Development of coordinated movement in chicks: I. Temporal analysis of hindlimb muscle synergies at embryonic days 9 and 10

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Abstract
In this study, we examined electromyographic activity for an ensemble of hindlimb muscles during spontaneous activity in chick embryos to advance understanding of early motor coordination and its relationship to later emerging behaviors. Four-channel recordings were obtained from 6 muscles in ovo at embryonic Days 9 and 10. Analyses indicated that when muscles are repetitively active, patterns during embryonic motility are distinct from those for other behaviors. For example, unlike the muscle patterns for locomotion, extensor muscles and flexor muscles are synchronously activated at 50% of the extensor cycle period. Furthermore, flexor and extensor bursts are similar in duration and show little correlation with extensor cycle period. Finally, our data sugest that the ensemble of muscles active can vary from cycle to cycle. This study provides the basis for future studies that will examine neural and biomechanical interactions underlying the development of coordinated movement.