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Dear Chris,
I recently read that fatigue may be all in my mind, and that there may be ways to use brain power to go faster, or harder. That sounds exciting, but is there any truth to that?
— Noah

Dear Noah,
We all know what fatigue feels like. We’ve all experienced that exasperating feeling when our legs give out on a critical climb, or when our sprint fails to materialize at the critical moment. But the causes of fatigue are a bit more mysterious.

For many years, there was the widely held belief that the pooling of lactic acid in our legs was the cause. While that may have been what your high school track coach told you, that’s not it. The answer is actually a lot more complex than you’d think and involves many different physiological causes, including muscle damage, glycogen depletion, and body temperature. Still, none of these reasons by itself fully explains fatigue, despite what some researchers might tell you.

One of the most exciting theories explaining fatigue has only recently been proposed. It suggests there’s a “central regulator” of fatigue, which integrates all of the different past theories and ultimately allows our mind to decide where our limits are. That is, fatigue could be, in part, a psychological thing.

So, to answer the question of whether we can use mind power to improve performance, by quieting sensations of fatigue, the answer is yes. How much fatigue we “feel” can be a conscious choice that can be influenced by the length of the race, or how much is left in a race; mental cues we give ourselves and the things we focus on during an effort; and other mental tricks that help you adapt in some way to feelings of fatigue and discomfort.

However, it is important to emphasize that our body’s limiters are there for a reason: namely, they have evolved to protect us from doing damage. The limits they set, therefore, do not represent our maximum, but rather a point at which we can safely perform, and include a protective buffer from efforts that might lead to long-lasting harm and even death.

“There are absolute ceilings that your body cannot go past,” says Dr. Stephen Cheung, an exercise physiologist and professor in the kinesiology department at Brock University in St. Catherine’s, Ontario, whose research interests include the effects of environmental stress on human physiology and performance. “For example, if your body temperature goes to 42 degrees Celsius, the proteins in your cells are going to start to denature, to break down. There is no amount of psychology that is going to push you past that. So, I don’t want people to think that there are no such things as limiters.”

One question this brings up is how close and how often you are willing to go toward your limits and push these boundaries? Do you want to try this in training rides, or weekend group rides? Should you reserve this for races or maximal efforts like an hour record attempt?

“One of the main concepts here is about how to essentially turn off or disable the emergency handbrake that we have on our voluntary effort, or how hard we’re willing to work,” says Cheung. “There are several different models of fatigue, of where the body will ultimately break down. The psychological component really is about how close are we willing to push ourselves to those limits. Your brain is integrating all of the different signals it is getting about body temperature, pain, and so forth, and saying, ‘At this point in time, how hard am I willing to work?’ It is a feedback and feed-forward system where every second you are constantly deciding on whether to push on or not, in real-time.”

Finally, it is critical to understand that while you can develop ways to push yourself harder, the limits are there for a reason, in much the same way that an engineer will design structures with a safety factor, such that the design is never being pushed to its limits. The human body is the same.

We dive even deeper into the subject of fatigue and its root causes in the following episode of Fast Talk.