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Changes in human muscle protein synthesis
after resistance exercise
A. CHESLEY, J. D. MAcDOUGALL, M. A. TARNOPOLSKY, S. A. ATKINSON, AND K. SMITH
Departments of Physical Education, Medicine, and Pediatrics, McMaster University, Hamilton,
Ontario L8S 4K1, Canada
CHESLEY,
A., J. D.
MACDOUGALL,
M. A.
TARNOPOLSKY,
S. A.
ATKINSON, AND
K.
SMITH.
Changes in human musclepro-
tein synthesis after resistance exercise. J. Appl. Physiol. 73(4):
l383-1388,1992.-The purpose of this study was to investigate
the magnitude and time course for changes in muscle protein
synthesis (MPS) after a single bout of resistance exercise. Two
groups of six male subjects performed heavy resistance exercise
with the elbow flexors of one arm while the opposite arm served
as a control. MPS from exercised (ex) and control (con) biceps
brachii was assessed 4 (group A) and 24 h (group B) postexer-
cise by the increment in L-[ l-‘3C]leucine incorporation into
muscle biopsy samples. In addition, RNA capacity and RNA
activity were determined to assess whether transcriptional
and/or translational processes affected MPS. MPS was signifi-
cantly elevated in biceps of the ex compared with the con arms
of both groups (group A, ex 0.1007 t 0.0330 vs. con 0.067 t,
0.0204 %/h; group B ex 0.0944 t 0.0363 vs. con 0.0452 t 0.0126
%/h). RNA capacity was unchanged in the ex biceps of both
groups relative to the con biceps, whereas RNA activity was
significantly elevated in the ex biceps of both groups (group A,
ex 0.19 2 0.10 vs. con 0.12 t 0.05 pg protein
l
h-’
l
pg-’ total
RNA; group B, ex 0.18 -+ 0.06 vs. con 0.08 t 0.02 pg pro-
tein
l
h-’ . pg-l total RNA). The results indicate that a single
bout of heavy resistance exercise can increase biceps MPS for
up to 24 h postexercise. In addition, these increases appear to
be due to changes in posttranscriptional events.
L- [ l- 13C] leucine incorporation; ribonucleic acid capacity; ribo-
nucleic acid activity
IT IS WELL KNOWN
that a program of heavy resistance
training can lead to substantial gains in strength and
muscle hypertrophy
(l&14,24).
The observed increases
in muscle size are due to acute and chronic increases in
muscle protein turnover such that protein synthesis ex-
ceeds protein degradation (9,
10).
Although both acute
and chronic increases in protein synthesis have been
demonstrated in muscles of animals undergoing hyper-
trophy in response to tenotomy or stretch (9,
lo),
such
perturbations do not really simulate resistance training
as performed by humans (23, 25). Thus there are few
data available regarding the time course and magnitude
of the acute changes in muscle protein synthesis (MPS)
after resistance exercise in humans.
On the basis of a review of animal studies involving
muscle stretch, various exercise protocols, or electrical
stimulation, Booth et al.
(4)
postulated that acute in-
creases in muscle protein synthesis occur
l-2
h postexer-
cise and may remain elevated above basal levels for an
undefined period thereafter. It also appears that the
magnitude of the increase in MPS is dependent on the
type, intensity, and duration of exercise (3,4). Increases
in total mixed and myofibrillar protein synthetic rates
ranging from
25
to 65% have been documented in rat
gastrocnemius and tibialis anterior
17
and 41 h after the
completion of a single bout of concentric or eccentric
resistance exercise
(30, 31).
In humans, MPS has been
shown to increase by
26%
in vastus lateralis
4
h after a
single bout of low-intensity treadmill running (6). In ad-
dition, whole body protein synthesis (WBPS) was un-
changed for up to
2
h after an acute bout of circuit-type
resistance exercise performed at
70%
of the one-repeti-
tion maximum
(22),
whereas WBPS increased in resis-
tance- #trained males
24
h after a simi .lar exercise protocol
when compared with age-matched sedentary controls
(21).
MPS has been shown to account for -2530% of
WBPS
(15),
and thus increases in WBPS are likely to be
due in part to increases in MPS.
