Endogenous Anabolic Hormonal and Growth Factor Responses to Heavy Resistance Exercise in Males and Females

Abstract

To examine endogenous anabolic hormonal responses to two different types of heavy resistance exercise protocols (HREPs), eight male and eight female subjects performed two randomly assigned protocols (i.e. P-1 and P-2) on separate days. Each protocol consisted of eight identically ordered exercises carefully designed to control for load, rest period length, and total work (J) effects. P-1 utilized a 5 RM load, 3-min rest periods and had lower total work than P-2. P-2 utilized a 10 RM load, 1-min rest periods and had a higher total work than P-1. Whole blood lactate and serum glucose, human growth hormone (hGH), testosterone (T), and somatomedin-C [SM-C] (i.e. insulin-like growth factor 1, IGF-1) were determined pre-exercise, mid-exercise (i.e. after 4 of the 8 exercises), and at 0, 5, 15, 30, and 60 min post-exercise. Males demonstrated significant (p less than 0.05) increases above rest in serum T values, and all serum concentrations were greater than corresponding female values. Growth hormone increases in both males and females following the P-2 HREP were significantly greater at all time points than corresponding P-1 values. Females exhibited significantly higher pre-exercise hGH levels compared to males. The P-1 exercise protocol did not result in any hGH increases in females. SM-C demonstrated random significant increases above rest in both males and females in response to both HREPs.(ABSTRACT TRUNCATED AT 250 WORDS)

Full text

228
Endogenous Anabolic Hormonal and Growth Factor Responses
to Heavy Resistance Exercise in Males and Females
W. I Kraemer2, S. E. Gordon2, S.f. Fleck4, L. J. Marchitelli1 , R. Mello1, f. E. Dziados1 , K. Friedl1 , E. Harman1,
C. Maresh3, A. C. Fry2
Physiology Division, U. S. Army Research Institute of Environmental Medicine, Natick, MA 01760-5007,
2Center for Sports Medicine, The Pennsylvania State University, University Park, PA 16802, 3Exercise Science Program and
the Department of Physiology and Neurobiology, The University of Connecticut, Storrs, CT 06259, 4Sport Science Program,
U. S. Olympic Committee, Colorado Springs, CO 80909 USA
Abstract
W. J. Kraemer, S. E. Gordon, S. J. Fleck, L. J.
Marchiteii, R. Mello, J. E. Dziados, K. Friedl, E. Harman, C.
Maresh and A. C. Fry, Endogenous Anabolic Hormonal and
Growth Factor Responses to Heavy Resistance Exercise in
Males and Females. mt J Sports Med, Vol 12, No 2, pp 228—
235, 1991.
Accepted: June 20, 1990
To examine endogenous anabolic hormonal re-
sponses to two different types of heavy resistance exercise
protocols (HREPs), eight male and eight female subjects per-
formed two randomly assigned protocols (i. e. P-i and P-2)
on separate days. Each protocol consisted of eight identically
ordered exercises carefully designed to control for load, rest
period length, and total work (J) effects. P-l utilized a 5 RM
load, 3-mm rest periods and had lower total work than P-2. P-
2 utilized a 10 RM load, 1-mm rest periods and had a higher
total work than P-i. Whole blood lactate and serum glucose,
human growth hormone (hGH), testosterone (T), and soma-
tomedin-C (SM-C] (i. e. insulin-like growth factor 1, IGF-l)
were determined pre-exercise, mid-exercise (i. e. after 4 of the
8 exercises), and at 0, 5, 15, 30, and 60 mm post-exercise.
Males demonstrated significant (p <0.05) increases above
rest in serum T values, and all serum concentrations were
greater than corresponding female values. Growth hormone
increases in both males and females following the P-2 HREP
were significantly greater at all timepoints than correspond-
ing P-i values. Females exhibited significantly higher pre-ex-
ercise hGH levels compared to males. The P-i exercise proto-
col did not result in any hGH increases in females. SM-C de-
monstrated random significant increases above rest in both
males and females in response to both HREPs. These data
suggest that the hormonal response patterns to HREPs are
variable and in females differ from those in males due to sig-
nificantly higher pre-exercise and exercise-induced serum T
levels in males and higher pre-exercise serum hGH concen-
trations in females.
