 2019
Zakres stron: 203 - 210

Abstrakt

Abstract

The aim of this study was to compare skeletal muscle response to elbow flexors eccentric exercise in athletes and non-athletes. A set of eccentric (ECC) exercises was performed in a group of 12 athletes and 12 non-athlete controls. Maximal isometric force, electromyographic (EMG) activity of the biceps brachii and the resting elbow angle were assessed before, immediately, 48 hours, 5 and 10 days after high-intensity ECC exercises. During the set of the ECC exercises each participant performed 25 eccentric contractions of elbow flexors. Each contraction consisted of lowering a dumbbell from the flexed (elbow joint angle: 50°_)$\left. 5{{0}^{\underline{{}^\circ }}} \right)$to the extended elbow (elbow joint angle: 180°_)$\left. 18{{0}^{\underline{{}^\circ }}} \right)$position. The weight of the dumbbell was set at 80% of one-repetition maximum (1RM). The ECC contractions caused a decrease in maximal isometric force in both groups. The variable dropped by 8% in non-athletes and by 24% in athletes. Furthermore, the EMG RMS increased significantly only for non-athletes 10 days after the ECC exercise compared to baseline values. The present study showed different effects of ECC exercise on force and EMG in athletes and non-athletes, indicating a more pronounced force response in athletes and electromyographic response in non-athletes.

Key words

  • athletes
  • force
  • electromyography
  • eccentric contraction
Otwarty dostęp

Mechanism of Action and the Effect of Beta-Hydroxy-Beta-Methylbutyrate (HMB) Supplementation on Different Types of Physical Performance - A Systematic Review

Data publikacji: 21 Aug 2019
Zakres stron: 211 - 222

Abstrakt

Abstract

Beta-hydroxy-beta-methylbutyrate (HMB) has been used extensively as a dietary supplement for athletes and physically active people. HMB is a leucine metabolite, which is one of three branched chain amino acids. HMB plays multiple roles in the human body of which most important ones include protein metabolism, insulin activity and skeletal muscle hypertrophy. The ergogenic effects of HMB supplementation are related to the enhancement of sarcolemma integrity, inhibition of protein degradation (ubiquitin pathway), decreased cell apoptosis, increased protein synthesis (mTOR pathway), stimulation of the growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis and enhancement of muscle stem cells proliferation and differentiation. HMB supplementation has been carried out with various groups of athletes. In endurance and martial arts athletes, HMB supplementation revealed positive effects on specific aerobic capacity variables. Positive results were also disclosed in resistance trained athletes, where changes in strength, body fat and muscle mass as well as anaerobic performance and power output were observed. The purpose of this review was to present the main mechanisms of HMB action, especially related to muscle protein synthesis and degradation, and ergogenic effects on different types of sports and physical activities.

Key words

  • HMB
  • ergogenic aids
  • supplementation
  • athletes
Otwarty dostęp

Lower-Body Power Relationships to Linear Speed, Change-of-Direction Speed, and High-Intensity Running Performance in DI Collegiate Women’s Basketball Players

Data publikacji: 21 Aug 2019
Zakres stron: 223 - 232

Abstrakt

Abstract

Basketball players need to sprint and change direction, and lower-body power (often measured by jump tests) should contribute. How different jumps relate to linear and change-of-direction (COD) speed, and high-intensity running has not been analyzed in Division I (DI) collegiate women’s basketballers. Twelve players completed the vertical jump (VJ), two-step approach jump (AppJ), and standing broad jump (SBJ). Average (AvgP) and peak power (PeakP), and PeakP: body mass (P:BM) were derived from VJ height; relative SBJ was derived from SBJ distance. Players also completed: 10 m and ¾ court sprints (linear speed), the pro-agility shuttle (COD speed), and the Yo-Yo Intermittent Recovery Test Level 1 (YYIRT1; high-intensity running). Pearson’s correlations (p < 0.05) calculated relationships between the jump and running tests. The AppJ correlated to the ¾ court sprint and pro-agility shuttle (r = -.663 to -.805). AvgP and PeakP correlated to the 10 m sprint, ¾ court sprint, and pro-agility shuttle (r = .589-.766). P:BM and relative SBJ correlated with all running tests (linear and COD speed r = -.620 to -.805; YYIRT1 r = .622.803). The AppJ stresses the stretch-shortening capacities of the legs, and this quality is important for faster linear and COD speed. AvgP and PeakP are influenced by body mass; while larger athletes produce greater power, they also may display slower 10 m sprint and pro-agility shuttle times, and lesser YYIRT1 performance. Strength coaches should ensure players can generate high relative power (i.e. P:BM, relative SBJ) for faster linear and COD speed, and high-intensity running.

Key words

  • agility
  • female athletes
  • jump tests
  • quickness
  • relative power
  • sprinting
Otwarty dostęp

Ketogenic Diet and Skeletal Muscle Hypertrophy: a Frenemy Relationship?

