Effects of aging on interjoint coordination during arm reaching

Introduction: Moving the arm towards an object is a complex task. Movements of the arm joints must be well coordinated in order to obtain a smooth and accurate hand trajectory. Most studies regarding reaching movements address young subjects. Coordination differences in the neural mechanism underlying motor control throughout the life stages is yet unknown. The understanding of these changes can lead to a better comprehension of neuromotor pathologies and therefore to more suitable therapies. Methods: Our purpose was to investigate interjoint coordination in three different aging groups (children, young, elderly). Kinematics and kinetics specific variables were analyzed focusing on defined parameters to get insight into arm coordination. Intersegmental dynamics was used to calculate shoulder and elbow torques assuming a 2-link segment model of the upper extremity (upper arm and forearm) with two friction-less joints (shoulder and elbow). A virtual reality environment was used to examine multidirectional planar reaching in three different directions (randomly presented). Results: Seven measures were computed to investigate group interlimb differences: shoulder and elbow muscle torques (peak and impulse), work performed by shoulder and elbow joints, maximum velocity, movement distance, distance error at final position, movement duration and acceleration duration. Our data analysis showed differences between movement performances for all analyzed variables, at all ages. Conclusion: We found that the intersegmental dynamics for the interlimb (left/right) comparisons were similar for the elderly and children groups as compared to the young. In addition, the coordination and control of motor tasks changes during life, becoming less effective in old age.