The -mechanisms that mediate acute changes in MPS
in response to resistance exercise are not yet known.
Wang-and Booth
(30, 31)
found increases in RNA activ-
ity after a single bout of concentric or eccentric resis-
tance exercise. RNA activity reflects changes in post-
transcriptional events and is used as an index of the effec-
tiveness of the ribosomal machinery in translating
existing mRNA species into protein molecules (27).
There is also indirect evidence suggesting that RNA ac-
tivity may change before RNA capacity (an index of
changes in transcriptional events) during conditions in-
volving acute changes in muscle activity (3).
The purpose of this study was to examine the magni-
tude and time course of changes in mixed muscle protein
synthetic rates in humans after a single bout of resis-
tance exercise. In addition, RNA capacity and RNA activ-
ity
(27)
were measured to indicate overall changes in
transcriptional and/or translational control processes,
respectively.
METHODS
Subjects.
Twelve healthy males who regularly engaged
in resistance training served as subjects. They were ad-
vised of the risks associated with the study and provided
written informed consent. The study was approved by
the University Human Ethics Committee. Subjects were
assigned to either a
4
h postexercise group
(group A)
or a
24
h postexercise group
(group
B). Subjects were re-
0161-7567192 $2.00 Copyright 0 1992 the American Physiological Society 1383
1384
PROTEIN SYNTHESIS AFTER WEIGHT LIFTING
TABLE
1. Subject descriptive data
Group
Characteristic A
AiF, Yr 25.1k3.9
Height, m 1.76kO.09
Body weight, kg 79.3t5.1
Lean body weight, kg 67.Ok5.1
Body fat, % 15.4k5.1
Years of training 4.9k6.6
Daily energy intake, kcal 3,076+602
Values are means + SD; n = 6 in each group.
B
23.1k2.3
1.80+0.05
83.Ok10.7
73.3k8.6
11.4t5.0
4.U3.3
3,196+1057
cruited so that the two groups could be equated on the
basis of resistance training experience and maximal el-
bow flexor strength. Group characteristics are provided
in Table 1.
Preexperimmtal mmsurements. Maximum elbow flexor
strength [single maximum repetition (lRM)] of the domi-
nant arm was determined for the biceps curl, preacher
curl, and concentration curl exercises. Body density was
determined by hydrostatic weighing, with residual lung
volume measured by helium dilution. Percent body fat
was then calculated according to the Brozek method (5).
Three-day food records (including 1 weekend day) were
obtained from each subject for the determination of
mean daily energy and protein intakes with use of a com-
puter program for nutrient analysis (Nutritionist III, Sil-
verton, OR).
Experimental protocol. The six subjects in group A per-
formed the resistance exercise protocol on the day of the
leucine infusion, whereas the six subjects in group B ex-
ercised the day before the leucine infusion. Measure-
ments were made after 3 days of rest during which no
resistance training was performed. The exercise protocol
consisted of four sets of
6-12
repetitions of the biceps
curl, preacher curl, and concentration curl with a resis-
tance equal to 80% of the 1 RM. All sets were performed
to muscular failure, and rest periods of 3 min were pro-
vided between sets and exercises. For 2 h before and dur-
ing the entire leucine infusion protocol, subjects received
50% of their individual mean energy intake as a defined
formula diet (Ensure, Ross Laboratories, Montreal,
Canada) to ensure a consistent rate of appearance of en-
dogenous energy and protein. Feedings were given in
equal aliquots every 30 min (17 aliquots total) during the
study protocol. Group A received a primed continuous
infusion of L-[ lJ3C]leucine beginning 0.68 t 0.20 h pos-
texercise, whereas group B was infused
20.41 t 0.24
h
postexercise. Subjects in group B were instructed to re-
frain from strenuous activity after the resistance exercise
protocol.