Data publikacji: 21 Aug 2019
Zakres stron: 233 - 247

Abstrakt

Abstract

Ketogenic diet (KD) is a nutritional regimen characterized by a high-fat and an adequate protein content and a very low carbohydrate level (less than 20 g per day or 5% of total daily energy intake). The insufficient level of carbohydrates forces the body to primarily use fat instead of sugar as a fuel source. Due to its characteristic, KD has often been used to treat metabolic disorders, obesity, cardiovascular disease, and type 2 diabetes. Skeletal muscle constitutes 40% of total body mass and is one of the major sites of glucose disposal. KD is a well-defined approach to induce weight loss, with its role in muscle adaptation and muscle hypertrophy less understood. Considering this lack of knowledge, the aim of this review was to examine the scientific evidence about the effects of KD on muscle hypertrophy. We first described the mechanisms of muscle hypertrophy per se, and secondly, we discussed the characteristics and the metabolic function of KD. Ultimately, we provided the potential mechanism that could explain the influence of KD on skeletal muscle hypertrophy.

Key words

  • ketogenic diet
  • skeletal muscle hypertrophy
  • resistance training
  • signaling
  • muscle protein synthesis
20 Artykułów

Strength & Power

Otwarty dostęp

Rest Redistribution Functions as a Free and Ad-Hoc Equivalent to Commonly Used Velocity-Based Training Thresholds During Clean Pulls at Different Loads

Data publikacji: 21 Aug 2019
Zakres stron: 5 - 16

Abstrakt

Abstract

This study determined whether redistributing total rest time into shorter, but more frequent rest periods could maintain velocity and power output during 3 traditional sets of 6 clean pulls using 80% (TS80), 100% (TS100) and 120% (TS120) of power clean 1RM with 180 seconds of inter-set rest and during 3 “rest redistribution” protocols of 9 sets of 2 clean pulls using 80% (RR80), 100% (RR100) and 120% (RR120) of power clean 1RM with 45 seconds of inter-set rest. The total number of repetitions performed above 10 and 20% velocity loss thresholds, mean and peak velocity maintenance (the average of all 18 repetitions relative to the best repetition; MVM, PVM), and decline (the worst repetition relative to the best repetition; MVD, PVD) were calculated. For MVM, PVM, MVD, and PVD, there were small-to-moderate effect sizes in favour of RR80 and RR100, but large effects favouring RR120, compared to their respective TS protocols. The number of repetitions within a 20% velocity loss threshold was 17.7 ± 0.6 during RR and 16.5 ± 2.4 during TS (effect size 0.69); and the number of repetitions within a 10% velocity loss threshold was about 13.1 ± 3.7 during RR and 10.7 ± 3.6 during TS (effect size 0.66). Therefore, RR generally allowed for a better overall maintenance of velocity and power, especially at heavy loads. Coaches who wish to implement velocity-based training, but who do not wish to purchase or use the associated equipment, may consider rest-redistribution to encourage similar training stimuli.

Key words

  • power
  • cluster sets
  • fatigue
  • weightlifting
  • resistance training
  • traditional sets
Otwarty dostęp

Genetic Markers Associated with Power Athlete Status

Data publikacji: 21 Aug 2019
Zakres stron: 17 - 36

Abstrakt

Abstract

Athletic performance is a multifactorial phenotype influenced by environmental factors as well as multiple genetic variants. Different genetic elements have a great influence over components of athletic performance such as endurance, strength, power, flexibility, neuromuscular coordination, psychological traits and other features important in sport. The current literature review revealed that to date more than 69 genetic markers have been associated with power athlete status. For the purpose of the present review we have assigned all genetic markers described with reference to power athletes status to seven main groups: 1) markers associated with skeletal muscle structure and function, 2) markers involved in the inflammatory and repair reactions in skeletal muscle during and after exercise, 3) markers involved in blood pressure control, 4) markers involved in modulation of oxygen uptake, 5) markers that are regulators of energy metabolism and cellular homeostasis, 6) markers encoding factors that control gene expression by rearrangement of chromatin fibers and mRNA stability, and 7) markers modulating cellular signaling pathways. All data presented in the current review provide evidence to support the notion that human physical performance may be influenced by genetic profiles, especially in power sports. The current studies still represent only the first steps towards a better understanding of the genetic factors that influence power-related traits, so further analyses are necessary before implementation of research findings into practice.

Key words

  • genetic markers
  • genetic polymorphism
  • power athletes
  • strength athletes
  • athletes status
Otwarty dostęp

Caffeine Supplementation for Powerlifting Competitions: an Evidence-Based Approach

