Does strength training impair
growth in adolescents? If you think so you are falling into an old myth.
It has been known for decades that junior competitive weightlifters have an increased bone mineral density (BMC) well above the age-matched controls' mean (1). The effect of this type exercise appears to overcome any race or age-related BMC differences (1).
In another old study, BMD values of the spine and
femoral neck of junior weightlifters were found to be significantly greater
when compared with adult reference data (i.e., 20-39 yr old men) (2). It has
found that strength accounting for 30-65% of the variance, and that in elite
junior weightlifters, muscle strength has a major influence on BMD due to the
influence of the chronic overloads experienced in training (2).
Several studies found that strength training, with proper technique and strict
supervision, can increase strength in preadolescents and adolescents. Studies
have reported that resistance training can be effective in producing strength
gains among prepubescents, as shown by a meta-analysis (3).
The effectiveness
of resistance training can be influenced by factors such as age and maturation,
gender, as well as the frequency, duration and intensity of the training
program (3). From this meta-analysis it appears that a training frequency of
twice per week is sufficient to induce strength gains in children (3).
A subsequent meta-analysis confirmed that resistance training appears to
enhance strength and muscular endurance in children and youth, and that the magnitude
of the effect appears to be a function of gender, training method, and
experimental design (4).
Gains in strength can be attributed to a neurologic mechanism that
enables them to increase the number of motor neurons that are “recruited” to
fire with each muscle contraction (5,6,7,8,9).
Strength training augments the muscle growth that normally occurs with
puberty in boys and girls by actual muscle hypertrophy (5,8,10,11) .
Regular physical activity, sport participation, and
training for sport have no effect on attained stature, timing of peak height
velocity (PHV), rate of growth in stature (12), and no effect on the timing of
menarche in swimmers, track athletes, and rowers (12).
No apparent adverse effect on linear growth, growth
plates, or the cardiovascular system were observed (5,6,13,14,15,16). However, caution should be used for young athletes with
preexisting hypertension (5), and youth who have received chemotherapy with
anthracyclines (17).
Evidence is also available for the role
of activity in modulating the external geometry
and trabecular architecture during growth, potentially enhancing skeletal
strength with the magnitude of the effect of a 7% to 8% increase in peak BMD (18).
Strength can be increased by 30% to 50% in children and adolescents after 8 to 12 weeks of a well-designed strength training program, with at
least 2 sessions per week to maintain strength (19).
After 15 months of resistance training female
adolescents (aged 14 to 17 years) increased leg strength (40%) and femoral neck
BMD (20). After a 2-month
resistance-training program (6 exercises, 3 x 10 repetitions maximum [RM], 3
times per week) in 19 untrained preadolescent males (11-13 years old), significant
posttraining isometric strength gains were observed (17.5%) and mean testosterone
along with free androgen index value were increased (21). However, 2 months of detraining
resulted in a significant loss (9.5%) of isometric strength. Authors concluded that
resistance training induced strength changes independent of the changes in the anabolic
and androgenic activity in preadolescent males (21).
Safety and injury
Since balance and postural control skills mature to adult levels by ∼7 to 8 years of age (22) it is not advisable to start strength programs before
achievement of those skills (5). Specific skill proficiency in their sport
should also be attained before embarking on a disciplined strength-training
program (5).
Some research indicate that children have participated in weightlifting
programs with few injuries (23,24,25), however strict supervision and adherence
to proper technique are mandatory for reducing the risk for injury (5).
Several reports indicate that few injuries occur in
carefully supervised programs (25) and the most common cause of injury appears
to be loss of form when heavy weights are lifted (26). Proper technique, good
supervision and training programs appropriate to the athlete's level of
physical and emotional maturity are important in this regard (25).
Some of the case reports of injuries related to strength training,
include epiphyseal plate fractures and lower back injuries, primarily
attributed to the misuse of equipment, inappropriate weight, improper
technique, or lack of qualified adult supervision (18). For this reason, trained
fitness professionals play an essential role in ensuring proper technique,
form, progression of exercises, and safety (18).
The incidence and severity of pain in 13 regions of the body, as well as
the site and type of powerlifting injury, were investigated in one study (27).
The low back region was shown to be the site with the greatest number of
injuries (49) (27), and was also the region with the highest percent of
subjects recording an elevated occurrence and level of pain associated with
powerlifting (27).
Two cases of bilateral radius and ulnar fractures in
adolescent weight lifters were described in another report, but the fractures
healed without complications (28). The authors stressed that these injuries can
be prevented if coaches, trainers, and sports medicine physicians are aware of
their occurrence and undertake necessary preventative measures (28).
Specifically, adequate supervision with spotters at the end of each bar, appropriate foot wear, and, above all, the maximum level of concentration are key factors in preventing these injuries were recommended (28).
Specifically, adequate supervision with spotters at the end of each bar, appropriate foot wear, and, above all, the maximum level of concentration are key factors in preventing these injuries were recommended (28).
References
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