A 22-gauge plastic catheter was inserted into a suitable
hand vein for blood sampling while a second catheter was
inserted into a vein of the contralateral proximal forearm
vein for isotope infusion. A priming dose of
L- [
l-
‘3C]leucine
(1
mg/kg) was administered by a Harvard
syringe pump followed by a constant infusion of
L-[ l-
13C]leucine (1 mg l kg-’ l h-l) for -6 h (5.4-6.4 h). In all
cases the L-[1-13C]leucine was from the same batch
(MSD Isotopes, Pointe-Claire, Canada) and was con-
firmed to be 99% isotopic pure and sterile by the com-
pany. Batch dilutions (15 g/ml) of the isotope were made
under aseptic conditions, and on the day of the infusion
the isotope was further diluted with sterile saline and
microfiltered immediately before infusion. Arterialized
blood samples (hot box at 65 t 5°C) (1) for the determi-
nation of plasma cu-ketoisocaproic acid (cu-KIC) enrich-
ment were obtained from the hand before the start of the
infusion, 2 h after the priming dose (t = 2 h), approxi-
mately midway (t = 4 h), and at the end of the infusion
protocol (t = 6 h). Blood was collected into heparinized
tubes and centrifuged immediately. The plasma was
stored at -70°C until analysis.
Percutaneous needle biopsies from the distal lateral
portion of the biceps brachii were obtained under local
anesthesia 2 h after the leucine priming dose and once
more at the completion of the leucine infusion protocol.
The 2-h period between the priming dose and the first
biopsies was chosen to ensure that an isotopic plateau
had been reached. This has been demonstrated in a pre-
vious study from our laboratory under similar conditions
(22). Two biopsies were obtained at 2 h (one each from
the control arm and exercised arm) and two more after
the completion of the infusion. The muscle samples were
visibly dissected of fat and connective tissue, frozen in
liquid nitrogen, and transferred to a -7OOC freezer until
analysis.
Analytic techniques. Tissue was weighed wet, freeze-
dried, ground to a fine powder in liquid nitrogen, and
transferred to tubes containing 3 ml of 0.2 N ice-cold
perchloric acid (PCA). After 20 min of centrifugation at
4”C, the remaining pellet was redissolved in 5 ml of 0.2 N
PCA and centrifuged once more. This step was repeated.
Tissue lipids were then extracted by a series of 5-ml sol-
vent washes followed by 5 min of centrifugation. The
order of the washes was as follows: 1) 1% potassium ace-
tate in ethanol, 2) ethanol-chloroform (3:1), 3) ethanol-
ether (3:l), and 4) ether. Protein was solubilized in 3 ml
of 0.3 M NaOH in a 37°C water bath for 60 min. A 50-~1
aliquot of the supernatant was removed and added to
4.95 ml of 0.3 N NaOH. The alkali-soluble protein was
transferred to clean tubes. Total muscle protein content
was determined by the method of Lowry et al. (11). RNA
was then extracted by dissolving the remaining pellet in 2
ml of 1 M PCA and centrifuging as before. The superna-
tant was transferred to clean tubes for the determination
of RNA. The pellet was rewashed and the supernatant
combined with the RNA supernatant: Samples were then
frozen for the subsequent determination of total RNA by
the method of Tsanev and Markov (26). DNA was ex-
tracted by the addition of 5 ml of 2 M PCA to each tube
followed by incubation for 1 h in a 70°C water bath. The
protein fraction was repelleted by centrifugation for 20
min and the supernatant kept for DNA determination by
the method of Schneider and Greco (17).
The procedure used to isolate and measure
L-[
l-
13C]leucine content in muscle tissue was a modification
of the technique described by Smith et al. (20). The pro-
tein pellet obtained after protein/nucleic acid extraction
was hydrolyzed in 6 M HCl, and the resulting amino acid
mixture was applied to an ion-exchange column as previ-
ously described. The samples were then dried in a rotary
evaporator and derivitized with 50-75 ~1 of N-methyl-t-
PROTEIN SYNTHESIS AFTER WEIGHT LIFTING
1385
w
;;I +fy
L
I5
03-
3
m2-
r n
T-
E
JO
CL +2 +4 +6
Time (hours)
FIG. 1. Enrichment of plasma cu-ketoisocaproic acid (wKIC) for
combined groups over period during which muscle protein synthesis
was estimated. Muscle biopsies were taken at 2 and 6-h point of infu-
sion protocol. Note isotopic steady state over this period. Units are
atom percent excess (APE), and values are means + SE (n = 12).
butyldimethylsilyltrifluoroacetamide and an equal vol-
ume of pyridine in an oven at 85OC for 60-90 min.
