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625
Journal of Strength and Conditioning Research, 2004, 18(3), 625–629
q2004 National Strength & Conditioning Association
S
TRENGTH
A
DAPTATIONS AND
H
ORMONAL
R
ESPONSES
TO
R
ESISTANCE
T
RAINING AND
D
ETRAINING IN
P
READOLESCENT
M
ALES
C
HARILAOS
K. T
SOLAKIS
,
1
G
EORGE
K. V
AGENAS
,
1
AND
A
THANASIOS
G. D
ESSYPRIS
2
1
Department of Physical Education and Sports Science and
2
School of Biology, Department of Biochemistry and
Molecular Biology, University of Athens, Athens, Greece.
A
BSTRACT
.Tsolakis, C.K., G.K. Vagenas, and A.G. Dessypris.
Strength adaptations and hormonal responses to resistance train-
ing and detraining in preadolescent males. J. Strength Cond. Res.
18(3):625–629. 2004.—Ninteen untrained preadolescent males
(11–13 years old) were randomly placed into an experimental
trained group (STG, n59) and a control group (n510). Informed
consent was obtained from the children and their parents. The
STG was submitted to a 2-month resistance-training program (6
exercises, 3 310 repetitions maximum [RM], 3 times per week),
followed by a 2-month detraining program. The effectiveness of
the resistance program was determined by measuring pre- and
posttraining and detraining differences in isometric and isotonic
(10RM) strength and hormonal responses in testosterone (T), sex
hormone binding globulin, and free androgen index (FAI). Their
maturation stage was evaluated according to Tanner. Significant
posttraining isometric strength gains (17.5%) and mean T and
FAI value increases (p,0.05–0.001) were observed in STG. De-
training resulted in a significant loss (9.5%, p,0.001) of isomet-
ric strength whereas the hormonal parameters of STG remained
practically unaltered. The relative (D%) postdetraining hormonal
responses correlated significantly with the respective isometric
strength changes. In conclusion, the resistance training induced
strength changes independent of the changes in the anabolic and
androgenic activity in preadolescent males. Further research is
needed to fully clarify the physiological mechanisms underlying
the strength training and detraining process.
K
EY
W
ORDS
. strength training, isokinetic training, androgens,
untrained boys
I
NTRODUCTION
The physiological muscle-growth changes in boys
during the early stages of puberty are attribut-
ed mainly to the increase in boys’ androgen lev-
els (10). These changes are usually observed af-
ter the age of 11, correlate with developmental-stage
changes, and are considered significant in the functional
growth of muscle tissue (20,21, 40).
Many individuals in their preadolescent period in-
creasingly participate in systematic resistance-training
programs that, if all basic principles of design and safety
are followed, lead to an increase in muscular strength (6),
improve health, and prevent possible exercise-related in-
juries (20) attributed to muscle weakness and muscle-
strength imbalance during development (28). Although
the mechanisms that produce these changes in adoles-
cents have been thoroughly researched (18, 25, 34, 37),
little research exists regarding preadolescents.
Among adults, strength gains induced by resistance
training are attributed mainly to neurological adapta-
tions in the early stages of training and domination of
muscle hypertrophy over time (25). Neuromuscular per-
formance in adults decreases slowly during detraining via
reversible neurological and hormonal adaptations (13,
26). Regarding children, the changes in strength are at-
tributed to neurological factors (34), whereas muscle hy-
pertrophy is much more limited than it is in adolescents
(11, 24). Consequently, the probable decrease in strength
gains during detraining is mainly attributed to reduced
neuromuscular activation and reduced motor coordina-
tion (6).
Data on the influence of prolonged resistance training
and detraining on androgen levels of adults are contra-
dictory because of inherent methodological differences of
the relative studies (1, 12, 15, 16); however, there is a
relative lack of similar information about preadolescent
males (23, 25). Therefore, we investigated the influence
of a short, 2-month, supervised, progressive resistance-
training program with isotonic equipment and a 2-month
detraining program on strength adaptations, serum hor-
mones testosterone (T), sex hormone binding globulin
(SHBG), and free androgen index (FAI) in Greek pread-
olescents who lacked any previous training experience.