Key words
Growth hormone, insulin-like growth factor 1,
testosterone, anaerobic exercise, somatomedins, resistance
exercise, blood lactate
Introduction
Heavy resistance exercise is a potent exercise
stimulus for muscle tissue hypertrophy and strength develop-
ment (22, 27). The differences observed between males and
females have classically been attributed to the higher concen-
trations of testosterone in males (13). Still, females generally
demonstrate similar relative training responses in muscular
strength (2). Furthermore, the relative changes in cross-
sectional area, reflecting cellular hypertrophy, are com-
parable (7, 27, 28). The responses in serum testosterone to re-
sistance exercise in females have been examined, but the re-
sponses of other trophic hormones such as growth hormone
and somatomedin C (insulin-like growth factor 1) have not
been previously reported (11, 18, 31, 32). The purpose of this
investigation was to examine the acute response patterns of
several musculotrophic factors (i. e. serum testosterone,
growth hormone and somatomedin-C) to heavy resistance ex-
ercise, compared between males and females. These responses
were further explored by comparison of two distinctly differ-
ent heavy resistance exercise protocols, one with longer rest
and heavier weight (P-I), which is typically used to increase
strength, muscle hypertrophy, and one with more repetitions
and shorter rest periods (P-2), which is typically used to im-
prove muscular strength, hypertrophy, and high intensity
muscular endurance (19).
Int.J.SportsMed. 12(1991)228—235
GeorgThieme Verlag StuttgartNewYork
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Endogenous Anabolic Hormonal and Growth Factor Responses to Heavy Resistance mt. J. Sports Med. 12(1991) 229
Methods
Eight male and eight female subjects gave writ-
ten informed consent to participate in this investigation. The
physical characteristics of the subjects were (51 1 SD): age
(yrs), males, 24.7 4.5, females, 23.1 3.3; height (cm),
males, 178.5±8.2, females 161.6±8.1; body mass (kg),
males, 82.1 12.1, females, 60.4±4.46; body fat (%), males,
16.1 4.5, females, 28.5±6.1. All subjects had recreational
experience with resistance training but none were competitive
lifters. All subjects were healthy and none were using medica-
tions. Each subject denied any history of anabolic steroid use.
All females were determined to be eumenorrheic according to
methods previously described (8) and as defined by regular
28—32 day menstrual cycles over the previous year. None of
the females had used oral contraceptives or an intrauterine
device within the past year (8). A minimum of two weeks were
utilized for experimental protocol familiarization, descriptive
testing, and load verifications (5 RM and 10 RM) for each ex-
perimental exercise protocol. Determination of each subject's
percent body fat using hydrostatic weighing (computer inter-
faced with a load cell) and standard body composition
methodology as previously described (12, 33) was also accom-
plished during this time.
During the preliminary testing period, one rep-
etition maximum (1 RM) testing was performed for each lift
with a warm-up of 5—10 repetitions at 40—60% of the perceived
maximum. After a 1-mm rest and stretching, 3—5 repetitions
were performed with 60—80% of the perceived maximum.
Three to four subsequent attempts were then made to deter-
mine the 1 RM with 3—5 minutes rest between lifts. The test-re-
test reliability for each of the lifts was between 0.91 and 0.95. A
complete range of motion and proper technique were required
for each successful 1 RM trial. No injuries were observed in
any of the testing. No I RM determinations were made for the
sit-up exercise as only the 5 RM and 10 RM loads were deter-
mined for use in the experimental protocol.
The two distinctly different heavy resistance
exercise protocols (HREPs) were performed in random order.
