- Fatigue comes from both the effort to do something and the actual doing itself.
- When we change what we're doing, we bring the same effort but reduced fatigue for the new task.
- Rotating through and across tasks and activities could allow for better performance over time.
Thinking about fatigue can be really tiring. Fatigue can also mean a lot of different things depending on context. A common thread, though, is that when we say something is "fatiguing" we mean continuing to do the thing is getting harder and harder and eventually impossible to maintain.
Is Fatigue an Inside-Out or Outside-In Problem?
In sensorimotor neuroscience, fatigue is often studied in terms of the ability to perform a motor task—like holding a certain muscle contraction, doing a specific number of repetitions of something, or performing something like running or cycling—over time. For about as long as physiology has been an area of study, folks have been interested in fatigue, what causes it, how it can be defined, and how it can be altered.
Researchers often talk about "central" or "peripheral" contributions to fatigue. Central usually is the "inside" bit in the brain, related to the ability to want to do something, while peripheral is more of the "outside" bit, related to the muscles actually doing the actions and what those actions feel like. Of course, just about all real-world fatigue is a bit of both, but central and peripheral do work as fuzzy boundaries for research purposes.
A Change is As Good As a Rest
Which is why a study by Fabio Laginestra and colleagues in Italy, France, and the U.S. caught my attention. They wanted to know if the level of fatigue you started with affected your ability to perform a new activity, which you then did to—you guessed it—fatigue. I liked this approach because it feels a bit more relevant to real life, where we are often doing multiple things and never really start almost anything "fully fresh."
The researchers in this project asked their participants to do an isolated knee-extension exercise to "failure"—where they couldn't continue. They did this on different days and altered the level of fatigue folks had before doing this task.
The "control" situation was done "fresh," without doing anything before. The two experimental conditions were either with prior knee extension actions performed normally or by electrically stimulating the muscles to do the contractions. In both cases, knee extension occurred—but one involved both central and peripheral fatigue and one only peripheral.
The results from this study showed that central motor drive during prior activity is relatively less of a fatiguing factor than peripheral activation. This suggests our intention to produce high performance (our volitional central motor drive) can be maintained across activities that don't necessarily activate our muscles the same way. That is, doing slightly different activities allows us to continue activity beyond what we might be able to do if we just did one thing where both peripheral and central factors build up.
Change is Productive Procrastination
This study resonated with me on several levels.
For one, it reminded me of how I used to try to write and work. Back when I was in graduate school, I used to try and push through periods when I had trouble writing. I was very tired and clearly had writer's block, but I would sit in front of my computer with my keyboard in front of me all day anyway trying to achieve something.
Eventually, I discovered that if I read a book (Stephen King was my go-to for a lot of this) or did some martial arts training I could later return to the same work but in a different state of mind. In so doing I was way more "productive" and also enjoyed things more.
Later, as a professor, I encouraged research trainees to work diligently but to be sure to take breaks for walking, reading, or whatever they needed to do. I asked them to think of doing these things as part of the other processes they were working on—a kind of productive procrastination.
What's more, my own training in martial arts reflects the "a change is as good as a rest" mantra. Back in the day, I would try to train everything I knew in each tradition I studied in many of my sessions. This was exhausting on many levels.
Eventually, I realized I could do a little bit of a lot of things and cover just about as much stuff each week if I rotated through each system in each session. The different Okinawan, Japanese, and Chinese martial arts empty hand and weapon systems I study allow for enough of a change in each that it's like getting a break when I switch from one to the other.
The upshot of how this study can apply to everyday life may be that it's best to do a little bit of a lot rather than lots of one thing. This runs contrary to how many folks approach most tasks—but it could be a transformative concept to apply in your life.
(c) E. Paul Zehr (2023)
Laginestra FG, Cavicchia A, Vanegas-Lopez JE, Barbi C, Martignon C, Giuriato G, Pedrinolla A, Amann M, Hureau TJ, Venturelli M. Prior Involvement of Central Motor Drive Does Not Impact Performance and Neuromuscular Fatigue in a Subsequent Endurance Task. Med Sci Sports Exerc. 2022 Oct 1;54(10):1751-1760. doi: 10.1249/MSS.0000000000002965. Epub 2022 May 25. PMID: 35612382; PMCID: PMC9481724.