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The Time Course for Elevated Muscle Protein Synthesis Following Heavy Resistance Exercise

Authors:

Abstract

It has been shown that muscle protein synthetic rate (MPS) is elevated in humans by 50% at 4 hrs following a bout of heavy resistance training, and by 109% at 24 hrs following training. This study further examined the time course for elevated muscle protein synthesis by examining its rate at 36 hrs following a training session. Six healthy young men performed 12 sets of 6- to 12-RM elbow flexion exercises with one arm while the opposite arm served as a control. MPS was calculated from the in vivo rate of incorporation of L-[1,2-13C2] leucine into biceps brachii of both arms using the primed constant infusion technique over 11 hrs. At an average time of 36 hrs postexercise, MPS in the exercised arm had returned to within 14% of the control arm value, the difference being nonsignificant. It is concluded that following a bout of heavy resistance training, MPS increases rapidly, is more than double at 24 hrs, and thereafter declines rapidly so that at 36 hrs it has almost returned to baseline.
RAPID COMMUNICATION
The Time Course for Elevated Muscle Protein
Synthesis Following Heavy Resistance Exercise
J. Duncan MacDougall, Martin J. Gibala, Mark
A.
Tarnopolsky,
Jay
R.
MacDonald, Stephen
A.
Interisano, and Kevin
E.
Yarasheski
Catalogue Data
MacDougall, J.D., Gibala, M.J., Tarnopolsky, M.A., MacDonald, J.R., Interisano, S.A.,
and Yarasheski, K.E. (1995). The time course for elevated muscle protein synthesis
following heavy resistance exercise.
Can.
J.
Appl. Physiol.
20(4): 480-486.
O
1995
Canadian Society for Exercise Physiology.
Key
words:
L-[-I3C] leucine, muscle hypertrophy, training frequency, mass spectrometry
Mots-cle's:
leucine L-[-I3C], hypertrophie musculaire, frhquence d'entrainement, spec-
tromPtre de masse
It has been shown that muscle protein synthetic rate (MPS) is elevated in humans by 50%
at 4 hrs following a bout of heavy resistance training, and by 109% at 24 hrs following
training. This study further examined the time course for elevated muscle protein synthesis
by examining its rate at
36
hrs following a training session. Six healthy young men
performed 12 sets of
6-
to 12-RM elbow flexion exercises with one arm while the opposite
arm served as a control. MPS was calculated from the in vivo rate of incorporation of
L-[l ,2-13C2] leucine into biceps brachii of both arms using the primed constant infusion
technique over 11 hrs. At an average time of
36
hrs postexercise, MPS in the exercised arm
had returned to within 14% of the control arm value, the diflerence being nonsigniJicant. It
is concluded that following a bout of heavy resistance training, MPS increases rapidly,
is more than double at 24 hrs, and thereafter declines rapidly so that at
36
hrs it has
almost returned to baseline.
On a dhja montrh que le taux de synthbe de prothine musculaire (SPM) est hlevh duns
l'homme de 50% a 4 h apris une seance d'entrainement et de 109% a 24 h apt-t?s
l'entrainement. La prhsente htude continue l'examen du c-ours temporel de la synthese
MacDougall, Gibala, Tarnopolsky, MacDonald, and Interisano: Department of
Kinesiology, McMaster University, Hamilton, Ontario L8S 4Kl; Yarasheski: Metabolism
Division, Washington University School of Medicine, St. Louis, MO 631 10, USA.
Can. J. Appl. Physiol. 1995.20:480-486.
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Protein Synthesis Following Exercise
48
1
klevke de protkine en examinant le faux
h
36 h aprts une skance d'entrainement. Six
jeunes hommes en bonne santt! ont effectut! un total de 12 skries de 6- 12-RM d'exercices
de flexion du coude avec un seul bras, l'autre agissant comme tkmoin. Nous avons calcuM
la SPM
a
partir de l'enrichissement du leucine L-[l ,2-'3C2] duns des biopsies du biceps
brachii prilevkes des deux bras en employant la technique d'infusion constant amorck
pendant 11 h.