Each experimental test was performed at the same time of day
on separate days with a minimum of 72 hours rest between ex-
perimental sessions. The experimental design of each protocol
is shown in Table 1. The P-I exercise protocol was a five repeti-
tion maximum (5 RM) based workout which incorporated
longer rest intervals (i. e. three minutes) and heavier weight (5
RM) lifted. The P-2 exercise protocol was a 10 RM based
workout with one minute rest between sets. As heavy re-
sistance exercise protocols, both routines produce increases in
muscular strength and hypertrophy. The P- 1 protocol is one
typically utilized for "strength" training, while the P-2 proto-
col is typically used by serious resistance trainees for the
development of strength, hypertrophy, and high intensity
muscular endurance (19). The same order of exercise was used
in both HREPs. P-2 workouts for both male and females con-
sisted of significantly (p <0.05) greater total work (J): males
P-l, 49,980 10,473.9, P-2, 60,427.3 13,428.8; females P-
1, 24,501.1 2,827.0, P-2, 31,580.3± 3,278. Understand-
ably, total work for the females in both P- 1 and P-2 was signifi-
cantly less than that of the male subjects. Still, the relative loads
(% 1 RM) utilized were not significantly different between
males and females in any of the lifts performed. Depending
Table 1 Experimental heavy resistance exercise protocols
Exercise order Repetition maxim
number of sets
P-i
urn (RM) and
P-2
1. Bench press 5 RM x 5 sets 10 RM x 3 sets
2. Double leg extensions 5 RM x 5 sets 10 RM x 3 sets
3. Military press 5 RM x 3 sets 10 RM x 3 sets
4. Bent leg incline
sit-ups 5 RM x 3 sets 10 RM x 3 sets
5. Seated rows 5 AM x 3 sets 10 RM x 3 sets
6. Latpull down 5 RM x 4sets 10 RM x 3 sets
7. Arm curls 5 RM x 3 sets 10 RM x 3 sets
8. Leg press 5 AM x 5 sets 10 RM x 3 sets
P-1 used 5 AM load and 3-mm rest periods, P-2 used 10 RM load and
1-mm rest periods;
* Exercises 4 and 7 were performed using free weights, all other exer-
cises were performed using a Universal weight machine.
uponthe exercise, the 5 RM represented a range of 80—95% of
the 1 RM, and the 10 RM represented a range of 70—85% of the
1RM.
All exercises were structured proportionally
for each subject with grip widths and positions marked and
kept constant for each exercise. Each workout was designed to
provide the same relative exercise stress for comparative pur-
poses. Lifting work was calculated as weight X vertical dis-
tance moved per repetition X number of repetitions. The com-
puter program took into consideration the vertical distance
moved of both the iron plates and the centers of gravity of the
lifter's body segments. These distances were obtained from
measurements on the subjects and equipment when they were
in the starting and ending exercise positions. Anthropometric
tables were used to locate body segment centers of gravity and
to estimate the body segment weights from total body weight
(34).
All subjects refrained from ingestion of alco-
hol or caffeine for 24 hrs prior to testing. Dietry analysis
(Nutri-Calc, PCD System, Inc., Penn Yan, NY) for the 3 days
prior to each experimental session was obtained from a food
diary and demonstrated normal RDA caloric, nutrient, vi-
tamin, and mineral intakes. Values were: (mean I SD)
62.1 4.6% carbohydrate, 12.3 protein, and
25.6 5.3% fat. While it was not the purpose of the study to
match diets on each test day, similar caloric, vitamin, mineral,
and nutrient intakes were observed prior to each test. Urine
nitrogen determinations verified that all subjects were within
the normal range for positive nitrogen balance prior to each
test session. Experimental testing of the female subjects was
timed to the early follicular phase (2—4 days after the onset of
menses) (8).
