_{by Douglas Krohn, M.D., Pediatrician}

_{February 2010}

It has long been recognized by athletes that different approaches to strength training will yield slightly different results. Lifting relatively heavy weights for fewer reps appears to increase the size and strength of muscles, whereas lifting somewhat lighter weights for a greater number of reps seems to improve the endurance of our muscles and give them a contoured appearance – what people often refer to as “tone” or “definition.” The question here is which of these two approaches yields better results?

When strength training is initiated, low weight should ALWAYS be used until technique is perfected, and training should always be done under the strict supervision of a trained professional (for example, a gym teacher or a certified personal trainer). It is recommended that this supervision be continued for children and adolescents even after they are comfortable with technique, and that the lowest possible ratio of instructor to athlete be utilized: one trainer per athlete would be ideal, but ratios of up to 1:10 are acceptable.

Once the athlete is demonstrating proper technique, the appropriate weight would be one that allows for somewhere between 8 and 15 reps: weights that are too heavy to lift 8 times are just too much and should not be used; when a weight can be easily lifted more than 15 times, it is probably time to go up on the weight in a modest increment. Those athletes who are looking for increased endurance should aim for whatever weight results in about a 12-15 rep set, while those who are looking for strength would settle on a weight that results in fatigue after about an 8-12 rep set. Most young athletes will benefit more from endurance training than from strength training.

There are a few other things to keep in mind. Strength training should address all major muscle groups, including the trunk and legs, and not just focus on the chest, arms and muscles that you show off at the beach. For children and adolescents, strength training should be done as a supplement to the other sports that the young athlete plays (for example, soccer or swimming), and should not be the sole form of exercise. In order to achieve the benefits of strength training, workouts should occur 2-3 times per week and last at least 20 minutes. Training more than 4 times per week has not been shown to add any benefit, but is associated with an increased risk of injury. Workouts should always include a 10 minute warm-up and cool-down period, and increases in weights used should never exceed 10%.

One nice thing about strength training is that beneficial results can be expected in about 8 weeks. However, you must keep it up – expect the fruits of all this good work to vanish in about 6 weeks’ time if you don’t stick with your regimen.

Source: Strength training by children and adolescents. American Academy of Pediatrics Council on Sports Medicine and Fitness. Pediatrics 2008 Apr;121(4);835-40.