Here's some evidence to refute the myths:
A statement from the Mayo Clinic.
Metcalf JA, Roberts SO. (1993). Strength training and the immature athlete: an overview.
The developing musculoskeletal structures of the immature athlete are uniquely
susceptible to injury, particularly at the physes. These growth plates are
present in arm and leg bones, and some may not close until the late teen years.
Early literature suggested that weight training might be inappropriate for these
athletes. However, recent evidence suggests that, properly done,
strength/resistance training may not only be safe, it may also help reduce the
risk of injury for the young athletes. Nurses are often called upon to advise
coaches of formal and community athletic programs, and need to know the
underlying physiology of developing bone and muscle as well as the current
recommendations related to training.
Malina RM. (2006). Weight training in youth-growth, maturation, and safety: an evidence-based
review. Clin J Sport Med.;16(6):478-87.
OBJECTIVE: To review the effects of resistance training programs on pre- and
early-pubertal youth in the context of response, potential influence on growth
and maturation, and occurrence of injury. DESIGN: Evidence-based review.
METHODS: Twenty-two reports dealing with experimental resistance training
protocols, excluding isometric programs, in pre- and early-pubertal youth, were
reviewed in the context of subject characteristics, training protocol,
responses, and occurrence of injury. RESULTS: Experimental programs most often
used isotonic machines and free weights, 2- and 3-day protocols, and 8- and
12-week durations, with significant improvements in muscular strength during
childhood and early adolescence. Strength gains were lost during detraining.
Experimental resistance training programs did not influence growth in height and
weight of pre- and early-adolescent youth, and changes in estimates of body
composition were variable and quite small. Only 10 studies systematically
monitored injuries, and only three injuries were reported. Estimated injury
rates were 0.176, 0.053, and 0.055 per 100 participant-hours in the respective
programs. CONCLUSION: Experimental training protocols with weights and
resistance machines and with supervision and low instructor/participant ratios
are relatively safe and do not negatively impact growth and maturation of pre-
and early-pubertal youth.
Rians CB, Weltman A, Cahill BR, Janney CA, Tippett SR, Katch FI. (1987). Strength training for prepubescent males: is it safe? Am J Sports Med. 1987 Sep-Oct;15(5):483-9.
This study examined the safety of one type of strength training for prepubescent
males. Eighteen males (average age, 8.3 +/- 1.2 years) participated in a 45
min/session, three session/week, 14 week supervised strength training program
with an attendance rate of 91.5%. Concentric work was done almost exclusively.
KinCom analysis showed significant strength gain in this group (P less than
0.05), while an age, sex, and activity matched control group did not gain
strength. Safety was evaluated by injury surveillance, blood pressure and heart
rate monitoring, scintigraphy, and creatine phosphokinase measurement. Effects
on growth and development, flexibility, and motor performance were also
investigated, as these are factors with an impact on sports injury occurrence.
Results showed that in the short term, supervised concentric strength training
results in a low injury rate and does not adversely affect bone, muscle, or
epiphyses; nor does it adversely affect growth, development, flexibility, or
motor performance. As the safety question is multifaceted, this should not lead
to the conclusion that strength training for prepubescents is uniformly safe.
Further research is needed.