Data publikacji: 21 Aug 2019
Zakres stron: 37 - 48

Abstrakt

Abstract

In this paper, we review the effects of caffeine on muscle strength and provide suggestions for caffeine supplementation in powerlifting competitions. The currently available studies indicate that caffeine ingestion may enhance strength in two powerlifting competition events, the squat and the bench press. For the deadlift, the same might be expected even though studies directly using this event are lacking. Optimal doses of caffeine are likely in the range from 2 to 6 mg·kg−1, and are highly individual. When using caffeine-containing capsules, 60 minutes pre-exercise seems to be a good timing of caffeine consumption. For other sources such as caffeinated chewing gum, a shorter period (5 to 10 min) from consumption to the start of the exercise seems to be effective. For shorter duration powerlifting competitions (e.g., 2 hours), one pre-competition dose of caffeine could be sufficient for acute performance-enhancing effects that might be maintained across all three events. For longer duration competitions (with longer rest periods between one repetition maximum attempts), there might be a benefit to repeated dosing with caffeine; for example, ingesting smaller doses of caffeine before each attempt or event. During training, powerlifters may consider ingesting caffeine only before the training sessions with the highest intensity. This approach might eliminate the attenuation of caffeine’s effects associated with chronic caffeine ingestion and would help in maximizing performance benefits from acute caffeine ingestion at the competition. Nonetheless, withdrawal from caffeine (e.g., no caffeine intake seven days before competition) does not seem necessary and may have some indirect negative effects.

Key words

  • ergogenic
  • performance-enhancing
  • supplements
  • strength sports
  • 1RM
Otwarty dostęp

The Influence of Grip Width on Training Volume During the Bench Press with Different Movement Tempos

Data publikacji: 21 Aug 2019
Zakres stron: 49 - 57

Abstrakt

Abstract

The aim of the study was to determine the effect of the wide-grip bench press (WGBP) and the close-grip bench press (CGBP) on the number of performed repetitions (REPs) and time under tension (TUT) using a variable tempo of movement. Twenty (20) women experienced in resistance training were enrolled in the study (1RM-CGBP = 55.2 ± 9.5 kg; 1RM-WGBP = 52.7 ± 8.5 kg). Participants performed 5 sets of the BP with a maximal number of REPs at 70%1RM. Different tempos of movement, i.e., slow (6/0/X/0) and fast (2/0/X/0), and grip widths, i.e., the CGBP and the WGBP, were employed. The following variables were registered: maximal number of repetitions in every set (REPSet1-5), total number of repetitions performed in 5 sets (TREP), maximal time under tension in every set (TUTSet1-5) and total time under tension in 5 sets (TTUT). The two-way ANOVA revealed statistically significant differences between the WGBPFAST and the WGBPSLOW in TUTSet1-5 (p < 0.05) and TTUT (p < 0.01), as well as between the CGBPFAST and the CGBPSLOW in TUTSet1-5 (p < 0.01) and TTUT (p < 0.01). Significant differences between the WGBPFAST and the WGBPSLOW were also observed in REPSet1-5 (p < 0.01) and TREP (p < 0.01) as well as between the CGBPFAST and the CGBPSLOW in REPSet1-5 (p < 0.01) and TREP (p < 0.01). No significant differences between the WGBPSLOW and the CGBPSLOW nor the WGBPFAST and the CGBPFAST were found. The study demonstrates that the tempo of movement, regardless of the width grip, has a significant effect on the volume of effort in resistance training.

Key words

  • resistance exercise
  • repetition
  • time under tension
  • close-grip
  • wide-grip
Otwarty dostęp

A Comparison Between The Recovery Responses Following an Eccentrically Loaded Bench Press Protocol Vs. Regular Loading in Highly Trained Men

Data publikacji: 21 Aug 2019
Zakres stron: 59 - 67

Abstrakt

Abstract

The purpose of this study was to compare the physiological responses of a single bout of an eccentric accentuated bench press protocol (120% of 1RM in the eccentric phase/80% in the concentric phase; [120/80]) versus a regular high-intensity exercise protocol (80%/80%; [80/80]) in resistance-trained men. Eleven men (age = 25.6 ± 3.9 y; body mass = 84.6 ± 11.2 kg; body height = 176.4 ± 3.9 cm) with 6.3 ± 3.4 y of resistance training experience performed each protocol in counterbalanced, randomized order. Isometric, isokinetic and ballistic tests were performed at the bench press (IBPF, ISOK and BTP, respectively) at baseline (BL), 15-min (15P), 24-h (24P), and 48-h (48P) post-exercise for each testing session. In addition, muscle thickness of the pectoralis major (PecMT) was measured at the same timepoints via ultrasound. Significantly greater reductions in BTP (p < 0.001), peak force during both ISOK (p = 0.005) and IBPF (p = 0.006) at 15P were detected in 120/80 compared to 80/80. BTP was still significantly (p = 0.009) impaired at 48P following the 120/80 protocol, while no differences were noted following 80/80. PecMt was significantly elevated following both 120/80 and 80/80 (p < 0.05) at 15P, but significant differences between the trials were present at 15P and 24P (p = 0.005 and p = 0.008, respectively). Results indicated that heavy eccentric loading during the bench press exercise caused greater performance deficits than a bout of traditionally loaded high intensity resistance exercise. Power performance appears to be more influenced by the 120/80 protocol than isometric peak force. Eccentrically loaded exercise sessions should be separated by at least 48 hours to obtain a complete recovery of the initial muscle morphology and performance.

