Application of an Electromyographic Index of Gait Instability to Developmental Process of Supported Walking in Normal Neonates and Infants

The purpose of this study was to see whether an electromyographic (EMG) index of gait instability is applicable to the developmental process of supported walking in normal neonates and infants. In six neonates ranging in age from 14 to 26 days after birth, EMGs of stepping were recorded at approximately from one to four week intervals until around four months. Additionally, longitudinal-EMGs of one subject were recorded at one or two week intervals until just before independent walking. EMG patterns of the lateral gastrocnemius (an ankle plantarflexor) and vastus medialis (a knee extensor) in the latter part of swing phase indicating unstable walking, not seen in the neonatal period up to first postnatal month, tended to increase in young infants at around three postnatal months. These results suggest the addition of voluntary infant stepping to reflex neonate stepping from around three months. From six to twelve months, these marked activities tended to decrease, gradually coming to resemble adult stable walking through development of strength, balance, and postural control. In conclusion, muscular activities of the lateral gastrocnemius and vastus medialis in the latter part of swing phase indicate unstable walking, findings which are applicable to developmental changes during newborn stepping and infant supported walking.