Subjects reported for the experimental session
and venous blood samples were obtained in a semi-recumbant
position, which was used for all samples. Testing was started in
the morning (8—10 a. m.) and each subject was tested at the
same time of day to reduce the effects of any diurnal variations
on the hormonal concentrations. The venous blood samples
were obtained from an indwelling 20 gauge teflon (3.75 cm)
cannula placed in a superficial arm vein on the radial aspect of
the arm. The teflon cannula was kept patent with a continuous
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* = p <0.05 from corresponding pre-exercise value;
a = p < 0.05from corresponding P-i workout;
b = p <0.05 from corresponding female value.
flow of isotonic saline (30 mlhr 5.Priorto obtaining a rest-
ing blood sample, a 20-mm equilibration period was utilized.
Subjects knew they would not immediately start to exercise
after the resting blood sample was obtained. The exercise pro-
tocol started 10 mm after the resting blood sample had been
obtained. This procedure was shown during pilot testing to
eliminate any significant anticipatory increases in hormonal
responses previously thought to affect the examination of ex-
ercise responses (6). Water intake was allowed ad libitum
throughout the exercise protocols and recovery. Blood
samples were obtained pre-exercise, mid-exercise (i. e. after 4
exercises) and at 0 (immediately post), 5, 15, 30, and 60 mm
following each exercise protocol. All blood samples were
processed, centrifuged for 15 minutes at 3000 x g, serum
harvested, and stored at — 120 °C until analyzed.
Fresh blood samples were immediately ana-
lyzed in duplicate for whole blood lactate by an enzymatic-
amperometric method (Lactate Analyzer-640, Wolverine
Med Inc. Inc., Grand Rapids, MI). Serum samples were as-
sayed for glucose concentrations by an automated glucose oxi-
dase reaction (23-Glucose Analyzer, Yellow Springs, Inc.,
Yellow Springs, OH). Blood was analyzed in triplicate for
hemoglobin using the cyanmethemoglobin method (Sigma
Chemical Co., St. Louis, MO) and for hematocrit by micro-
capillary technique. Relative percent changes in plasma
volume were calculated according to equations by Dill and
Costill (9).
Serum testosterone (T), human growth hor-
mone (hGH), and somatomedin-C (SM-C) (i. e. insulin-like
growth factor, IGF-l) concentrations were determined in du-
plicate blinded analyses by radioimmunoassay (RIA). Male
and female RIAs for T were performed in different assays to
allow for appropriate sensitivity adjustments of the standard
curves. Determinations of different serum immunoreactivity
values were accomplished with the use of a Beckman 5500
gamma counter and on-line data reduction system. Serum
samples were analyzed in duplicate for T using an 125j solid
phase radioimmunoassay (Diagnostic Products Corp., Los
Angeles, CA), which was sensitive to a detection limit of 0.38
nmoll Intra- and inter-assay variances were calculated to
be less than 3.6% and 4.7%, respectively, with a 3.3% crossre-
activity with dihydrotestosterone. Serum samples were ana-
lyzed in duplicate for human growth hormone utilizing an 125j
liquid phase RIA with a double antibody technique (Cam-
bridge Medical Diagnostics, Bellerica, MA). The assay was
sensitive to a detection limit of 0.24 igF Intra- and inter-
assay variances were calculated to be less than 4.2% and 4.8%
respectively. Serum samples were analyzed in duplicate for
SM-C (IGF-l) using an 251 double antibody disequilibrium
RIA with a preliminary ODS-silica extraction procedure (mc-
Star Corp., Stiliwater, MN). Total serum SM-C (JGF-1) was
determined in this assay. The assay was sensitive to a detection
limit of <2.0 nmolF 1and had <0.01 % crossreactivity with
IGF-2. Intra- and inter-assay variances were less than 4.5%
and 4.9%, respectively.
Statistical analyses of the data were accom-
plished utilizing a multivariate two-way analysis of variance
with repeated measures. Tukey post-hoc tests were calculated
to determine pairwise differences. Significance in this inves-
tigation was chosen at p <0.05.
230 mt.J. Sports Med. 12(1991) W. .1. Kruemer et al.
