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

Background Whole-body vibration (WBV) is a popular exercise method known for its neuromuscular benefts, though the underlying mechanisms remain unclear. WBV activates distinct refexes based on vibration amplitude and voluntary muscle activity: low-amplitude vibration or voluntary contraction typically triggers the tonic vibration refex (TVR), whereas highamplitude vibration or quiet standing activates the bone myoregulation refex (BMR). Muscle spindles, which are sensitive to sympathetic input, may exhibit increased responsiveness to vibration during brief skin cooling. Objectives This study investigated the refex 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 refex latency with CPT (36.0 ±6.1 ms, p< 0.0001) was signifcantly 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 fndings ofer valuable insights into developing targeted WBV programs.