Volume 24 (2010): Issue 2010 (June 2010)

This review contrasts two approaches to motor control that have dominated the field over the past years. One of them is built on ideas of the control theory; it assumes that neuronal structures perform computations and operates with notions such as motor programs and internal models. The alternative approach is based on physics and neurophysiology. It refutes the assumption of neural computations and operates with such notions as neuronal thresholds and equilibrium states. The two approaches have different goals. The former tries to produce a formal description of how any system, irrespective of its physics and physiology, can produce typical features of biological movement. This research may be very productive and important for such fields as robotics and prosthetics. The latter approach tries to produce a formal description of how neuromotor processes within the actual systems for movement production (for example, the human body) are organized to produce coordinated movements. Its goal is to turn motor control into a subfield of physics of living systems. Recent developments of the equilibrium-point hypothesis, referent configuration hypothesis, and the ideas of synergic control represent important steps towards achieving this goal.

The effect of a 60-day 6° head-down tilt of bed rest with and without prolonged passive muscle "stretching" training on the mechanical properties of the human triceps surae muscle was studied in 13 healthy male subjects. One group (n = 6; mean age 30.8 ± 3.1 years) underwent a 60-day head-down tilt, and a second group (n = 7; mean age 30.4 ± 1.2 years) underwent head-down tilt with prolonged passive muscle stretching. Head-down tilt without prolonged passive muscle "stretching" training showed maximal voluntary contraction declined by 34 % (p < 0.05) and the electrically evoked tetanic tension at 150 impulses·s^-1 and isometric twitch contraction reduced by 17 % (p < 0.02) and 18 % (p < 0.05), respectively. Time-to-peak tension, and half-relaxation time of the twitch slightly decreased by 3% (p > 0.05), and 7 %, respectively, but total contraction time slightly increased. The difference between electrically evoked tetanic tension and the maximal voluntary contraction expressed as a percentage of electrically evoked tetanic tension (referred to as force deficiency), has also been calculated. The force deficiency increased by 61 % (p < 0.001). After head-down tilt with prolonged passive muscle "stretching" training, the time-to-peak tension did not change, and half-relaxation time of the twitch decreased. In addition, there was a 14 % lengthening in the total duration of the twitch. The results of prolonged passive muscle "stretching" training demonstrated a clear deterioration of voluntarily and electrically induced muscle contractions. Passive "stretching" training caused a decrease by 29 % (p < 0.05) in the maximal voluntary contraction. The isometric twitch contraction, and electrically evoked tetanic tension both showed reductions by 17 %, and by 19 % (p < 0.05), respectively. The force deficiency decreased significantly by 21 % (p < 0.02). The rate of rise of electrically evoked tetanic tension and feature of voluntary contractions significantly reduced during head-down tilt with prolonged passive muscle "stretching" training. These basic experimental findings concluded that prolonged passive "stretching" training of a single muscle did not prevent a reserve of neuromuscular function.

The purpose of this study was to examine the effects of static and dynamic stretching within a pre-exercise warm-up on vastus medialis muscle activity during instep kicking and ball velocity in soccer players. The kicking motions of dominant legs were captured from using six synchronized high-speed infra-red cameras at 200 Hz and Electromyography at 100 Hz. There was significant difference in vastus medialis activity after dynamic stretching relative to no stretching condition (0.12 ± 0.06 mV) versus static stretching relative to no stretching condition (-0.21 ± 0.10 mV) with p < 0.001). In addition, there was also a significant difference in ball velocity after dynamic stretching relative to no stretching condition (4.53 ± 2.10 m/s) versus static stretching relative to no stretching condition (-1.48 ± 2.43 m/s) with p < 0.003. We concluded that dynamic stretching during the warm-up, as compared to static stretching, is probably more effective as preparation for optimal muscle activity and finally have high ball velocity which is required in soccer.

Body posture is determined by many factors, including central regulation connected with anti-gravitational mechanism which develops in ontogenesis. Postural disorders arise as a result of a compensatory anti-gravitational mechanism, in which the main component is reduced postural tone (volume and distribution disorders). Compensation mechanisms consist in improper alignment of particular body segments (distribution disorders) (e.g., increase or decrease of spinal curvatures, external or internal rotation of the lower limbs, valgus and varus deformity of the knees and feet). Such disorders may constitute a reason for abnormal component development, thus limiting trunk rotational mobility.

An aim of the study was to assess the range of trunk rotational mobility.

Pupils (n=123) aged 13-15 underwent the following parameter evaluations: 1. Posture according to Kasperczyk's scoring method, 2. Postural tone volume by analysis of pelvis control in the long sitting, 3. Range of trunk rotation with use of upper tension test (muscle latissimus dorsi and thoracolumbar fascia).