Key words

  • eccentric
  • muscle architecture
  • strength
Otwarty dostęp

Biomechanical Analysis of Successful and Unsuccessful Snatch Lifts in Elite Female Weightlifters

Data publikacji: 21 Aug 2019
Zakres stron: 69 - 79

Abstrakt

Abstract

The aim of this study was to identify biomechanical factors affecting successful and unsuccessful snatch attempts in elite female weightlifters during the 2013 World Weightlifting Championships. Fourteen female competitors took part in this study. Their successful and unsuccessful snatch lifts with the same load were recorded with 2 camcorders (50 Hz), and selected points were digitized manually on to the body and the barbell using the Ariel Performance Analysis System. The kinetic and kinematic barbell movement as well as the athlete’s body movement variables during the liftoff phase were examined. The results of this study show statistical differences (p ≤ 0.05) between successful and unsuccessful attempts in relation to the angle values in the knee and hip joints in preparation for the aerial phase position. Similarly, the center of gravity velocity was significantly higher in successful attempts during the catch phase. Thus, coaches should pay particular attention to the accuracy of the execution in preparation for the aerial phase position and to the velocity of the center of gravity of the competitors during the catch phase.

Key words

  • weightlifting
  • barbell
  • technique
  • kinematics
Otwarty dostęp

Postactivation Potentiation of Bench Press Throw Performance Using Velocity-Based Conditioning Protocols with Low and Moderate Loads

Data publikacji: 21 Aug 2019
Zakres stron: 81 - 98

Abstrakt

Abstract

This study examined the acute effects of the bench press exercise with low and moderate loads as well as with two predetermined movement velocity loss percentages on bench press throw performance and surface electromyographic (sEMG) activity. Ten trained men completed 5 main trials in randomized and counterbalanced order one week apart. Mean propulsive velocity (MPV), peak velocity (PV) and sEMG activity of prime movers were evaluated before and periodically for 12 minutes of recovery under five conditions: using loads of 40 or 60% of 1 RM, until mean velocity dropped to 90 or 70%, as well as a control condition (CTRL). MPV and PV were increased 4-12 min into recovery by 4.5-6.8% only after the 60%1RM condition during which velocity dropped to 90% and total exercise volume was the lowest of all conditions (p < 0.01, Hedges’ g = 0.8-1.7). When peak individual responses were calculated irrespective of time, MPV was increased by 9.2 ± 4.4 (p < 0.001, Hedges’ g = 1.0) and 6.1 ± 3.6% (p < 0.001, Hedges’ g = 0.7) under the two conditions with the lowest total exercise volume irrespective of the load, i.e. under the conditions of 40 and 60% 1RM where velocity was allowed to drop to 90%. sEMG activity of the triceps was significantly greater when peak individual responses were taken into account only under the 60%1RM condition when velocity dropped to 90% (p < 0.05, Hedges’ g = 0.4). This study showed that potentiation may be maximized by taking into account individual fatigue profiles using velocity-based training.

Key words

  • velocity loss
  • mean propulsive velocity
  • peak velocity
  • EMG activity
Otwarty dostęp

Comparison of Peak Ground Reaction Force, Joint Kinetics and Kinematics, and Muscle Activity Between a Flexible and Steel Barbell During the Back Squat Exercise

Data publikacji: 21 Aug 2019
Zakres stron: 99 - 108

Abstrakt

Abstract

The flexible barbell is purported to improve training gains compared with an Olympic steel barbell (SB) during the back squat exercise with Division I collegiate American football programs. The two bars loaded at 30% 1-repetition maximum were compared with ten trained Division I American football players (n = 10; age = 19.5 years; body mass = 89.4 kg; body height = 182.0 cm) completing 10 repetitions of the back squat exercise. Analysis included integrated-peak values of electromyography of the rectus femoris, biceps femoris, rectus abdominis, erector spinae, external oblique, vastus lateralis, ground reaction forces, and joint kinematics and kinetics of the hip, knee, and ankle. The flexible bar elicited significant increases in peak joint kinetics (Hip Moment: 229 ± 54 Nm vs. 209 ± 52 Nm; Hip Power: 494 ± 151 W vs. 382 ± 134 W; Knee Power: 305 ± 108 W vs. 241 ± 63 W), peak vertical ground reaction forces (1195 ± 209 N vs. 1120 ± 203 N), and muscle activity (Vastus Lateralis: 75.7 vs. 66.5%, Rectus Abdominis: 190 vs. 115%, Rectus Femoris: 69.8 vs. 59.9%, External Oblique: 115 vs. 69.0%). Greater vertical ground reaction forces, hip moment, hip power, knee power, and muscle activity of the vastus lateralis, rectus abdominis, rectus femoris, and external oblique suggest the FB provides biomechanical and physiological mechanisms for training gains over the SB for 30% of 1-repetition maximum loads.

