Coordination of intrinsic and extrinsic foot muscles during walking
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The human foot undergoes complex deformations during walking due to passive tissues and active muscles. However, based on prior recordings it is unclear if muscles that contribute to flexion/extension of the metatarsophalangeal (MTP) joints are activated synchronously to modulate joint impedance, or sequentially to perform distinct biomechanical functions. We investigated the coordination of MTP flexors and extensors with respect to each other, and to other ankle–foot muscles.
We analyzed surface electromyographic (EMG) recordings of intrinsic and extrinsic foot muscles for healthy individuals during level treadmill walking, and also during sideways and tiptoe gaits. We computed stride-averaged EMG envelopes and used the timing of peak muscle activity to assess synchronous vs. sequential coordination.
We found that peak MTP flexor activity occurred significantly before peak MTP extensor activity during walking (P < 0.001). The period around stance-to-swing transition could be roughly characterized by sequential peak muscle activity from the ankle plantarflexors, MTP flexors, MTP extensors, and then ankle dorsiflexors. We found that foot muscles that activated synchronously during forward walking tended to dissociate during other locomotor tasks. For instance, extensor hallucis brevis and extensor digitorum brevis muscle activation peaks decoupled during sideways gait.
The sequential peak activity of MTP flexors followed by MTP extensors suggests that their biomechanical contributions may be largely separable from each other and from other extrinsic foot muscles during walking. Meanwhile, the task-specific coordination of the foot muscles during other modes of locomotion indicates a high-level of specificity in their function and control.
KeywordsFoot Ankle Metatarsophalangeal flexion and extension EMG Walking Muscle coordination
Extensor digitorum brevis
Extensor hallucis brevis
Extensor hallucis longus
Flexor digitorum brevis
Flexor digitorum longus and flexor hallucis longus
Flexor digitorum longus
Flexor hallucis longus
Financial support from the Italian University Ministry (PRIN project), Italian Space Agency (COREA grant), EU FP7-ICT program (MINDWALKER Grant # 247959 and AMARSi Grant # 248311) and Whitaker International Program is gratefully acknowledged.
Conflict of interest
The authors declare that they have no conflict of interest.
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