Positive tension test was recorded in 32 children (21 unilateral and 11 bilateral). Diversification of statistical averages of scoring for body posture, from the lowest (x=6.41) in 91 subjects with negative tension test, to the highest (x=7.72) in 11 subjects with double-sided positive result was recorded. Statistical analyzes confirmed significance of correlation between body posture's quality and trunk's rotational mobility (r=0.286 at p=0.001), as well as between volume of postural tone and range of trunk's rotational mobility. Coefficients of correlation amount to, respectively, for tension test and free sitting position r=0.187, p=0.038; and for tension test and corrected sitting position r=0.253, p=0.05. Disorders of muscle tone volume and distribution cause limitation of trunk rotational mobility development.

Fatigue is an indispensible part of a basketball game which may affect an athlete's shooting kinematics. Although kinematic analyses of various sports related movements were extensively done, this study is the first to consider the effects of fatigue on the kinematics of free throw shooting. After measuring the resting heart rate, ten collegiate level, male basketball players (21.8±1.6 y; 192.8±3.6 cm; 84.1±8.5 kg) were asked to perform free throws. Two successful and two unsuccessful free throws were selected. Thereafter, participants were asked to complete the fatigue protocol, which included 30m sprints and 5 vertical jumps at each end, until they reached volitional exhaustion. Additional two successful and two unsuccessful free throws were collected. All shots were recorded by using two digital cameras operating at 60 Hz and placed in a stereoscopic view. The elbow, trunk, knee and ankle joint angles were measured before and after the ball release and at the ball release point. The selected joint angles were compared between successful and unsuccessful free throws, as well as before and after the completion of fatigue protocol. The results demonstrated that fatigue did not effect free throw shooting kinematics (p>0.05) and there was no significant joint angle difference between successful and unsuccessful shots (p>0.05). This study suggested that high level athletes are able to cope with the possible detrimental effects of fatigue while performing coordinated movements such as free throw shooting.

We intended to compare the anthropometry of male and female Ironman triathletes with the anthropometry of male and female ultra-swimmers. Body mass, body mass index and body fat were lower in both male and female triathletes compared to swimmers. Body height and length of limbs were no different between the two groups. In the multi-variate analysis, in male triathletes, body mass (p=0.015) and percent body fat (p=0.0003) were related to race time; percent body fat was also related to the swim split (p=0.0036). In male swimmers, length of the arm was related to race time (p=0.0089). In female triathletes and swimmers, none of the investigated anthropometric variables showed an association with race time. We concluded that Ironman triathletes and ultra-swimmers were different regarding anthropometry and that different anthropometric variables were related to race time. We assume that other factors, such as training and equipment, as opposed to anthropometry, may better predict race time in male and female Ironman triathletes.

The objective of this study was to determine whether running a 24-h race would cause oxidative damage and changes in the blood antioxidant defense capacity in endurance-trained athletes. Fourteen male amateur runners (mean age 43.0±10.8 y, body weight 64.3±7.2 kg height 171±5 cm, weekly covered distance 81±43 km, training history 8±9 y) who participated in a 24-hr ultra-marathon and volunteered to give blood samples during the race were enrolled for this study. Blood samples were taken before the run, after completing the marathon distance (42.217 km), after 12 h and at the conclusion of the race.

The capacity of erythrocyte antioxidant defense system was evaluated by measuring the activities of superoxide dismutase (SOD), glutathione peroxidase (GPX), catalase (CAT), glutathione reductase (GR), concentrations of non-enzymatic antioxidants (uric acid and glutathione-GSH), and selected biomarkers of oxidative stress (i.e., plasma level of malondialdehyde (MDA) and plasma antioxidant capacity by FRAP ("ferric-reducing ability of plasma")). Moreover, in order to elucidate between-group differences in the total capacity of the blood antioxidant defense system, an index of antioxidant potential (POTAOX) was calculated as a sum of standardized values of activities of antioxidant enzymes (SOD, CAT, GPX, GR) and non-enzymatic antioxidants (uric acid, GSH).

A progressive decline was observed in activities of SOD and CAT with the distance covered during the race, while the opposite trend was found in activities of GPX and GR that tended to increase. A significant decrease was recorded in GSH content after completing the marathon distance, which tended toward slightly higher values, without reaching the baseline level, at the finish of the race. Plasma concentration of uric acid (UA) was not significantly affected, except for the value recorded after 12 h of running that was significantly (p<0.05) lower, while both markers of oxidative stress (FRAP and MDA) increased significantly after completing the marathon distance. Comparison of the calculated values of the POTAOX index recorded pre-race and throughout the competition implies that the most drastic decline in the total antioxidant capacity occurred at mid-race (i.e. after 12 h of running).

