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

Jakob Škarabot,Kirsty M Hicks,Glyn Howatson,Stuart Goodall,Paul Ansdell,Callum G Brownstein,Rade Durbaba

doi:10.1007/s00221-019-05590-3

Jakob Škarabot, Kirsty M Hicks + Show 5 more

Open Access

https://doi.org/10.1007/s00221-019-05590-3

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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. In addition, 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.

Highlights

Corticospinal excitability is constantly modulated during passive and active movements
Fascicle length was modulated during passive ankle movement both in SOL (F4,24 = 109.9, p < 0.001; Fig. 3a) and tibialis anterior (TA) (F4,24 = 239.9, p < 0.001; Fig. 3b), such that fascicle length changed linearly (Fig. 3) with changes in joint angle throughout the 20° of range of motion (p ≤ 0.003 and p ≤ 0.002 for SOL and TA, respectively)
The stimulus intensity at Resting motor threshold (rMT) was higher in SOL (54 ± 8% SO) compared to TA (48 ± 7% SO; t11 = 3.0, p = 0.012)

Summary

Introduction

Corticospinal excitability is constantly modulated during passive and active movements. Elucidating the direct effect of muscle length-related feedback on the corticospinal tract output during dynamic contractions is challenging due to the influence of postsynaptic control mechanisms (Valadão et al 2018; Barrué-Belou et al 2018), and potential differences in neural drive that can influence neurophysiological responses (Abbruzzese et al 1994; Morita et al 2000). The firing of muscle spindle afferents increases proportionally to the magnitude of the stretch, but remains low during shortening of a muscle (Matthews 2011; Day et al 2017). This behaviour at the somatosensory receptor level might, in turn, modulate the corticospinal responses.

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