Test-retest reliability of v-wave responses in the soleus and gastrocnemius medialis

This study was designed to assess the reliability of the first volitional (V) wave, which can be used as a measure of efferent neural drive, while also reflecting reflex excitability. Ten subjects volunteered for one familiarization session followed by an experimental test session and an identical retest session spaced 3 to 8 days apart. V-waves were evoked in the tibial nerve during plantar flexion maximal voluntary isometric contractions (MVCs). Test-retest reliability was assessed using the intraclass correlation coefficient (ICC), along with standard error of measurement and 95% confidence intervals for the following variables: MVC force, surface electromyogram activity (EMG), and the peak-to-peak V-wave amplitude in soleus (SOL) and gastrocnemius medialis (GM). The superimposed M-wave (MSUP) accompanying V-wave stimulation was also obtained for normalization purposes. Substantial reliability was documented for V/MSUP in both SOL (ICC = 0.86) and GM (0.90), as well as for the non-normalized V-wave in SOL (0.92). Moderate reliability was displayed for the non-normalized V-wave response in GM (0.78). Substantial reliability was also established for EMG/MSUP (>0.82) and MVC force (0.98). This study provides novel evidence that V-wave responses can be consistently measured in the SOL and GM, thus advocating its continued use in future research.