The first misconception is that the prepubes-cent athlete cannot benefit from strength training because of insuffi-cient circulating levels of andro-gens.6 However, this has been dis-pro
Trang 1Because of the increasing demands
for performance and the decreasing
ages of participation and peak
per-formance, young athletes are
con-tinually being asked to perform at
higher levels and to improve at a
quicker pace than ever before As
the demands increase, the athletic
community has been asked to
sup-ply the means to increase athletic
performance, and the medical
com-munity has been asked to validate
the safety of these methods
Strength training has become one
of the most popular and rapidly
evolving modes of enhancing
ath-letic performance Although
initial-ly limited to those sports thought to
require strength for optimal
perfor-mance, such as football and rugby,
some form of strength training has
now been adopted in virtually every
sports activity
It is commonplace for adult
ath-letes, both male and female, to
par-ticipate in some form of strength training to enhance performance and endurance and to reduce the risk of injury While the effective-ness, risks, and methods of training for the adult population have been extensively studied,1,2 the role of strength training for children and adolescents remains a topic of con-troversy and often heated debate.3-5
A number of important questions have been asked Can strength training increase the muscular strength in young athletes? Is strength training safe? Can strength training result in increased athletic performance?
The initial controversy surround-ing strength trainsurround-ing for the young athlete evolved from unfounded statements and three misconcep-tions regarding the risks and poten-tial benefits to the athlete The first misconception is that the prepubes-cent athlete cannot benefit from
strength training because of insuffi-cient circulating levels of andro-gens.6 However, this has been dis-proved over the past decade, as research has documented that young athletes do in fact gain strength with a properly planned and super-vised training regimen.4,7-13
The second misconception is that athletes participating in strength training lose both the flexibility and the range of motion necessary for optimal performance in their chosen sport This has also been refuted by recent studies, with some research-ers reporting increased flexibility when flexibility training was incor-porated into a training regimen.10
The third misconception is that strength training is dangerous and exposes the young athlete to unnec-essary risk of injury This particu-lar question remains a cause for concern for parents and general physicians The persistence of this concern is largely due to the inap-propriate comparison of injury rates with different modes of
train-Dr Guy is Fellow in Sportsmedicine, Boston Children’s Hospital, Boston, Mass Dr Micheli is Director, Division of Sports Medicine, Boston Children’s Hospital; and Associate Clinical Professor of Orthopaedic Surgery, Harvard Medical School, Boston Reprint requests: Dr Micheli, Boston Children’s Hospital, 319 Longwood Avenue, Boston, MA 02115.
Copyright 2001 by the American Academy of Orthopaedic Surgeons.
Abstract
Strength, or resistance, training for young athletes has become one of the most
popular and rapidly evolving modes of enhancing athletic performance Early
studies questioned both the safety and the effectiveness of strength training for
young athletes, but current evidence indicates that both children and
adoles-cents can increase muscular strength as a consequence of strength training.
This increase in strength is largely related to the intensity and volume of
load-ing and appears to be the result of increased neuromuscular activation and
coor-dination, rather than muscle hypertrophy Training-induced strength gains are
largely reversible when the training is discontinued There is no current
evi-dence to support the misconceptions that children need androgens for strength
gain or lose flexibility with training Given proper supervision and appropriate
program design, young athletes participating in resistance training can increase
muscular strength and do not appear to be at any greater risk of injury than
young athletes who have not undergone such training.