Preparative gas chromatography, for the isolation of
leucine, was done with a Pye Unicam 304 series chro-
matograph fitted with a postcolumn splitter
(99:l
split
ratio) and a wide-bore glass column (6 mm ID
X
4.6 m) as
previously described (20). The leucine was collected from
the postcolumn splitter in a home-made demountable
glass U trap cooled in liquid nitrogen. The leucine col-
lected in the U trap was removed by the addition of 0.5 ml
of lithium citrate buffer (pH 2.2) to the trap followed by
heating at 90°C for 30 min. The liquid was then trans-
ferred to a 20-ml Vacutainer tube, and the U trap was
rinsed with a further 0.5 ml of buffer. The rubber stop-
pers from the Vacutainers were degassed overnight in a
sealed glass flask in an oven under vacuum at 90°C. The
samples were degassed at 140-150°C in a heating block
for 30 min and placed on ice. Approximately 25 mg of
ninhydrin were added to each tube on ice, and the Vacu-
tainer was evacuated on a vacuum line. The ninhydrin
reaction was carried out in a 90°C water bath for 30 min.
The tubes were then allowed to cool to room temperature
and were filled with nitrogen. The 13C0, enrichment of
the samples was determined by isotope-ratio mass spec-
trometry according to the method of Scrimgeour et al.
(18).
Plasma cu-KIC enrichment was determined by capil-
lary gas chromatography/mass spectrometry according
to the method described by Tarnopolsky et al. (22).
Muscle protein synthetic rate was calculated according
to the equation
FMPS = (LE, x lOO)l(K,, x t)
where FMPS is the fractional muscle protein synthetic
rate (%hh), t is the incorporation time (in h) betweer
biopsy samples taken from the same arm (15), LE, is the
increment in 13C abundance in muscle protein obtained
between t = 2 h and
t
= 6 h biopsy samples from each
arm, and &, is the mean plasma wKIC enrichment for
t=2,4,and6hbl d oo samples (corrected for background
enrichment from the t = 0 h sample).
Biopsy samples for two subjects in group A were found
to be of insufficient size for measurement of protein syn-
thetic rate and RNA activity, and thus data are presented
for only four subjects in group A and six subjects in group
B. Subject descriptive data, elbow flexor strength, train-
ing intensity and volume, and leucine infusion parame-
ters were analyzed with a one-way analysis of variance
(ANOVA). Muscle protein, total RNA, and DNA concen-
trations were analyzed with a two-way ANOVA with re-
peated measures. Protein synthetic rates and RNA activ-
ity were analyzed with a two-way ANOVA with repeated
measures for unequal sample sizes. A Tukey post hoc
analysis was used when significant differences between
means were obtained. P < 0.05 was selected as being in-
dicative of statistical significance. Values are expressed
as means t SD.
RESULTS
The two groups did not differ as to age, height, body
weight, lean body weight, energy intake, or training his-
tory (Table 1). The mean 1 RM for the three biceps exer-
cises was similar between groups as were the mean train-
ing intensity and volume (product of the weight lifted
and the total number of repetitions) for the experi-
mental day.
The mean plasma wKIC enrichments over the three
separate sampling points during infusion were 4.87 t
0.95 and 4.63 t 0.96 atom percent excess for groups A and
B, respectively. These values were consistent over time
with a coefficient of variation of <8.7%, thus demonstrat-
ing isotopic steady state (Fig. 1).
Total muscle protein expressed as a percentage of
muscle wet weight was similar between groups and be-
tween the exercised and control biceps. In addition, mus-
cle RNA and DNA concentrations were similar between
groups and between arms (Table 2). The values of enrich-
ment of 13C in muscle are presented in Table 3. Muscle
protein synthetic rates were significantly elevated in ex-
ercised compared with control biceps of both groups
(group A,
0.1007
t
0.0330
vs.
0.067
t
0.0204
%/h; group B,
0.0944 t 0.0363 vs. 0.0452 t 0.0126
%/h; Fig. 2). The
observed differences in MPS were apparently due to a
significant increase in RNA activity in the exercised vs.
control biceps of both groups (group A,
0.19 t 0.10 vs.
