Immediate Effect of Enhanced Sensory Inputs on Lower Extremity Muscle Activation Patterns and Stepping Performance During Supported Treadmill Stepping in Infants with Hypotonia

This study investigated whether supported stepping on treadmills with enhanced sensory inputs could cause immediate differences in lower limb muscle activation patterns and stepping performance in infants with hypotonia. Infants with hypotonia (aka abnormal low muscle tone) were found delayed in independent walking, produced less steps and may have delayed in neuromuscular control during supported treadmill stepping. While enhanced sensory inputs during treadmill stepping could change and/or improve their performance on treadmills, understanding the performance of their supported stepping ability before walking may be helpful to design appropriate early treadmill intervention in the future. However, previous studies mainly focused on hypotonic infants diagnosed with Down syndrome or myelomeningocele only. For other infants who are also hypotonic, there is still insufficient evidence for the immediate benefit of adding these sensory inputs to treadmill stepping. In this study, infants with hypotonia were supported stepping on four different treadmill belt surfaces, including normal treadmill, treadmills with visual flow, friction, and sticky belt surfaces. A total of eight infants with hypotonia were recruited, with data of seven infants could be used for analysis. Average age of infants were 13.1 months old. Infants were recruited if they were younger than 24 months of corrected age (that is, infant's age minus the number of weeks early they were born); be able to sit independently for at least 30 seconds; not able to walk not able to walk independently or have learnt walking independently for less than one month; had been diagnosed with developmental delay; and be assessed as hypotonia. The results of this study showed that both treadmills with “sticky” and “visual flow” belt surfaces could increase the mean muscle activation amplitude of the lateral gastrocnemius in hypotonic infants at stance phase during stepping. We also found that hypotonic infants in this study preferred using all four lower limb muscles co-contracting (All) pattern during treadmill stepping, and stepping on “friction” treadmill may contribute to produce more mature muscle activation patterns and increased stepping frequency in hypotonic infants. However, the number of cases in this study is still insufficient, and more samples need to be recruited in the future.