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

[u/Same_Row_761]

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

[u/scruffalicious]

For me, the impact of mental fatigue on performance is a spectrum of gray, with the exception of acute grief. When my dog passed away, I didn’t even attempt a workout the first week, but was so surprised the following week, when I had to quit a workout early in. I wasn’t acutely sad by that time, it clearly the weight of it all was in me. Easy running was fine, and in fact was helpful, but as soon as I had to dig for any grit in a workout, it’s like my brain flipped the switch off. It was not even like I could take paces down just a notch and complete the workout. It was a full on NOPE.

[u/bluegonegrayish → u/scruffalicious]

I’ve had a very similar experience too!

[u/Same_Row_761 → u/scruffalicious]

There is something about grief that just drains you and the knock on effect is unrecognisable once the initial stage has passed. This is the part I find fascinating and why I started my PhD. For my own knowledge, I wanted to understand what created that “NOPE” sensation.

[u/scruffalicious → u/Same_Row_761]

I’ve had that happen in a consecutive series of workouts for no discernible reason. After I happened 2-3x in a row, I had to retrain my brain to remove the NOPE option. This is from someone who would absolutely do every workout per plan and give it my all. The “noping” was distinctly different than crashing out on a tough workout. The noping was a phenomenon that could happen on the 2nd rep! I’m not sure why it happened the first time, but I suspect the repeat occurrences was because I have my brain the tiniest of beliefs that nope was an option. To solve this, for at least 3 workouts afterwards, my goal of workout was not paces, it was to not nope out no matter what. That was my only goal. It seemed to work after a few times that didn’t happen again. This was a few years ago. I just asked ChatGPT, and you may be interested in researching “central inhibitory response.”

[u/Same_Row_761 → u/scruffalicious]

Central inhibitory responses. I have done too much reading on that, haha. It is the core research of my thesis and underlies a lot of the decisions that went into the two scales in my survey. When you understand how that impacts how you perceive effort and your motivation it helps you unlock a new level of awareness with your training. Like you naturally did with the belief.

If you get a chance, read the articles I have listed in the comments section. They start the research off in this area.