Adolescents with Down syndrome exhibit greater force and delay in onset of tapping movements.

This study examined the control of force and timing during finger tapping sequences of adolescents with Down syndrome. Participants performed both unimanual and bimanual tapping tasks with one self-paced test trial after three audible-synchronized practice trials with concurrent feedback of force output. All tasks consisted of a target force of 2N and a target intertap interval of 500 msec. Adolescents with Down syndrome exhibited a greater magnitude of positive constant error and variable error for peak force than typical adolescents. They also exhibited a greater magnitude of negative constant error and variable error for intertap interval than typical adolescents. Although normally developing comparison adolescents exhibited a linear relationship between peak force and press duration or time-to-peak force, the relationship was not familiar to adolescents with Down's syndrome. This may suggest differences in the manner of motor unit recruitment between the group with Down's syndrome and comparison adolescents.