Pain May Come with Gain in Childhood Exercise

Studies Find Exercise Triggers Both Beneficial and Disease-associated Factors, May Help Researcher Determine Optimum Workout
Irvine, Calif., Nov. 12, 2002 — The phrase “no pain, no gain,” used by coaches to prod school-age athletes, may have more meaning than they ever imagined, two UCI College of Medicine studies have found.

The studies appear in the October issues of Pediatrics and Pediatric Research and suggest new ways to mark the boundary between healthy and unhealthy exercise. The research also may help physicians and others develop optimal levels of exercise that may help stave off the current epidemic of obesity in adults and children.

Dr. Dan Cooper, professor of pediatrics, and his colleagues from the Center of the Study of Health Effects of Exercise in Children found that even a single, intense bout of exercise in teens and preteens raises levels of cellular chemicals that are usually associated with disease, while the same bout builds muscle mass and increases fitness.

“Physical activity in children gives two signals, one that marks a healthy response and one that may be telling us the exercise stress on the body has gone too far,” said Cooper, a specialist in the effects of exercise on growth and development. “The healthy signals in cells help the body grow, build muscle mass and increase lung capacity. But the bad signals are catabolic. They actually encourage degradation of cells and are commonly linked to diseases. The mystery we need to solve is how much exercise is too much, and how much of these changes in signal levels are a normal product of development.”

Cooper’s team reported in the Pediatrics study that after 11 healthy teenage boys had a 90-minute strenuous wrestling practice session, levels of cell messengers called IGF-I and insulin, both indicators of growth, decreased at the same time as levels of inflammation-inducing messengers had robust increases. For example, Cooper’s team found an eight-fold increase in a substance called IL-6. This substance is usually elevated in common diseases like colds and flus and in more serious childhood diseases like pediatric arthritis. In high concentrations, IL-6 causes fatigue, muscle aches and malaise.

In the study reported in Pediatric Research, 30 non-athletic boys ages 8 to 11 years old were tested. The boys engaged in running, playing soccer, jumping and other aerobic games for five weeks. While these boys were engaged in a less intense exercise then the wrestlers, the same cellular messengers that are associated with disease rose, but to a lesser extent than they did in the wrestlers.

“We now know there is a stress response to exercise that can be measured even in healthy children,” Cooper said. “These stress mediators are known to influence growth and development of many tissues like muscle and bone. A little stress may be OK, but we need to determine how much is healthy. We think this research will one day play an important role in understanding what the healthiest physical activity levels are for children. In addition, for children who suffer from chronic diseases where many of these stress factors are already elevated, this research may help provide these kids with physical activity levels that are safe.”

Some of the cellular messengers, especially IL-6 and related chemicals, are known to play a role in obesity and diabetes. These messengers are also found to be elevated in asthmatics during exercise. Cooper and his colleagues are now looking at how responses in these cellular messengers vary in different age groups in girls as well as in boys. They are investigating whether the changes seen in healthy children also appear in children who suffer from childhood chronic diseases such as asthma, obesity or cystic fibrosis, or in children who have had heart surgery.

Cooper’s colleagues in the study include Dr. Dan Nemet, Youngman Oh, Ho-Seong Kim and MaryAnn Hill of UCI. His colleagues in the Pediatrics Research study include Nemet, Timothy Scheett and Robert Newcomb of UCI, and James Stoppani and Carl Maresh of the University of Connecticut.

The studies were supported by the National Institutes of Health and the Joseph W. Drown Foundation.