M
ETHODS
Nineteen untrained high school boys, 11–13 years of age,
were placed randomly into 2 groups: an experimental
trained group (STG, n59) and a control group (CG, n5
10). The subjects’ personal characteristics are given in Ta-
ble 1. They participated voluntarily after learning the
purpose of the study and the potential risks associated
with a strength-training program and after obtaining
their parents’ written consent. The University of Athens,
Department of Physical Education, approved the study.
Their subjects’ maturation stage was evaluatedaccording
to Tanner (36) on the basis of external genitals andpubic
hair development. All subjects were classified as late
stage 1 or early stage 2 and confirmed by their serum
concentrations of T (38), which reflected also their pre-
adolescent status (36). Before their selection, all subjects
underwent medical evaluation (preparticipation sports
examination) to exclude those with chronic diseases, or-
thopedic limitations, or other inhibiting factors.
Experimental Approach to the Problem
Our study intended to determine whether a short resis-
tance-training program and detraining of equal duration
could influence strength levels and relative hormonal fac-
tors in sedentary preadolescent boys.
The STG was submitted to a 2-month resistance-train-
ing program. The training-program variables were de-
626 T
SOLAKIS
,V
AGENAS
,
AND
D
ESSYPRIS
Table 1. Anthropometric characteristics of STG and CG (mean 6SD).*
Groups nAge (y) Height
(cm) Weight
(kg) %
Body fat
STG
CG
STG vs. CG**
9
10 11.78 60.84
12 60.82
NS
152.18 65.91
156.82 68.68
NS
43.02 69.5
43.18 610.74
NS
14.05 63.11
12.74 62.64
NS
* STG 5experimental group; CG 5control group; NS 5not significant.
** Independent T-test.
signed according to the basic principles described by
Kraemer and Fleck (19). Every training session included
3 sets of a predetermined 10 repetitions maximum (RM)
of 6 different exercises for the upper body in a variable-
resistance machine (supine bench press, wide grip cable,
pull-downs, biceps curl, triceps extensions, seated row,
overhead press). The exercise program was designed for
the upper extremities because children’s arms are pro-
portionally weaker than their legs (29, 31), and in this
context, the subjects might have been capable of greater
strength gains after the end of the training protocol. The
subjects were allowed a 1-minute rest between each set
and a 3-minute rest between each of the 6 different ex-
ercises. The duration of the training sessions was about
60 minutes 3 times per week (48 hours between each
training session). Each session was supervised by a coach
and included a warm-up of about 10 minutes with jog-
ging, static stretching, and light exercises of the involved
muscle groups and approximately 5–8 minutes of stretch-
ing to cool down. The subjects were submitted to a test
(10RM) every 15 days to readjust the training effort. The
training period was followed by a 2-month detraining pe-
riod during which the subjects did not participate in any
training program except their school physical education
classes. Before the beginning of the 2-month training at
the end of the second month and at the end of the de-
training period, blood samples were obtained from thean-
tecubital vein in resting conditions (subjects remained
seated for 10–15 minutes on arrival at the laboratory) for
hormonal determination. The CG was not subjected to re-
sistance training but followed similar anthropometric test
and blood assay protocols. No injuries resulted from the
training sessions. Few subjects complained of delayed
muscle pain and limited range of motion in the initial 3
sessions, which disappeared after the first week of train-
ing followed by extra stretching exercises.
Measurements
Isokinetic Strength. A specially designed strain guage
loaded upper extremity dynamometer was used to mea-
sure the pre- and postexercise concentric strength of the
elbow flexion in the right arm. Each subject was placed
in an adjustable seat fastened with 3 special belts which
helped the immobilization of the chest, shoulder and
back. The isometric strength of the elbow flexion at a 908
angle was recorded.
After a satisfactory warm-up with mild exercises and
stretching of muscle groups of the upper extremities and
body, each subject performed 3 maximal efforts lasting
approximately 3 seconds with a 60 second interval be-
tween. The subjects were informed of the procedure be-
fore the efforts, and each maximal effort was reinforced
by verbal encouragement. The best of the three efforts
were retained for further analysis.