A
36 h en moyen aprts I'entrainement, la SPM du bras travaillk s'ktait
rendue jusqu'a moins de 14% de la valeur du bras tkmoin, la divergence e'tant non
significative. On conclut que la SPM accroit rapidement aprts une skance d'entrainement
de rbistance lourde, qu'elle atteint sa valeur
rl
24 h, et qu'elle dkcroit rapidement
subskquemment, regagnant a peu prts sa valeur initiale
a
36 h.
Introduction
We have previously shown that the biceps brachii mixed muscle protein synthetic
rate (MPS) is elevated in experienced weight trainers by 50% approximately
4 hrs after training, and by 109% approximately 24 hrs after training (Chesley
et al., 1992; MacDougall et al., 1992). The present study further investigated the
time course for elevated protein synthesis by examining its rate at approximately
36 hrs following a training session.
Methods
As in our previous study (Chesley et al., 1992), MPS was measured in biceps
brachii following an acute bout of heavy resistance exercise by the elbow flexors
of one arm so that the opposite arm served as a control. Since the duration that
protein synthesis might remain elevated in the exercised arm was unknown, our
original plan was to examine MPS 36 hrs following training and then at subsequent
12-hr intervals until MPS returned to that of the control arm.
SUBJECTS AND DESIGN
Six healthy young men (23
f
1.7 yrs) who regularly engaged in heavy resistance
(bodybuilding) training served as subjects. They did not differ from our previous
subjects as to age, height, body weight, or training experience. They were advised
of the risks associated with the study, in accordance with the university's human
ethics committee, and provided written informed consent.
Subjects refrained from resistance exercise training for 3 days. At approxi-
mately 7 p.m. on the evening of the 4th day, they performed a typical training
session for the elbow flexors of one randomly chosen arm. As in our previous
study, the session was supervised by a coinvestigator and consisted of 4 sets of
single arm biceps, concentration and preacher curls at 80% of maximum
(
I
-RM)
so that a total of 12 sets was completed in all. Each set was undertaken to
muscular "failure" and a rest period of 3 to 4 min was provided between sets.
The young men were instructed to consume their normal breakfast and lunch the
following day and to report back to the laboratory at 5 p.m. to consume a standard
meal. The energy content of the meal was 1,200 Kcal and consisted of 70%
carbohydrate, 16% protein, and 14% fat. Two hours later a 20-Ga catheter was
inserted into a hand vein for blood sampling and a second catheter was positioned
in a contralateral forearm vein for isotope tracer infusion. Subjects read or watched
Can. J. Appl. Physiol. 1995.20:480-486.
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482 MacDougall, Gibala, Tarnopolsky, et al.
movies until their normal bedtime and slept in the laboratory overnight. The rate
of tracer incorporation into biceps brachii was measured in both arms between
8 p.m. that night and 7 a.m. the following morning so that the midpoint would
be
36
hrs after their previous training session.
MEASUREMENT PROCEDURES
The in vivo rate of MPS was determined from the enrichment of L-[1,2-"C2]
leucine in biopsy samples using an 1 1-hr primed constant intravenous infusion. A
priming dose of L-[l ,2-I3C2] leucine (>99% isotopic purity, Tracer Technologies,
Somerville, MA) was administered (7.58 pmol
.
kg-'), followed by a constant
infusion (7.58 pmol
.
kg-'
.
h-I) for 12.5 hrs using a Harvard syringe pump.
Arterialized blood samples (hot box at 65°C) were taken prior to infusion and
at 1.5, 10.5, 11.5, 12, and 12.5 hrs for determination of plasma [1,2-I3C2]
-
a-ketoisocaproic acid (a-KIC). Needle biopsies were taken from biceps brachii
of both arms 90 min following the priming dose and 11 hrs later.
