This study aimed to investigate and compare the muscle activation patterns of the lower limbs in infants with hypotonia during supported treadmill stepping under four different sensory conditions: no modification, with printed visual flow patterns, with added friction, and with sticky material on the treadmill belt.
This cross-sectional study enrolled 7 infants with hypotonia (mean age: 13.1 months) who were either unable to walk independently or had just begun independent walking. Each infant was supported to step on a treadmill (0.18 m/s, Pediatric treadmills 2, Carlin’s Creations) under four different sensory conditions for 45 seconds, with the conditions presented in random order. During stepping, muscle activities of four primary gait muscles, including rectus femoris (RF), tibialis anterior (TA), biceps femoris (BF), and lateral gastrocnemius (LG) were recorded using electromyography (sampling rate: 2000 Hz; Trigno Wireless Biofeedback System, Delsys Inc.). Muscle activities for each muscle were respectively normalized relative to their resting state activity levels and body weight. This study examined the normalized mean amplitude of muscle activities for each muscle and muscle activation patterns, defined by the combinations of "on" and "off" states of the four muscles (16 states), respectively for the stance and swing phases.
Muscle activities of left and right lower limbs were comparable; therefore, data were pooled for analysis. Compared to “no modification” condition, there were higher mean lateral gastrocnemius activities (normalized to body weight) in “sticky” (p=0.008) and “visual flow” (p=0.026) conditions during stance phase. Furthermore, a lower percentage of “all firing” pattern in “friction” than in “sticky” and “visual flow” treadmill conditions during stance phase (p=0.023, p=0.006) was found. Besides, there were higher percentage of “BF-LG” pattern in “friction” than in other conditions during stance phase (no : p=0.021, sticky: p=0.011, Visual flow: p=0.012) and swing phase (no: p=0.042, Visual flow: p=0.028).
Supported stepping on treadmill with enhanced sensory inputs may alter muscle activities in infants with hypotonia. Using “friction condition” is likely to facilitate more mature muscle activation patterns (less co-contraction of all muscles and more BF-LG pattern) while stepping on a treadmill.
Findings of this study can be utilized to design treadmill training program for infants with hypotonia.
Muscle activation patterns
Treadmill stepping