Isotonic Strength. Each subject’s 10RM was deter-
mined on elbow flexion with adjustable dumbbells. The
start position during isokinetic testing was 408of elbow
flexion. After a satisfactory warm-up with a light weight
(1.5 kg), the 10RM was found within 3–4 trials and was
measured within 0.5 kg (the maximum weight that could
be lifted 10 times correctly without any other muscle-
group support). An adult instructor could identify when
the upper arm was not immobilized and when the try was
not through the full predetermined range of motion. The
rest interval between trials was 1 minute.
Blood Tests. After 2 days of rest and 12 hours of fast-
ing, approximately 5 ml of blood was drawn from a fore-
arm (antecubital) vein with a gauge needle 21-G 31.5-
in. vacutainer, set up between 0830 and 0900 hours, to
avoid the influence of the diurnal variations in serum
hormones. The blood was allowed to clot at room temper-
ature (228C) and the serum was separated by centrifu-
gation at 3,000gfor 15 minutes and stored at 2308C until
analyzed (within 30 days). Testosterone was determined
by a commercial RIA kit Direct Testosterone I
125
(Farmos
ORION Diagnostica, Finland). Intra- and interassay var-
iations were 4.6% and 4.9% and the assay sensitivity was
0.30 nmol/L. The specificity was very good with minor
cross-reactions. Sex hormone binding globulin was deter-
mined by IRMA method (Farmos). Intra- and interassay
variations were 3.2% and 5.5% with a sensitivity of 0.5
nmol/L. All samples for T and SHBG were determined in
duplicate (as well as the standard curve), and high- and
low-quality control sera were included in the test. Dupli-
cate values were very satisfactory (T, r50.96; SHBG, r
50.98).
Finally, the FAI counted using the type (Farmos):
concentration of total T (nmol/L)
FAI 53100
concentration SHBG (nmol/L)
Anthropometry. All 19 subjects were measured for
height, weight, and tricep and subscapular skinfolds. The
last measurements were taken with a Harpenden skin-
fold caliper (17). All anthropometric and body composition
measurements were taken on all 3 occasions by the same
investigator, who was previously controlled for his test-
retest reliability (r.0.92).
Statistical Analyses
Pre-, post-, and detraining values for all measured vari-
ables were compared via a 2-way analysis of variance
(ANOVA) (2 33) with repeated measures. Post hoc anal-
yses included 1-way repeated-measures ANOVA and in-
dependent Bonferoni tests. T-test for independent vari-
ables were used for comparison of the means of the hor-
monal parameters examined between the STG and the
CG. Pearson product moment correlation was used to ex-
S
TRENGTH AND
H
ORMONAL
R
ESPONSES OF
T
RAINING IN
B
OYS
627
Table 2. Hormonal concentrations and ioskinetic strength of STG (n59) and CG (n510) (mean 6SD).†
Variables Group Pretraining Posttraining Detraining
T (nmol/L) STG
CG 4.9 65.7
6.1 64.45 10.9 66.2*
6.6 64.05 10.7 67.6**
7.2 63.98***
SHBG (nmol/L) STG
CG 69 630.9
64.2 621.84 61.5 642.2
73.7 625.7 78.2 650.5
65.1 623.3
FAI STG
CG 15.6 626.1
12.7 615.1 28.49 633.5***
12.1 613.6 22.7 627.4
a
14.6 615.6
Isometric strength
(kg) STG
CG 85.11 68.26
83.06 66.95 100.16 68.39*
83.94 67.13 90.64 67.60*
84.60 67.01
Isotonic strength
(kg) STG
CG 3.22 61.62
3.35 60.85 461.54
3.60 60.84 3.80 61.58
3.75 60.71
*p,0.001.
** STG values greater than CG values, p,0.05.
*** p,0.05 (1-way analysis of variance significance for pre-, post-, and detraining values; Bonferroni post hoc analysis).
† STG 5experimental group; CG 5control group; T 5testosterone; SHBG 5sex hormone binding globulin; FAI 5free androgen
index.
amine bivariate relationships between percentage chang-
es (%D) in strength and the hormonal responses. The data
in the tables are presented as mean 6SD. Significance
in this investigation was set at p#0.05.