Enrichment of plasma [l ,2-l3C2]
-
a-KIC (atom
%
excess) was determined
by electron impact ionization gas chromatography-mass spectrometry (Hewlett-
Packard 5980A-MSD), as has been previously described (Tarnopolsky et al.,
1991). Enrichment of muscle [I ,2-"C2] leucine (mole
%
excess) was determined
by capillary gas
chromatography/combustion
isotope-ratio mass spectroscopy as
described by Yarasheski et al. (1992). MPS was calculated for each sample
according to the method of Nair et al. (1988) using plasma [1,2-'"2]
-
a-KIC
as the precursor pool enrichment, as we have previously detailed (MacDougall
et al., 1992). Data are expressed as
%
.
hr-I, where the incorporation time is the
time between biopsies for each subject. Differences in MPS between control and
exercised arms and possible changes in plasma [l,2-13C2]
-
a-KIC during the
infusion procedure were assessed by analysis of variance.
Results
Enrichment for plasma [l,2-'3C2]
-
a-KIC at each sampling time is shown in
Table 1. Each sample was analyzed in duplicate and the intra-assay coefficient
of variation was 0.82%. Although there was a tendency for enrichments to decline
slightly toward the end of the infusion period, this was not statistically significant.
Plasma enrichments were remarkably consistent between the 1.5- and 10.5-hr
Table
1
Plasma
[1,2-13C2]
-
a-KIC
Enrichment (atom
%
excess)
Sampling time
1.5 hrs 10.5 hrs
1
1.5 hrs 12.0 hrs 12.5 hrs
Note.
N
=
6.
Differences are not statistically significant.
Can. J. Appl. Physiol. 1995.20:480-486.
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Protein Synthesis Following Exercise 483
points, which represented the major portion of the time (9 1
%)
over which MPS
was measured.
MPS for both control and exercised arms are illustrated in Figure 1. Dupli-
cate analysis for enrichment of muscle protein
[
1
,2-"C2] leucine were performed
on each sample and the intra-assay coefficient of variation was 2.66%. Although
MPS was approximately 14% higher in the exercised arm than in the control
arm, this difference was not statistically significant.
MPS in the control arms (0.0408 f0.0103% hr-2) was similar to the mean
value of 0.0538 (f0.0148% hr-I) which we found in the control arms in our
previous study (Chesley et al., 1992). The results of the present study have been
combined with our previous data to illustrate MPS at 4, 24, and 36 hrs following
exercise (Figure 2).
Discussion
Combined data from the subjects in the present study and from the two groups
in our previous study indicate that biceps brachii MPS is elevated by 50, 109,
and 14% at 4, 24, and 36 hrs, respectively, following a bout of heavy resistance
training (Figure 2). Although a single within-group design at the three time points
would have been preferable, we rejected it on ethical grounds because it would
have required a total of six biopsies from biceps of each
arm.
We are aware of
the limitations of a between-group design, and for this reason took care to match
our three groups according to age, body size, and training background; we had
them perform the identical exercises at the same volume and intensity.
CONTROL EXERCISED
ARM ARM
Figure
1.
Rate of muscle protein synthesis in biceps brachii for the control and exer-
cised arms 36 hrs after resistance training.
N
=
6, values are means
SE.
The differ-
ence between both arms was not statistically significant.
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484
MacDougall, Gibala, Tarnopolsky, et al.
HRS. POST EXERCISE
Figure
2.
Increase in muscle protein synthetic rate
4, 24,
and
36
hrs after a single re-
sistance training bout. Values indicate the difference between MPS in the exercised
and control arm. Data at
4
and
24
hrs are from a previous study (see text). "Significant
at
p
<
0.05.
The method for measuring MPS was modified somewhat from our previous
approach in that we infused doubly labeled (L-[l ,2-'VC,]) leucine and maintained
the constant infusion over 12.5 hrs instead of singly labeled (L-[I-'"]) leucine
over 6 hrs. Our finding in the present study, that MPS in the control
arm
was
similar to control arm values in the previous study, indicates that the two methods
yield similar results. Moreover, since it is the
diference
in MPS between the
exercised and nonexercised arms that indicates an elevated muscle protein synthe-
sis, possible methodological differences have been controlled for.
