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

The intervention occurred in a laboratory for pediatric motor development of department of physical therapy in a university. With body weight supported by the researcher, infants stepped on treadmills with enhanced sensory input (that is four different treadmill belt surfaces including normal treadmill, treadmill with visual flow, friction, and sticky) in random sequence. - “normal”: original treadmill with smooth black belt surface - “friction”: treadmill belt surface covered with non-slip mats to increase friction, limit sliding of feet on the belt, and induce stepping - “sticky”: with double sided tape attached to the belt surface, create a condition which is similar with Velcro used in other studies to induce stepping on treadmill - “visual flow”: smooth treadmill belt surface with black and white checker-board pattern, producing visual flow when the belt is moving Each infant had to complete these four treadmill sessions in random sequence which was decided in advance: The researcher arranged 24 possible combination of sequences of the four treadmill sessions, and then randomly sorted these 24 combination of sequences by computer. Finally, according to the sequence of recruitment, infant would be tested for the four treadmill sessions in the sequence of the corresponding sequences sorted by computer. Treadmills were set to a constant speed of 0.18 m/s. Infants stepped for 45 seconds on each treadmill, and rested for 1 minute between different treadmills. The approximate total duration of the treadmill sessions for each infant was 10 minutes; trials would be stopped if infants kept crying, and continued after infants being comforted, so it may take up to 30 minutes for infants to complete the whole treadmill sessions. If there were no stepping movements from infants during each treadmill trial, the researcher would guide infants to make stepping movements by patting their lower limbs, driving the lower limbs to step, or shifting the center of gravity. Sitting in front of the treadmills, parents also encourage infants to step by the ways of singing, watching video, playing toys or more. When carrying out “visual flow” treadmill stepping, parents were asked to use toys to induce or encourage infants to look down at the visual flow of the belt surface. During all the trials, two high-speed cameras, one at right-anterior and another at right-posterior of the treadmill, recorded infants’ stepping. Muscle activation patterns in lower extremities and stepping performance were recorded at the same time during infants' stepping.