J Am Acad Orthop Surg 2001;9:29-36
Jeffrey A Guy, MD, and Lyle J Micheli, MD
Trang 2ing, such as weight training,
resis-tance training, and power lifting
Injury rates with these modes of
training can vary greatly, and
ex-trapolation from one to another can
be misleading
The literature in recent years has
helped dispel some misconceptions
about strength training for children
and adolescents Unfortunately,
however, information from the
med-ical community on these topics may
appear to be inconsistent, depending
on the experience of the practitioner
and his or her knowledge of recent
studies on strength training Not
surprisingly, parents, coaches, and
trainers remain confused and
uncer-tain about strength training and
often refrain from its use
Definitions
The term “strength training” is
defined as the use of progressive
resistive methods to increase one’s
ability to exert or resist force.4 The
term “resistance training” may also
be used in the same context and is
often considered synonymous
This type of training is both
con-trolled and progressive, often
utiliz-ing various modalities, such as free
weights, individual body weight,
hydraulics, and elastic bands, to
name a few To be successful, a
par-ticular training regimen must be
individualized and must involve a
timely progression in intensity,
thereby stimulating strength gains
that are greater than those
associ-ated with normal growth and
de-velopment
One particular area of confusion
is in the use of the terms “strength
training” and “resistance training”
in relation to the terms “weight
lift-ing” and “power lifting.” The latter
terms should be used only to
de-scribe techniques of training at high
intensities with the goal being to lift
maximal amounts of weights, often
in competition
When reviewing the literature, the age group involved in discus-sion can be particularly confusing
For the purposes of this review, the definitions by Faigenbaum and Bradley4will be utilized The terms
“prepubescent” and “child” refer to girls and boys prior to the develop-ment of secondary sex characteris-tics, roughly defined as up to the age of 11 years for girls and up to age 13 for boys The terms “pubes-cent” and “adoles“pubes-cent” are applied
to girls aged 12 to 18 and boys aged
14 to 18 The term “young athlete”
is a more comprehensive term and will be used when discussion in-cludes both the prepubescent and the pubescent athlete
Effectiveness of Strength Training for Young Athletes
The topic of strength training by adult athletes has been the subject
of extensive research.14 However, the role of strength training for the young athlete remains controversial despite recent studies at a number
of centers
During the 1970s, there were few studies available As a result, many clinicians discouraged strength training for children It was felt that prepubescent children were incapable of developing much strength and that physical weak-ness after puberty is merely the result of insufficient physical exer-tion.15 This stance was reflected in
a 1983 position paper of the Ameri-can Academy of Pediatrics in which
it was stated that “prepubertal boys
do not significantly improve strength
or increase muscle mass in a weight training program because of insuffi-cient circulating androgens.”6
Furthermore, several early stud-ies failed to demonstrate increased strength in children engaged in strength-training programs.16,17 In
1978, Vrijens16reported no strength
gains in a study of 10- to 17-year-old boys undergoing training ses-sions three times a week for a total
of 8 weeks’ duration Of interest, the training program involved low resistance and employed only one set of exercises per session In a similar study, Docherty et al17
found that 12-year-old boys did not benefit from strength training fol-lowing their competitive season The frequency of training was three times weekly for a total of 4 to 6 weeks However, both the low intensity of two sets per session and the short duration of the study may have compromised the results of the study
These studies have been cited in the literature as proof that strength training is ineffective for young ath-letes; however, careful evaluation suggests that these results may have been flawed by methodologic shortcomings The nature of con-trol groups is important because as children continue to grow, a prepu-bescent athlete may in fact develop
an increase in strength from normal growth alone, thus confounding any benefit from a training gram In addition, the training pro-gram itself may not provide the intensity, frequency, or length of training necessary to allow the prepubescent athlete to develop enough muscular strength to over-come differences observed with normal growth alone
The past 15 years has seen a pro-gressive and increased interest in the topic of strength training, and a number of controlled studies have examined the benefits and risks of youth strength training One of the earliest clinical studies supporting strength training for prepubescent children was by Sewall and Mich-eli.10 Eighteen prepubescent boys and girls participated in pneumatic resistance training for three 30-minute sessions per week for a total
