The isometric handgrip (IHG) exercise is a relatively simple test that measures the hemodynamic response to a “pressor” stimulus. However, the response is a function of multiple factors, including sympathetic and parasympathetic output, negative feedback baroreceptor loop, local factors, cardiac function, and feedforward central commands [1]. Isometric handgrip exercise increases cardiac output due to increased metabolic demands on the body. Multiple hemodynamic parameters govern cardiac output. Abnormal changes in hemodynamic parameters during IHG may reflect the early stages of cardiovascular disease [2]. In addition, the role of IHG in the management of hypertension has been envisaged; training for more than six weeks could reduce blood pressure and cause modulation of cardiac autonomic function [2, 4,5,6]. Further, the isometric handgrip (IHG) test might be an approach to the early detection of individuals prone to developing hypertension [7, 8]. The isometric handgrip exercise causes changes in hemodynamic parameters and heart rate variability, with individual differences. Heart rate variability is an effective procedure to evaluate cardiovascular autonomic dysfunction [9]. The present study aimed to delineate the effects of baseline measurements on post-exercise hemodynamic responses. Nowadays, machine learning models have been developed to predict various diseases [10, 11]. The baseline measurements, along with post-exercise hemodynamic responses, could be used as features in predicting cardiovascular disease.
In this hospital-based cross-sectional study, 45 male students aged between 17 to 22 years enrolled from SMS Medical College, Jaipur (Rajasthan, India) after approval from the Institutional Ethical Committee. The study evaluated the effect of baseline measurements on hemodynamic responses and heart rate variability after doing the IHG exercise.
To evaluate the effect of baseline status, measurement of absolute responses was followed by calculation of relative responses (see Data Analysis). The relationships between absolute and relative responses were evaluated using correlation.
The participants avoided tea, coffee, and food for at least 2 hours before data collection. Researchers did the recording between 09:00 AM and 12:00 PM to prevent the effect of diurnal variation. They clinically examined participants to rule out any morbidity. If the participant was found healthy, researchers collected hemodynamic and heart rate variability data in three phases as follows:
The participants were instructed to hold the hand dynamometer to provide a maximal voluntary contraction as a baseline. The tension was called maximal isometric tension (Tmax). After a rest of one minute, the participants compressed the dynamometer to 30% of the maximal effort (Tmax) for 5 minutes. Researchers measured the blood pressure, pulse rate, and ECG signals before, during, and after IHG exercise.
Researchers measured systolic and diastolic blood pressure and pulse rate (PR) in the participant's non-tested arm in all the phases. An automated digital device was used to avoid a manual error. Further, researchers calculated pulse pressure (PP), mean arterial pressure (MAP), and rate pressure product (RPP).
The ECG signals for heart rate variability (HRV) were recorded using RMS Polyrite D (version 1.0) after a supine rest for 15 minutes. The resting ECG was recorded at a sampling frequency of 256 Hz. The tachogram (RR-interval series) was constructed from ECG signals. Researchers calculated time and frequency domain measures using Kubois software. The time-domain measures include the standard deviation of all RR intervals (SDNN), the square root of the mean of the sum of the squares of differences between adjacent RR intervals (RMSSD), and pNN50, which is the percentage of consecutive RR intervals that differ by more than 50 milliseconds. The frequency-domain measures include total power, power in the high frequency (HF) band (0.15–0.40Hz), power in the low frequency (LF) band (0.04–0.15 Hz), and LF/HF ratio [12,13,14].
The absolute readings were further processed to find out the relative readings. Let the baseline, phase 1, and phase 2 values of parameter X be represented by bX, X1, and X2, respectively. Then, the relative value of X1 is given by ΔX1=X1-bX.
Similarly, the relative value of X2 is given by ΔX2=X2-bX.
Based on normality, the quantitative variables were expressed as mean (SD) or median (IQR). The comparison of absolute values of parameters during baseline (bX), phase1 (X1), and phase 2 (X2) were performed using the Friedman test. The relative values of parameters during phase 1(ΔX1) and phase 2 (ΔX2) were compared using the Wilcoxon signed-rank test. Further, Pearson's coefficient measured the relationship between absolute and relative changes. The level of significance was considered at 5%. The JASP version 0.16.1.0 was used for statistical analysis (JASP Team) and MATLAB [15, 16].