Key words

  • biomechanics
  • electromyography
  • joint power
Otwarty dostęp

The Effect of Load Placement on the Power Production Characteristics of Three Lower Extremity Jumping Exercises

Data publikacji: 21 Aug 2019
Zakres stron: 109 - 122

Abstrakt

Abstract

The purpose of this study was to compare the power production characteristics of the jump squat (JS), hexagonal barbell jump (HEXJ), and jump shrug (JShrug) across a spectrum of relative loads. Fifteen resistance-trained men completed three testing sessions where they performed repetitions of either the JS, HEXJ, or JShrug at body mass (BM) or with 20, 40, 60, 80, or 100% of their BM. Relative peak power (PPRel), relative force at PP (FPP), and velocity at PP (VPP) were compared between exercises and loads. In addition, power-time curves at each load were compared between exercises. Load-averaged HEXJ and JShrug PPRel were statistically greater than the JS (both p < 0.01), while no difference existed between the HEXJ and the JShrug (p = 1.000). Load-averaged JShrug FPP was statistically greater than both the JS and the HEXJ (both p < 0.001), while no statistical difference existed between the JS and the HEXJ (p = 0.111). Load-averaged JS and HEXJ VPP were statistically greater than the JShrug (both p < 0.01). In addition, HEXJ VPP was statistically greater than the JS (p = 0.009). PPRel was maximized at 40, 40, and 20% BM for the JS, HEXJ, and JShrug, respectively. The JShrug possessed statistically different power-time characteristics compared to both the JS and the HEXJ during the countermovement and propulsion phases. The HEXJ and the JShrug appear to be superior exercises for PPRel compared to the JS. The HEXJ may be considered a more velocity-dominant exercise, while the JShrug may be a more force-dominant one.

Key words

  • jump squat
  • hexagonal barbell jump
  • jump shrug
  • force-velocity curve
  • power-time curve
Otwarty dostęp

The Influence of the Menstrual Cycle on Muscle Strength and Power Performance

Data publikacji: 21 Aug 2019
Zakres stron: 123 - 133

Abstrakt

Abstract

This study aimed to investigate the fluctuations of muscle performance in the Smith machine half-squat exercise during three different phases of the menstrual cycle. Thirteen resistance-trained and eumenorrheic women volunteered to participate in the study (58.6 ± 7.8 kg, 31.1 ± 5.5 years). In a pre-experimental test, the half-squat one-repetition maximum (1RM) was measured. Body mass, tympanic temperature and urine concentration of the luteinizing hormone were estimated daily for ~30 days to determine the early follicular phase (EFP), the late follicular phase (LFP), and the mid-luteal phase (MLP) of the menstrual cycle. On the second day of each phase, performance of the Smith machine half-squats was assessed using 20, 40, 60 and 80% of one repetition maximum (1RM). In each load, force, velocity, and power output were measured during the concentric phase of the exercise by means of a rotatory encoder. The data were analyzed using one-way repeated measures ANOVA coupled with magnitude-based inferences. Overall, force, velocity and power output were very similar in all menstrual cycle phases with unclear differences in most of the pairwise comparisons and effect sizes >0.2. The results of this investigation suggest that eumenorrheic females have similar muscle strength and power performance in the Smith machine half-squat exercise during the EFP, LFP, and MLP phases of the menstrual cycle.

Key words

  • women
  • half-squat exercise
  • resistance training
  • periodization, velocity
Otwarty dostęp

Similar Muscular Adaptations in Resistance Training Performed Two Versus Three Days Per Week

Data publikacji: 21 Aug 2019
Zakres stron: 135 - 143

Abstrakt

Abstract

The purpose of the present study was to compare changes in muscle strength and hypertrophy between volume-equated resistance training (RT) performed 2 versus 3 times per week in trained men. Thirty-six resistance-trained men were randomly assigned to one of the two experimental groups: a split-body training routine (SPLIT) with muscle groups trained twice per week (n = 18) over four weekly sessions, or a total-body routine (TOTAL), with muscle groups being trained three times per week (n = 18) over three weekly sessions. The training intervention lasted 10 weeks. Testing was carried out pre- and post-study to assess maximal muscular strength in the back squat and bench press, and hypertrophic adaptations were assessed by measuring muscle thickness of the elbow flexors, elbow extensors, and quadriceps femoris. Twenty-eight subjects completed the study. Significant pre-to-post intervention increases in upper and lower-body muscular strength occurred in both groups with no significant between-group differences. Furthermore, significant pre-to-post intervention increases in muscle size of the elbow extensors and quadriceps femoris occurred in both groups with no significant between-group differences. No significant pre-to-post changes were observed for the muscle size of elbow flexors both in the SPLIT or TOTAL group. In conclusion, a training frequency of 2 versus 3 days per week produces similar increases in muscular adaptations in trained men over a 10-week training period. Nonetheless, effect size differences favored SPLIT for all hypertrophy measures, indicating a potential benefit for training two versus three days a week when the goal is to maximize gains in muscle mass.

