Mental fatigue is a state of tiredness and diminished functioning. It is a normal, transient response to exertion. It can be difficult to know when an athlete is mentally fatigued. The signs of mental fatigue are more subtle than physical fatigue and will fly under the radar to the untrained eye. Some athletes may even report they feel fine but once you have objective measures available to you, it will be clear if your athlete is experiencing mental fatigue.
Mental fatigue can creep up on athletes without them being aware and impact their sports performance leading the athlete to wonder why they are making poor decisions, making more mistakes, and underperforming physically. Teams and clubs may not even be aware of why their athletes aren't performing at their peak and assume it is physical fatigue the athlete is experiencing. This can lead to frustration for the athlete and the club when the solution is simple, we need a way to assess and monitor mental fatigue. Fortunately, there are a number of simple objective measures that can be used to corroborate our suspicions and/or identify unnoticed states of mental fatigue.
With the right tools, mental fatigue can be easily monitored by coaches and clubs, who can then better predict performance, optimise training load, and even prevent performance slumps. It is worth considering how many performance benefits are being missed out on by not assessing the athlete’s brain?
Research in mental fatigue has shown,
Mental fatigue decreased cycling time to exhaustion by nearly 2 minutes (16% decline in performance). Athletes cycled at 80% of peak power for 12:34 (12 minutes and 34 seconds) in the control condition but only 10:40 when mentally fatigued.
Mental fatigue decreased power output during two 10-min self-paced cycling bouts. When mentally fatigued, athletes produced by 17.5% less power when cycling at a fairly light pace and 8% less power at a hard pace.
Mental fatigue decreased time to exhaustion in a sub-maximal contraction of the knee extensors by an average of 36 seconds (13% decline in performance). Athletes were able to maintain the contraction for 4:26 in the control condition but only 3:50 when mentally fatigued.
29 studies published between 2009 and April 2018 and focusing on the impact of mental fatigue on sport-related performance. Taken all studies together, it appears that mental fatigue impairs endurance performance, motor skills performance and decision-making performance.
Perception of effort, rather than severe locomotor muscle fatigue or intolerably unpleasant muscle pain, is the cardinal exercise stopper during high-intensity aerobic exercise.
Fatigue impairs athletes’ ability to select actions optimally.
Athletes’ involuntary attention and selective attention were damaged after mental fatigue.
Mental Fatigue is the silent killer of performance and is often overlooked.
The research on the impact of mental fatigue on sports performance is clear. In order to make sure our athletes are performing at their best, we must monitor mental fatigue. Mental load is just as important to track as physical load.
One of the quickest ways to assess an athlete's mental fatigue levels objectively is by performing the Psychomotor Vigilance Task (PVT). In this task, performers are presented with a visual stimulus (e.g., a colored circle) and are asked to respond (by tapping the screen) as quickly and as accurately as possible when it appears.
The PVT comes in 3-, 5- and 10-min versions. Having an athlete perform this short objective test pre-and post-training, allows you to monitor their mental fatigue levels easily. You will need to monitor their PVT performance measures over weeks to get clear insights into how their mental fatigue varies with time and, importantly, what is typical and atypical for them. The PVT is a simple visual reaction test with long pauses (1-8 seconds) between each stimulus for the 5-minute and 10-minute versions, and short pauses between each stimulus (1-4 seconds) for the 3-minute version. If an athlete is mentally fatigued you will see an increase in their lapse count (number of excessively slow responses, a key indicator of inattentiveness) and their average response times.
What does it look like when my athlete is mentally fatigued?
When your athlete is displaying mental fatigue you will typically see slower response times, increased response variation, and increased lapse count, which have been associated with mental and physical fatigue. You can learn more about the PVT in research articles at the end of this article.
Below you can see a PVT performed pre-training and post-training. At the post-training assessment, this athlete was 19% slower, 8% less consistent, and lapsed 4 times (the athlete's responses were slower than 500 ms on four occasions - that's very slow).
Pre Training PVT
Post Training PVT
Reaction 383ms (19% slower)
Variation 27% (8% less consistent)
Lapses = 4 (responses slower than 500 ms)
How do I Implement the PVT?
Simple. Perform the PVT pre- and post-cognitive training and monitor the cognitive measures over time. You will need to keep an eye on reaction time, variation, accuracy and lapse count.
If you notice your athletes;
Reaction time, variation and lapse count prior to starting their cognitive training is increasing over the course of a week it might be time to reduce the cognitive load so your athlete can recover.
Session 3 - Clear decrease in performance.
If you notice your athletes;
Reaction time, variation and lapse count are all increasing post-session: this would indicate you have applied enough cognitive load to induce mental fatigue. This is a good thing, as long as they can recover.
Post Session - Decrease in performance due to sufficient cognitive load.
If you notice your athletes;
Pre-and post-training PVT measures are not changing much: this would indicate the cognitive load from the training session is not stressing the athlete very much. If your goal is to have a low load week or you are close to a competitive event this is acceptable. Just like physical training your athletes must be able to recover from the workout UNLESS you are purposely overreaching them.
Post Session - Slight decrease in performance due to insufficient cognitive load deliberate
Cognitive Load Management
The PVT can assist you in developing and adjusting your cognitive training plan. As the plan increases in difficulty, are your athletes adapting and becoming more fatigue resistant to the training plan like they would in physical training? If so you should notice that the pre- and post-assessment PVT measures (e.g., speed, consistency, lapses) fluctuate less. Alternatively, have you made the training plan too hard, and they cannot mentally recover from the very high cognitive load? You may notice a higher than normal pre-training PVT reaction time with more variation and lapses.
The PVT will also allow you to see if the cognitive training plan is too easy. If this is the case the pre- and post-assessment PVT performance metrics will not change much.
This simple task can assist you in finding the sweet spot of any plan designed to optimize your athlete's mental training load.
Mental Fatigue Research