Electromyographic developmental changes in one individual from newborn stepping to mature walking
Introduction
During the first 3 years of life, human bipedal locomotion develops gradually towards mature walking throughout a series of phases: newborn stepping, infant supported walking (Fig. 1), infant independent walking, and child walking [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]. In the 20th century, some studies have provided detailed technical descriptions (kinematics, kinetics, temporal events, and electromyography (EMG)) of the developmental process of infant locomotion, although to study gait in babies using adult techniques [13], [14] is very difficult.
McGraw [1] analyzed seven selected phases in the development of erect locomotion from newborn stepping to mature erect walking, using film analysis, and pointed out the relations between several reflexes and the development of motor behavior. Touwen [15] clarified the interactions between reflexes and the development of motor behavior, emphasizing the longitudinal study of motor development. Using EMG can provide information about the maturation of gait that is both significant and otherwise unavailable in conventional motion analysis.
Although the study of human locomotion in infants using EMG is difficult, some cross-sectional and longitudinal EMG studies on the development of gait have been done [2], [3], [5], [6], [7], [9], [11]. Forssberg [6], Thelen et al. [5], and Okamoto et al. [2], [7], [11] have studied the developmental process from newborn stepping until infant supported walking prior to independent walking, and Sutherland et al. [9] and Okamoto et al. [3], [7], [11] have researched the learning process from early infant independent walking to mature walking. These studies have generally described developmental changes of various leg muscular activities in both supported and unsupported walking. We are unaware, however, of any studies that have described EMG developmental changes from newborn stepping all the way to mature walking longitudinally in the same individual.
The purpose of this study was to study longitudinal developmental changes of human locomotion in terms of leg muscle activity. EMGs of the same subject were recorded over 7 years, from 3 weeks after birth to 7 years of age, so that the entire span of gait development could be examined in one individual.
Section snippets
Methods
We made longitudinal observations on a female infant from 3 weeks after birth until 7 years of age. At the beginning, to induce newborn stepping, the examiner held the infant under the arms with the soles of the feet touching a horizontal flat surface. Well-coordinated walking movements were observed fairly consistently from shortly after birth to around 3 or 4 months. Although newborn stepping could not simply be arbitrarily elicited at the will of the examiner, we were able to select
Results
Based on the longitudinal EMG findings of the present investigation as well as from previous studies [2], [3], [7], [11], we divided the early development of gait into the following four phases: neonatal stepping, onset of young infant stepping, initial young infant stepping, and infant supported walking. Subsequent maturation of gait was also divided into four phases: onset of infant walking, initial infant walking, immature child walking, and mature walking. The data in Fig. 2, Fig. 3, Fig. 4
Discussion
During the first 3 years of life, movements related to walking appear to begin with gross patterns of muscle activation, frequently including co-activation of mutual antagonists. We observed a progression from excessive gross activation to more efficient and economical production of muscle activities in the lower limbs. This was seen, not only in supported walking and then in subsequent independent walking, but also in neonatal primitive walking (Fig. 7, Fig. 8) [2], [3], [5], [6], [7], [9],
Acknowledgements
The authors express deep gratitude to Dr H. Yamashita, H. Tsutsumi (Kansai Medical University), and Dr Y. Goto (Hyogo University of Teacher Education) for their cooperation.
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