Brief skin cooling modulates the reflexes generated by whole‑body vibration

Abstract

Background: Whole-body vibration (WBV) is a popular exercise method known for its neuromuscular benefits, though the underlying mechanisms remain unclear. WBV activates distinct reflexes based on vibration amplitude and voluntary muscle activity: low-amplitude vibration or voluntary contraction typically triggers the tonic vibration reflex (TVR), whereas high-amplitude vibration or quiet standing activates the bone myoregulation reflex (BMR). Muscle spindles, which are sensitive to sympathetic input, may exhibit increased responsiveness to vibration during brief skin cooling. Objectives: This study investigated the reflex mechanisms activated by WBV during quiet standing and their modulation by skin cooling. Methods: Thirty healthy young adults participated. The latency of the soleus TVR, induced by Achilles tendon vibration, and the latency of the soleus BMR, induced by WBV, were measured. These assessments were repeated during the cold pressor test (CPT), involving left-hand immersion in cold water. Results: The soleus TVR latency was 36.2 ± 5.1 ms, while the soleus BMR latency was 40.4 ± 5.0 ms. During CPT, Achilles tendon vibration latency remained unchanged (36.2 ± 5.7 ms, p = 0.319). However, the WBV-induced reflex latency with CPT (36.0 ± 6.1 ms, p < 0.0001) was significantly shorter than the soleus BMR latency and aligned with the TVR latency (p = 0.711). Conclusion: WBV activates BMR in a quiet standing position, but with skin cooling, the TVR predominates, likely due to heightened spindle sensitivity. These findings offer valuable insights into developing targeted WBV programs.