Michael Barkasi

philosopher and cyclist

Is physical endurance mind over body?

As your musculoskeletal and cardiorespiratory systems are stressed under the load of an endurance task like sustained cycling, they presumably send feedback to the brain triggering automatic cessation responses. From a first-person perspective, the effort hurts and you feel the urge to stop. A commonsense idea is that you’re able to resist this urge and “push through the pain”. If that’s right, there’s presumably some physiological basis (presumably in the brain) for this resistance. The post-perceptual cognitive centers of the brain inhibit automatic responses (which would prompt you to stop) from earlier in the central and peripheral nervous system. Lots of studies show that patches of the prefrontal cortex, especially the inferior frontal cortex and dorsolateral prefrontal cortex (dlPFC), play an important role in facilitating this inhibition of automatic responses. For example, if you somehow shut these areas off, a subject’s ability to inhibit (resist) their urges and automatic responses diminishes.

A cool recent study attempts to test some of these ideas rigorously. What they did was stimulate the dlPFC using transcranial direct current stimulation while subjects performed a physical endurance task. Specifically, a cable was attached to subjects’ right ankle, then via pulleys that cable connected to weight. Subjects, by essentially performing a static leg extension, were asked to hold the weight up off the ground as long as possible (average time of hold was a little under 4 minutes). The authors expected to find that increasing activity in the dlPFC via the transcranial stimulation would increase the time subjects were able to hold the weight. The idea was that since the dlPFC facilitates a person’s ability to resist their urge to stop, increasing activity in the dlPFC would increase their ability to resist that urge. Surprisingly to the authors, this is not what they found. Transcranial stimulation of the dlPFC did not increase the time subjects could hold the weight.

While it would not have surprised me if the authors’ hypothesis had been confirmed by the experiment, I was not surprised it wasn’t. There are two reasons for this.

First, as a cyclist who’s spent countless hours pushing through horrendous pain on all sorts of efforts, my experience is that (usually) you either have it, or you don’t. For example, say I start an all-out hour effort where my goal is to produce the maximum average power I can over that hour. I usually know within the first two or three minutes whether I can complete the hour within range (say, plus or minus 3%) of my best power output. I either “feel strong” and get good response from my muscles, or my muscles feel week and respond as if they are fatigued. If I am fatigued and feeling weak, no amount of trying to push through the pain will make a difference. I’m going to fail. The same goes for efforts of other lengths: 30 seconds, 5 minutes, an hour, it’s all the same. As I often say, I’m much more machine-like than I want to admit: my body’s response patterns are pretty independent of my subjective feeling. There have been plenty of times when I’ve felt tired and had sore muscles, or when pedalling has just hurt worse than normal, but still performed at my peak; likewise, I’ve felt great, but put out crappy numbers. Of course, some minimal capacity to push through the pain is required; one can’t approach these things with no motivation or just give up as soon as their body screamed for them to stop. But if you have that minimal capacity to resist the urge to stop, further willpower (at least for me) doesn’t modulate performance.

The second reason I wasn’t surprised comes from my perspective as a cognitive scientist. The authors’ hypothesis assumes a pretty simplistic model of how cognitive functions are realized in the brain. Specifically, it assumes that automatic response inhibition is something some one area of the brain (the dlPFC) “does” all on its own, as if that area was like a modular unit or homunculus responsible for your will power. But that’s not how the brain, or cognitive functions, work (and, really, at this point cognitive scientists should know that). Except for all but the most simple, psychological functions like response inhibition are realized by complex, massively distributed networks across the entire nervous system. Sometimes the physical basis of these functions extends outside the body entirely (e.g., think of how tools like a pen and paper, or your smart phone, extend your cognitive capacities) or depend on complex environmental interactions which shape neural responses in real time. (For example, think about how social cues from other people around you shape your responses in real time.) Sure, it’s probably the case that the dlPFC is a key necessary component to response inhibition. That’s why, if you knock it out, subjects’ ability to inhibit their responses decreases. But that doesn’t mean that it’s the end of the story, and certainly isn’t reason to suspect that enhancing dlPFC activity will enhance response inhibition.

So, if you’re an athlete, what does this mean? Well, probably not much, since the study itself is looking at just one small piece to this puzzle. (The study does a nice literature review, covering more of the pieces.) But, if I can speculate a bit, here are some takeaways. First, your capacity to will your way to better performance is pretty limited. Endurance performance is mostly settled at the level of the basic metabolic functioning of your muscles, not regulation by the brain (although of course the latter matters in many ways). Either your muscles are primed and fuelled to perform, or they aren’t. Second, if you find yourself giving in to the pain or urge to stop, don’t beat yourself up over it. It doesn’t mean you’re weak. That urge to stop is likely just the collapse of your body’s ability to metabolize fuel at the rate needed to continue; it’s not merely a subjective feeling for you to overcome — you probably had no choice.

Me, resisting the urge to stop pedalling about halfway through a 20 minute time trail in 35 degree celsius heat. February 2020, Canadian Sport Institute Ontario.

Is physical endurance mind over body?