Anti-Gravitational Growth-Associated Changes in the Mobilization of Leg Muscles during Walking in One Girl

Abstract

Growth-related changes in the mobilization of leg muscles during walking were studied in human subject. Mobilization of soleus, lateral portion of gastrocnemius (LG), and tibialis anterior (TA) muscles during the first walking steps in the life of a 12-month and 11-day old baby girl was checked by recording electromyogram (EMG). The same recordings were also performed, when she became 15 years old. The body balance during walking was also monitored by recording the ground reaction forces on a three-dimensional force plate. Co-contraction of ankle plantar-flexors (soleus and LG) and dorsi-flexor (TA) was observed during the first walking in her life. The EMG amplitudes and the step intervals were not constant. But disturbance of body balance toward both anterior/posterior and right/left directions was minor, although some degree of fluctuation was noted in the vertical force during the body-support phase. The relatively stable forces toward anterior and posterior direction, without heel-strike followed by toe-kick, suggested that her landing patterns were flat-foot strike. Data also suggested that the immature walking was not directly related to the poor body balance. The co-contraction of antagonists disappeared and walking patterns were normalized at the age of 15. It was speculated that afferent input may play an important role in the learning of walking motor performance in new-born babies, since the afferent neural input is closely related to the antigravity activity of muscle.