of 9 weeks The children involved
in training had a statistically
Trang 3signif-icant (P<0.05) mean increase in
strength of 42%, compared with a
9% increase for control subjects
The study also showed that, even
over a 9-week period, prepubescent
children have a baseline increase in
strength due to normal growth and
maturation
Similar findings were
demon-strated by Weltman et al,18 who
examined the effects of hydraulic
strength training on prepubertal
boys Twenty-six boys participated
in a strength training program three
times a week for 14 weeks, and
dif-ferences in isokinetic strength for
flexion and extension at the knee
and elbow joints were evaluated
Compared with an untrained
con-trol group, subjects involved in
training had an increase in strength
of up to 36% for concentric work
and an increase in torque of up to
45% for all eight motions tested
(P<0.05) The findings in this study
suggest that short-term, supervised
concentric strength training with
use of hydraulic resistance is both
effective and safe for prepubertal
boys, with no injuries sustained
while training
As further evidence in support of
strength training for prepubescent
children accumulated, researchers
began to manipulate training
regi-men variables (e.g., frequency,
in-tensity of exercise, and duration of
training) in search of an optimal
pro-gram Because overuse injuries are
not uncommon in the pediatric
pop-ulation,19,20Faigenbaum et al7
investi-gated the effects of a shortened
fre-quency of training (twice a week)
while maintaining a high level of
in-tensity In an 8-week study,
prepu-bescent subjects underwent a
twice-weekly training schedule based on an
individual’s 10-repetition-maximum
(10-RM) strength (i.e., the maximum
weight that could be lifted ten times
with good form) The prepubescent
children were found to have a mean
increase of 74% in 10-RM strength
values compared with nontrained
control subjects Faigenbaum et al8
found similar results in prepubescent subjects in a 1996 study: a mean increase of 53% in leg extension and a 41% mean increase in chest-press val-ues after 8 weeks of strength training
Thus, at a given intensity, twice-weekly training programs appear to increase strength in children to a level equivalent to that found with schedules requiring participation three times per week
Taking into consideration the number of variables involved in determining the effectiveness of resistance training, Falk and Tenen-baum5 conducted a meta-analysis
of nine studies demonstrating in-creased strength All children in the studies were under the age of 13 years In the combined studies, the resistance training group had a 71.6% increase in strength over the control group There was no ad-vantage at any particular age, and there were no differences between the sexes
Thus, current evidence indicates that resistance training can result in marked strength gains in the pre-pubescent child While the ultimate duration and intensity continue to be debated, children develop strength gains with workouts as infrequent
as twice weekly At this time, there
do not appear to be any sex- or age-related differences
Physiologic Mechanisms for Strength Development
Although the literature supports the contention that children may demonstrate strength gains with a proper training regimen, it is more difficult to define how and why this occurs and what the underlying mechanisms are Numerous fac-tors, including muscle hypertrophy, increase in muscle cross-sectional area, motor-unit coordination, cen-tral nervous system activation, and psychological drive, may all
con-tribute to increases in strength These factors have been extensively studied in adults, but few studies have evaluated the underlying mechanism of strength gains in children
In an attempt to determine the contribution of muscle hypertrophy
to increased strength, several re-searchers have included morpho-logic variables in their evaluation of strength changes.7,9,18,21-23 Weltman
et al18 found little or no change in anthropometric and body composi-tion measures in prepubescent boys over a 14-week training period No statistically significant differences were found in body circumference
or skin-fold measurements Body density as measured by hydrostatic weighing was also unchanged Ramsay et al9found no statistically significant changes in anthropomet-ric indicators in prepubescent boys over a 20-week resistance training period No changes were seen in the cross-sectional area of either the midportion of the upper arm or the midthigh as measured with com-puted tomography
Because prepubescent children lack circulating androgens, it is not surprising that strength gains seen
in resistance training are not associ-ated with the muscle hypertrophy seen in the adult population (at least not in short-term studies) Neural adaptations have been implicated
