Force time-history affects fatigue accumulation during repetitive handgrip tasks

Area of Science:

• Occupational Health
• Human Physiology
• Biomechanics

Background:

• Muscle fatigue is a known risk factor for workplace injuries, especially in repetitive tasks.
• Understanding fatigue accumulation and recovery in complex tasks is crucial for injury prevention.

Purpose of the Study:

• To investigate the impact of a complex force-time history on muscle fatigue and recovery during a handgrip task.
• To analyze how varying submaximal effort levels influence fatigue accumulation and recovery patterns.

Main Methods:

• Surface electromyography (EMG) of brachioradialis (BRD) and flexor carpi ulnaris (FCU) was measured.
• Participants performed a handgrip task with a "pyramid" of 15%, 30%, 45%, 30%, 15% maximum voluntary contraction (MVC) plateaus.
• Grip force and EMG parameters (average EMG, mean power frequency) were compared between the first and fatigued last cycles.

Main Results:

• Peak grip force decreased by 20.5% MVC in the final cycle.
• Fatigue accumulation was evident, with grip force decreasing after initial plateaus.
• Apparent voluntary force recovery was observed during the final 15% MVC plateau, especially after lower preceding efforts.

Conclusions:

• Complex force-time histories influence muscle fatigue and recovery dynamics.
• Preceding task demands play a significant role in the accumulation of fatigue.
• Voluntary force recovery can occur within a complex task if subsequent efforts are of lower intensity.