0.12
t 0.05 pg protein l h-l l pgvl of RNA; group B,
0.18 t
0.06
vs. 0.08 t 0.02 pug protein l h-’ l p8-l of RNA; Fig. 3).
TABLE
2.
Muscle protein content and total RNA
(capacity) and DNA concentration
Protein Content,
5% wet wt RNA, DNA,
pg/mg protein pg/mg protein
Group A
Ex 14.8zk5.4 6.3k1.5 4.7kl.7
Con 15.0+5.6 5.421.5 4.6~11.6
Group B
Ex
17.3k5.8 5.4k1.6 4.5k1.3
Con 16.Ok6.6 5.3kO.9 4.9-tl.4
Values are means + SD; n = 4 for group A and 6 for group B.
Ex,
exercised biceps; Con, control biceps.
1386
PROTEIN SYNTHESIS AFTER WEIGHT LIFTING
TABLE
3. L-[l-‘3C]leucine enrichment in biceps muscle
-
from control and exercised arms
Subj Control Exercised
2A 0.0060 0.0109
4A 0.0096 0.0104
5A 0.0104 0.0135
6A 0.0038 0.0153
1B 0.0060 0.0221
2B 0.0106 0.0196
3B 0.0106 0.0129
4B 0.0057 0.0188
5B 0.0072 0.0116
6B 0.0064 0.0115
Values are expressed as atom percent excess.
DISCUSSION
The purpose of this study was to determine the magni-
tude and time course for acute changes in MPS after an
isolated bout of heavy resistance exercise. Because of the
number of biopsies required, we considered it necessary
to examine two groups, each at a different time point
(rather than a single group at two time points). Our in-
terpretation of the time course data is thus based on the
assumption that postexercise changes in MPS would
have been similar for both groups. In an attempt to en-
sure this, groups were equated according to body size,
strength, and training history and performed identical
exercise protocols.
A second assumption is that plasma a-[13C]KIC label-
ing is a valid index of the precursor pool available for
MPS. Plasma cu-KIC labeling reflects the probable intra-
cellular fate of leucine and as such has been employed in
several studies for calculating rates of whole body and
MPS (2,6,7,15,16,21,22). Recent data have confirmed
that cu-KIC labeling closely approximates the labeling of
leucyl-tRNA in postabsorptive surgical patients
(19).
Measurement of labeled leucyl-tRNA was not attempted
in this study because of the large tissue requirements and
difficulty of isolation of this procedure.
Our finding that MPS was
50 (group A)
and
109%
(group
B) higher in the exercised biceps than in the con-
trol biceps indicates that the resistance exercise was a
potent stimulator of protein synthesis. Net muscle
c
Eo.150-
P
$ 0.125.
0
t; 0.100-
z
7 0.075.
>
co
z 0.050-
F
0
a 0.025-
L
O.OOO-
T
0 CONTROL
q
EXERCISE
B
FIG. 2. Muscle protein synthetic rates in biceps of control and exer-
cised arms for groups A (4 h postexercise) and B (24 h postexercise).
Values are means t SD. * Significant difference (P < 0.05) between
arms.
A B
0 CONTROL
*
m EXERCISE
FIG. 3. RNA activity in biceps muscle from control and exercised
arms for groups A and B. Values are means + SD. * Significant (P <
0.05) difference between arms.
growth (hypertrophy) can be considered as being the dif-
ference between the change in MPS and the change in
protein degradation. The extent to which protein degra-
dation also occurred as a result of the exercise is un-
known, but on the basis of data for animal muscle sub-
jected to stretch overload or tenotomy (9,
lo),
one can
assume it to have been significant. Moreover one can
calculate that if the increases in MPS that we found were
not also accompanied by a concomitant increase in pro-
tein degradation, in several weeks of training they would
result in increase in muscle size that greatly exceeds that
which is known to occur
(12).
The time course for increases in MPS in the biceps
brachii extended from
4
to
24
h postexercise. This is in
agreement with a model proposed by Booth et al.
