Corticospinal excitability of tibialis anterior and soleus differs during passive ankle movement

Škarabot, Jakob, Ansdell, Paul, Brownstein, Callum, Hicks, Kirsty, Howatson, Glyn, Goodall, Stuart and Durbaba, Rade (2019) Corticospinal excitability of tibialis anterior and soleus differs during passive ankle movement. Experimental Brain Research, 237 (9). pp. 2239-2254. ISSN 0014-4819

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Abstract

The purpose of this study was to assess corticospinal excitability of soleus (SOL) and tibialis anterior (TA) at a segmental level during passive ankle movement. Four experimental components were performed to assess the effects of passive ankle movement and muscle length on corticospinal excitability (MEP/Mmax) at different muscle lengths, subcortical excitability at the level of lumbar spinal segments (LEP/Mmax), intracortical inhibition (SICI) and facilitation (ICF), and H-reflex in SOL and TA. Additionally, the degree of fascicle length changes between SOL and TA was assessed in a subpopulation during passive ankle movement. Fascicles shortened and lengthened with joint movement during passive shortening and lengthening of SOL and TA to a similar degree (p<0.001). Resting motor threshold was greater in SOL compared to TA (p≤0.014). MEP/Mmax was facilitated in TA during passive shortening relative to the static position (p≤0.023) and passive lengthening (p≤0.001), but remained similar during passive ankle movement in SOL (p≥0.497), regardless of muscle length at the point of stimulus (p=0.922). LEP/Mmax (SOL: p=0.075, TA: p=0.071), SICI (SOL: p=0.427, TA: p=0.540) and ICF (SOL: p=0.177, TA: p=0.777) remained similar during passive ankle movement. H-reflex was not different across conditions in TA (p=0.258), but was reduced during passive lengthening compared to shortening in SOL (p=0.048). These results suggest a differential modulation of corticospinal excitability between plantar and dorsiflexors during passive movement. The corticospinal behaviour observed might be mediated by an increase in corticospinal drive as a result of reduced afferent input during muscle shortening and appears to be flexor-biased.

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