Postural muscle responses and adaptations to backward platform perturbations in young people with and without intellectual disability.

This study examines postural muscle responses to backward perturbations in young people (16-20 years) with and without intellectual disability (ID). The study included 56 young people with ID and 43 age-matched without ID volunteers. The subjects stood on a platform that was moved backwards in a surface translation. Lower and upper leg muscles and lower back spine muscles were recorded with surface electromyography (EMG). Muscle onset latency, time to peak amplitude (EMG), adaptation of muscle responses to repeated perturbations (using integrated EMG (IEMG) for epochs), and synergies and strategies were assessed. The result showed no differences between the two groups in muscle onset latency, synergies, and strategies. Young people with ID reduced their time to peak amplitude in investigated muscles, a response that was different from the group without ID. Also, young people with ID tended to adapt their IEMG less compared to the controls. These findings suggest that young people with ID have limited ability to use somatosensory information and adapt their postural muscle responses to repeated external perturbations.