I needed to read this today: I have been feeling the physical and psychological effects of overtraining. After today’s workout, I am going to take 3-4 days off starting tomorrow to give my body time to recover. Someone asked me this morning when the last time I took more than a few days off in a row? You know I couldn’t remember….

Personal Best: Workouts Have Their Limits, Recognized or Not

Intense endurance exercise depletes muscles of their energy supply, glycogen. Muscles store enough glycogen only for an hour and a half to two hours of activity, Dr. Saltin said.

It takes a day for trained endurance athletes to replenish glycogen. Athletes with less training have less of the enzyme that restores glycogen — glycogen synthetase. It can take up to two days for them to restore this muscle fuel.

In addition, connective tissue in muscles can be damaged and needs time to recover. In a study of runners in an annual local race that is a bit longer than two marathons, Dr. Saltin and his colleagues found that the athletes’ muscles lost their elasticity as their connective tissues weakened.

Running got harder and harder, so much so that the energy required for a set pace at the end of the race was 50 percent higher than it had been at the start.

So how to avoid a self-defeating training program? There are no hard and fast rules, because individual athletes vary so much. A training program that one person thrives on will break another, equally talented athlete.

Dr. Raglin said even the experts, researchers like himself who study overtraining, had trouble defining the symptoms. Psychological changes are the most consistent signs of a problem, he said.

In the early stages of overtraining, athletes constantly feel tired; by the end stage, they may be nagged by depression.

Recreational athletes must be attuned to their fatigue, Dr. Raglin said. If it persists for several days, they should take a day off or simply do a lot less during workouts. A diary or notes on how they feel can help.

And that does not mean that difficult regimens are out of the question, Dr. Raglin said. He should know — he’s training for a contest in March, the Arnold 5K Pump and Run, in which competitors must bench press their body weight up to 30 times and then run a five-kilometer race.