Endothelial nitric oxide (NO) synthase gene (NOS3) is taken into account as one of the main regulators of blood pressure and basal vascular dilation - two main factors found to be limiting for endurance performance.

We compared genotypic and allelic frequencies of the NOS3 G894T polymorphism in two groups of men of the same Caucasian descent: elite endurance athletes (rowers; n=63) and sedentary controls (n=160).

We have not found any statistical difference in G894T genotype and allele frequencies in endurance orientated athletes compared to sedentary controls. The difference in G allele frequency between the rowers and controls did not reach statistical significance (73.5% vs. 67.2%, P = 0.307), similar to genotype distribution amongst the rowers (58.7% GG; 39.4% GT; 6.4% TT) compared to controls (43.7% GG; 46.9% GT; 9.4% TT) (P=0.129).

In summary, our results are in contradiction to the hypothesis that NOS3 G894T polymorphism is associated with the physical performance status in rowing. Of course, our findings do not mean that other polymorphisms in NOS3 gene do not have any beneficial effect on performance parameters, but to confirm that hypothesis, we need further studies.

Objective: To evaluate sex differences in functional performances of youth track and field athletes.

Methods: Four tests of functional capacity were administered to 309 youth 11-15 years training for track and field at sport schools, 136 boys and 173 girls. Grip strength, standing long jump, 2 kg medicine ball throw and 20 m sprint were measured; height, weight and adiposity were also. Two age groups were compared, 11-13 and 14-15 years. ANCOVA was used to test sex differences by age group in the total sample (disciplines combined) and specific disciplines; age, height and weight were covariates.

Results: For the total sample, males in both age groups performed better than females in the four tests but sex differences were greater among 14-15 year olds. Within disciplines, sex differences among sprinters and middle distance and distance runners were greater at 14-15 years. Results varied for general athletics; the magnitude of sex differences was similar for strength in both age groups, greater for the throw at 11-13 years and greater for the jump and sprint at 14-15 years.

Conclusion: Although sex differences in performance were apparent among athletes 11-13 years, they were greater among athletes 14-15 years, reflecting to a large extent the male adolescent spurt in body size, muscle mass, strength and power. Sex differences were more established in sprinters and middle distance and distance runners, and more variable in participants in general athletics.

The purpose of this study was to examine a relationship between the degree of liking and disliking of sport and physical activity, and stress development.

We conducted a survey on Japanese junior high school students (129 boys, 139 girls) in 2007. The survey included such entries as 1) positive vs negative attitude toward physical education classes, 2) the degree of physical education classes-related stress, and 3) personality qualities (goal orientation, sports competence and active coping).

In our survey concerning the degree of predilection for physical education classes, the results were as follows: 171 subjects in Group A said they liked physical education classes; 39 subjects in Group B said they didn't like and 57 subjects in Group C chose "neither". Comparing the degree of stress from physical education classes, Group A scored significantly lower than the others by Tukey's multiple comparison test (p<0.05).

Also, in order to find the key factor which determines the degree of liking and disliking of physical education classes, we measured various values among 52 subjects with a high degree of stress as a dependent variable, and analyzed the personality aspects as an independent variable. As a result, we found a negative correlation between stress levels and sports competence, whereas ego orientation and active coping had a positive effect on the degree of stress.

We showed that those liking physical education experienced low degrees of stress. Conversely, those individuals disliking sport and physical activity should not be expected to experience reduced stress while participating in sports. Furthermore, we can indicate sports competence as a determinant of stress reduction. Consequently, in order to stimulate regular participation in sports activity and to release its stress-reducing potential, it is necessary to develop childhood physical education classes to foster sports competence.

The main goal of this study was to analyze the residential environment (built environment), by exploring the relationship between neighborhood walkability characteristics using Geographic Information System (GIS) and level of physical activity (PA). A randomly selected sample of 135 adults from Olomouc, Czech Republic was divided into low and high walkability neighborhoods based on the walkability index (calculated using GIS). The average daily number of steps (using Yamax SW-700 pedometer) between the groups also was measured. Result showed that participants living in the high walkable areas took more steps a day than participant in the low walkable areas. Furthermore, the mean body mass index (BMI) level was inversely correlated with the number of steps on weekdays and during the whole week. On weekend days it was still inversed throughout with the number of steps; taken but the but the relationship was not statistically significant.