It should be recognized that the values reported for MPS at 4 and 24 hrs
represent the average values over the 4 hrs during which MPS was measured.
Similarly, the 36-hr value is the average value over 11 hrs (i.e., between 30.5
and 41.5 hrs after exercise). The assumption in presenting these data at a single
time point is that MPS is linear over the assessment period. This may not of
course be the case. We interpret our finding-that at 36 hrs, MPS in the exercised
arm was not significantly higher than in the control arm (in 4 subjects it was
higher but in 2 subjects it was not)-as indicating that, at this point, MPS was
already returning to its preexercise rate. The relatively large standard error at
this point probably reflects interindividual differences in the rate at which addi-
tional protein synthesis is completed after training. In addition, since MPS at
this point in time was not significantly elevated, we decided that further investiga-
tion at, say, 48 hrs was unnecessary.
Since the elevated MPS following heavy resistance exercise occurs in the
absence of an elevation in
RNA
concentration (Chesley et al., 1992), its up-
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Protein Synthesis Following Exercise 485
regulation appears to be the result of posttranscriptional events (Chesley et al.,
1992; Wong and Booth, 1990). The method we have used is a measure of mixed
muscle protein synthetic rate. The extent to which muscle hypertrophy occurs is
dependent upon
net
protein synthesis, that is, the difference between protein
synthesis and degradation. It is apparent that the observed increases in MPS are
accompanied by a concomitant increase in muscle protein degradation, or else
muscle size would increase to a much greater extent than is known to occur with
resistance training (MacDougall et al., 1980).
Degradation of muscle protein may to a large extent be due to the mechanical
damage that occurs to contractile protein during heavy resistance exercise. We
have recently documented disruption of muscle fine structure in biceps brachii
following exercise similar to that in the present study and have found that,
24 hrs after exercise, some degree of myofibrillar disruption could be detected
in as many as 80% of the fibres examined with electron microscopy (Gibala et
al., 1995).
Knowledge of the time course for elevated MPS following resistance exer-
cise is important to athletes and professionals in muscle rehabilitation who are
interested in optimum methods for increasing muscle size and strength. Empiri-
cally, one might hypothesize that the most effective training frequency would
be such that the subsequent training session should not occur until the protein
synthesis stimulated by the previous session has returned to its pretraining rate.
If this is true, the present data suggest an optimum recovery time of at least
36
to 48 hrs between training sessions; however, the time course for changes in
protein degradation is not known.
In summary, the data from the present and our previous study (Chesley et
al., 1992) indicate that when experienced subjects undertake a bout of heavy
resistance training, the protein synthetic rate in the exercised muscle increases
rapidly, is more than double approximately 24 hrs following exercise, and there-
after declines so that at
36
hrs it is almost back to baseline.
References
Chesley, A., MacDougall, J.D., Tarnopolsky, M.A., Atkinson, S.A., and Smith, K. (1992).
Changes in human muscle protein synthesis after resistance exercise.
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Gibala, M.J., MacDougall, J.D., Tarnopolsky, M.A., Stauber, W.T., and Eloriagga, A.
(1995). Changes in human skeletal muscle ultrastructure and force production after
acute resistance exercise.
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(
1980). Effects
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in muscle protein synthesis following heavy resistance exercise in humans: A pilot
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Schwarcz, H. (1991). Whole body leucine metabolism during and after resistance
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and Booth, F.W. (1990). Protein metabolism in rat tibialis anterior muscle
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Acknowledgment
This study was supported by the Natural Sciences and Engineering Research Council of
Canada and by a Mass Spectrometry Research Grant (NIH-RR 00954).
The authors acknowledge the technical assistance of Brian Roy and Barbara Wilhelm and
the secretarial assistance of Mary Cleland.
Received March
22,
1995; accepted in final form July 31, 1995.
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... Muscle hypertrophy is the result of accumulated short-term increases in myofibrillar protein synthesis (MyoPS) after muscle damage has decreased [43]. In a human study, muscle protein synthesis rate (MPS) increases 50% over baseline for 4 hours after heavy resistance training, and then, at 24 hours after the training session has finished, MPS is 109% greater than at baseline, but MPS drops off so rapidly that by 36 hours it's back to the 14% baseline rate [44]. On the other hand, Dreyer et al. [45] found MPS to be 50% for both men and women 2 hours after RT. ...
