A kinematic analysis of hindlimb motility in 9- and 10-day-old chick embryos.

Although chick embryonic leg movements appear jerky and disorganized, the underlying motor patterns are coordinated. This apparent conflict in results was investigated using kinematic analyses to provide detailed quantitative descriptions of leg movements during spontaneous motility in 9- and 10-day-old chick embryos. In many respects, hip, knee, and ankle movements were highly variable. There was variation in movement durations and in the number of leg joints that participated in a given movement. Motion could begin with either flexion or extension. Furthermore, the limb could return to its rest position between movements or move continuously to produce sequences of variable lengths. Patterns of interlimb coordination included alternating, synchronous and independent movements of the legs. We propose that these variable features account for the uncoordinated appearance of embryonic leg movements. In addition to variable features, however, some consistent characteristics were identified. For example, when more than one joint was active, activity typically began and ended synchronously. Furthermore, all active joints generally extended or flexed together and movements were symmetrical. These data are consistent with previous EMG results. Therefore, despite the variability in some parameters that results in the perception that embryonic leg movements are random and uncoordinated, our kinematic analyses show that an organized pattern of interjoint coordination is a prominent feature. This basic pattern shows some similarities to, but is less complex than, kinematic patterns found during a variety of posthatching behaviors.