OVERTRAINING IS INSIDIOUS: Ryan Hall’s Overtraining: A Cautionary Tale. “Researchers have known since the late 1980s that chronic and extreme endurance training has a tendency to lower testosterone levels, causing depression, fatigue, and lack of motivation. More recently, however, exercise-induced low testosterone has been recognized as one of many common biomarkers for a more systemic breakdown: training that is so hard, frequent, and long, and with such inadequate rest along the way, that fitness, performance, energy levels, and mood all fall off a cliff.”

This can happen with weight training, too. One thing I do — like the old bodybuilders who, like me, didn’t use any steroids — is to take a clean week off every 8-10 weeks, when I don’t do more than walk for 30 minutes now and then.