... Aged men showcase anabolic resistance of MPS to RE [44] To MPS was ↑ to a larger degree after bolus the following pulse initially (1-3h: 95% contrast to 42%) and later (3-5h: 193% contrast to 121%) ...
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This systematic review examines the synergistic and individual influences of resistance exercise, dietary protein supplementation, and sleep/recovery on muscle protein synthesis (MPS). Electronic databases such as Scopus, Google Scholar, and Web of Science were extensively used. Studies were selected based on relevance to the criteria and were ensured to be directly applicable to the objectives. Research indicates that a protein dose of 20 to 25 grams maximally stimulates MPS post-resistance training. It is observed that physically frail individuals aged 76 to 92 and middle-aged adults aged 62 to 74 have lower mixed muscle protein synthetic rates than individuals aged 20 to 32. High-whey protein and leucine-enriched supplements enhance MPS more efficiently than standard dairy products in older adults engaged in resistance programs. Similarly, protein intake before sleep boosts overnight MPS rates, which helps prevent muscle loss associated with sleep debt, exercise-induced damage, and muscle-wasting conditions like sarcopenia and cachexia. Resistance exercise is a functional intervention to achieve muscular adaptation and improve function. Future research should focus on variables such as fluctuating fitness levels, age groups, genetics, and lifestyle factors to generate more accurate and beneficial results.
... MPS is quantitatively assessed as an average over short (i.e., hourly) or long (i.e., days, weeks, and months) time durations [4][5][6][7][8][9][10][11], via the precursor-product method. Tis method involves the administration of naturally occurring stable isotopically labelled amino acids combined with sampling of biological fuids (e.g., plasma and/or saliva) and skeletal muscle tissue (via percutaneous biopsy), and mass spectrometry (MS), which are used to determine the rate at which the labelled amino acids are incorporated into skeletal muscle protein over a predefned period of time [2,3]. ...
... vastus lateralis). Although, to the authors' knowledge, no direct comparative assessment has ever been made between diferent muscle groups, the MPS response to exercise has been independently characterised in other muscles/muscle groups (e.g., soleus [93], biceps brachii [4,6,7], and deltoid [94]). Indeed, Trappe et al. [72] previously reported that the increase in MPS in the m. ...
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Methods Five electronic databases (PubMed (Medline), Web of Science, Embase, Sport Discus, and Cochrane Library) were searched for controlled trials that assessed the MPS response to RE in healthy, adult humans, postabsorptive state. Individual study and random-effects meta-analysis arewere used to inform the effects of RE and covariates on MPS. Results from 79 controlled trials with 237 participants were analysed. Results Analysis of the pooled effects revealed robust increases in MPS following RE (weighted mean difference (WMD): 0.032% h⁻¹, 95% CI: [0.024, 0.041] % h⁻¹, I² = 92%, k = 37, P < 0.001). However, the magnitude of the increase in MPS was lower in older adults (>50 y: WMD: 0.015% h⁻¹, 95% CI: [0.007, 0.022] % h⁻¹, I² = 76%, k = 12, P = 0.002) compared to younger adults (<35 y: WMD: 0.041% h⁻¹, 95% CI: [0.030, 0.052] % h⁻¹, I² = 88%, k = 25, P < 0.001). Individual studies have reported that the temporal proximity of the RE, muscle group, muscle protein fraction, RE training experience, and the loading parameters of the RE (i.e., intensity, workload, and effort) appeared to affect the MPS response to RE, whereas sex or type of muscle contraction does not. Conclusion A single bout of RE can sustain measurable increases in postabsorptive MPS soon after RE cessation and up to 48 h post-RE. However, there is substantial heterogeneity in the magnitude and time course of the MPS response between trials, which appears to be influenced by participants' age and/or the loading parameters of the RE itself.
