Abstract
BackgroundVariations in the amplitude of surface electromyograms (EMGs) are typically considered to advance inferences on the timing and degree of muscle activation in different circumstances. Surface EMGs are however affected by factors other than the muscle neural drive. In this study, we use electrical stimulation to investigate whether architectural changes in tibialis anterior (TA), a key muscle for balance and gait, affect the amplitude of surface EMGs.MethodsCurrent pulses (500 μs; 2 pps) were applied to the fibular nerve of ten participants, with the ankle at neutral, full dorsi and full plantar flexion positions. Ultrasound images were collected to quantify changes in TA architecture with changes in foot position. The peak-to-peak amplitude of differential M waves, detected with a grid of surface electrodes (16 × 4 electrodes; 10 mm inter-electrode distance), was considered to assess the effect of changes in TA architecture on the surface recordings.ResultsOn average, both TA pennation angle and width increased by respectively 7 deg. and 9 mm when the foot moved from plantar to dorsiflexion (P < 0.02). M-wave amplitudes changed significantly with ankle position. M waves elicited in dorsiflexion and neutral positions were ~25% greater than those obtained during plantar flexion, regardless of where they were detected in the grid (P < 0.001). This figure increased to ~50% when considering bipolar M waves.ConclusionsFindings reported here indicate the changes in EMG amplitude observed during dynamic contractions, especially when changes in TA architecture are expected (e.g., during gait), may not be exclusively conceived as variations in TA activation.
Highlights
Variations in the amplitude of surface electromyograms (EMGs) are typically considered to advance inferences on the timing and degree of muscle activation in different circumstances
General considerations Ankle Ankle at dorsiflexion position (DF) corresponded to approximately 30° of flexion and Ankle at plantar flexion position (PF) to 40° of extension
Results from a representative participant The effect of foot position on tibialis anterior (TA) architecture and M waves is well appreciated by inspecting results from a single, representative participant
Summary
Variations in the amplitude of surface electromyograms (EMGs) are typically considered to advance inferences on the timing and degree of muscle activation in different circumstances. We use electrical stimulation to investigate whether architectural changes in tibialis anterior (TA), a key muscle for balance and gait, affect the amplitude of surface EMGs. Surface electromyograms (EMGs) provide key, relevant information on the timing and relative degree of muscle activation [1, 2]. Changes in the amplitude of surface EMGs may not indicate variations in the muscle neural drive. It is well established the amplitude of EMGs detected by surface electrodes positioned symmetrically at both sides of the muscle innervation zone may be remarkably small (i.e., end-plates’ location; [9, 10]). Even though not well explored in the literature, changes in muscle
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