Electromyographic characteristics at the onset of independent walking in infancy.

In order to elucidate electromyographic characteristics of infant walking at the onset of independent gait, we longitudinally recorded electromyograms from muscles of both legs during the learning process of walking in an infant, from ten months after birth until about three years of age. We found electromyographic characteristics of infant gait up to around one month after learning to walk that are not usually seen in adult gait. In stance phase from foot contact until push off, the role of the vastus medialis for maintaining stability became clear as a slightly squatted position was used to lower the center of gravity. Orderly reciprocal or cocontraction patterns of activity in the rectus femoris and biceps femoris or in the tibialis anterior and gastrocnemius were found to be related to returning the body's center of mass toward its initial position. In the latter half of swing phase, the vastus medialis and gastrocnemius showed strong activities with the knee extending and ankle plantarflexing for active leg extension to prevent falling. These characteristically excessive muscle activities in infant walking are considered to express weak muscle strength and an immature balancing system. As months and years pass, the muscles become stronger and balance matures, obviating the need for so much myoelectric activity.