Effects of balance constraints during a double-step reaching task

Area of Science:

• Neuroscience
• Biomechanics
• Motor Control

Background:

• Upper limb tasks require rapid hand corrections during unstable postural situations.
• Accurate execution of upper limb tasks relies on integrated postural and reaching control mechanisms.

Purpose of the Study:

• To investigate how varying postural stability conditions affect upper limb motor performance during reaching tasks with dynamic targets.

Main Methods:

• 19 participants performed reaching tasks towards targets that changed position at different time intervals (200 or 600 ms).
• Tasks were conducted under varied postural conditions: bipedal on firm surface, bipedal on foam, and unipedal on foam.
• Data collected included on-screen performance (motion time, spatial error), balance metrics (center of pressure displacements), and index finger kinematics.

Main Results:

• Increased postural instability impacted finger kinematics and center of pressure (CoP) dynamics (displacements, speed, smoothness) but not screen-based precision or duration.
• The timing of target changes significantly affected on-screen performance, finger kinematics, and CoP dynamics.

Conclusions:

• Postural and reaching control systems effectively maintain accurate hand movements in less stable environments, even with non-static targets.
• While control systems protect end-effector performance under instability, this protection diminishes with reduced time for motion correction.