Postural adjustments for jumping reaction movement in mentally retarded children: findings from EMG patterns

EMG patterns during a jumping reaction task were studied in 53 mentally retarded children. EMGs were recorded from the knee extensors (VM and RF) and the knee flexors (hamstrings). Lack of synchronization between onset of phasic discharge in the VM and the RF and between onset in the hamstrings and the knee extensors was characteristic of retarded children. Deviation from the EMG pattern of normal adults decreased with increasing MA. The premotor time tended to be prolonged with increasing time differences between the VM and the RF responses. Shorter RT between the VM and the RF was consistent across EMG patterns. These were more apparent in subjects with MAs above 7 than in those with MAs below 6. It is suggested that the asynchronized EMG pattern reflects postural requirements due to poor formation of preparatory set.