UBC Theses and Dissertations
Use of bracing and EMG biofeedback to investigate the relationship between soleus and gastrocnemius excitation during cycling Wilkes, Julia
Introduction Our basic understanding of muscle synergies is incomplete. The interaction among the triceps surae muscles (medial and lateral gastrocnemius, soleus) is still under investigation. Studies have shown that these muscles respond differently to cadence manipulations. These excitation differences might relate to the role of gastrocnemius in knee flexion, a role that soleus does not serve. Purpose The purpose was to investigate the response of the medial and lateral gastrocnemius muscles when soleus excitation was eliminated using bracing and biofeedback during cycling. Methods Participants cycled under braced and unbraced conditions over two sessions. During each session, cycling protocol involved a normalization ride with no brace and no feedback, followed by a second ride without feedback, and a prolonged ride with feedback. The biofeedback consisted of a moving bar graph representing the average soleus excitation for the first half of the pedal cycle and was updated with every pedal stroke. Electromyography of seven muscles was collected and analyzed. Results In the unbraced condition, soleus excitation was not modified with visual biofeedback. While wearing the brace, the integrated electromyography (iEMG) of all triceps surae muscles decreased by 30%. With the addition ofEMG biofeedback, soleus and lateral gastrocnemius iEMG decreased a further 26% and 21% respectively by the end of the feedback period while medial gastrocnemius excitation did not change. Tibialis anterior excitation was significantly increased while rectus femoris and biceps femoris excitation did not change. Gluteus maximus iEMG decreased with bracing and biofeedback. Conclusions While unbraced, soleus excitation was not reduced with biofeedback as it is difficult to modify joint position in this learned motor task. When the known task was modified by applying an ankle-foot orthosis, participants successfully modified soleus excitation under less-familiar task requirements. Participants voluntarily activated the tibialis anterior muscle, and it is proposed that through reciprocal inhibition pathways, soleus EMG was reduced. Lateral gastrocnemius excitation also decreased. With soleus excitation decreased, medial gastrocnemius excitation was unchanged likely due to its on going role in knee flexion. This effect was localized to the ankle joint as proximal muscles were unaffected by bracing and by voluntary changes in soleus excitation.
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