The effect of task uncertainty on muscle activation patterns in 8-10-year-old children

Postural muscle activity accompanying voluntary arm movements has been researched extensively in adults; however, few studies of this kind have been conducted with children. It is not clear whether children respond like adults to internal perturbations, and if so, whether this response is similar across a variety of task conditions. The aims of the present study were to determine the postural muscle activity demonstrated by 8-10-year-old children when performing a rapid shoulder flexion movement and to compare the pattern produced under simple reaction-time versus complex reaction-time conditions.

Fifteen children with typical motor development participated in this comparative design study. The activity of anterior deltoid and contralateral rectus abdominis, internal oblique, erector spinae, rectus femoris, biceps femoris, tibialis anterior and gastrocnemius muscles was recorded via surface electromyography (EMG). Two tasks were performed: a simple task involving a right shoulder flexion movement; and a complex task involving a right or left shoulder flexion movement. Reaction time (RT) and movement time (MT) of the arm action were also recorded.

Muscle latencies in the complex task were longer than those for the simple task, although only the gastrocnemius muscle showed a significant difference (p = 0.013). Reaction time was also significantly later in the complex task (p = 0.003). Movement time was not significantly different between conditions.

A decrease in task certainty delayed postural muscle activation and reaction time in children aged 8-10 years. The study also demonstrated that children in this age group utilized a mixed postural strategy rather than a proximal-to-distal or distal-to-proximal pattern, reported in adult studies. Movement time remained unchanged.