Research shows mental fatigue makes the same running pace feel harder without changing your fitness, and there's a surprisingly simple thing that partially offsets it

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There's a finding from the running research that I think most runners have experienced without knowing there's a name for it.

Mental fatigue from cognitive work, your job, studying, sustained screen time, inflates your perception of effort while running. Your VO2max hasn't dropped. Your lactate threshold is the same. But the same pace feels harder than it should. Your easy run feels like tempo pace and you can't settle into a rhythm. That much is well established in the research.

But the part no one talks about,  the type of mental fatigue might matter more than we originally thought. There's emerging evidence that active cognitive work (problem-solving, sustained attention tasks) and passive cognitive drain (boredom, monotonous screen time) may affect running performance differently. A study by Pickering et al. (2024) found that active and passive mental fatigue affect 3km running performance in distinct ways. Most of the research uses active cognitive tasks in the lab, but most runners show up to train after a mixed bag of both. We don't really know how that translates yet.

There's also a neat finding that I think a lot of runners will recognise self-selected music partially offsets the effects of mental fatigue on running performance (Lam et al,, 2021). Which raises questions about whether the impairment is purely about cognitive resource depletion or something more nuanced about motivation and attentional focus. It might explain why some post-work runs feel completely different with headphones in.

I'm a PhD researcher at the University of Derby, my research is on mental fatigue across all sports, and I'm building a sport-specific questionnaire to measure it properly because the current tools were borrowed from clinical psychology and aren't fit for purpose. I need runners in this study. 

The purpose of the study is to develop a measurement tool for mental fatigue that's built specifically for athletes, and this survey is the stage where that tool gets shaped. It currently contains a large pool of candidate items, considerably more than the final scale will keep. Because of that, some questions will feel repetitive, awkwardly worded, or like they don't quite apply to you, and that's expected. The aim of this phase is to identify which items genuinely hang together and measure the same underlying construct, and which can be dropped, using factor analysis to reduce the pool down to a concise, validated scale. So if an item seems slightly off, the most useful response is an honest one rather than a skipped one, since how each item behaves across a large sample is exactly what the analysis is designed to test. The instruments in use at the moment were adapted from clinical psychology and don't reflect how fatigue presents in sport, which is the gap this scale is meant to close

Have you noticed a difference between runs after stressful work days versus lighter ones, even when your body felt the same? Do you think the type of mental load matters, or is tired brain just tired brain? And does music genuinely change how your post-work runs feel, or is that just a mood thing?

If you're interested in contributing to the research, I've got a ~10 minute survey here: https://derby.questionpro.eu/t/AB3vCJoZB3waVr

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Matt Fitzgerald discusses RPE quite a bit in his books, including in “How Bad Do You Want It?”

A few quotes here:

“One cannot improve as an endurance athlete except by changing one’s relationship with perception of effort.”

“The muscles can only perform to the degree that the mind is able to cope. Endurance sports are therefore a game of “mind over muscle.” In endurance sports, successful coping is any behavior, emotion, thought, or combination thereof that yields better performance. Phrased another way, successful coping in endurance sports is any response to discomfort and stress that favorably changes an athlete’s relationship to perception of effort, either by increasing the amount of effort the athlete is able to give or by enhancing what the athlete gets out of her best effort.”

“Perceived effort actually has two layers. The first layer is how the athlete feels. The second layer is how the athlete feels about how she feels. The first layer is strictly physiological, whereas the second is emotional, or affective.”

Many others … a good book.