Abstract
Rapid aiming movements are typically used to study upper limb motor control and development. Despite the large corpus of work in this area, few studies have examined kinematic manual asymmetries in children who have just started formal schooling and until now, none have characterized how children coordinate their joints to complete these movements (i.e., interjoint coordination). In the present study, manual asymmetries in kinematics and interjoint coordination in strongly right-handed 6-year-old children were investigated when reaching for ipsilateral and contralateral targets with their dominant right arm and the non-dominant left arm. Overall, manual asymmetries in interjoint coordination are apparent for both 6-year-old children and young adults, although young children completed the task by adopting a different strategy than adults. Also, control strategies employed by 6-year-old children were influenced by both the location of the target as well as the arm used to perform the task. Specifically, compared to all other conditions, children’s trajectories were more curved when performing contralateral movements with the non-dominant left arm, which were driven by smaller shoulder excursions combined with larger elbow excursions for this condition. Based on these results, we argue that the differences in interjoint coordination reflect the stage of development of 6-year-old children, the origin of which derives from maturational (e.g., hand dominance) and environmental factors (e.g., school-based experience).
Highlights
The manner in which the neuromotor system plans and controls goal-directed aiming movements with the dominant and non-dominant arm has been an interest of researchers for more than 125 years
Given that the primary aim of the study was to investigate possible interlimb differences when performing aiming movements to two target locations that required differing biomechanical configurations, the results section is focused on interaction effects directly related to manual asymmetries, target location, and age
Movements performed to the contralateral target presented longer duration (P < 0.001), were slower and were completed with greater shoulder excursion (P < 0.001) and less elbow excursion (P < 0.001) as compared to the ones performed to the ipsilateral target
Summary
The manner in which the neuromotor system plans and controls goal-directed aiming movements with the dominant and non-dominant arm has been an interest of researchers for more than 125 years. The percentage of stop time (i.e., percentage of task with zero velocity) was smaller when performing the task with the non-dominant hand, which the authors hypothesize is due to improved proprioception to the non-dominant hand control system. They point to research by Sainburg and Kalakanis (2000)—one of the studies that contributed to the dynamic dominance hypothesis (Sainburg, 2002)—in which hand trajectories and joint coordination patterns support the idea that the dominant arm is proficient for muscle and interjoint interaction, while the non-dominant arm is more adept at using proprioceptive feedback
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