High-gain visual feedback exacerbates ankle movement variability in children

Neuromuscular variability and spatial accuracy in children and older adults

Our ability to control movements is influenced by the developmental status of the neuromuscular system. Consequently, movement control improves from childhood to early adulthood but gradually declines thereafter. However, no study has compared movement accuracy between children and older adults. The purpose of this study was to compare endpoint accuracy during a fast goal-directed movement task in children and older adults. Ten pre-adolescent children (9.7 ± 0.67 yrs) and 19 older adults (71.95 ± 6.99 yrs) attempted to accurately match a peak displacement of the foot to a target (9° in 180 ms) with a dorsiflexion movement. We recorded electromyographic activity from the tibialis anterior (agonist) and soleus (antagonist) muscles. We quantified position error (i.e. spatial accuracy) as well as the coordination, magnitude, and variability of the antagonistic muscles. Children exhibited greater position error than older adults (36.4 ± 13.4% vs. 27.0 ± 9.8%). This age-related difference in spatial accuracy, was related to a more variable activation of the agonist muscle (R²: 0.358; P < 0.01). These results suggest that an immature neuromuscular system, compared to an aged one, affects the generation and refinement of the motor plan which increases the variability in the neural drive to the muscle and reduces spatial accuracy in children.

Age-related differences in the motor planning of a lower leg target matching task

While the development and execution of upper extremity motor plans have been well explored, little is known about how individuals plan and execute rapid, goal-directed motor tasks with the lower extremities. Furthermore, the amount of time needed to integrate the proper amount of visual and proprioceptive feedback before being able to accurately execute a goal-directed movement is not well understood; especially in children. Therefore, the purpose of this study was to initially interrogate how the amount of motor planning time provided to a child before movement execution may influence the preparation and execution of a lower leg goal-directed movement. The results displayed that the amount of pre-movement motor planning time provided may influence the reaction time and accuracy of a goal directed leg movement. All subjects in the study had longer reaction times and less accurate movements when no pre-movement motor planning time was provided. In addition, the children had slower reaction times, slower movements, and less accurate movements than the adults for all the presented targets and motor planning times. These results highlight that children may require more time to successfully plan a goal directed movement with the lower extremity. This suggests that children may potentially have less robust internal models than adults for these types of motor skills.