by some as primarily responsible for strength gains.9,22 Ozmun et al22
addressed this issue in a study of the effects of thrice-weekly biceps curls on prepubescent children over the course of 8 weeks Significant isotonic and isokinetic strength in-creases were found in the trained group (22.6% and 27.8%, respective-ly), with no changes in either skin-fold or arm-circumference measure-ments While these findings confirm that strength gains are not the result
of muscle hypertrophy, the increased electromyographic measurements (17% greater amplitude in the trained
Trang 4group) suggest that the early gains
in strength seen in prepubescent
children are due in part to increased
muscle activation
Only one other study has
ad-dressed the neural adaptations in
strength training in children
Blimkie et al,12 looking at isotonic
strength changes in prepubescent
children, found a significant (P<
0.05) increase in strength over a
10-week training period Although
there were no differences in muscle
cross-sectional area, an increasing
trend in motor unit activation was
noted, as determined by interpolar
twitch It has also been suggested
that intrinsic muscle adaptations,
increased motor activation,
im-proved motor skill performance,
and coordination of the involved
muscle groups may all play a role
in the muscle strength seen with
resistance training.9
Although at this time it may be
difficult to separate out the
contri-butions and relative importance of
each variable, it appears that
neu-romuscular activation, motor
coor-dination, and intrinsic muscular
adaptations all contribute to the
increased strength seen in
prepu-bescent athletes undergoing
resis-tance training Similar mechanisms
are found in adolescents and
young adults,14but strength gains
seen in prepubescent children
ap-pear to be largely independent of
muscle size Not surprisingly, the
training-induced gains in strength
seen in postpubertal boys are
accompanied by increased
cross-sectional area of muscle.16
Persistence of
Training-Induced Gains
The removal of stimulus, or
“de-training,” is defined as the
tempo-rary or permanent reduction or
with-drawal of a training stimulus, which
may result in the loss of physiologic
and anatomic adaptations, as well as
a decrease in athletic performance.8
There are few studies of detraining
in adults and even fewer in the pre-pubescent population Furthermore, attempts to evaluate the persistence
of resistance-induced strength gains
in prepubescent subjects after with-drawal of a training stimulus may
be confounded by the concomitant growth-related strength increases.24
In a study of detraining in pre-pubescent children, Sewall and Micheli10suggested that the loss of strength due to withdrawal from training was greater than, and not offset by, the anticipated growth-related increases in strength over the same time period In 1989, Blimkie et al12proposed a model of the effects of growth, resistance training, maintenance training, and detraining on strength devel-opment in children In a study using that model,13the strength gains seen in the training group regressed over time in both the maintenance and detraining groups
to levels close to, but still above, those of the untrained control sub-jects (Fig 1)
In a study by Faigenbaum et al8
evaluating the effects of strength training and detraining on children, the results were consistent with those
of Blimkie.13 Despite a 53% increase
in training-induced leg-extension strength over 8 weeks, a subsequent
8 weeks of detraining led to rapid
and significant (P<0.05) decreases in
both leg extension (−28%) (Fig 2) and chest press performance (−19.3%) In the same period, the performance of the untrained control subjects in-creased slightly The magnitude of loss for the trained group was ap-proximately 3% per week A com-parison of groups at completion of detraining found no statistically sig-nificant difference in leg extension Although the available data are limited, it appears that strength gains secondary to resistance train-ing durtrain-ing prepubescence are tran-sient and regress toward untrained control levels The degree of regres-sion appears to depend on the mag-nitude of strength gains, level of inactivity, and duration of detrain-ing Unfortunately, the amount of training required to maintain or at
Pretraining
75
T
MT
DT
C
65
55
45
Posttraining Detraining
•m
Figure 1 Graphic illustration of Blimkie’s model demonstrating the effects of resistance training (T), maintenance training (MT), and detraining (DT) on strength development during normal growth (C) during childhood The values for both the maintenance and detraining groups regressed with time to levels close to, but above, those of the untrained control subjects (Adapted with permission from Blimkie CJR: Resistance training during
pre- and early puberty: Efficacy, trainability, mechanisms, and persistence Can J Sport Sci
17;4:264-279.)