... hours after an RT bout in untrained individuals (112) and may even return to baseline in trained individuals (113,114). When paired conceptually with the lack of a consistent, independent effect of frequency in the present meta-analysis, multiple potential explanations exist. ...
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Background: Weekly set volume and frequency are used to manipulate resistance training (RT) dosage. Previous research has identified higher weekly set volume as enhancing muscle hypertrophy and strength gains, but the nature of the dose-response relationship still needs to be investigated. Mixed evidence exists regarding the effects of higher weekly frequency. Objective: Before meta-analyzing the volume and frequency research, all contributing RT sets were classified as direct or indirect, depending on their specificity to the hypertrophy/strength measurement. Then, weekly set volume/frequency for indirect sets was quantified as 1 for 'total,' 0.5 for 'fractional,' and 0 for 'direct.' A series of multi-level meta-regressions were performed for muscle hypertrophy and strength, utilizing 67 total studies of 2,058 participants. All models were adjusted for the duration of the intervention and training status. Results: The relative evidence for the 'fractional' quantification method was strongest; therefore, this quantification method was used for the primary meta-regression models. The posterior probability of the marginal slope exceeding zero for the effect of volume on both hypertrophy and strength was 100%, indicating that gains in muscle size and strength increase as volume increases. However, both best fit models suggest diminishing returns, with the diminishing returns for strength being considerably more pronounced. The posterior probability of the marginal slope exceeding zero for frequency's effect on hypertrophy was less than 100%, indicating compatibility with negligible effects. In contrast, the posterior probability for strength was 100%, suggesting strength gains increase with increasing frequency, albeit with diminishing returns. Conclusions: Distinguishing between direct and indirect sets appears essential for predicting adaptations to a given RT protocol, such as using the 'fractional' quantification method. This method's dose-response models revealed that volume and frequency have unique dose-response relationships with each hypertrophy and strength gain. The dose-response relationship between volume and hypertrophy appears to differ from that with strength, with the latter exhibiting more pronounced diminishing returns. The dose-response relationship between frequency and hypertrophy appears to differ from that with strength, as only the latter exhibits consistently identifiable effects.
... We measured MPS and associated kinase phosphorylation 30 minutes after exposure to an insulin/leucine trigger, following a 16 h incorporation + 24 h washout period with EPA and DHA. While the timecourse of elevated MPS post anabolic trigger has been investigated in humans [39], our reliance on a single time point within our vitro model may have limited our potential to capture the optimal kinase signaling window in response to EPA and DHA. ...
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... In the exercised legs, muscle protein synthesis and mTORC1 signaling were not activated by the injection of PBS but by that of MSCs 72 h post-exercise. After a single bout of resistance exercise, muscle protein synthesis increases at 3 h and remains elevated for 48 h (MacDougall et al., 1995;Phillips et al., 1997). In the rodent exercise model used in the present study, the elevation of muscle protein synthesis is confirmed until 24 h after the exercise bout (Ogasawara et al., 2016). ...
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Skeletal muscle mass is critical for activities of daily living. Resistance training maintains or increases muscle mass, and various strategies maximize the training adaptation. Mesenchymal stem cells (MSCs) are multipotent cells with differential potency in skeletal muscle cells and the capacity to secrete growth factors. However, little is known regarding the effect of intramuscular injection of MSCs on basal muscle protein synthesis and catabolic systems after resistance training. Here, we measured changes in basal muscle protein synthesis, the ubiquitin‐proteasome system, and autophagy‐lysosome system‐related factors after bouts of resistance exercise by intramuscular injection of MSCs. Mice performed three bouts of resistance exercise (each consisting of 50 maximal isometric contractions elicited by electrical stimulation) on the right gastrocnemius muscle every 48 h, and immediately after the first bout, mice were intramuscularly injected with either MSCs (2.0 × 10 ⁶ cells) labeled with green fluorescence protein (GFP) or vehicle only placebo. Seventy‐two hours after the third exercise bout, GFP was detected only in the muscle injected with MSCs with concomitant elevation of muscle protein synthesis. The injection of MSCs also increased protein ubiquitination. These results suggest that the intramuscular injection of MSCs augmented muscle protein turnover at the basal state after consecutive resistance exercise.
