Factors responsible for force steadiness impairment with fatigue

Area of Science:

• Neuromuscular physiology
• Motor control
• Human fatigue

Background:

• Fatigue is known to impair motor performance, particularly fine force control.
• The precise mechanisms linking muscle fatigue to reduced force steadiness remain incompletely understood.
• Muscle activation patterns are hypothesized to play a significant role in this impairment.

Purpose of the Study:

• To investigate the specific contribution of altered muscle activation to the loss of fine force control during fatigue.
• To differentiate between central and peripheral factors influencing force variability post-fatigue.

Main Methods:

• Three experiments were conducted involving fatigue protocols.
• Muscle activation was manipulated: left free, controlled via electromyography, or suppressed via electrical stimulation.
• Force variability was measured before and after fatigue at different force levels.

Main Results:

• When muscle activation was uncontrolled, fatigue increased activation at moderate forces and increased force variability universally.
• Controlling muscle activation prevented increased force variability, except at low force levels.
• Electrical stimulation to suppress voluntary activation rendered force variability unaffected by fatigue.

Conclusions:

• The impairment of force steadiness with fatigue is largely explained by increased muscle activation at moderate forces.
• Central mechanisms contribute to force fluctuations, particularly at low force levels, independent of voluntary activation changes.
• Understanding these mechanisms is crucial for rehabilitation and performance enhancement.