Normal aging affects unconstrained three-dimensional reaching against gravity with reduced vertical precision and...

Area of Science:

• Motor control and neuroscience
• Human aging research
• Biomechanics of movement

Background:

• Reaching movements are fundamental for daily activities and crucial in neurological rehabilitation.
• Previous research often simplifies movements by removing gravity or reducing degrees of freedom.
• Aging is associated with reduced accuracy in reaching, possibly due to impaired corrective movements.

Purpose of the Study:

• To investigate age-related changes in reaching movements under natural conditions, including gravity and unconstrained motion.
• To explore how accuracy deficits in older adults relate to shoulder, elbow, and finger kinematics.
• To examine age-differences in motor planning and online correction during reaching.

Main Methods:

• Collected 3D kinematic data and electromyography from young (25±6 years) and older adults (68±3 years).
• Participants performed second-long reaches to vertically aligned targets.
• Analyzed movement initiation time, accuracy, trajectory variability, and muscle activation patterns.

Main Results:

• Older adults demonstrated longer movement initiation times and greater inaccuracy.
• Target height significantly affected trajectory curvature variability more in older adults.
• Older adults showed reduced shoulder abduction variability and increased biceps-triceps co-contraction.

Conclusions:

• Age-related deficits exist in motor planning and online correction for reaching movements against gravity.
• Older adults display altered upper extremity movement strategies and muscle activation.
• Findings highlight the impact of aging on uncompensated reaching movements.