If an athlete is unaccustomed to a particular workout, certain blood markers will increase, and harder workouts result in proportionally higher blood markers. All of these markers are found in the muscle. During exercise, small tears in the muscle allow them to leak from the muscle into the bloodstream. These tears are normal and usually do not lead to injury, but they allow the markers to leak from the muscle into the bloodstream. Higher intensity exercise leads to higher markers in the bloodstream, so values are typically higher in the athlete than in the sedentary individual.
Cortisol increases the body's ability to produce energy.
During exercise, this is beneficial to the athlete. However, if cortisol levels remain high over long periods of time, the body will break down its own muscle tissue in order to continue producing energy. This leads to fatigue and an inability to train effectively. Values of these four blood markers vary with gender and training phase. The value ranges below represent data accumulated from swimmers at the junior national, national, and collegiate level.