The study showed significant increase in the absolute SBP [W = 5.75 ;
One-way repeated-measures ANOVA to compare various absolute hemodynamic parameters before (baseline), during (phase 1), and after 5 minutes (phase 2) of handgrip exercise
SBP | bSBP | 114 | 10 | 34.785 | < .001 | bSBP | SBP1 | 5.747 | < .001 |
SBP1 | 120 | 12 | bSBP | SBP2 | 4.057 | < .001 | |||
SBP2 | 120 | 12 | SBP1 | SBP2 | 1.69 | 0.284 | |||
DBP | bDBP | 78 | 10 | 74.235 | < .001 | bDBP | DBP1 | 8.622 | < .001 |
DBP1 | 90 | 14 | bDBP | DBP2 | 4.061 | < .001 | |||
DBP2 | 80 | 10 | DBP1 | DBP2 | 4.561 | < .001 | |||
HR | bHR | 80 | 19 | 74.279 | < .001 | bHR | HR1 | 8.523 | < .001 |
HR1 | 86 | 20 | bHR | HR2 | 5.394 | < .001 | |||
HR2 | 86 | 18 | HR1 | HR2 | 3.129 | 0.007 | |||
PP | bPP | 38 | 12 | 12.358 | 0.002 | bPP | PP1 | 3.335 | 0.004 |
PP1 | 31 | 12 | bPP | PP2 | 0.699 | 1 | |||
PP2 | 37 | 12 | PP1 | PP2 | 2.635 | 0.03 | |||
MAP | bMAP | 89.333 | 10 | 79.416 | < .001 | bMAP | MAP1 | 8.905 | < .001 |
MAP1 | 99.333 | 13.333 | bMAP | MAP2 | 4.771 | < .001 | |||
MAP2 | 94 | 10.667 | MAP1 | MAP2 | 4.135 | < .001 | |||
RPP | bRPP | 92.4 | 17.84 | 76.227 | < .001 | bRPP | RPP1 | 8.637 | < .001 |
RPP1 | 107.1 | 24.84 | bRPP | RPP2 | 5.438 | < .001 | |||
RPP2 | 101.48 | 18.63 | RPP1 | RPP2 | 3.199 | 0.006 |
One-way repeated-measures ANOVA to compare various absolute heart rate variability measures before (baseline), during (phase 1), and after 5 minutes (phase 2) of handgrip exercise
SDNN | bSDNN | 0.059 | 0.04 | 7.112 | 0.029 | bSDNN | SDNN1 | 0.159 | 1 |
SDNN1 | 0.064 | 0.039 | bSDNN | SDNN2 | 2.385 | 0.058 | |||
SDNN2 | 0.073 | 0.059 | SDNN1 | SDNN2 | 2.226 | 0.086 | |||
RMSSD | bRMSSD | 0.067 | 0.058 | 9.911 | 0.007 | bRMSSD | RMSSD1 | 0.527 | 1 |
RMSSD1 | 0.061 | 0.066 | bRMSSD | RMSSD2 | 2.424 | 0.052 | |||
RMSSD2 | 0.068 | 0.071 | RMSSD1 | RMSSD2 | 2.951 | 0.012 | |||
pN50 | bpN50 | 0.211 | 0.374 | 11.227 | 0.004 | bpN50 | pN501 | 0.427 | 1 |
pN501 | 0.26 | 0.268 | bpN51 | pN502 | 2.666 | 0.027 | |||
pN502 | 0.378 | 0.46 | pN501 | pN502 | 3.092 | 0.008 | |||
TP | bTP | 1087 | 2077.8 | 4.844 | 0.089 | bTP | TP1 | 0.211 | 1 |
TP1 | 1204 | 2390.5 | bTP | TP2 | 2.003 | 0.145 | |||
TP2 | 1427 | 3198 | TP1 | TP2 | 1.792 | 0.23 | |||
HF | bHF | 322.08 | 826.42 | 5.404 | 0.067 | bHF | HF1 | 0.742 | 1 |
HF1 | 356.4 | 832.54 | bHF | HF2 | 1.537 | 0.384 | |||
HF2 | 534.79 | 967.96 | HF1 | HF2 | 2.279 | 0.075 | |||
LF/HF | bLF/HF | 0.66 | 0.46 | 70.136 | < .001 | bLF/HF | LF/HF1 | 8.21 | < .001 |
LF/HF1 | 1.1 | 1.05 | bLF/HF | LF/HF2 | 5.545 | < .001 | |||
LF/HF2 | 0.9 | 0.78 | LF/HF1 | LF/HF2 | 2.666 | 0.027 |
Further, researchers compared relative cardiovascular responses and found a significant decrease in phase 2 compared to phase 1 (Table 3). Similarly, the relative change in all heart rate variability parameters, except LF/HF ratio, were higher during phase 2 as compared with phase 1 (Table 4).
