Training effects on muscle fatigue in man.

Area of Science:

• Exercise Physiology
• Muscle Physiology
• Neuromuscular Function

Background:

• Muscle fatigue is a complex phenomenon affecting performance.
• Understanding the interplay between electrical and mechanical factors in fatigue is crucial for optimizing training.
• The adductor pollicis muscle is a key hand muscle relevant to many functional tasks.

Purpose of the Study:

• To investigate the effects of a 3-month training program on electrical and mechanical failures during fatigue in the human adductor pollicis muscle.
• To determine if training alters the time course of muscle force decline and recovery.
• To elucidate the role of intracellular processes in fatigue-induced tension decay.

Main Methods:

• Eight subjects underwent a daily training regimen involving 10 sets of 20 fast voluntary contractions (0.5s) at 30-40% maximal force.
• Contractile properties were assessed using supramaximal electrical stimulation (30 Hz) to elicit 60 contractions (1s each) with 1s intervals.
• Surface muscle action potentials (SAP) and mechanical outputs (force, tension, relaxation) were measured before and after training, and during fatigue protocols.

Main Results:

• Training significantly increased isometric tetanus tension (+13%), tension development rate (+18%), and relaxation rate (+12%).
• Fatigue-induced force loss was significantly reduced post-training (-17% vs. -36% in controls).
• Training lessened the slowing of tension development and relaxation during fatigue and reduced the augmentation of SAP duration and area during fatigue.

Conclusions:

• Three months of training enhances the contractile properties and fatigue resistance of the adductor pollicis muscle.
• Training mitigates both mechanical and electrical aspects of fatigue, suggesting improved intracellular mechanisms.
• Intracellular processes are likely the primary drivers of tension decay during fatigue in this muscle group.