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.

Always check with your doctor before you start a vigorous exercise program or make a major increase in the intensity of your routine. Exercise does not harm a healthy heart, but could precipitate a heart attack if you have heart damage.

Dr. Gabe Mirkin has been a radio talk show host for 25 years and practicing physician for more than 40 years; he is board certified in Sports Medicine and three other specialties.

Dr. Mirkin's daily features on fitness have been heard on CBS Radio News stations since the 1970's. He has written 16 books including The Sportsmedicine Book, the best-selling book on the subject that has been translated into many languages. His latest book is The Healthy Heart Miracle, published by HarperCollins.

Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. A Boston native, Dr. Mirkin did his residency at the Massachusetts General Hospital. He has served as a Teaching Fellow at Johns Hopkins Medical School, Assistant Professor at the University of Maryland, and Associate Clinical Professor in Pediatrics at the Georgetown University School of Medicine. He has run more than forty marathons and is now a serious tandem bicycle rider with his wife, nutritionist Diana Mirkin.