Independence between the amount and structure of variability at low force levels

Area of Science:

• Motor Control
• Human Physiology
• Biomechanics

Background:

• Understanding motor variability is crucial for explaining human movement control.
• Previous research has primarily focused on higher force levels, leaving low-force variability under-explored.

Purpose of the Study:

• To investigate the amount (standard deviation, coefficient of variation) and structure (approximate entropy) of force variability at very low isometric force levels.
• To examine the influence of visual feedback gain on force variability characteristics.

Main Methods:

• Participants performed index finger abduction isometric tasks at five distinct low force levels (0.4-4.0 N).
• Two visual feedback gain conditions (high and low) were employed.
• Analysis included statistical measures of force variability (S.D., CV) and complexity (ApEn).

Main Results:

• Force output scaled to target levels.
• Standard deviation of force increased non-linearly with force level and decreased with higher visual gain.
• Coefficient of variation decreased with both increasing force level and visual gain.
• Approximate entropy did not change with force level but was higher with high visual gain.

Conclusions:

• Motor unit recruitment at low forces increases force magnitude and variability amount but not structural complexity.
• Separate control processes appear to influence the amount and structure of motor variability at low force levels.
• Visual feedback gain modulates both the amount and structure of force variability.