R
ESULTS
The mean values of the hormonal variables are given in
Table 2. Subjects who participated in the weight-training
program exhibited 124% increase (p,0.001) in the mean
T concentration and 75% increase (p,0.05) in the FAI
values. The STG demonstrated significant isometric
strength gains (17.5%, p,0.001), whereas the CG
showed no significant gains in any of the above-men-
tioned parameters.
At the end of the detraining period, the mean hor-
monal concentrations of the STG were not significantly
different from the posttraining concentrations, whereas
strength significantly decreased (9.5% p,0.001). The
mean detraining T concentration and the mean FAI val-
ues of the CG increased by 9% and 21% (p,0.05). No
significant differences were observed in any of the
strength measurements between groups. Significant cor-
relation was observed in the relative (D%) postdetraining
changes between hormonal parameters (T, FAI; r5
20.68, p,0.05) and isometric strength (r520.91, p,
0.01) in the STG.
D
ISCUSSION
The present study demonstrated that 2 months of a pro-
gressive, supervised resistance strength-training pro-
gram in preadolescent boys resulted in significant in-
creases in the level of T and FAI values and maintenance
of posttraining changes after a 2-month detraining peri-
od. Isometric strength significantly improved but de-
creased significantly at the end of the detraining period
toward untrained control values, suggesting that
strength gains in children are impermanent and revers-
ible. No significant association was observed between the
relative changes in isometric or isotonic (10RM) strength
and the changes in hormonal parameters during pos-
training period. After the end of the detraining period,
significant correlation was observed in the relative (D%)
postdetraining changes between hormonal parameters (T,
FAI; r520.68, p,0.05) and isometric strength (r5
20.91, p,0.01) in the STG.
The influence of resistance training on the strength of
preadolescent boys has been extensively studied. It is
generally accepted that it can successfully and safely in-
crease muscular strength (2, 3, 20). In the present study,
a significant improvement (17.5%) of their isometric
strength was found. Although direct comparisons be-
tween investigations of the same age groups and duration
are limited (9, 32), the magnitude of the strength gains
observed in the present study was smaller and probably
attributed to their different training frequency (9), inten-
sity, and testing modality (9, 32).
Detraining in adults was characterized by a relative
reduction of muscular strength through reversible neu-
romuscular and hormonal adaptations (13, 26). There is
insufficient information about the changes in resistance-
training–induced strength gains during detraining in pre-
adolescents. Few studies (2, 8) investigated the effects of
detraining with an inclusion of a CG to explain probable
growth-related increases in strength. In our study, after
8 weeks of detraining, the trained subjects’ strength de-
creased significantly by 9.5%, converging toward the con-
trol values, whereas the CG subjects showed no signifi-
cant changes in strength during the same detraining pe-
riod. Although the magnitude of the initial strength gain
and the detraining duration could partly explain the re-
versible response of strength (2), other factors seem to be
important as well. No significant correlation was ob-
served between the initial strength and the respective
strength loss, either in isotonic (10RM) or isometric
strength for this STG. The STG maintained approximate-
ly 64% of the strength gained during training, probably
because of the high intensity of the training program (20),
which is an important factor related to the magnitude of
the improvement of the muscular strength (4). The im-
permanent and reversible process of strength and the
preserved hormonal gains during the detraining period
could help coaches design in-season conditioning pro-
grams, though more details need to be examined regard-
ing the point at where the studied parameters will re-
gress to their pretraining values. No significant differ-
ences in strength between groups were found at the end
of the detraining period. The nonsignificant strength
gains occurred in the CG, which indicate the subjects’
growth process, combined with the 9.5% significant de-
creases of the STG, were found to be consistent with the
model proposed by Blimkie et al. (6) concerning the effects
628 T
SOLAKIS
,V
AGENAS
,
AND
D
ESSYPRIS
of growth, resistance training, and detraining during
childhood.
To our knowledge, little is known about the influence
of resistance training upon androgen (T, SHBG, FAI) se-
cretion and bioavailability in preadolescent boys (24, 32).
