What Happens to the Structure of Movement Variability as you Fatigue?
After a brief hiatus, we are back :)
📝 Weekly paper summary
Category
Cross-sectional
Context
The notion of motor synergies explores how well humans can exploit system degeneracy to yield consistent task outcomes (i.e., how well joints can covary to result in lower variability of an important performance variable). Previous research suggested that individuals may adapt to the accumulation of fatigue (decreased force production, increased metabolite accumulation, etc.) by decreasing the involvement of fatigued elements and increasing the involvement of non-fatigued elements (i.e., covarying) to maintain the task goal. However, this was never measured directly using Uncontrolled Manifold analyses that decompose the structure of movement variability at a joint level surrounding a specific task goal. Therefore, this investigation aimed to examine whether the fatigue accrued from exercise during a pointing task influenced the structure of movement variability during a finger-pressing task. The authors hypothesized that, following the fatiguing protocol, the variability along the UCM (which represents the variability of redundant movement solutions) would increase as the human movement systems shifts to using non-fatigued elements to accomplish the task objective.
Correctness
- The authors determined both objectively (decrease in maximum voluntary contraction strength) and subjectively (volitional task failure) that participants were "fatigued" following the exercise.
- A disadvantage of the study was that it was for finger pressing and not "traditional" exercises used in many strength and conditioning or therapy contexts.
Contributions
- The findings of this study further supports some of the ideas presented in the November 21, 2021 Newsletter that movement variability along the UCM (seems to increase with minor fatigue (i.e., up to, but not beyond, the point in which some global performance measure changes) as people "hunt" for more movement solutions when elemental variables start to fatigue. Once those newly leveraged elemental variables become fatigued, the pool of solutions that can maintain the task outcome decreases further until the only movement solutions that remain are those which increase the variability of the task performance (also see Möhler et al., 2022). The potential implications of these findings, which I highlighted previously, are as follows:
- Perhaps inducing minor fatigue during training can potentiate increased movement variability and, thus, increase training transfer to novel contexts and constraints.
- Aiming to increase movement variability for (endurance) athletes or workers as an outcome of training may act as a "motor control" buffer (as opposed to typical physiological buffers) that prolongs performance during their activities.
- Pushing people "too far" (i.e., to the point in which some global performance measures decrease excessively) may narrow the solution pool, which could impair the transfer of training.
🧠 Fun fact of the week
Most people think the world's largest organism must be a blue whale. But, the largest organism on earth, which is now over 2000 years old, is a sprawling fungus in eastern Oregon! How big is this single fungus organism? It's about 10 square kilometres, much larger than a blue whale!
🎙 Podcast recommendation
Demis is the CEO of DeepMind, one of the most innovative companies in the world working on Artificial Intelligence. I think you'll enjoy listening to this conversation with Lex!
🗣 Quote of the week
"What really frightens and dismays us is not external events themselves, but the way in which we think about them. It is not things that disturb us, but our interpretation of their significance."
- Epictetus