"Overtraining, fatigue, and burnout are a state of mind. Certainly, we all get tired after putting in miles of laps, but the notion of burnout is really a psychological one."
-Three-time Olympian Janet Evans
During my swimming career, I took the above sentiment to heart. More was always better -- more pool sessions per week, more laps, more dryland training. I even went so far as to perform 1000 "abs" per day for a while, as per Evans' recommendation.
As it turns out, I'm not Janet Evans, and neither are you, probably. (Unless you are, in which case, thanks for reading, Janet!) Looking back, I was always in my best shape at the very beginning of the college season, after having trained more moderately during the summer. By mid-season, I was exhibiting numerous signs of overtraining, like constant lethargy, decreased performance in competition, and low motivation to train.
A week or two of strategic overreaching (an abrupt and generous increase in training volume) and subsequent supercompensation through a deload (an abrupt reduction in training volume) or complete rest is one thing. But training past exhaustion day after day, week after week, is simply counterproductive and a recipe for overtraining.
The knock here isn't on Evans, of course. Her training methods obviously worked for her. Some genetically-gifted individuals will be able to train twice a day, every day, no problem. Most mere mortals, however, will not. The key is to find your unique sweet spot in terms of training frequency.