Table 2 The mean (± 1 SD) responses of serum glucose and whole blood lactate to the heavy resistance exercise protocols
Males Pre Mid 05 15 30 60
Serum
Glucose
(mmol
P-i:
P-2:
5.03(0.35)
5.32(0.87)
5.09(0.21)
4.77(0.79)
5.19(0.30)
4.91(0.77)
5.24(0.24)
5.21(1.11)
5.16(0.32)
5.19(0.97)
5.09(0.28)
5.17(0.67)
4.88(0.25)
4.68(0.45)
Whole Blood
Lactate
(mmol P1: 1.33(0.40) 3.12*
(0.98) 439*(3.13) 2.63*
(0.90) 2.15*
(0.71) 1.63(0.44) 1.27(0.19)
P-2: 1.15(0.26) 7•87a
(2.69)
8.61 a
(2.84) 852ab
(2.69) 646a
(2.75) 372a
(1.24) 244a
(0.93)
Females
Serum
Glucose
(mnioi )
P-i:
P-2:
5.14(0.38)
5.06(0.41)
5.14(0.38)
5.19(0.94)
4.83(0.35)
5.23(0.49)
4.86(0.23)
5.27(0.75)
4.93(0.21)
5.10(0.78)
4.76(0.36)
4.80(0.55)
4.59(0.35)
4.54(0.31)
WholeBlood
Lactate
(mmol P.1: 1.40(0.43) 337*(0.78) 3j4*(1.21) 2.41*
(0.81) 2.31*
(1.12) 1.71(0.98) 1.48(0.73)
P-2: 1.36(0.50) 757a
(1.03) 787a(1.57) 620a
(1.79) 506a(0.99) 348a
(0.88) 2.15(0.85)
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Endogenous Anabolic Hormonal and Growth Factor Responses to Heavy Resistance mt. J. Sports Med. 12 (1991) 231
Fig. 1 Mean (+ SE) serum testosterone
concentrations for males and females to P-i
and P-2 HREPs are presented. * = p <0.05
from corresponding pre-exercise values
and + = p <0.05 from corresponding
female values
Results
The effects of the two resistance exercise proto-
cols on whole blood lactate and serum glucose values for
males and females are shown in Table 2. No changes or differ-
ences were observed in serum glucose concentrations. Whole
blood lactate concentrations were significantly elevated by
both protocols in both males and females, and concentrations
were increased more in the P-2 exercise protocols than in the
P-i workout for both males and females. There was only a tran-
siently higher concentration in the male P-2 exercise protocol
compared to the females (at 5-mm recovery period interval).
Serum testosterone responses are shown in
Fig. 1. Concentrations were increased in males by both exer-
cise protocols and for up to 15 mm into the recovery periods.
Mid-exercise values in males were significantly greater in P-2
than in P-l. All male values were significantly higher than
corresponding female values at every timepoint measured.
Additionally, the 60-mm values for P-I were significantly
greater than corresponding P-2 serum T concentrations for
males.
Growth hormone responses are shown in Fig.
2. Markedly different response patterns were observed be-
tween the two HREPs for both males and females, with a sig-
nificantly greater increase in hGH concentrations in P-2; mid-
exercise values in the males were significantly greater than in
P-i. In P-i, significant increases in serum levels above pre-ex-
ercise values were observed for the males at mid-exercise and
at 30 mm following the exercise protocol. No significant hGH
increases above pre-exercise values were observed in P-i for
female subjects. Furthermore, in both P-i and P-2 HREPs,
females exhibited significantly higher pre-exercise serum
hGH values than males. In P-2, females demonstrated signifi-
cant increases in serum hGH at mid-exercise and at 0, 5, and 15
mm following exercise, and males increased hGH at all time
points. For both males and females, P-2 values, other than pre-
Serum testosterone (nmolI—1) Serum testosterone (nmol I_I)
a 0,0 or a P o a 0, p .j a Oi
S S S Sb S aS 000 Sb 5 0 ebbSe cob cob
I _____________________________________________________________________________________________
• ÷
-I :. •:.
H
:_______________________
L°JH
ItI *
H
H-
*
I +
:..*_I
I +
0
0
_f
I +
JH +
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232 Int.J.SportsMed. 12 (1991) W. J. Kraemeretal.