... In this regard, the significant changes in body composition variables describing skeletal muscle mass, appendicular skeletal muscle mass and body cell mass should be viewed as strictly related to the observed changes in cellular water compartmentalization rather than as a result of muscle protein synthesis (MPS), which is not expected after only few days, although quite intensive, of physical activity. Sustained resistive exercise targeting muscles over several weeks is, in fact, needed to induce cumulative periods of positive net protein balance, which requires that the rate of MPS exceeds the rate of muscle protein breakdown (MacDougall et al. 1995;Phillips et al. 1997). Before MPS-related muscle growth takes place, muscles can appear larger following acute training due to sarcoplasmic hypertrophy. ...
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Purpose To evaluate the effects of wild trekking by examining, in postmenopausal women, the physiological adaptations to an intensive 5-day wild trek and comparing their responses to those displayed by a group of men of comparable age, training status and mountaineering skills. Methods Six healthy, active postmenopausal women in their sixth decade of life participated in the study. Six men of comparable age and training status were also enrolled for gender-based comparisons. The participants traversed the Selvaggio Blu wild trek (Sardinia, Italy) completing a total of 56 km, for an overall height differential of 14,301 m. During all 5-day trek, subjects were supervised by two alpine guides. Changes in body composition, cardiorespiratory fitness, and metabolic patterns of energy expenditure were evaluated before and after the intervention. Results Total energy expenditure during the trek was significantly higher (p = 0.03) in women (12.88 ± 3.37 kcal/h/kg) than men (9.27 ± 0.89 kcal/h/kg). Extracellular (ECW) and intracellular water (ICW) increased significantly following the trek only in women (ECW: − 3.8%; p = 0.01; ICW: + 3.4%; p = 0.01). The same applied to fat-free mass (+ 5.6%; p = 0.006), fat mass (− 20.4%; p = 0.006), skeletal muscle mass (+ 9.5%; p = 0.007), and appendicular muscle mass (+ 7.3%; p = 0.002). Peak VO2/kg (+ 9.4%; p = 0.05) and fat oxidation (at 80 W: + 26.96%; p = 0.04; at 100 W: + 40.95%; p = 0.02; at 120 W: + 83.02%; p = 0.01) were found increased only in women, although no concurrent changes in partial pressure of end-tidal CO2 (PETCO2) was observed. Conclusions In postmenopausal women, a 5-day, intensive and physically/technically demanding outdoor trekking activity led to significant and potentially relevant changes in body composition, energy balance and metabolism that are generally attained following quite longer periods of training.
... Changes in mRNA during and following exercise are transient, and research in model systems has shown that the relationship between changes in mRNA and protein is timedependent (see Figure 3A; [44]). The timing of muscle/tissue sampling is, therefore, a critical methodological issue that directly impacts the magnitude of the observed exercise-induced changes in mRNA [51,53,[65][66][67][68][69][70][71] and likely contributes to the observed discordance between exercise-induced changes in mRNA and training-induced changes in proteins and phenotype [5,48,49,54]. Further research is required to establish a comprehensive time course for changes in mRNA in response to exercise; this time course should also be investigated in different populations (e.g., men, women, young, elderly, physically active, and sedentary) and following different exercise modalities, intensities, frequencies, and durations [62]. ...
... The range of protein requirement in both resistance training [28,30] and endurance athletes [18,31] may be attributed to the measurement conditions related to physical activity, such as no exercise for 48 h [30], after 8 h of exercise [18,28], and after 24 h of exercise [31]. These results have been obtained only in resistance-trained athletes; nonetheless, a single exercise session increases muscle protein synthesis 24 to 48 h later, thereby increasing sensitivity to dietary protein intake [50][51][52]. Therefore, the protein requirements for athletes and persons with high physical activity should be set using the IAAO method after considering various situations including physical activity level, during exercise, and elapsed time after exercising. ...
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