According to the researchers, using more specific language – fatigability vs perceived fatigue – to describe experiences of fatigue may be helpful in designing treatments.
Fatigue is “a very important and common problem in patients with neurological diseases,” but “it’s very poorly understood,” said Celnik, professor and chair of the Department of Physical Medicine and Rehabilitation at Johns Hopkins University.
The study, published in the Journal of Neuroscience in March, only included healthy patients, but it provides important baseline information about how our brains process and prioritize fatigue, which the researchers rely on. now in the context of the “long covid”.
Fatigability vs perception of fatigue
In the study, researchers asked participants to squeeze a small device called a force transducer between their thumb and index finger as much as possible.
Once the force they were exerting fell below 40% of their base level, they were told to stop and then asked how tired they felt.
In theory, all participants experienced similar levels of muscle fatigue, but their perception of this fatigue varied.
Participants were then asked to perform a manual coordination task. People who reported less fatigue on the previous strength task had less precise coordination; those who said they felt more tired were more specific.
The hand coordination movement was designed to test participants’ motor control in light of their perceived fatigue. The movement itself was not physically tiring.
Agostina Casamento-Moran of Johns Hopkins University, the lead author of the study, was surprised to see such a big difference between performance fatigue and perceived fatigue.
“When we started, we had no idea that the subjective experience of fatigue would become the main focus of the story,” she said.
She, Celnik and others are increasingly using the term fatigability to refer to a decline in performance, and fatigue to refer to a person’s perception of experience.
There’s immediate value in using more specific language, said Natalie Tronson, a behavioral neuroscientist at the University of Michigan.
“People often think of ‘fatigue’ in terms of ‘oh, people are tired all the time.’ But fatigue is so much more pervasive and detrimental than that,” said Tronson, who did not participate in the interview. study.” And so this understanding of perception in relation to physical fatigue and what that means and how we should conceptualize it or talk about it is really, really important.”
Distinguishing fatigability from fatigue would also help better standardize the scoring of perceived fatigue, making it easier to validate and compare data across different studies, said Bharat Biswal of the New Jersey Institute of Technology. Last year, Biswal published a study showing changes in the brains of covid-19 survivors suffering from fatigue.
“Some have a scale of 1 to 1oo, there are other studies where they have a scale of 1 to 5,” said Biswal, a professor of biomedical engineering, who was not involved in the study. “It’s a good opportunity for us to figure it out.”
He also says it’s important to separate the neurological underpinnings of motor fatigue from mental fatigue, because the brain regions associated can vary widely. Being more specific about which brain regions are affected could lead to better treatment options, Biswal said.
Could the cerebellum provide an answer?
The cerebellum is a cerebral structure located above the brainstem. It is best known for its role in coordinated movement and balance and is important for cognition and emotion, including perception.
The study showed that people who reported less fatigue not only had worse motor control, but also showed reduced activity in the cerebellum.
Celnik sees this as an indicator that fatigue perception and motor control may be battling for cerebellar attention. “It’s a competition for resources,” he said, which may explain why people who reported less fatigue had worse motor control.
Limiting brain resources this way could possibly be a protective mechanism for coping with fatigue, Casamento-Moran said.
Having more precise motor control when you feel tired could indicate better awareness of your body, which can, for example, help prevent someone from overextending themselves physically and possibly injuring themselves.
But any protective role the cerebellum might play is speculative, Casamento-Moran said.
“The findings represent further progress in understanding how we experience and regulate fatigue,” said Brian Walitt of the National Institutes of Health. Walitt studies the clinical and biological features of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS).
But “because only healthy volunteers were part of this study,” said Walitt, who was not involved in the study, “it provides no direct insight into medically strenuous conditions.”
Casamento-Moran takes the next step. With what she and her colleagues have learned from this new research, Casamento-Moran is studying the perception of fatigue in people with long-term covid, probing “why they feel the way they feel” and how it affects their abilities. cognitive and motor, she said.
Based on these findings and other work the researchers have done on fatigue, they recommend these strategies for people with fatigue:
- Use a “rhythm” strategy. With stimulation, patients conserve their energy as best they can by limiting their activity.
- Avoid trying to learn new information when you are tired. In a 2019 study, Celnik and collaborators found that when healthy participants performed a task that caused muscle fatigue (fatigability) and then were asked to learn a new physical skill, they performed poorly by compared to participants who did not suffer from muscle fatigue. Moreover, it was more difficult for them to learn this new movement in the following days, suggesting that working beyond performance fatigue to learn a skill is counterproductive. Not only will you not learn as well in the moment, Celnik said, but it could also negatively impact your ability to learn a new skill even days later.
- Be kind to yourself. Casamento-Moran says the field is progressing and hopes there will be more concrete advice and rehab treatments, but there are still many intricacies about fatigue that experts don’t understand. “So if you’re tired, be kind to yourself. Take a break,” she said.
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