Overtraining can occur following years of overloading without adequate recovery. Elite level runners and cyclists follow training regimes which are highly demanding but absolutely necessary to significantly improve performance. For example, there is very little longitudinal data to show improvements in running economy. Studies by Paavolainen et al. (1999) and Millet et al. (2002) where two months of explosive weight-training improved running mechanics slightly. The current women’s marathon record holder trained for 5 years to induce a 14% improvement in running economy (Jones 2006). Professional cyclists improved mechanical efficiency by 8% after 7 years of training. Therefore, tens of thousands of training hours gone into improving economy/efficiency of movement nets about 1-3% per annum. The balance between overload and overtraining is very fine indeed.
In 1984, a marathoner gave this account of his experience with overtraining: “I hated running. I hated it with a passion … In retrospect, I now know what was wrong and what was causing my problems. I had three episodes of heat stroke. That, combined with all the years of hard training at such a high level without ever taking a break, damaged a part of my brain … My endocrine system was so screwed up that I had very low hormone levels … For several years, I was on a wild-goose chase to get my hormone levels normal again. I wasn’t competing anymore but still felt awful. I was also so exhausted i’d fall asleep at my desk at work … I didn’t have the energy to do normal things and was always in a bad mood“.
Wischnia B. Comeback at Comrades. Runners World 1994; 29 (8): 76-7