Ankle Flexors Produce Peak Torque at Longer Muscle Lengths After Whole-body Vibration

Introduction: Whole-body vibration (WBV) has become a popular training method in recent years. This study investigated the effect of WBV on the length-tension relationship of the ankle dorsi- and plantarflexors as measured by a Biodex dynamometer (Biodex Medical Systems Inc, Shirley, NY).

Methods: Twenty healthy young adult males participated in this study and were exposed to two treatments. The first treatment (nonvibration) involved passive stretching of the plantarflexors at end range of motion (ROM) for five 1-min bouts. The second treatment involved the same passive stretch with superimposed WBV (frequency = 26 Hz) for five 1-min bouts on a rotary vibration plate (Galileo 900; Novotec, Pforzheim, Germany). Voluntary ROM, peak torque, and corresponding joint angle of the plantar- and dorsiflexors were recorded pre- and posttreatment. Within-treatment (before and after) and between-treatment (WBV and nonvibration) outcomes were assessed by repeated-measures MANOVA.

Results: No significant changes in the measures of ankle dorsiflexion were found within or between treatments. No significant changes in the measures of ankle plantarflexion were found after the nonvibration treatment. After WBV, however, there was a significant 7.1 degree shift in the angle (P = 0.001) of peak plantarflexor torque production corresponding to a longer muscle length.

Conclusion: This study shows that stretched human ankle plantarflexors respond to WBV by generating peak voluntary torque at longer muscle lengths. This has possible benefits for the rehabilitation of patients with neuromuscular disorders (e.g., stroke) who experience short ankle flexor resting lengths.