Fig. 2 Mean (+ SE) serum human growth
hormone concentrations for males and
females to P-i and P-2 HREPs are pre-
sented. * = p <005 from corresponding
pre-exercise values and + = p <0.05 from
corresponding female values
exercise, were all significantly greater than corresponding P-i
serum hGH concentrations.
Fig. 3 shows the responses of serum soma-
tomedic-C (insulin-like growth factor 1) to P-i and P-2 re-
sistance exercise protocols. In P-i, males demonstrated sig-
nificant increases in serum values immediately following exer-
cise, and females significantly increased serum SM-C 60 mm
following exercise. For the females, P-I values at 60 mm post-
exercise were significantly greater than corresponding P-2
values. In P-2, SM-C significantly increased above resting
levels at mid-exercise, 0 and 5 mm for the males and at mid-
exercise and immediately following exercise for the females.
For the females, P-2 values at mid-exercise were significantly
greater than corresponding P-I values.
Changes in plasma volume shifts during re-
covery were negligible. The greates % change in plasma
volume were observed pre- to immediately post-exercise and
were as follows ( 1 SD):
males P-i —4.1 8.4%, P-2 —4.1 8.8%; females,
P-i = —0.5 7.7%, P-2 —6.0 7.2%.
Discussion
The most remarkable finding of this investiga-
tion was the difference in hGH stimulation by the two re-
sistance exercise protocols for both men and women. The
more anaerobic P-2 HREP produced a clear and sustained
elevation of hGH, while the P-i exercise protocol had virtually
no effect on hGH concentrations in the female subjects. Fur-
thermore, a substantially lower hGH response in the P-i com-
pared to the P-2 protocol was observed in the males. While the
relative contributions of various physiological mechanisms to
the observed response patterns remain unclear, changes in
hGH have been shown to be influenced by hypoxia, acid base
shifts, and breath holding (10, 26, 29). Differential response
patterns of hGH using heavy and light leg press exercise proto-
cols have been shown previously for men in a study by Van
Helder et al. (30). The data from this investigation demon-
Serum human growth hormone (pg F Serum human growth hormone (tg F
-:
+
1%)
*
-p
-4
F-"
-o
0
Ca
.7'
-I
'C -
= U,
C,
C.,
nl
S
= H
____ * II It
C —
a-;
rcG
en
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Serum somatomedin-C (nrnolI—1) Serum somatomedin-C (nmol .1_i)
P P
0 0 0
*
H
,
-.
H
H H
H
H
+
Th
b C
C o V.
C
S
H
—1
-'
*
H
It II
Endogenous Anabolic Hormonal and Growth Factor Responses to Heavy Resistance mt. J. Sports Med. 12 (1991) 233
Fig. 3 Mean (+ SE) serum somatomedin-
C (IGF-1) concentrations for males and
females to P-i and P-2 HREPs are pre-
sented. * = p <0.05 from corresponding
pro-exercise and + = p <0.05 from corre-
sponding female values
strate that hGH responses in men are sensitive to both HREPs,
but the high volume, 10 RM load, using short rest periods ap-
pears to augment the magnitude of the hGH response in both
males and females. The adaptational importance of an aug-
mented response of serum hGH to such a high volume, 10 RM
load, and short rest protocol HREP, (i. e. P-2) for exercise pre-
scription of resistance training for women during various
phases of the menstrual cycle remains to be investigated. At
present, the combined effects of a higher volume, shorter rest,
and moderate intensity resistance workout produce a dra-
matic stimulus to serum hGH responses. Studies are needed to
partition out the individual effects of single variables.
The baseline differences in serum hGH con-
centrations between males and females are almost certainly re-
lated to the estrogen sensitization of somatotrophs which gives
a well-established increased responsiveness to a wide variety
of stimuli in women (26). It is unclear why female responses to
the HREPs were not greater than those observed for the males.
