Changes in the variability of movement trajectories with practice.

Area of Science:

• Motor control
• Biomechanics
• Neuroscience

Background:

• Understanding movement variability is crucial for motor control research.
• Phase plane analysis offers insights into the dynamics of limb movement.

Purpose of the Study:

• To quantify trajectory variability during elbow flexion/extension.
• To investigate the relationship between practice, movement speed, and variability.
• To explore the central nervous system's control over movement trajectories.

Main Methods:

• Human subjects performed elbow flexion/extension movements in a visual step tracking paradigm.
• Trajectory variability was measured using ellipse area (standard deviations in position and velocity) at 10-ms intervals.
• Movement amplitude (10 and 30 degrees) and practice trials (up to 1000) were manipulated.

Main Results:

• Trajectory variability decreased in both acceleration and deceleration phases with practice.
• Deceleration phase variability remained higher than acceleration phase variability, even after extensive practice.
• Faster, shorter duration movements exhibited greater trajectory variability, indicating a speed-variability tradeoff.
• Variability increased during acceleration, related to movement amplitude and speed, with compensatory mechanisms in deceleration.

Conclusions:

• The central nervous system controls entire limb movement trajectories.
• Variations in accelerative forces are compensated by decelerative forces, refined through practice.
• Practice improves movement trajectory consistency by refining the coordination of accelerative and decelerative forces.