(4),
suggesting that NIPS increases above basal levels
l-2
h
postexercise and remains elevated for an indefinite time
thereafter. In the present study the time required to
reach isotopic plateau and to allow labeled leucine to ac-
cumulate in the biceps precluded the assessment of IMPS
sooner than
4
h postexercise. It is possible that protein
synthetic rates were elevated before this time point, but
studies examining a shorter time course have not been
performed in humans. Tarnopolsky et al.
(22)
found no
change in WBPS rates in experienced bodybuilders
2
h
after the completion of a circuit-type resistance exercise
protocol. Because MPS accounts for 25-30s of WBPS
(ES),
these results suggest that either MPS may have
been unaffected at this time or increases in MPS oc-
curred but were masked by larger decreases in protein
synthesis in other tissues. Our finding that MPS re-
mained elevated for up to
24
h postexercise is consistent
with findings of an elevated WBPS at this time point
after a single bout of circuit-type resistance exercise
(21).
MPS has been shown to be acutely elevated
12-17
and
36-41
h in rat gastrocnemius and tibialis anterior after a
single bout of concentric or eccentric resistance exercise,
respectively (30,
31).
The duration of increases in MPS in humans after an
isolated bout of resistance exercise is not known. Vari-
ables that may affect this include the intensity and vol-
ume of the exercise, the muscle or muscle groups in-
volved, the type of muscle contractions performed, and
the state of training of the subject. There appears to be
an optimal training frequency of two or three per times
PROTEIN SYNTHESIS AFTER WEIGHT LIFTING
1387
week for exercising a muscle group to ensure gains in
muscle mass (14,29). Less or more frequent training may
result in little or no muscle growth and suggests that the
time course for changes in MPS may be intimately asso-
ciated with training frequency and subsequent recovery
from exercise.
After the resistance exercise, there were wide interindi-
vidual differences for leucine enrichment in the control
and exercised arms (Table 3). The source of this varia-
tion is unknown, but it may be due to differences in
training history, differences in muscle fiber composition,
and/or the degree of muscle damage and satellite cell
activation. There is some evidence suggesting that the
basal rate of MPS is higher in type I than in type II
muscle fibers (8), although this has not been substan-
tiated by measurements of protein synthesis in humans
(15). Another possibility is that muscle damage of the
type associated with high-intensity eccentric muscle con-
tractions may have occurred in the exercised biceps.
Such damage may result in increased MPS through the
possible release of growth factor and subsequent satellite
cell activation (28).
To assess whether transcriptional and/or posttran-
scriptional events were responsible for the increases in
MPS, RNA capacity and activity were measured in both
exercised and control arms. RNA capacity expressed as
the total RNA content relative to noncollagenous protein
content (RNA concentration) can be considered an index
of changes in transcription (27). RNA activity expressed
as the amount of protein synthesized per unit time per
unit of RNA can be considered an index of how quickly
the ribosomal machinery can decode mRNA molecules
into protein (ribosomal efficiency) (27). RNA capacity
was unchanged in the exercised biceps of both groups,
but RNA activity was significantly elevated compared
with that in the unexercised biceps. These findings are
similar to those of previous studies that have examined
acute changes in RNA capacity and RNA activity after
stretch or weight-training protocols (10, 30, 31). It thus
appears that posttranscriptional events are important in
mediating acute changes in MPS in response to muscle
overload. The molecular signals, however, that stimulate
this enhanced rate of translation in response to resis-
tance exercise are presently unknown.
In summary, protein synthetic rates were elevated in
biceps muscle both at 4 and 24 h after a single unilateral
heavy resistance training session. An upregulation of
posttranscriptional events may be the mechanism that
initiates and maintains an acute increase in MPS after
resistance exercise.
The authors thank Stuart Phillips, John Moroz, and Joan Martin
for technical assistance.
This study was supported by the Natural Science and Engineering
Research Council of Canada. M. A. Tarnopolsky is funded by a Na-
tional Institute of Nutrition Post Doctoral Fellowship.
Present address of K. Smith: Dept. of Physiology, University of
Dundee, Dundee DDl 4HN, UK.
Address reprint requests to J. D. MacDougall.
Received 9 December 1991; accepted in final form 17 April 1992.
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