Comparison of relative hemodynamic parameters during (phase 1) and after 5 minutes (phase 2) of IHG exercise
SBP | ΔSBP1 | 6 | 12 | 413 | 0.018 |
ΔSBP2 | 4 | 7 | |||
DBP | ΔDBP1 | 12 | 10 | 736 | < .001 |
ΔDBP1 | 6 | 8 | |||
HR | ΔHR1 | 7 | 6 | 694.5 | < .001 |
ΔHR2 | 4 | 4 | |||
PP | ΔPP1 | −5.333 | 9.677 | −3.964 | < .001 |
ΔPP2 | −1.378 | 7.779 | |||
MAP | ΔMAP1 | 9.667 | 7.667 | 916 | < .001 |
ΔMAP2 | 4.667 | 7.333 | |||
RPP | ΔRPP1 | 13.057 | 7.909 | 3.769 | < .001 |
ΔRPP2 | 9.647 | 6.083 |
Comparison of various relative heart rate variability parameters during (phase 1) and after 5 minutes (phase 2) of IHG exercise
RMSSD | ΔRMSSD1 | −0.001 | 0.032 | 314 | 0.022 |
ΔRMSSD2 | 0.01 | 0.046 | |||
pN50 | ΔpN501 | 0 | 0.11 | 213 | 0.002 |
ΔpN502 | 0.049 | 0.129 | |||
SDNN | ΔSDNN1 | 0 | 0.021 | 269 | 0.005 |
ΔSDNN2 | 0.006 | 0.032 | |||
TP | ΔTP1 | −2.7 | 1067.8 | 334 | 0.038 |
ΔTP2 | 557.5 | 2461 | |||
HF | ΔHF1 | −34.32 | 433.16 | 309 | 0.03 |
ΔHF2 | 101.9 | 572.9 | |||
LF/HF | ΔLF/HF1 | 0.47 | 0.57 | 715 | < .001 |
ΔLF/HF2 | 0.24 | 0.27 |
To find the effect of baseline values on post-exercise responses, the authors calculated Pearson's correlation between absolute and relative responses. The study showed a significant effect of baseline values on the relative DBP, PP, and MAP in phases 1 and 2. However, baseline values had no significant impact on relative changes in SBP, HR, and RPP in phases 1 and 2 (Table 5). The relative values of all heart rate variability parameters in phase 1 were significantly correlated with baseline values. However, baseline values had no significant association with relative changes in phase 2 heart rate variability measures (Table 6).
Relationship between absolute and relative changes in hemodynamic parameters before (baseline), during (phase 1), and after 5 minutes (phase 2) of isometric handgrip exercise
SBP | bSBP | ΔSBP1 | −0.17 | 0.264 |
bSBP | ΔSBP2 | −0.158 | 0.299 | |
SBP1 | ΔSBP1 | 0.594 | < .001 | |
SBP2 | ΔSBP2 | 0.497 | < .001 | |
DBP | bDBP | ΔDBP1 | −0.41 | 0.005 |
bDBP | ΔDBP2 | −0.367 | 0.013 | |
DBP1 | ΔDBP1 | 0.397 | 0.007 | |
DBP2 | ΔDBP2 | 0.362 | 0.015 | |
HR | bHR | ΔHR1 | −0.197 | 0.195 |
bHR | ΔHR2 | −0.274 | 0.069 | |
HR1 | ΔHR1 | 0.09 | 0.557 | |
HR2 | ΔHR2 | −0.054 | 0.724 | |
PP | bPP | ΔPP1 | −0.408 | 0.005 |
bPP | ΔPP2 | −0.339 | 0.023 | |
PP1 | ΔPP1 | 0.594 | < .001 | |
PP2 | ΔPP2 | 0.492 | < .001 | |
MAP | bMAP | ΔMAP1 | −0.317 | 0.034 |
bMAP | ΔMAP2 | −0.304 | 0.042 | |
MAP1 | ΔMAP1 | 0.401 | 0.006 | |
MAP2 | ΔMAP2 | 0.363 | 0.014 | |
RPP | bRPP | ΔRPP1 | −0.077 | 0.615 |
bRPP | ΔRPP2 | −0.147 | 0.336 | |
RPP1 | ΔRPP1 | 0.401 | 0.006 | |
RPP2 | ΔRPP2 | 0.244 | 0.107 |
Relationship between absolute and relative changes in heart rate variability parameters before (baseline), during (phase 1), and after 5 minutes (phase 2) of isometric handgrip exercise
TP | bTP | ΔTP1 | −0.819 | < .001 |
bTP | ΔTP2 | −0.163 | 0.286 | |
TP1 | ΔTP1 | 0.206 | 0.174 | |
TP2 | ΔTP2 | 0.59 | < .001 | |
HF | bHF | ΔHF1 | −0.763 | < .001 |
bHF | ΔHF2 | −0.116 | 0.447 | |
HF1 | ΔHF1 | 0.224 | 0.139 | |
HF2 | ΔHF2 | 0.544 | < .001 | |
LF/HF | bLF/HF | ΔLF/HF1 | 0.335 | 0.025 |
bLF/HF | ΔLF/HF2 | 0.188 | 0.215 | |
LF/HF1 | ΔLF/HF1 | 0.832 | < .001 | |
LF/HF2 | ΔLF/HF2 | 0.737 | < .001 | |
RMSSD | bRMSSD | ΔRMSSD1 | −0.581 | < .001 |
bRMSSD | ΔRMSSD2 | −0.078 | 0.611 | |
RMSSD1 | ΔRMSSD1 | 0.347 | 0.02 | |
RMSSD2 | ΔRMSSD2 | 0.605 | < .001 | |
pN50 | bpN50 | ΔSpN501 | −0.524 | < .001 |
bpN50 | ΔSpN502 | −0.027 | 0.86 | |
pN501 | ΔSpN501 | 0.193 | 0.203 | |
pN502 | ΔSpN502 | 0.438 | 0.003 | |
SDNN | bSDNN | ΔSDNN1 | −0.634 | < .001 |
bSDNN | ΔSDNN2 | −0.023 | 0.882 | |
SDNN1 | ΔSDNN1 | 0.151 | 0.323 | |
SDNN2 | ΔSDNN2 | 0.585 | < .001 |