Trang 5least slow down this regression has
yet to be determined While these
findings may bring into question
the need for maintenance programs
for children, more information is
required before specific
recommen-dations can be made
Risks of Resistance
Training for Young
Athletes
The past 20 years have seen a
marked increase in the participation
of children in competitive sports,
and the popularity continues to
grow Approximately 30 million
children (50% of boys and 25% of
girls) are involved in either
competi-tive organized sports or
community-based sports programs.3 To ad-dress the question of whether strength training by the prepubes-cent child is associated with an un-acceptable risk of injury, we must first revisit the relevant definitions
The terms “strength training” and
“resistance training” are used to refer to progressive resistance to enhance performance or ability by using submaximal amounts of weight The terms “weight lifting”
and “power lifting” usually refer to the use of maximal amounts of weight at high intensities during competition
It has been estimated that more than 17,000 weight-lifting or power-lifting injuries in adolescents re-quiring emergency room visits oc-cur annually.25 However, most of
these injuries happen at home or school and are not the result of su-pervised activity In several stud-ies of adolescents, the incidence of injury ranged between 7% and 40%.26,27 Almost 75% of the inju-ries were strains, with the most common site being the lower spine There are also numerous case re-ports or small series of serious weight-lifting and power-lifting injuries, such as cardiac rupture due to impact by a dropped bar-bell,28 spondylolysis and spondy-lolisthesis,29 and growth-plate injuries in the wrist.30 Most of these injuries were attributed to improper lifting techniques, exces-sive loading, or inadequate teaching
or supervision Not surprisingly, recommendations about the partici-pation of young athletes in these activities vary from supervised par-ticipation only25 to proscription of weight lifting, power lifting, and body building, as well as the use of maximal amounts of weight in training programs, for both chil-dren and adolescents.31
Strength training for young ath-letes has received widespread sup-port.3,4,10,11,18,24,32,33 Rians et al,33
looking at subclinical musculo-skeletal injury (as evaluated on bone scan) or muscle damage (as estimated on the basis of serum creatine phosphokinase determina-tion), found no evidence of injury
in prepubescent boys after 14 weeks
of resistance training Similar find-ings by Blimkie et al21found only mildly elevated creatine phospho-kinase values and concluded that short-term (duration of 20 weeks) resistance training by prepubertal boys did not pose any particular risk in terms of subclinical or clini-cal musculoskeletal injury
Perhaps a better assessment of the risk of injury associated with resistance training would come from prospective studies of closely monitored and supervised training programs with appropriately
pre-*
*
35
30
25
20
15
10
Pretraining Posttraining Mid-detraining Post-detraining
Figure 2 The effects of strength training and detraining on children demonstrated in the
study by Faigenbaum et al 8 were consistent with Blimkie’s model 13 The trained group
(solid circles) had a 53% increase in training-induced leg-extension strength over 8 weeks,
but a subsequent 8 weeks of detraining led to a rapid and significant decrease ( − 28%) in
leg-extension performance, while the performance of the untrained control subjects (open
circles) increased slightly (asterisk indicates statistically significant [P<0.05] difference
between control value and previous value for trained group) A comparison of groups at
the completion of the 16-week detraining period revealed no significant difference from
the control value for leg extension (Adapted with permission from Faigenbaum AD,
Westcott WL, Micheli LJ, et al: The effects of strength training and detraining on children.
J Strength Cond Res 1996;10:109-114.)
Trang 6scribed training loads There have
been no reported cases of serious
injuries in these studies.9,10,18
There-fore, it appears that the risks and
concerns associated with youth
strength training are no greater than
those associated with other sports
and recreational activities common
to this age group.4 However, this is
based on the understanding that a
given strength training program is
competently supervised and the
young athlete is properly instructed
and underscores the need for
pre-participant history, blood pressure
measurements, flexibility screening,
and a preparticipation physical
examination As with adult
ath-letes, while no studies have
demon-strated enhanced performance with
strength training, experience
strong-ly supports its use
Anabolic Steroid Use
For years, athletes have taken
exog-enous substances to manipulate
their athletic performance It is not
surprising that modern athletes
often turn to ergonomic aids like
anabolic androgenic steroids to
enhance muscle growth, increase
strength, and improve physical
performance It has been
esti-mated that over 1 million persons
in the United States are currently
using anabolic steroids, with a
total expenditure of more than
$100 million a year.34 Although
there is a potential for enhancing
performance, anabolic androgenic
steroids can have severe
physio-logic and emotional side effects,
such as a heightened risk for
coro-nary disease, cholestatic jaundice,
abnormal liver function, hepatic
tumors, stunted growth,
gyneco-mastia, and many psychotic
disor-ders In addition, there is the risk
of transmission of diseases such as
acquired immunodeficiency
syn-drome and viral hepatitis through
needle sharing
Early use of anabolic steroids in the United States was primarily by individuals involved in weight training However, gains in size and strength prompted their use by other athletes Today, anabolic steroids are consumed by both male and female power athletes, endurance athletes, and nonath-letes Given the increasing pres-sure for athletes to perform better and earlier, it is no surprise that the use of anabolic steroids has breached the boundary of age