Key words

  • frequency
  • strength training
  • hypertrophy
  • volume
Otwarty dostęp

Isokinetic Strength of Rotators, Flexors and Hip Extensors is Strongly Related to Front Kick Dynamics in Military Professionals

Data publikacji: 21 Aug 2019
Zakres stron: 145 - 155

Abstrakt

Abstract

Achieving the maximum possible impact force of the front kick can be related to the isokinetic lower limb muscle strength. Therefore, we aimed to determine the regression model between kicking performance and the isokinetic peak net moment of hip rotators, flexors, and hip extensors and flexors at various speeds of contraction. Twenty-five male soldiers (27.7 ± 7.2 yrs, 83.8 ± 6.1 kg, 180.5 ± 6.5 cm) performed six barefoot front kicks, where impact forces (N) and kick velocity (m∙s-1) were measured. The 3D kinematics and isokinetic dynamometry were used to estimate the kick velocity, isokinetic moment of kicking lower limb hip flexors and extensors (60, 120, 240, 300°∙s-1), and stance lower limb hip internal and external rotators (30, 90°∙s-1). Multiple regression showed that a separate component of the peak moment concentric hip flexion and extension of the kicking lower limb at 90°∙s-1 can explain 54% of the peak kicking impact force variance (R2 = 0.54; p < 0.001). When adding the other 3 components of eccentric and concentric hip internal and external rotations at 30°∙s-1, the internal and external hip rotation ratios at 30°∙s-1 on the stance limb and the concentric ratio of kicking limb flexion and extension at 300°∙s-1 that explained the variance of impact force were 75% (p = 0.003). The explosive strength of kicking limb hip flexors and extensors is the main condition constraint for kicking performance. The maximum strength of stance limb internal and external rotators and speed strength of kicking limb hip flexors and extensors are important constraints of kicking performance that should be considered to improve the front kick efficiency.

Key words

  • strike
  • self-defense
  • impact force
  • peak moment
  • resistance training
Otwarty dostęp

A Preliminary Analysis of Relationships between a 1RM Hexagonal Bar Load and Peak Power with the Tactical Task of a Body Drag

Data publikacji: 21 Aug 2019
Zakres stron: 157 - 166

Abstrakt

Abstract

A critical job task for law enforcement officers that should be influenced by strength is the body drag. This study analyzed relationships between absolute and relative strength measured by a one-repetition maximum hexagonal bar deadlift (1RM HBD), with body drags completed with 74.84 kg and 90.72 kg dummies. Twenty recreationally-trained individuals completed the 1RM HBD in one session, with peak power measured via a linear position transducer. Over two subsequent sessions, participants dragged the 74.84 kg and 90.72 kg dummies with two techniques. The first technique followed Californian standards, where participants wrapped their arms around the dummy and lifted it to standing before timing commenced. In the adapted technique, timing included the initial manipulation of the dummy. Participants dragged the dummy as quickly as possible over a 9.75 m distance. Partial correlations and linear regression (controlling for sex; p < 0.05) analyzed relationships between the HBD and body drags. The standard 74.84 kg body drag correlated with every HBD variable (r = -0.477 to -0.666), and was predicted by the absolute 1RM HBD (r2 = 0.467). The adapted 74.84 kg drag correlated with all HBD variables (r = -0.535 to - 0.754), and was predicted by peak power and the 1RM HBD (r2 = 0.758). Both 90.72 kg drags correlated with absolute and relative 1RM HBD (r = -0.517 to -0.670). Strength related to all body drags; peak power may be more important for drags with lighter loads. Strength training should be a focus in law enforcement to enhance drag performance.

Key words

  • casualty drag
  • lower-body strength
  • police
  • tactical athlete
  • victim drag
Otwarty dostęp

Influence of Strength and Power Capacity on Change of Direction Speed and Deficit in Elite Team-Sport Athletes

Data publikacji: 21 Aug 2019
Zakres stron: 167 - 176

Abstrakt

Abstract

The aim of the present study was to investigate the influence of maximum strength and power levels on change of direction (COD) ability and deficit in elite soccer and rugby players. Seventy-eight elite athletes (soccer, n = 46; rugby, n = 32) performed the following assessments: squat and countermovement jumps (SJ and CMJ), 1 repetition-maximum in the half-squat exercise (HS 1RM), peak power (PP) in the jump-squat exercise, and 20-m linear sprint and Zigzag COD tests. Utilizing the median split analysis, athletes were divided into two groups according to their HS 1RM and PP JS (e.g., higher and lower HS 1RM and higher and lower PP JS). The magnitude-based inference method was used to analyze the differences between groups in the physical performance tests. Athletes in the high strength and power groups outperformed their weaker and less powerful counterparts in all speed and power measurements (i.e., 5-, 10-, and 20-m sprint velocity, Zigzag COD speed, and CMJ and SJ height). In contrast, stronger and more powerful athletes displayed greater COD deficits. The present data indicate that players with superior strength-power capacity tend to be less efficient at changing direction, relative to maximum sprinting speed, despite being faster in linear trajectories. From these results, it appears that current strength and power training practices in team-sports are potentially not the “most appropriate” to increase the aptitude of a given athlete to efficiently utilize his/her neuromuscular abilities during COD maneuvers. Nevertheless, it remains unknown whether more multifaceted training programs are effective in decreasing COD deficits.

