To improve for athletic competition, all athletes must suffer skeletal muscle damage. Without this damage their muscles will not grow and they will not become stronger. World-class competitive bicycle racers ride at close to their maximum heart rate for five to seven hours a day. Many researchers have been concerned that this very hard riding would damage their heart muscle as well as their skeletal muscles. A study from Freiburg University in Germany shows that hard exercise does not damage a healthy heart.
When muscles are damaged, they release enzymes into the blood stream. This study shows that the heart muscle is not damaged the way that skeletal muscles are ( Medicine and Science in Sports and Exercise, October 2003). Post exercise electrocardiograms and echocardiograms were normal as were blood levels of heart-specific enzymes, creatine kinase, creatine kinase MB and myoglobin. However, older bicycle racers did have a rise in another enzyme, brain natriuretic peptide, that is associated with heart function. The authors felt that this shows that older athletes may not adequately empty their heart's ventricles during the diastolic relaxation phase, and the increased pressure stretches the heart muscles to raise blood levels of this hormone.