Our previous work with this age group has demonstrated
that resistance training significantly increased T and FAI
levels of the STG (39), which could probably contribute as
an additional stimulus to the anabolic process during the
growth spurt of puberty. These increases could be asso-
ciated with changes in the cybernetic mechanisms (hy-
pothalamic neurons of gonadotropin-releasing hormone,
pituitary gonadotrophins) of the hypopituitary-gonadal
axis, which control the onset of puberty (35) and thus lead
to acceleration of the rhythm of the growth and develop-
ment (7), although such training of small duration could
not permit any definite conclusion because the mecha-
nisms do not influence the skeletal growth of the prepu-
bertal boys (3). Obviously, more research is needed to
clarify whether extension of the training period may in-
fluence the maturity status of the exercised subjects.
The results of our study, and especially the nonsignif-
icant correlation between pre- and postrelative strength
changes (D%) and anabolic hormones, may demonstrate
a lack of a potential role of T in strength acquisition. Sale
(33) pointed out that neural factors and the possible mus-
cle-fiber transition of type II to more glycolytic profiles
predominate on muscle hypertrophy in prepubescent chil-
dren. In contrast, Mero et al. (23) reported significant cor-
relation between hormones and force production after a
much longer training period (12 months) of combined dif-
ferent training regiments. The significant postdetraining
correlation between hormonal parameters and isokinetic
strength could probably explain the magnitude of ana-
bolic and catabolic process in adults (14, 16). Although
information about detraining adaptations on preadoles-
cent androgen levels is rare, the detraining period’s sig-
nificant association combined with the significant chang-
es in T and FAI, which practically remained unaltered,
probably shows the trainability status of the STG (30).
The concentration of T and SHBG in the STG re-
mained within the reference values range (38) at the end
of the training, which, in turn, shows that the strength
training of this study had no adverse effect on the hor-
monal mechanisms operating in prepubescent boys. The
lack of musculoskeletal injuries after the training period
also showed that this applied, supervised, concentric re-
sistance training does not appear to be a particularly
risky activity in healthy children. Therefore, resistance
training could be an effective part of the physicalexercise
programs for preadolescents (27), taking into account the
interaction between the training adaptations and the po-
tential physiological limits for each stage of development
(20). Numerous questions remain regarding the influence
of different combinations of the training factors (training
mode, intensity, volume, duration) to obtain the optimal
training regimen for specific improvement of strength
and the role of strength training in inducing androgen
responses on muscle hypertrophy or neuromuscular and
motor coordination changes in these subjects.
We conclude that (a) the 2-months resistance training
resulted in significant increases in mean hormonal levels
(T, FAI) and in isometric strength of preadolescent boys
and (b) the posttraining hormonal gains were preserved
for 2 months, whereas isometric strength decreased sig-
nificantly after the end of the detraining period.
P
RACTICAL
A
PPLICATIONS
The present data have important practical applications
and may be useful to coaches and clinicians who takead-
equate information on the subjects’ trainability status to
design preventive or rehabilitative strength-training pro-
grams to reduce the risk of exercise-related injuries or to
achieve optimal musculature, which helps and stabilizes
the growing parts of the human kinetics mechanisms
(22). Coaches and clinicians may also effectively design
the strength-training variables related to the periodiza-
tion, especially the appropriate length of rest between 2
training periods, or to the rehabilitation from sport-relat-
ed injuries for this age group while considering the tran-
sient nature of the training response, which, in an in-
season conditioning program, will result in inevitable and
undesirable strength loss.
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Acknowledgments
We would like to thank all the participants and their parents
for their enthusiastic contribution and patience shown during
the project. We are also thankful to Dr. S. Chantzikonstantinou,
professor of sports medicine, Department of Physical Education
and Sports Science, University of Athens, for his comments; to
Dr. D.A. Adamopoulos, M.D., Ph.D., chief endocrinologist,
Helena Venizelos Hospital, for reviewing and correcting our
manuscript; to Dr. A. Vagenas, assistant professor of statistics,
Department of Physical Education and Sports Science,
University of Athens, for his valuable advice; and to K. Tsolakis,
director of Biochemistry Laboratory, Sotiria Hospital, for his
expert technical assistance.
Address correspondence to Charilaos Tsolakis, Ph.D.,
tsolakis@phed.uoa.gr.
