Effects of vibration in inline skating on the Hoffmann reflex, force, and proprioception

Purpose: The objective of this study was to examine the effects of vibrations induced by inline skating on the Hoffmann (H) reflex, maximal voluntary isometric (MVC) force, and ankle proprioception. Methods: Accelerometers were used to measure the frequencies and amplitudes of the vibrations encountered at the skate and mid-tibia levels. The soleus H reflex was recorded before and after (for 30 min) inline skating for 30 min. Maximal plantarflexor contractions were performed against a strain gauge while EMG was recorded from the soleus and medial gastrocnemius muscles. An ankle position-matching test was carried out to measure proprioception at the ankle. A Modified Borg Scale was used to obtain the appreciation of leg numbness and fatigue during inline skating. Results: The vibrations measured at the skate chassis level had a mean frequency of 141.8 +/- 25.2 Hz and an amplitude of less than or equal to 5 g. These vibrations were transmitted to the lower limb as measured by a mean frequency of 34.4 +/- 27.7 Hz and an amplitude of less than or equal to 2 g at the mid-tibia level. The results demonstrate a clear inhibition (similar to35%) of the H reflex after skating that persisted for >35 min after skating. A 10% drop in MVC plantarflexor force was observed after inline skating. There was no accompanying change in EMG signal parameters. The ankle proprioception of the subjects decreased after skating, resulting in reproduction errors twice as large as before skating. Conclusion: Vibrations encountered during inline skating resulted in modifications of neuromotor functions related to the muscle spindles' primary afferent. These changes may partially be explained by presynaptic inhibition; however, a more plausible mechanism may be a decrease in the la afferent transmission induced by the vibration.