So, the old rule of thumb that “you’re never as tired as you think you are is true:”:http://www.nytimes.com/2006/02/05/sports/playmagazine/05robicpm.html?_r=3&pagewanted=print
bq. A spate of recent studies has contributed to growing support for the notion that the origins and controls of fatigue lie partly, if not mostly, within the brain and the central nervous system. The new research puts fresh weight to the hoary coaching cliché: you only think you’re tired.
bq.. In 1999, three physiologists from the University of Cape Town Medical School in South Africa took the next step. They worked a group of cyclists to exhaustion during a 62-mile laboratory ride and measured, via electrodes, the percentage of leg muscles they were using at the fatigue limit. If standard theories were true, they reasoned, the body should recruit more muscle fibers as it approached exhaustion — a natural compensation for tired, weakening muscles.
Instead, the researchers observed the opposite result. As the riders approached complete fatigue, the percentage of active muscle fibers decreased, until they were using only about 30 percent. Even as the athletes felt they were giving their all, the reality was that more of their muscles were at rest. Was the brain purposely holding back the body?
‘‘It was as if the brain was playing a trick on the body, to save it,’’ says Timothy Noakes, head of the Cape Town group. ‘‘Which makes a lot of sense, if you think about it. In fatigue, it only feels like we’re going to die. The actual physiological risks that fatigue represents are essentially trivial.’’