Fatigue induces long lasting detrimental changes in motor skill learning
Abstract
Fatigue from physical exertion, common in both everyday life and neurological diseases, impacts motor-skill learning. While fatigue is known to impair task execution, its influence on learning new skills remains unclear. Experiments revealed that muscle fatigue impairs motor-skill learning, evidenced by poorer task acquisition on subsequent practice days even after recovery from fatigue. This effect is partly mediated centrally and can be mitigated by altering motor cortex function. The practice of training to the point of fatigue should be reconsidered as it affects long-term skill learning.
Introduction
Repetitive practice is essential for gaining proficiency in motor skills, common in professions like music, surgery, and sports. Fatigue, defined as the degradation of maximum force after exertion, is a limiting factor in task execution. However, its effects on learning new skills are less understood. Existing studies offer contradictory results, and it is necessary to distinguish between performance under fatigue and actual learning impairment.
Results
Experiment 1
38 participants learned a sequential pinch force task over two days. Muscle fatigue induced on Day 1 impaired learning both on Day 1 and Day 2. Fatigued participants took additional training days to catch up to the performance levels of non-fatigued participants.
Experiment 2
20 participants trained their right hand under fatigue or non-fatigue and tested their untrained left hand. Fatigue impaired skill learning in both the fatigued and non-fatigued hands.
Experiment 3
45 participants were tested to determine if fatigue's effects were centrally mediated. Disruptive rTMS to the motor cortex alleviated fatigue's negative impact, suggesting central mediation.
Experiment 4
18 participants performed a cognitive task requiring minimal force control. Fatigue did not affect learning, indicating that the detrimental effects of fatigue are task-specific.
Discussion
Muscle fatigue negatively impacts motor-skill learning beyond mere performance degradation, with effects persisting across days. Central mechanisms mediate these effects, and training under fatigue may form maladaptive memories. The findings highlight the need to reconsider training and rehabilitation protocols involving fatigue.
KEY TERMINOLOGY
Fatigue: Degradation of maximum force output induced through voluntary physical exertion of task-relevant muscles.
Motor-Skill Learning: The process of acquiring new skills or improving existing skills involving movement and coordination.
Sequential Pinch Force Task: A task requiring participants to perform isometric pinch presses at different force levels to control cursor movement on a screen.
rTMS (Repetitive Transcranial Magnetic Stimulation): A technique used to disrupt motor cortex function to study its effects on skill learning and retention.
MVC (Maximum Voluntary Contraction): The maximum force a muscle can produce during voluntary contraction.
Centrally Mediated: Effects that are regulated by central nervous system processes, particularly in the brain.
Logarithmic Force-Distance Sensorimotor Map: A representation used in the pinch force task where force levels translate logarithmically to cursor movement distance.
Depotentiation TMS: A form of TMS used to reverse potentiating plasticity and disrupt skill retention.
Skill Measure: A composite measure of performance based on movement time and error rate.
Inter-Manual Transfer: The ability of skill training in one hand to transfer and improve performance in the untrained hand.