Training Beyond Exhaustion Can Prevent Learning

Summary: Overuse of our motor skills causes fatigue that can actually harm rather than help when it comes to sports training, practicing music or art, and rehabilitating injury.

Source: eLife Sciences

Researchers have found that muscle fatigue caused by overexertion when practicing a skill can affect the task in hand and impair learning afterwards.

The findings, published in the open-access journal eLife, suggest that the common practice of training beyond fatigue should be reconsidered as it could do more harm than good.

The saying goes that ‘practice makes perfect’. And although intense repetition of motor skills is a routine part of learning in many disciplines – from playing a musical instrument to becoming a better artist, a faster runner or perfecting intricate surgical techniques – it is well known that fatigue eventually starts to degrade our ability to practice a task.

“Surprisingly little is known about the effects of muscle fatigue on our ability to keep learning and getting better at a skill,” says first author Meret Branscheidt, former Postdoctoral Fellow in the Department of Physical Medicine and Rehabilitation in the Johns Hopkins University School of Medicine, US. “With this study, we set out to disentangle the effects of fatigue on performance of a task from its effects on the ability to learn and get better at it.”

The researchers asked 120 people to learn a pinch-force task over two days. They were given a device that transmits force into a signal received by a computer and asked to hold it between the thumb and index fingers of their dominant hand. During each trial, participants were asked to press the device at different force levels to control the motion of a cursor displayed on a computer screen.

On the first day, a subgroup was asked to continue pinching until they experienced muscle fatigue, which was measured by the extent of contraction they could achieve. On the second day both groups of participants performed the task without reaching the point of fatigue. The researchers found that the ability to get better at the pinch task on the second day was impaired in the group that reached fatigue on day one. In fact, it took them two additional days of training without fatigue to catch up to the same level as the normal (or ‘control’) group.

The most striking results, however, came from the researchers’ next experiment. When they tested performance of the untrained, unfatigued hand in the pinch task, they found that those people who had reached the point of exhaustion performed less well using both their fatigued and unfatigued hands. This suggested that fatigue impairs motor skill learning mechanisms in the brain. To confirm this, the team used magnetic stimulation to disrupt the brain processes thought to be involved in remembering a new skill. This partly alleviated the effect of fatigue on skill learning, which suggests that fatigue may affect the formation of memories that help people to retain new skills they have learned.

A man is kneeling down and holding a bar in a small area. The caption describes the scene further.

Astronaut Daniel Tani, Expedition 16 flight engineer, uses the short bar for the Interim Resistive Exercise Device (IRED) to perform upper body strengthening pull-ups. The IRED hardware is located in the Unity node of the International Space Station. The NASA image is in the public domain and was not taken as part of the research discussed.

Finally, they tested whether muscle fatigue only affects tasks that require high levels of motor control. They asked fatigued and non-fatigued participants to press 10 keys on a computer keyboard in the correct sequence and found no difference in performance on day one or two. This suggests that the detrimental effects of muscle fatigue on learning are specific to tasks that require finely tuned motor skills, but not for more mentally demanding tasks.

“We have shown that learning in a fatigued state results in detrimental effects on a person’s ability to acquire a new skill,” concludes senior author Pablo Celnik, Director of the Department of Physical Medicine and Rehabilitation at the Johns Hopkins University School of Medicine. “Our observations should be considered carefully when designing training protocols such as in sports and musical performance, as well as for rehabilitation programs.”

About this neuroscience research article

Source: eLife Sciences
Media Contact: Emily Packer – eLife Sciences
Publisher: Training Beyond Exhaustion Can Prevent Learning organized by Neuroscience News.
Image Source: NeuroscienceNews.com image is credited to NASA and is in the public domain.
Original Research: Abstract for “Fatigue induces long lasting detrimental changes in motor skill learning” by Meret Branscheidt, Panagiotis Kassavetis, Manuel Anaya, Davis Rogers, Han Debra Huang, Martin A Lindquist, Pablo Celnik in eLife. Published March 5,2019 (Accepted manuscript, PDF only. Full online edition to follow.)
doi: 10.7554/eLife.40578
Funding: The authors declare that there was no funding for this work. The authors declare that no competing interests exist.

Abstract

Fatigue induces long lasting detrimental changes in motor skill learning

Fatigue due to physical exertion is a ubiquitous phenomenon in everyday life and especially common in a range of neurological diseases. While the effect of fatigue on limiting skill execution are well known, its influence on learning new skills is unclear. This is of particular interest as it is common practice to train athletes, musicians or perform rehabilitation exercises up to and beyond a point of fatigue. In a series of experiments, we describe how muscle fatigue, defined as degradation of maximum force after exertion, impairs motor skill learning beyond its effects on task execution. The negative effects on learning are evidenced by impaired task acquisition on subsequent practice days even in the absence of fatigue. Further, we found that this effect is in part mediated centrally and can be alleviated by altering motor cortex function. Thus, the common practice of training while, or beyond, fatigue levels should be carefully reconsidered, since this affects overall long-term skill learning.

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