To develop an index of gait instability from electromyographic information, we made observations on infants from the time they first began to walk independently at about one year of age until around three years of age. From our findings we obtained the following criteria. (1) Very unstable gait: As seen in a child within the first month of learning to walk the vastus medialis is active in the latter half of swing phase, the tibialis anterior and rectus femoris are active during stance phase, and activity of the vastus medialis is continuous. These electromyographic characteristics are not usually seen in subsequent childhood gait or in adult gait, and they serve as markers of very unstable gait. (2) Unstable gait: Activity of the gastrocnemius in the latter half of swing phase is generally noted only within the first three months after a child learns to walk, and that activity is interpreted as a sign of unstable gait. (3) Slightly unstable gait: Activity of the gastrocnemius in the first half of stance phase and continuous activities of the biceps femoris and gluteus maximus from initial contact with the floor until push off are found in children until three years of age. These activities are considered electromyographic markers of slightly unstable gait.
To study the recovery of walking in an 85 year old man who had right hemiplegia after suffering a cerebral infarction, electromyograms (EMGs) were recorded from his leg muscles. We used signs for instability that we derived from EMG patterns seen in the developmental process of normal infants. The myoelectric activity at one month after the stroke showed many patterns indicative of unstable walking, closely resembling activity patterns seen in very unstable independent gait of a one year old baby in the first month of learning to walk. Seven months later, these patterns indicating unstable gait tended to have decreased or disappeared, although some marked activity betraying instability still remained. However, when the patient walked with the support of a hand cart and was able to hold his trunk upright, these excessive muscular activities decreased or disappeared, closely resembling the stable adult walking pattern. We recommend further study of the evaluation of recovery of walking after stroke by comparing the patient's EMG patterns to those not only of normal adult human gait, but also of the development of human walking in early childhood.
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.
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