The use of steroids in the adoles-cent population brings with it an additional level of concern com-pared to its use by older athletes
Estimates of steroid use in the ado-lescent population have placed the prevalence at approximately 5% to 7% for boys and 1% to 3% for girls.35-37 In a recent study of pre-adolescent middle-school students ranging in age from 9 to 13 years, approximately 2.7% of the students admitted using steroids.38 The majority of the students felt that steroids would make their muscles bigger and stronger While usage is not exclusive to any segment of the population, the literature suggests that the highest level is among ado-lescents from more affluent neigh-borhoods, presumably because of easier access to this relatively ex-pensive drug.39 Most of the steroids used by young athletes appear to have been obtained illegally, in-creasing the risk of purchasing mis-labeled or impure agents
The physical side effects in ado-lescent boys can range from acne and gynecomastia to more serious conditions, such as priapism, sodium retention edema, and liver dysfunc-tion after prolonged use In girls, clitoromegaly, hirsutism, and amen-orrhea are common, as well as per-manent deepening of the voice after prolonged use Use by children of both sexes may also result in dimin-ished adult height, as premature closure of the physis is possible
Perhaps the most serious side effects of steroid use occur in the behavioral sphere; in the transition
to adulthood, adolescents may be particularly vulnerable to the conse-quences of heightened aggression.40
As the relatively high consump-tion of steroids by young athletes continues, the need for early educa-tional intervention concerning their effects is becoming more apparent One such intervention is the ATLAS (Adolescents Training and Learn-ing to Avoid Steroids) program.34
The goal of that program is to edu-cate adolescent athletes, enhance healthy behaviors, and minimize the factors that encourage steroid use Although such programs ap-pear to be quite successful, they are limited in both number and avail-ability Therefore, one cannot over-emphasize the role of health pro-fessionals, educators, and parents
in providing a healthy and informed atmosphere for young athletes
Initiation of Training
The proper initiation of strength training for children and adoles-cents is critical Those supervising young athletes—coaches, trainers, and parents—should address several issues before initiating a program of training First is whether the ath-lete is prepared psychologically and physically to participate in the pro-gram This includes making sure that the athlete has had a prepartici-pation physical at school or at a physician’s office In addition, supervising adults should strive to minimize pressure and stress placed
on the athlete to perform
The second issue is whether the athlete understands what strength training is and what the goals of the program are This point cannot be overemphasized, as misinformed athletes are at increased risk for injury The athlete should under-stand the fundamental differences
Trang 7between strength training and
weight lifting and the goals of each
Athletes should understand that
while increasing one’s performance
is a reasonable and attainable goal,
increasing muscle size prior to the
onset of puberty is not Safety while
training should also be emphasized
The third issue is which strength
training program the athlete should
follow While the specifics of
indi-vidual training programs are
be-yond the scope of this article, the
program chosen should be tailored
to the athlete in question on the
basis of age, size, experience, and
sport.41 Access to certain facilities
and specific types of supervision
are important considerations, as not
everyone has a gym membership or
the finances to hire a personal trainer
Parents interested in being involved
in the training process can also
con-sult the wealth of information in the
literature on strength training for
adolescents.41-43 The objective is to have a well-informed, carefully supervised athlete participating in a balanced strength-training program with the goal of increasing strength and improving mental attitude and performance in sport
Summary
The past decade has seen growing support from both the medical and the scientific communities regarding the participation of young athletes in strength training programs Current evidence indicates that both prepu-bescent and puprepu-bescent children can,
in fact, increase muscle strength, but not necessarily athletic performance,
as a consequence of resistance train-ing This increase in strength is largely related to the intensity and volume of loading and appears to be the result of increased
neuromuscu-lar activation and coordination These increases in strength do not ap-pear to be a consequence of muscle hypertrophy, as they are in adults The training-induced strength gains are largely reversible when the train-ing is discontinued
There is no current evidence to support the misconceptions that chil-dren need androgens for strength gain, lose flexibility with training, or are at increased risk of injury Given the proper supervision and appropri-ate instruction and program design, children involved in resistance train-ing do not appear to be at greater risk of injury than other young ath-letes who have not undergone such training However, parents, coaches, and trainers should be aware that participation in unsupervised train-ing or in activities involvtrain-ing rapid and maximal loading places prepu-bescent children at increased risk of injury and is not recommended
References
1 Kraemer WJ, Duncan ND, Volek JS:
Resistance training and elite athletes:
Adaptations and program
considera-tions J Orthop Sports Phys Ther
1998;28:110-119.
