Mental fatigue
This section will be one of the more speculative sections of the entire course. We will be touching on emerging areas of research that, although appearing promising, are yet to have been rigorously tested in a trail and ultramarathon settings. The reason for including this speculative content, is that much of it has been widely publicised in running related media, and so it covers topics that your athletes may be interested in.
We’ve previously discussed the psychobiological model of fatigue and briefly touched on the concept of mental fatigue. It appears that mental fatigue decreases an athlete’s drive by increasing the perception of effort while also decreasing the perceived value of achieving the goal (i.e., decreasing an athlete’s motivation). This dual effect is supported by neurophysiological theories that suggest mental fatigue activates brain inhibition centres and deactivates facilitative centres (Schiphof-Godart, Roelands, & Hettinga, 2018).
Mental fatigue can be caused by prolonged periods of a demanding cognitive activity. It is well documented that this can impair cognitive performance, and it has also been shown to impair endurance performance despite physiological variables like heart rate, lactate accumulation, and neuromuscular function being unaffected. Although this effect is not fully understood yet, it has been proposed that this may be due to the accumulation of cerebral adenosine (Martin et al., 2018).
So, how might we go about improving resilience against the effects of mental fatigue? And will that actually improve endurance performance?
One of the proposed forms of mental training, often referred to as ‘brain endurance training,’ involves performing cognitively demanding tasks either before or during endurance training. A classic example of the sort of cognitively demanding tasks performed in these sessions is the Stroop task; this involves participants naming a colour in which words are printed while the words may spell out a different colour, e.g., the word red might be printed in blue ink. Another example are continuous performance tasks, where participants see a series of letters and respond to every letter that is presented except for a particular letter, e.g. X, for which they give no response.
The brain endurance training may involve performing these tasks for 30 to 90 minutes before or during exercise. Typically, when done concurrently it has been done while cycling or while performing a rhythmic hand-grip task, as these exercises can be stably set up in front of a computer. It may not be practical to perform these tasks while running, so pre-fatiguing would be the most viable option. Both prior and concurrent brain endurance training appear to improve hand grip, football, and cycling performance (Dallaway, Lucas, & Ring, 2018, Staiano et al., 2022, Staiano et al., 2023). Thus, it is possible that brain endurance training could improve running endurance performance as well. However, it is unclear if the duration of ultramarathons would mean any brain training effects are washed out.
Given this area of research is still emerging, and the fact can require an additional 30 to 90 minutes of training, at this stage there is probably insufficient evidence to be spending precious training time on these cognitively demanding tasks. However, many athletes may already be performing a form of brain endurance training when they train after work. Thus, I use this brain endurance training framework to help reframe those difficult training sessions for athletes where they may feel mentally wiped out after a long day.
It is also worth noting that caffeine has been shown to help reduce mental fatigue. This supports the hypothesis that mental fatigue could arise from the accumulation of cerebral adenosine, as caffeine works via antagonising adenosine receptors. Exogenous ketones have also been shown to help maintain cognitive performance (and increase dopamine levels) during a 100km ultramarathon (Poffé et al., 2023). However there were no differences in overall performance, and at the time of writing these results have not been replicated.
Key takeaways
1. Mental fatigue increases perceived exertion and decreases motivation, which then impairs physical performance
2. Brain endurance training may improve an athlete’s resilience against mental fatigue, and improve physical performance
3. Due to the time demands of brain endurance training, and the limited evidence currently available, it is probably not advisable for a time-limited athlete
4. Caffeine may be the simplest way to reduce mental fatigue
Dallaway, N., Lucas, S., & Ring, C. (2020). Concurrent brain endurance training improves endurance exercise performance..Journal of science and medicine in sport. https://doi.org/10.1016/j.jsams.2020.10.008.
Martin, K., Meeusen, R., Thompson, K., Keegan, R., & Rattray, B. (2018). Mental Fatigue Impairs Endurance Performance: A Physiological Explanation. Sports Medicine, 48, 2041-2051. https://doi.org/10.1007/s40279-018-0946-9.
Poffé, C., Robberechts, R., Stalmans, M., Vanderroost, J., Bogaerts, S., Hespel, P. (2023) Exogenous ketosis increases circulating dopamine concentration and maintains mental alertness in ultra-endurance exercise. Journal of Applied Physiology, 134, vol. 6. https://doi.org/10.1152/japplphysiol.00791.2022.
Schiphof-Godart, L., Roelands, B., & Hettinga, F. (2018). Drive in Sports: How Mental Fatigue Affects Endurance Performance. Frontiers in Psychology, 9. https://doi.org/10.3389/fpsyg.2018.01383.
Staiano, W., Marcora, S., Romagnoli, M., Kirk, U, & Ring, C. (2023). Brain Endurance Training improves endurance and cognitive performance in road cyclists. Journal of Science and Medicine in Sport, 27, vol. 7., 375-385. https://doi.org/10.1016/j.jsams.2023.05.008.
Staiano, W., Merlini, M., Romagnoli, M., Kirk, U., Ring, C., & Marcora, S. (2022). Brain Endurance Training Improves Physical, Cognitive, and Multitasking Performance in Professional Football Players. International journal of sports physiology and performance, 1-9 . https://doi.org/10.1123/ijspp.2022-0144.