エクササイズは麻薬中毒

に似ている。という説があるらしい。

Hardcore runners who can't bear to skip a workout may be hooked in a way that's similar to heroin addiction, according to a new study of rats.

The well-known "runner's high" may be the culprit: Human runners need to increase the distances they run to feel that euphoria, experts say.

And if these runners are forced to stop, they can show signs of depression.

Such "withdrawal symptoms" have led researchers to theorize that addictive chemicals are naturally released by the body during exercise.

Exercise Can Be Like Heroin, "Gym Rats" Show

ランニングを始めとするエクササイズ、「ランナーズ・ハイ」を経験するとそれを求めて走行距離をどんどん伸ばしたくなるらしい。で、強制的にランニングを抑えると禁断症状として鬱になるとの説。
うーん、単に走りたいのに走れない鬱憤が貯まるだけじゃないんだろうか。