Changes in joint kinematics and dynamic postural stability with free and restricted arm movements in children

Arm movements make a substantial and functionally relevant contribution to quiet standing and dynamic balance tasks. The impact of restricted arm movements on balance control is particularly important for children as their postural control system is not fully matured.

This study investigated the effects of arm movements on lower body joint kinematics and dynamic postural stability during anterior and lateral dynamic movements in children.

Eighteen boys (age, 10.1 ± 1.6 years) completed an anterior and a lateral jump-landing task under two different verbally conveyed instructions of arm position; (1) arms placed flat across the chest touching the contralateral shoulder (i.e., restricted arm movement) and (2) arm movement without restriction. Lower body joint kinematics were recorded and used to calculate mean joint position, joint range of motion (ROM) and joint movement variability.

Restricting arm movements resulted in a reduction of joint movement variability and joint ROM of the pelvis during the lateral jump (p <0.05), but increased joint movement variability and joint ROM of the pelvis during the anterior jump (p <0.05).

The reduced joint movement variability and joint ROM with restricted arm movements during the lateral jump may represent a potential compensatory 'stiffenin strategy', whilst the increase during the anterior jump suggest an exploratory strategy. These novel findings highlight that it is important for children to be introduced to different dynamic task constraints so that they can learn to control and organise the motor system degrees of freedom appropriately.