Effect of single and multiple passive stretching exercises upon heart rate variability in individuals with high and low flexibility levels

Purpose This study investigated heart rate variability indices within acute passive stretching sessions with different exercise amounts in individuals with low and high flexibility. Methods Fifty healthy men (23 ± 3 years) were randomly assigned into 4 subgroups: low flexibility-low amount, low flexibility-high amount, high flexibility-low amount, high flexibility-high amount. In groups with low amount of exercises, a single stretching of hamstrings to the maximal range of motion was performed; in high amount sessions, 6 exercises for lower and upper limbs were applied. In both protocols, individuals performed two 30-s sets using the passive static method. Heart rate variability indices in time and frequency domains were calculated from beat-to-beat intervals 15 min before, during the stretching, and along 30-min after exercise. Results Multifactorial ANOVA showed that in all cases, passive stretching induced parasympathetic suppression and sympathetic increase vs. baseline (p < 0.05). After exercise, interaction between repeated measures was significant only for exercise amount. An increase vs. baseline occurred in high frequency power (Δ% low amount: 6.7%, high amount: –9.7%; p < 0.05) and root mean square of successive differences (Δ% low amount: 17.1%, high amount: 14.1%; p < 0.05). The low frequency power (Δ% low amount: –4.2%, high amount: –6.9%; p < 0.05) and low-to-high frequency power ratio (Δ% high amount: –6.7%; p < 0.05) decreased. Conclusions Sympathetic modulation increased during acute stretching. Vagal increase and sympathetic reduction occurred during recovery, irrespective of flexibility. These changes were shorter after sessions including single (20 min) vs. multiple (30 min) exercises.