More than half of all runners will overdo it at least once in their running career. Overtraining is a result of not properly recovering between workouts on a repeated basis. Some types of workouts and training will make you more susceptible to overtraining, but the underlying cause is always a lack of recovery. While all driven athletes are prone to pushing too hard without properly recovering, researchers have identified a few training situations that make runners more vulnerable to overtraining.
They are:

1. Reaching too far in one training cycle.
Perhaps the most common cause of overtraining I encounter as a coach is by athletes who attempt to break their personal bests by too much in one training segment. While it can be especially difficult for a beginner runner or someone who is rapidly improving to assess what their potential might be, it’s important that every runner approach improving on a step-by-step basis.  Skipping a step or trying to make the jump from a 3:20 marathon to a 3:05 to qualify for Boston in one fell swoop will often lead to overtraining.

2. Not taking a break between training segments.
Another common cause of overtraining is not giving your body enough rest between training cycles. I work with many runners who want to jump from one training cycle to the next with little or no rest between. Many runners tend to finish a tough training segment where they pushed their bodies to new limits and raced well and immediately jump back into hard training toward the next goal. In doing so, these runners never give their bodies a chance to fully recover and absorb all the training from the last segment. They carry that fatigue with them and drastically increase the chance of overtraining.

3. Too many intense speed workouts.
Finally, performing too many speed workouts or VO2max training sessions in one training cycle has been proven to increase the risk of overtraining symptoms. From a physiological perspective, researchers have hypothesized that the increase in overtraining symptoms by runners who performed 8 weeks or more of speed work is the result of a rise in pH levels (too be effective, speed work should actually bring your pH levels down) and a stagnation in blood lactate levels.

Symptoms Of Overtraining 
It can be difficult to accurately determine if you are overtrained without a lab coat and fancy equipment. However, here are some clues you can use to help you determine if you’re recovering properly.

Heart Rate
During overtraining, you may have a higher than normal heart rate while resting and while sleeping. Record your heart rate each morning as soon as you wake up and before you get out of bed. Keep a small notebook by your night stand where you can record the data each day. If you find an extended period of time where your heart rate increases in the morning, you could be suffering the effects of overtraining.

Overtraining can lead to a decrease in hormone production, specifically the hormone catecholamine, which can influence the sympathetic nervous system. This can lead to increased feelings of stress and moodiness. If you’re feeling increasingly irritable or stressed, it might be a sign that you’re training too hard.

Susceptibility To Sickness 
Overtraining impairs the immune system, which leaves you more susceptible to contracting colds, the flu, and other viruses. If you find yourself getting sick more than usual, especially repeated bouts of the same virus, it could be a sign of overtraining.

Disturbed Sleeping Patterns
Finally, overtraining interferes with the bodies circadian rhythms, which can cause you to have trouble sleeping. Symptoms include waking up much earlier than normal or trouble getting or staying asleep.

Digging Yourself Out 
While I’ve spent a good amount of time discussing the causes and symptoms of overtraining, the treatment will be much shorter. You’ve probably even guessed it already–rest. If you’re overtrained, you need to focus on rest and recovery.