Cycling, while generally pleasurable, is ultimately all about pain and suffering at the sharp end of competition. Fatigue and exhaustion is something we have all felt at some time or other. What's less apparent is what causes fatigue on the bike and what we can do to avoid it.
Let's take a look at the science behind exhaustion.
Why Do We Get Tired?
At some point during every ride, no matter how easy the intensity, you will end up getting tired and not capable of sustaining that same workload. This is true whether it's a time trial up l'Alpe d'Huez, a sprint down the Champs Elysee or a leisurely Sunday afternoon ride.
It may come as a surprise, but even after 100 years of exercise physiology research, the physiological reasons why humans fatigue during exercise remains a complete mystery to scientists. We certainly have a number of clues and strong theories, but no single model of fatigue seems to be able to accommodate all physiological mechanisms or real-life situations.
Not Just a Word Game
Why do we care about fatigue or what causes it? Most cyclists are masochists, and nothing is more important than understanding and ultimately prolonging the onset of fatigue. At its core, every race or ride at some point comes down to how much pain and suffering you can put up with. If we understand the contributing causes of fatigue better, we then determine and optimize the training adaptations needed to extend our limits and improve our performance.
Fatigue can be viewed as the first signpost that the body cannot handle a particular workload. Once lactate acid begins to build up in your muscles and you start to feel the burn in your legs, your workload has become too high for your muscles. In contrast to this point of fatigue, the point of termination of exercise is better defined as the point of exhaustion--the moment when you can no longer sustain that workload and are forced to slow down or stop.
We will go with these rough definitions of fatigue and exhaustion as they relate to our interest in cycling:
Fatigue: sensations of tiredness and associated decrements in muscular performance and function. This can generally be thought of as a safety mechanism to prevent harm within your body.
Exhaustion: the point of voluntary termination of exercise at a particular workload.
The 7 Components of Fatigue
By examining each of these potential mechanisms of fatigue in isolation, we'll try to get a better handle on just how important they are in affecting the onset of fatigue, which might also help us to understand how we might extend our own limits.
This is the reason why blood manipulation by both legal and illegal means can be so effective for endurance cycling. The more red blood cells and hemoglobin coursing throughout your body, the more oxygen and nutrients you can deliver to your muscles. In turn, you can maintain a higher workload primarily through aerobic metabolism without going too deep into anaerobic metabolism. This focus on maximizing your cardiovascular efficiency is also one of the primary rationales behind prolonged base training prior to high-intensity training.