CoachPhysical activity is any movement of the body produced by the muscles that raises energy expenditure above rest: walking, climbing stairs, housework, sport. Training is physical activity repeated with the aim of improving a capacity. The body responds to a repeated demand by adapting: enlarging, strengthening or re-equipping the structures the demand loads — provided the demand is followed by the rest in which the adaptation is built.
示例
Example 10.10 (EPO in numbers)
Red blood cells make about 45% of the volume of normal blood. EPO abuse has pushed athletes to 55% and beyond, a blood so thick that the heart, slowed by sleep, cannot move it: several young cyclists died in their sleep in the years before tests existed. Training at altitude raises the same figure by two or three points, over weeks, under the body’s own control.