2 Costill DL, Coyle EF, Fink WF, Lesmes
GR, Witzmann FA: Adaptations in
skeletal muscle following strength
training J Appl Physiol 1979;46:96-99.
3 Faigenbaum AD, Kraemer WJ, Cahill
B, et al: Youth resistance training:
Position statement paper and
litera-ture review Strength Conditioning
1996;18:62-75.
4 Faigenbaum AD, Bradley DF: Strength
training for the young athlete Orthop
Phys Ther Clin North Am
1998;7:1059-1516.
5 Falk B, Tenenbaum G: The
effective-ness of resistance training in children:
A meta-analysis Sports Med 1996;22:
176-186.
6 American Academy of Pediatrics:
Weight training and weight lifting:
Information for the pediatrician Phys
Sportsmed 1983;11:157-161.
7 Faigenbaum AD, Zaichkowsky LD,
Westcott WL, Micheli LJ, Fehlandt AF:
The effects of a twice-a-week strength
training program on children Pediatr
Exerc Sci 1993;5:339-346.
8 Faigenbaum AD, Westcott WL, Micheli
LJ, et al: The effects of strength
train-ing and detraintrain-ing on children J
Strength Cond Res 1996;10:109-114.
9 Ramsay JA, Blimkie CJR, Smith K, Garner S, MacDougall JD, Sale DG:
Strength training effects in
prepubes-cent boys Med Sci Sports Exerc 1990;
22:605-614.
10 Sewall L, Micheli LJ: Strength training
for children J Pediatr Orthop 1986;6:
143-146.
11 Webb DR: Strength training in
chil-dren and adolescents Pediatr Clin
North Am 1990;37:1187-1210.
12 Blimkie CJR, Ramsay J, Sale D, MacDougall D, Smith K, Garner S:
Effects of 10 weeks of resistance train-ing on strength development in prepu-bertal boys, in Oseid S, Carlsen K (eds):
Children and Exercise XIII Champaign,
Ill: Human Kinetics, 1989, pp 183-197.
13 Blimkie CJR: Resistance training dur-ing pre- and early puberty: Efficacy, trainability, mechanisms, and
persis-tence Can J Sport Sci 1992;17:264-279.
14 Wilmore JH: Alterations in strength,
body composition and anthropometric measurements consequent to a
10-week weight training program Med
Sci Sports 1974;6:133-138.
15 Kulund DN, Töttössy M: Warm-up,
strength, and power Orthop Clin
North Am 1983;14:427-448.
16 Vrijens J: Muscle strength develop-ment in the pre- and post-pubescent
age Med Sport 1978;11:152-158.
17 Docherty D, Wenger HA, Collis ML, Quinney HA: The effects of variable speed resistance training on strength
development in prepubertal boys J
Hum Mov Stud 1987;13:377-382.
18 Weltman A, Janney C, Rians CB, et al: The effects of hydraulic resistance strength training in pre-pubertal males.
Med Sci Sports Exerc 1986;18:629-638.
19 Outerbridge AR, Micheli LJ: Overuse
injuries in the young athlete Clin
Sports Med 1995;14:503-516.
