Duration Of Vibration Effects On H-reflex Amplitude

Previous studies indicate muscle spindles recover in ~40 seconds or less after vibration. Yet, when analyzing muscle spindle activity post vibration, some studies use 100 seconds as the recovery timepoint. This inconsistency in recovery timepoint analysis may affect results interpretation. PURPOSE: Therefore, the current investigation analyzed H-reflex differences between the first 40 seconds and subsequent 40 seconds. METHODS: Six healthy participants (age: 23.6 ± 4.2 years, height: 159 ± 3.7 cm, weight: 68 ± 16.0 kg) were standing when electrical stimulations (1000 μs at .2 hz) was applied to the soleus muscle. Ten H-reflexes, separated by 8-10s, were taken before and after 20 minutes of Achilles tendon vibration (70 Hz at 1.2 mm, 100 Hz at 1.5 mm). H-reflexes were normalized to the max M-wave (%Mmax). A repeated ANOVA was run to analyze the differences between H-reflexes before vibration (PreH), right after the cessation of vibration to 40 seconds (Post 0 - 40s) and from 50 - 90 seconds after vibration (Post 50 - 90s). RESULTS: The initial ANOVA revealed a significant difference. A post hoc analysis revealed a significant difference between PreH and Post 0-40 H-reflexes - analysis showed that the Post 0 - 40 were 5% lower than pre values (p < 0.001). In contrast, no significant differences were seen between PreH and Post 50 - 90s; however, a significant difference was identified between Post 0 - 40 to Post 50 - 90 (p = .007). CONCLUSION: These results indicate no difference between preH and Post 50-90 suggesting H-reflex return to baseline at approximately 50 seconds post vibration period. The significant difference between post 0-40 and post 50-90 suggests an optimal window for assessing H-reflex remains less than 40 seconds post activity.