A hard workout only creates the potential for fitness. It’s realized when you recover afterwards. When you take it easy after a hard workout the body’s adaptive process kicks in and you become more fit. During recovery the body restores itself by rebuilding damaged cells, creating new neural pathways, expanding capillary beds, rebalancing its chemistry, developing muscles, and much more. During this physiological renovation it makes all of the body’s systems affected by the workout slightly better able handle the stress that produced the need for rest in the first place. This is called overcompensation. The overcompensation process is at the heart of adaptation and therefore race performance. The ultimate result is that the three determiners of your endurance fitness—aerobic capacity, anaerobic/lactate threshold, and economy—improve slightly. The amount of improvement is determined by the type of workout stress applied and how long the recovery lasted.

Recovery and adaptation are essentially the same thing. This adaptive process takes some time and can’t hurried. How much time you need to reduce fatigue and gain fitness depends on how great the preceding workout stress was. If it was only slightly more difficult than what your body was already adapted to then you will probably be ready for another stressful workout again in around 48 hours. A workout that was a great deal harder than your current level of adaptation was capable of handling requires a longer period of recovery.

Following a hard workout you experience fatigue. That is how nature tries to keep you from doing back-to-back hammer sessions that would tear the body down so much it could no longer adapt. An exceptionally high level of fatigue, indicating a very stressful workout, is risky. Combine this with too little recovery time and you’re on the way to overtraining. But the other side of the training coin isn’t much better. Only doing easy workouts day after day or taking several days off results in a loss of fitness. This is the opposite of overcompensation. The key to effective training is to strike a balance between these two determiners of high-performance—stress and recovery—so that fatigue is created and then reduced.

So there is no improvement in fitness without at least some fatigue. How much fatigue is necessary for this? Unfortunately, that’s hard to nail down because fatigue isn’t as easily measured as fitness, at least not yet. Precise tests, such as those used in measuring VO2max or anaerobic threshold, don’t exist for fatigue. That makes recovery an art more than a science. While there are some ways of determining it, fatigue requires a lot of guesswork in order to come up with the proper recovery dose for the given stress load that produced it. This means recovery from fatigue is mostly based on self-perception and sensations. But we’re slowly getting better at measuring it. Sport science generally comes up with something every few years for gauging what the body is experiencing following a hard workout or period of training. One such tool is heart rate variability. Such breakthroughs allow us to make better-educated guesses at how much recovery may be needed following a given workout. Even with such measurement, however, it’s still imprecise.

What further confounds all of this is that recovery is highly individualized. Not all recovery methods work equally well for all athletes following the same types of training sessions with similar levels of fatigue. The challenge is to figure out what works for you. The two most common and most effective are sleep and nutrition. But there are other options such as compression garments, pneumatic compression devices, massage, alternating hot-cold water emersion, and many more. There could be several things to try before finding the best for you. Even then their effectiveness may vary from one workout to the next. The solutions may be found by simply trying things. This isn’t easy because there are quite a few and some involve using special and somewhat expensive gear. They are also quite individualized. But you probably already have a great deal of experience with some of the methods. Most advanced athletes soon figure out these things as their racing careers progress.

Here’s one example of the individuality of recovery. Most advanced athletes find that an easy session—called “active recovery”—stimulates recovery and therefore contributes to adaptation whereas most novice athletes and many intermediates (second and third years in their sports) find that a day off from training—“passive recovery”—is usually the better option.

Connecting the dots for all of this leads to the conclusion that fatigue is good because it implies the potential for fitness, and that decreasing fatigue is an indicator of adaptation and therefore realized fitness. That’s a big deal. So the overarching lesson here is that recovery is just as critical to your success in sport as are hard workouts. If you are good at doing one but not the other you will fall well short of your potential. It takes both the stress of training and the adaptive process of recovery to be race ready.