Key words

  • soccer
  • agility
  • sprint velocity
  • COD performance
  • cutting
Otwarty dostęp

Knee Forces During Landing in Men and Women

Data publikacji: 21 Aug 2019
Zakres stron: 177 - 192

Abstrakt

Abstract

Sex differences in biomechanics may provide one explanation for the greater incidence of knee injuries in women, but few studies have compared internal forces. In this study, a musculoskeletal model was used to compare male and female, bilateral and unilateral landings based on motion capture and force plate data. Participants were classified as landing medially or laterally loaded based upon the mediolateral load share at the knee (bilateral: p < 0.001, η2=0.452; unilateral: p < 0.001, η2 = 0.444). Knee kinematics and ground reaction forces were not different between the two groups (p > 0.05, η2 = 0.001 – 0.059), but there were differences in muscular recruitment. Landing strategy did not appear to be dependent on sex. However, for both medially and laterally loaded bilateral landings men had greater gluteal (p = 0.017, η2 = 0.085) and hamstrings forces (p < 0.001, η2 = 0.183), whereas women had greater quadriceps forces (p = 0.004, η2 = 0.116). This study demonstrates an association between muscular recruitment and medially loaded landings. Landing strategy seems to be a function of skill not sex; however, within a particular landing strategy there may be sex differences in muscular activation that contribute to the difference in injury rates.

Key words

  • sex characteristics
  • knee injuries
  • anterior cruciate ligaments
  • mediolateral load share
Otwarty dostęp

Effectiveness of Whey Protein Hydrolysate and Milk-Based Formulated Drinks on Recovery of Strength and Power Following Acute Resistance Exercise

Data publikacji: 21 Aug 2019
Zakres stron: 193 - 202

Abstrakt

Abstract

Intensive resistance exercise can result in exercise-induced-muscle-damage, which commonly leads to reductions in acute muscle function. Post-exercise ingestion of carbohydrate-protein mixtures intends to attenuate these effects. This study aimed to compare the effectiveness of whey protein hydrolysate and milk-based formulated drinks on recovery of muscle function following resistance exercise. Thirty resistance-trained males were randomly assigned to either whey hydrolysate and dextrose drink (WH), milk-based drink (MB) or flavored-dextrose (CHO), and performed baseline assessments of perceived-muscle-soreness, the countermovement jump, the seated-medicine-ball throw and isokinetic assessment of the knee extensors and flexors maximal strength. Subsequently, participants performed resistance exercise consisting of various multi-joint barbell exercises. Following resistance exercise participants then consumed either WH (533 Kcal, 32.6 g Protein, 98.3 g Carbohydrate, 1.1 g Fat), MB (532 Kcal, 32.8 g Protein, 98.4 g Carbohydrate, 0.6 g Fat) or CHO (531 Kcal, 0 g Protein, 132.7 g Carbohydrate, 0 g Fat). All assessments were repeated 24 and 48 h post-resistance exercise. Muscle soreness was markedly increased at 24 h and 48 h in all groups (p < 0.001). However, for dynamic power measures (countermovement jump, seated-medicine-ball throw), CHO experienced a decrease for the countermovement jump only at 48 h, whereas WH and MB experienced significant decreases across the countermovement jump and the seated-medicine-ball throw (p < 0.05). All groups experienced significant decreases in isokinetic-extension torque at both 24 h and 48 h; however, flexion torque was decreased for CHO only at these time points (p < 0.05). Consumption of WH or MB did not enhance recovery of dynamic power-producing ability or soreness compared to CHO. Based on within-group effects WH and MB ingestion had seemingly marginal to small positive effects on recovery of isokinetic strength, however, there were no between-group differences for these variables.

Key words

  • strength training
  • ergogenic aids
  • muscle function
  • muscle damage
Otwarty dostęp

Force and Electromyographic Responses of the Biceps Brachii after Eccentric Exercise in Athletes and non-Athletes

Data publikacji: 21 Aug 2019
Zakres stron: 203 - 210

Abstrakt

Abstract

The aim of this study was to compare skeletal muscle response to elbow flexors eccentric exercise in athletes and non-athletes. A set of eccentric (ECC) exercises was performed in a group of 12 athletes and 12 non-athlete controls. Maximal isometric force, electromyographic (EMG) activity of the biceps brachii and the resting elbow angle were assessed before, immediately, 48 hours, 5 and 10 days after high-intensity ECC exercises. During the set of the ECC exercises each participant performed 25 eccentric contractions of elbow flexors. Each contraction consisted of lowering a dumbbell from the flexed (elbow joint angle: 50°_)$\left. 5{{0}^{\underline{{}^\circ }}} \right)$to the extended elbow (elbow joint angle: 180°_)$\left. 18{{0}^{\underline{{}^\circ }}} \right)$position. The weight of the dumbbell was set at 80% of one-repetition maximum (1RM). The ECC contractions caused a decrease in maximal isometric force in both groups. The variable dropped by 8% in non-athletes and by 24% in athletes. Furthermore, the EMG RMS increased significantly only for non-athletes 10 days after the ECC exercise compared to baseline values. The present study showed different effects of ECC exercise on force and EMG in athletes and non-athletes, indicating a more pronounced force response in athletes and electromyographic response in non-athletes.