It is possible that despite the same relative exercise stress, the
lower absolute total work for each of the HREPs might ac-
count for the lack of a greater exercise responsitivity. The rela-
tive stress (% 1 RM) for each HREP was comparable for men
and women. Still, the contribution of absolute total work, irre-
spective of other exercise variables (e. g. load, rest periods,
etc.), remains to be examined.
The absence of a consistent response pattern of
serum SM-C (IGF-1) may be due to a variety of mechanisms
involved with determining peripherial blood levels. A direct
response of SM-C to the increased hGH stimulation observed
in this study might not have been expected over the 1-hr re-
covery time period observed, since hGH stimulated mRNA
synthesis (which results in an increased SM-C production)
does not peak until 3 to 9 hrs later (1, 3, 14, 23). Due to the com-
plex interactions of SM-C secretion with transporter protein
attachment and release, receptor equilibrium, and receptor
binding actions, the serum response patterns may reflect a
more integrated response of such physiological mechanisms.
Alternatively, the significant increases which were observed
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234 ml. J. Sports Med. 12(199]) W. J. Kruerner ci a!.
could represent a non-hGH mediated release or transient in-
creases in serum transporter protein release due to receptor
binding turnover. Further study is needed to clarify such
mechanisms.
In contrast to the hGH hormonal response, T
was acutely stimulated by both HREPs in males. Previous
studies in male subjects have demonstrated that serum T re-
sponses are a function of the amount of muscle mass utilized in
the exercise protocol and the total work performed (11, 15, 18,
25, 31). Conversely, in this study, serum T concentrations in
females remained unaffected by either HREP. This suggests
that the serum increases observed in males is mediated
through the pituitary-testicular axis, either by increased secre-
tion rates or by alterations in testicular blood flow, instead of
through systematic fluid shifts or reduced hepatic clearance
rates (4,24).
Although levels of androstenedione are 10-
fold higher than Tin females and responsive to resistance exer-
cise, T and dihydrotestosterone are still the more potent
musculotrophic androgens (1, 13, 16, 17, 20, 31), with impor-
tant target receptors and effects in the upper body muscula-
ture. The lower levels of these androgens normally en-
countered in females and the absence of any stimulation by
these two different HREPs suggest reasons why females typi-
cally do not achieve levels of upper body muscularity and
strength achieved by males (2). While one study has demon-
strated that small increases in serum T may be possible in
females (6), our study supports previous investigations which
have not found any acute effects on serum T concentrations
(11, 18, 31, 32). Thus in females, it appears that other endo-
genous anabolic hormonal mechanisms may play a more
prominent role in physiological adaptations to heavy re-
sistance training.
In summary, heavy resistance exercise stimu-
lates acute endogenous anabolic responses. These responses
may differ depending upon the type of exercise protocol util-
ized. Growth hormone appears to be the most sensitive to
change in program design. Female hormonal responses in this
study appear to differ due to higher resting levels of growth
hormone during the early foilicular stage of menstrual cycle
and a general lack of testosterone responsiveness to either
heavy resistance exercise protocol. The adaptational effects of
such differential hormonal responses to heavy resistance exer-
cise on cellular adaptations in muscle, connective tissue, and
bone remain to be demonstrated.
Acknowledgements
The authors would like to thank Joann Ruble and
Carol Glunt for their help in the preparation of this manuscript. Also,
special thanks go to Dini McCurry, Charles Cruthirds, Peter Frykman,
and Alan Vela for their help in data collection and laboratory analyses.
The authors would also like to thank Dr. Paul Rock for his additional
help as a medical monitor. Finally, the authors would like to thank a
dedicated group of test subjects who gave a great deal of their time and
effort to make this study possible.
Human Research
Human subjects participated in these studies after
giving their free and informed voluntary consent. Investigators ad-
hered to AR 70—25 and USAMRDC Regulation 70—25 on Use of Vol-
unteers in Research.
The views, opinions, and/or findings contained in
this report are those of the author(s) and should not be construed as an
official Department of the Army position, policy, or decision, unless
so designated by other official documentation.
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