Adults up to 80 years old maintain effective movement planning when facing complex body dynamics

Aging significantly impacts motor performance, especially in multi-joint movement tasks where the nervous system needs to adequately coordinate mechanical interactions between joints. Effective coordination of multiple joints relies on intact feedforward control to predict movement dynamics in the initial phase of the movement, and on feedback control to fine-tune the execution in the final phase. The effect of aging on these specific control mechanisms remains controversial. Here, we investigated a pure-elbow motion task with a group of 50 young (20-35 years old), 80 old (55-70 years old) and 30 older-old (80 + years old) healthy participants. They performed 30° elbow flexions and extensions under two speed conditions as higher elbow velocities increase interaction torques at the shoulder, and demand greater neuromuscular effort for stabilization. The timing and magnitude of anticipatory EMG activity of the agonist shoulder muscle, necessary to counteract interaction torques, were similar across all age groups. Moreover, increasing elbow velocity did not result in any performance differences between young and older adults, indicating that shoulder stabilization during movement initiation remained intact with age. However, older adults exhibited reduced ability to stabilize the shoulder position until the end of the movement, leading to decreased accuracy with older age. These results suggest that feedforward control, which is essential for shoulder stabilization during movement initiation, is functionally stable during healthy aging and remains resilient to increased motor demands. In contrast, feedback control appears to deteriorate with age, potentially contributing to reduced movement precision in the final phase of the multi-joint movement.