Mental fatigue: can you harness it for performance?

The research

Twenty eight highly-trained cyclists took part in the study, in which the cyclists were split evenly between the brain endurance training group and the control group. Of particular relevance is that this study is the first to examine brain endurance training that is performed separately from the physical training itself. All subjects performed five training sessions per week, comprising of one strength training session and four cycling sessions. Following each training session, the subjects either performed brain endurance training or listened to neutral sounds. The brain endurance training consisted of mental tasks using apps on a mobile, such as the ‘Go/No Go’ task (in which response speed and accuracy is measured) and the ‘Flanker’ task (in which requires the ability to ignore irrelevant stimuli in order to do the task correctly).

Over the course of the 6-week study period, the supplemental training was performed for 30-minutes per week for the first two weeks, and the duration increased by 15-minutes every two weeks, finishing at 60-minutes per week. Both groups were tested for VO2max on one testing day. On the second testing day, they performed a time to exhaustion test at 80% of peak power output. Following this, the cyclists performed a 30-minute Stroop task. This a test designed to assess the ability to process information and perform cognitive tasks without interference. However, when deployed over extended time periods, it can also be used to induce mental fatigue. Following the Stroop task, the cyclists then performed a time-to-exhaustion test at 65% of peak power output.

In a second phase of the study, a different group of cyclists were split into brain endurance training and control groups. They performed the same training program except they only performed 30-minutes of brain endurance training throughout the study. However, the challenge of the tasks they performed was increased every two weeks. These subjects also performed different performance tests, using time trials rather than time to exhaustion tests. They performed a 5-minute time trial, a 30-minute Stroop task to test mental fatigue, and then a 60-minute progressive intensity ramp followed by a 20-minute time trial. The major difference between the two phases in this study was the types of performance tests used, and the progression of the brain endurance training.

What they found

The results were clear cut. In the first branch of the study, the results of the time to exhaustion tests at 80% and 65% of peak power output indicated that the cyclists performing brain endurance training improved significantly more than the control group (see figure 1). In the second branch of the study, the brain endurance trained subjects demonstrated a lower rating of perceived exertion during the ramp test and significantly faster 20-minute time trial performance. However, there was no difference in 5-minute time trial performance - perhaps because it wasn’t long enough for the benefits of the training to be seen. In both studies, these differences in performance were despite no differences in the physical training, and there were no differences in physiological measures between groups. Furthermore, both studies demonstrated improved mental performance following the initial test, indicating better mental resilience following intense physical exertion.

Figure 1: Time to exhaustion (TTE) with and without mental endurance training

Dark bars = mental endurance training cyclists; light bars = control group cyclists. Left graph = TTE at 80% of peak power; right graph = TTE at 65% at peak power. At both cycling intensities, the cyclists who performed mental endurance training obtained significantly greater performance gains than the cyclists who did no mental endurance training.

Practical implications

This research provides powerful evidence that you can improve your endurance just by training your brain. That’s a pretty powerful insight, particularly if you feel like you’re at or near your maximal training load from a physical perspective. Fortunately, it appears that you don’t have to continually increase your physical training loads to improve your performance.  If you’re interested in the specific training that was performed, the SOMA-NPT mobile app was used (which includes a flanker task, a go/no-go task, and an AX-continuous performance test (CPT). This app requires a monthly subscription of $50, which may be prohibitive for many amateur athletes. The good news however is that these tasks can be found elsewhere, and it’s likely that there is nothing particularly special about these tasks (beyond providing a significant mental challenge), which means that a wide range of mental training apps (eg maths agility tasks) are likely to be suitable too. Hopefully, future research will evaluate other types of tasks that many of us may already be performing in daily life, and which can be used as a stimulus.

In terms of time commitment, the subjects performed brain endurance training five times per week and progressed from 30-minutes per week to 60-minutes per week over six weeks in one of the studies and remained at 30-minutes in the other. That’s obviously a large time commitment. Unfortunately, there’s no evidence as to how much brain training is required to establish an effect. If you have this amount of time available to perform that much training, give it a go. However, as with all types of training, there is often a pretty large benefit from relatively small amounts of initial training. Therefore, something like 30-minutes, three times per week could be a great entry point, and the authors indicate that 2 hours per week is almost certainly sufficient.

If you do choose to use ‘brain endurance training’, be sure that you account for this training when evaluating your total workloads. It’s easy to ignore it because it’s not physical as there’s no mileage or tonnage associated with its performance. That doesn’t mean it’s not demanding on your body; it obviously causes fatigue (as evidenced by the performance losses associated with mentally strenuous tasks). Therefore, too much mental training performed too often may well lead to overtraining, even if you’re physical training doesn’t change at all!

Along those lines, while creating states of mental fatigue can help improve performance over time, it’s important to remember that it is a stressor in the short term, and as we discussed above, it clearly can have a negative impact on performance. When you want to perform at your best – eg on a race day - you’ll want to minimize the amount of mental fatigue that you’re experiencing in the run up to an event, whether that fatigue comes from brain endurance training or everyday life.  More is not better, and you do need to rest prior to important competitions. That includes your brain as well as your body!

Finally, while brain endurance training and the creation of mental fatigue should be used wisely, increasing the amount of mental training could be potentially beneficial if you experience an injury and your training loads must be lowered. Brain endurance training clearly improves performance in endurance activities, even if it’s not completely clear as to why or how this occurs. If you experience a minor setback and have to lower your training volume, adding brain endurance training or increasing the amount of brain endurance training may just help you improve your performance.

References

1. Sports Med. 2017 Aug;47(8):1569-1588.  doi: 10.1007/s40279-016-0672-0.

2. Medicine & Science in Sports & Exercise 47(5S):p 198, May 2015. | DOI: 10.1249/01.mss.0000476967.03579.44

3. J Sci Med Sport. 2023 Jul;26(7):375-385.  doi: 10.1016/j.jsams.2023.05.008.  Epub 2023 May 21