Key words

  • athletes
  • force
  • electromyography
  • eccentric contraction
Otwarty dostęp

Mechanism of Action and the Effect of Beta-Hydroxy-Beta-Methylbutyrate (HMB) Supplementation on Different Types of Physical Performance - A Systematic Review

Data publikacji: 21 Aug 2019
Zakres stron: 211 - 222

Abstrakt

Abstract

Beta-hydroxy-beta-methylbutyrate (HMB) has been used extensively as a dietary supplement for athletes and physically active people. HMB is a leucine metabolite, which is one of three branched chain amino acids. HMB plays multiple roles in the human body of which most important ones include protein metabolism, insulin activity and skeletal muscle hypertrophy. The ergogenic effects of HMB supplementation are related to the enhancement of sarcolemma integrity, inhibition of protein degradation (ubiquitin pathway), decreased cell apoptosis, increased protein synthesis (mTOR pathway), stimulation of the growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis and enhancement of muscle stem cells proliferation and differentiation. HMB supplementation has been carried out with various groups of athletes. In endurance and martial arts athletes, HMB supplementation revealed positive effects on specific aerobic capacity variables. Positive results were also disclosed in resistance trained athletes, where changes in strength, body fat and muscle mass as well as anaerobic performance and power output were observed. The purpose of this review was to present the main mechanisms of HMB action, especially related to muscle protein synthesis and degradation, and ergogenic effects on different types of sports and physical activities.

Key words

  • HMB
  • ergogenic aids
  • supplementation
  • athletes
Otwarty dostęp

Lower-Body Power Relationships to Linear Speed, Change-of-Direction Speed, and High-Intensity Running Performance in DI Collegiate Women’s Basketball Players

Data publikacji: 21 Aug 2019
Zakres stron: 223 - 232

Abstrakt

Abstract

Basketball players need to sprint and change direction, and lower-body power (often measured by jump tests) should contribute. How different jumps relate to linear and change-of-direction (COD) speed, and high-intensity running has not been analyzed in Division I (DI) collegiate women’s basketballers. Twelve players completed the vertical jump (VJ), two-step approach jump (AppJ), and standing broad jump (SBJ). Average (AvgP) and peak power (PeakP), and PeakP: body mass (P:BM) were derived from VJ height; relative SBJ was derived from SBJ distance. Players also completed: 10 m and ¾ court sprints (linear speed), the pro-agility shuttle (COD speed), and the Yo-Yo Intermittent Recovery Test Level 1 (YYIRT1; high-intensity running). Pearson’s correlations (p < 0.05) calculated relationships between the jump and running tests. The AppJ correlated to the ¾ court sprint and pro-agility shuttle (r = -.663 to -.805). AvgP and PeakP correlated to the 10 m sprint, ¾ court sprint, and pro-agility shuttle (r = .589-.766). P:BM and relative SBJ correlated with all running tests (linear and COD speed r = -.620 to -.805; YYIRT1 r = .622.803). The AppJ stresses the stretch-shortening capacities of the legs, and this quality is important for faster linear and COD speed. AvgP and PeakP are influenced by body mass; while larger athletes produce greater power, they also may display slower 10 m sprint and pro-agility shuttle times, and lesser YYIRT1 performance. Strength coaches should ensure players can generate high relative power (i.e. P:BM, relative SBJ) for faster linear and COD speed, and high-intensity running.

Key words

  • agility
  • female athletes
  • jump tests
  • quickness
  • relative power
  • sprinting
Otwarty dostęp

Ketogenic Diet and Skeletal Muscle Hypertrophy: a Frenemy Relationship?

Data publikacji: 21 Aug 2019
Zakres stron: 233 - 247

Abstrakt

Abstract

Ketogenic diet (KD) is a nutritional regimen characterized by a high-fat and an adequate protein content and a very low carbohydrate level (less than 20 g per day or 5% of total daily energy intake). The insufficient level of carbohydrates forces the body to primarily use fat instead of sugar as a fuel source. Due to its characteristic, KD has often been used to treat metabolic disorders, obesity, cardiovascular disease, and type 2 diabetes. Skeletal muscle constitutes 40% of total body mass and is one of the major sites of glucose disposal. KD is a well-defined approach to induce weight loss, with its role in muscle adaptation and muscle hypertrophy less understood. Considering this lack of knowledge, the aim of this review was to examine the scientific evidence about the effects of KD on muscle hypertrophy. We first described the mechanisms of muscle hypertrophy per se, and secondly, we discussed the characteristics and the metabolic function of KD. Ultimately, we provided the potential mechanism that could explain the influence of KD on skeletal muscle hypertrophy.

Key words

  • ketogenic diet
  • skeletal muscle hypertrophy
  • resistance training
  • signaling
  • muscle protein synthesis

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