Some runners who are training for specific races or certain goals run too hard, run too many miles, and don't allow for proper recovery time. They assume that running every day
will help them get fitter and faster. Overtraining is the leading cause of injury and burnout
The solution: Here are some ways to avoid overtraining:
Increase your mileage gradually. Don't let your weekly mileage increase by more than 10%.
Try to give yourself periodic "rest weeks" by dropping your mileage by 50% every fourth week.
After a hard run, take a day off. Rest days are important for your recovery and performance.
Add some cross-training activities to your schedule. Doing activities other than running prevents boredom, works different muscles, and can give your running muscles and joints a break.
Also see: What Should I Do When a Run Isn't Going Well?