Muscles from the same muscle group do not necessarily share common drive: evidence from the human triceps surae

Abstract

It has been proposed that movements are produced through groups of muscles, or motor modules, activated by common neural commands. However, the neural origin of motor modules is still debated. Here, we used complementary approaches to determine: i) whether three muscles of the same muscle group (soleus, gastrocnemius medialis [GM] and lateralis [GL]) are activated by a common neural drive ; and ii) whether the neural drive to GM and GL could be differentially modified by altering the mechanical requirements of the task. Eighteen human participants performed an isometric standing heel raise and submaximal isometric plantarflexions (10%, 30%, 50% of maximal effort). High-density surface electromyography recordings were decomposed into motor unit action potentials and coherence analysis was applied on the motor units spike trains. We identified strong common drive to each muscle, but minimal common drive between the muscles. Further, large between-muscle differences were observed during the isometric plantarflexions, such as a delayed recruitment time of GL compared to GM and soleus motor units and opposite time-dependent changes in the estimates of neural drive to muscles during the torque plateau. Finally, the feet position adopted during the heel raise task (neutral vs internally rotated) affected only the GL neural drive with no change for GM. These results provide conclusive that not all anatomically defined synergist muscles are controlled by strong common neural drive. Independent drive to some muscles from the same muscle group may allow for more flexible control to comply with secondary goals such as joint stabilization.

Corticomuscular Coherence and Motor Control Adaptations after Isometric Maximal Strength Training

“…This result allows us to hypothesize that a longer training duration could be relevant to significantly decrease the CMC magnitude in both α-and ß-band, as reported by previous studies [7,11]. Finally, recent findings suggest that the muscle composing the TS could share less common input in comparison to other muscle groups [54]. The authors suggest that this strategy may allow more flexible control to comply both movement execution and balance control.…”

Analysis of motor unit spike trains estimated from high-density surface electromyography is highly reliable across operators

“…In two different experiments, HDsEMG was recorded from the Gastrocnemius lateralis (GL) and Gastrocnemius medialis (GM) [experiment I, (Hug et al, 2021)] and the tibialis anterior (TA) [experiment II, (Del Vecchio et al, 2019)]. These muscles were selected because they usually yield to different numbers – and accuracy - of decomposed units.…”

“…These muscles were selected because they usually yield to different numbers – and accuracy - of decomposed units. For example, Hug et al (2021) highlighted the challenge of extracting motor units from the GL muscle. In contrast, the TA muscle is known to be a reliable muscle for HDsEMG decomposition (Del Vecchio et al, 2020).…”

Analysis of motor unit spike trains estimated from high-density surface electromyography is highly reliable across operators

“…In two different experiments, HDsEMG was recorded from the Gastrocnemius lateralis (GL) and Gastrocnemius medialis (GM) [experiment I, (Hug et al, 2021)] and the tibialis anterior (TA) [experiment II, (Del Vecchio et al, 2019)]. These muscles were selected because they usually yield to different numbers -and accuracy -of decomposed units.…”

“…Therefore, we focused on data from four contraction intensities collected from different participants. Of note, the two original studies (Del Vecchio et al, 2019;Hug et al, 2021) measured only males and therefore the present study only considers decomposition from data collected in males.…”