Question: You have written articles with the "rules" of exercise for adults, but I have never seen this for children. I have a 9-year-old son whom I would like to be fit and healthy. What are the guidelines for children of this age?

Answer: Actually, there is not much research on prepubescent children because many experimental procedures are not appropriate for use with children, and some children are much more developed at any given age than others. However, there are a few differences between children and adults that, if understood, can work ef-fec-tive-ly with your son.

First, there is really no restriction for children in terms of exercise or activity. However, children have a lower tolerance for ex-treme heat or extreme cold, and they tend to acclimatize to abnormal environmental conditions less rapidly than adults. The reasons for these differences are they have a larger body surface area (skin area) to body mass (weight) than adults, they have less of an ability to sweat than adults, and their cardiovascular systems are not as able to maintain exercise under a heat load.

The American Academy of Pediatrics recommends that children be allowed a "longer and more gradual" program of acclimatization if they are going to train in the heat. They also recommend that parents and coaches be aware of the needs for fluid replacement during continuous exercise in the heat.

Also, children are much less goal- oriented than adults and prefer short-term, intermittent activities with a high recreational component and variety, rather than monotonous, prolonged activities. I remember managing a summer activities program for fourth-graders many years ago. These children would play really hard for a short period of time then just sit down on the grass and rest. When they were rested, they were up and into the activity again, without any urging on my part.

If they are involved in fitness activities such as jogging, cycling or swimming, children do best when going with a parent, or with their dog, so that it doesn't seem like they are officially exercising.

The best fitness activities relate to some sport such as soccer, or a game such as "kick the can." We found that just having a pad of cement with lines, bankers and nets and different kinds of balls stimulated spontaneous fitness activities - especially if we also restricted TV time.

Older children like strength training, but programs of this type must be supervised by an adult who knows how to modify the program. Children should focus on high-repetition, low-resistance lifting to avoid injury to growth plates in the bones.