Weight training has become increasingly integrated into the workout routines of both competitive athletes and weekend warriors. Done properly, it is not only safe but decreases the likelihood of injury. There is no question that children benefit from being active. With child obesity reaching pandemic proportions, most sensible parents welcome their child’s interest in sports. Given the obvious benefits of weight training for athletes, the question is bound to arise: is it safe for child athletes to train with weights?

Heavy lifting puts considerable stress on still-growing muscles, bones and hearts. In a study performed by the Center for Sports Medicine and Health Fitness in Peoria, Illinois, eighteen boys, age seven to age nine, were placed on a fourteen week supervised weight training program. Ten more age-and-activity-matched boys did not undergo the training program and were used as a control group.

The weight training group performed three 45-minute training sessions a week, working eight upper body and seven lower body motions per workout on hydraulic machines. The boys who trained showed significant strength increases in all 15 motions compared to those who didn’t train. Additionally, the ones who trained showed significant increases in both flexibility and vertical jump.

A bone scan was done. It showed no damage to bone, muscle or growing bone end plates. A blood test for muscle damage also showed no damage. There were no significant changes in resting heart rate, blood pressure, height, sexual maturity rating, hemoglobin, or blood testosterone levels between the trained and untrained groups. The trained group gained weight, but showed no change in body composition.

Only one subject suffered form a training-related injury, a mild shoulder strain cured by a week of rest. It is safe to conclude, then, that supervised weight training is safe for prepubescent male athletes. It caused no detectable bone, muscle, or growing bone end plate damage, and did not affect growth, development or flexibility. It didn’t even cause a high rate of injury.

There are a couple of cautionary notes, however. The type of training involved only concentric training, the kind of resistance applied by hydraulic machines, and the subjects were under close supervision by fitness and medical professionals.

What is concentric work? Contrast the effects of free weight training with hydraulic resistance training. Consider the example of doing a bicep curl with a dumbbell. The target muscle, the bicep, undergoes a controlled shortening as you raise the weight (this is the concentric contraction). It also lengthens in a controlled way on the way down (the eccentric contraction). Hydraulic machines typically don’t include the eccentric contraction, nor the overall major-muscle activity of keeping the rest of the body stable while performing the rep. In adults, concentric and eccentric contractions have different effects, and thus the particular study cannot be generalized beyond concentric contractions.

The second cautionary note reflected the close supervision under which the children trained. It was most likely the major factor in the low injury rate during the study.