If you want to improve as a runner, it's important to understand how to manage fatigue and the role it plays in endurance training. Let's take a look at how a runner can find the right training balance and use fatigue strategically.
Why Fatigue Is Necessary
Training consists of the workout and the recovery process. Running breaks down your muscle fibers. The harder you run, the more muscle fibers you damage. Your body then works to rebuild these damaged fibers, and with proper recovery, they can grow back stronger than they were before. This is how training helps you get stronger and faster.
It's almost impossible to fully recover from a workout in 24 hours. It might be possible following a very easy run, but any type of speed, tempo or long run requires anywhere from 2 to 14 days for full recovery (here's a breakdown of how long it takes to recover from different workouts).
This means that unless you only run two or three times per week, training while slightly fatigued is inevitable. The trick is to figure out how to run enough miles to build aerobic capacity without overtraining, and to use fatigue to make your training more effective.