Isometric exercise is defined as a sustained muscular contraction with no joint movements. Conventionally, no work was done during the exercise. The oxygen consumption is moderate compared to isotonic exercise. The cardiovascular effects of static or isometric exercise primarily reflect the response to increased afterload or blood pressure. In contrast, the response to isotonic exercise is due to volume overload on the heart [12]. The high muscle tension and reduced blood flow produce a unique “pressor” reflex increase in systemic arterial pressure [17]. The reflex increases sympathetic activity in the heart and vessels and decreases parasympathetic activity, increasing BP, heart rate, and total peripheral resistance through arteriolar constriction. The sympathetic output varies in contracting and non-contracting skeletal muscle and is differentially controlled by a central command and the metaboreflex in healthy conditions. Further, studies on animals and humans showed the effect of cardiovascular diseases, such as diabetes, hypertension, and heart failure, on altered “pressor” reflex function [18]. The hemodynamic response to isometric handgrip exercise results from a complex interaction of multiple factors, including sympathetic and parasympathetic output, norepinephrine uptake, baroreceptor loop, cardiac function, central commands, and age [1, 19]. Most studies showed the effect of IHG exercise on cardiovascular responses. The present study evaluated changes in absolute and relative responses compared to baseline measurements.
Similar to the present study, Laird et al. showed the effect of submaximal (25% maximal) IHG in 32 normal adolescents. They found significant increases in mean heart rate, systolic, diastolic, and mean blood pressures [20]. Aminoff et al. reported increased heart rate and blood pressure during sustained IHG were partly due to central command and partly due to activation of the afferent limb reflex arc from contraction of muscles. At least a 15 mmHg increase in diastolic pressure was considered normal [21]. The present study enrolled only males within a narrow range of age to eliminate the effects of age on post-exercise responses. Cauwenberghs et al. observed a positive correlation of age with blood pressure and pulse pressure changes in 3 minutes of 40% maximal IHG. They showed significantly higher heart rate and diastolic BP after exercise in males compared to females [2]. In addition, Goulopoulou et al. showed greater mean arterial pressure responses in adults compared to children (
The present study evaluated the effects of IHG exercise on heart rate variability parameters. Kluess et al., in a study on 34 participants (age, 20 ± 1 year), compared heart rate variability parameters during spontaneous breathing, venous-occluded exercise (60% maximal voluntary contraction, 0.5 Hz), and immediate postexercise arterial occlusion. Similar to the present study, researchers found increased LFnu (+9.39 ± 16.83%) and MAP (+25.40 ± 17.55 mm Hg) after exercise. On the contrary, mean R-R interval (−230.73 ± 125.79 msec) and SDNN (−38.54 ± 36.02 msec) showed decrease (
The present study found that initial baseline status affects cardiovascular responses after IHG exercise. In a meta-analysis of seven randomized controlled trials, Yin et al. found the effect of isometric handgrip (IHG) training on resting BP and heart rate. They analyzed the association between IHG training and participants with different initial BP status. The participants in training groups showed significantly decrease in SBP [MD= −8.33, 95% CI: −11.19 to −5.46;
The present study evaluated the acute effects of IHG exercise on cardiovascular responses. Many studies suggested IHG training as an intervention for hypertension. On the contrary, Moldoven et al. found that IHG training for 8–10 weeks had an impact on resting arterial blood pressure and heart rate variability in an investigation. However, blood pressure and heart rate variability parameters had no significant effects [
The present study concludes that initial baseline status should be considered while evaluating the post–IHG exercise responses. The study showed a significant effect of baseline measurements on post–IHG exercise diastolic blood pressure, pulse pressure, and mean arterial pressure, and the heart rate variability parameters.