20 Micheli LJ: Sports injuries in children and adolescents: Questions and
con-troversies Clin Sports Med 1995;14:
727-745.
21 Blimkie CJR, MacDougall D, Sale D, Thonar E, Smith K, Garner S: Soft-tissue trauma and resistance training
Trang 8in boys [abstract] Med Sci Sports Exerc
1989;21(suppl):S89.
22 Ozmun JC, Mikesky AE, Surburg PR:
Neuromuscular adaptations following
prepubescent strength training Med
Sci Sports Exerc 1994;26:510-514.
23 Sailors M, Berg K: Comparison of
responses to weight training in
pubes-cent boys and men J Sports Med Phys
Fitness 1987;27:30-37.
24 Blimkie CJR: Resistance training
dur-ing preadolescence: Issues and
contro-versies Sports Med 1993;15:389-407.
25 Mazur LJ, Yetman RJ, Risser WL:
Weight-training injuries: Common
injuries and preventative methods.
Sports Med 1993;16:57-63.
26 Risser WL, Risser JMH, Preston D:
Weight-training injuries in adolescents.
Am J Dis Child 1990;144:1015-1017.
27 Brown EW, Kimball RG: Medical
his-tory associated with adolescent
pow-erlifting Pediatrics 1983;72:636-644.
28 George DH, Stakiw K, Wright CJ:
Fatal accident with weight-lifting
equipment: Implications for safety
standards CMAJ 1989;140:925-926.
29 Kotani PT: Studies of spondylosis
found among weight lifters Br J
Sports Med 1971;6:4-7.
30 Ryan JR, Salciccioli GG: Fractures of the distal radial epiphysis in
adoles-cent weight lifters Am J Sports Med
1976;4:26-27.
31 American Academy of Pediatrics Committee on Sports Medicine:
Strength training, weight and power lifting, and body building by children
and adolescents Pediatrics 1990;86:
801-803.
32 Duda M: Prepubescent strength
train-ing gains support Phys Sportsmed
1986;14:157-161.
33 Rians CB, Weltman A, Cahill BR, Janney CA, Tippett SR, Katch FI:
Strength training for prepubescent
males: Is it safe? Am J Sports Med
1987;15:483-489.
34 Goldberg L, Elliot DL, Clarke GN, et al: The Adolescents Training and Learning to Avoid Steroids (ATLAS) prevention program: Background and
results of a model intervention Arch
Pediatr Adolesc Med 1996;150:713-721.
35 Windsor RE, Dumitru D: Anabolic steroid use by athletes: How serious
are the health hazards? Postgrad Med
1988;84:37-38, 41-43, 47-49.
36 DuRant RH, Rickert VI, Ashworth CS, Newman C, Slavens G: Use of
multi-ple drugs among adolescents who use
anabolic steroids N Engl J Med 1993;
328:922-926.
37 Buckley WE, Yesalis CE III, Friedl KE, Anderson WA, Streit AL, Wright JE: Estimated prevalence of anabolic steroid use among male high school
seniors JAMA 1988;260:3441-3445.
38 Faigenbaum AD, Zaichkowsky LD, Gardner DE, Micheli LJ: Anabolic steroid use by male and female middle
school students Pediatrics 1998;101:E6.
39 Windsor R, Dumitru D: Prevalence of anabolic steroid use by male and
female adolescents Med Sci Sports
Exerc 1989;21:494-497.
40 Rogol AD, Yesalis CE III: Anabolic-androgenic steroids and the adolescent.
Pediatr Ann 1992;21:175, 183, 186-188.
41 Faigenbaum AD, Westcott WL (eds):
Strength and Power for Young Athletes.
Champaign, Ill: Human Kinetics, 2000.
42 Kraemer WJ, Fleck SJ (eds): Strength
Training for Young Athletes
Cham-paign, Ill: Human Kinetics, 1993.
43 Sprague K, Sprague C (eds): Weight
and Strength Training for Kids and
Teenagers: A Responsible Guide for Parents, Teachers, Coaches, and Young Athletes Los Angeles: JP Tarcher, 1991.