Skeletal muscle IL-15/IL-15Rα and myofibrillar protein synthesis after resistance exercise.
01 Jan 2018-Scandinavian Journal of Medicine & Science in Sports (Scand J Med Sci Sports)-Vol. 28, Iss: 1, pp 116-125
TL;DR: In conclusion, IL‐15/IL‐15Rα signaling pathway is activated in skeletal muscle in response to a session of resistance exercise.
Abstract: In vitro and in vivo studies described the myokine IL-15 and its receptor IL-15Rα as anabolic/anti-atrophy agents, however, the protein expression of IL-15Rα has not been measured in human skeletal muscle and data regarding IL-15 expression remain inconclusive. The purpose of the study was to determine serum and skeletal muscle IL-15 and IL-15Rα responses to resistance exercise session and to analyze their association with myofibrillar protein synthesis (MPS). Fourteen participants performed a bilateral leg resistance exercise composed of four sets of leg press and four sets of knee extension at 75% 1RM to task failure. Muscle biopsies were obtained at rest, 0, 4 and 24 hours post-exercise and blood samples at rest, mid-exercise, 0, 0.3, 1, 2, 4 and 24 hours post-exercise. Serum IL-15 was increased by ~5.3-fold immediately post-exercise, while serum IL-15Rα decreased ~75% over 1 hour post-exercise (P<.001). Skeletal muscle IL-15Rα mRNA and protein expression were increased at 4 hours post-exercise by ~2-fold (P<.001) and ~1.3-fold above rest (P=.020), respectively. At 24 hours post-exercise, IL-15 (P=.003) and IL-15Rα mRNAs increased by ~2-fold (P=.002). Myofibrillar fractional synthetic rate between 0-4 hours was associated with IL-15Rα mRNA at rest (r=.662, P=.019), 4 hours (r=.612, P=.029), and 24 hours post-exercise (r=.627, P=.029). Finally, the muscle IL-15Rα protein up-regulation was related to Leg press 1RM (r=.688, P=.003) and total weight lifted (r=.628, P=.009). In conclusion, IL-15/IL-15Rα signaling pathway is activated in skeletal muscle in response to a session of resistance exercise.
Summary (2 min read)
Jump to: [Take down policy] – [Experimental protocol 123] – [Serum IL-15 and IL-15Rα 154] – [Both antibodies were diluted into BSA-blocking buffer containing 4% bovine serum albumin in 175] – [RNA Isolation and quantitative real-time reverse transcription polymerase chain reaction 187 (qRT-PCR). 188] and [Skeletal muscle IL-15/IL-15Rα expression and myofibrillar protein synthesis. 306]
Take down policy
- IL-15Rα has not been determined in human skeletal muscle.
- Therefore, despite the 67 fact that in vitro studies indicate a role for skeletal muscle IL-15 in anabolism, studies in 68 humans are inconclusive.
- Of 119 the 16 participants included in the original study, 14 were analysed in the present investigation 120 due to insufficient muscle tissue in the two subjects excluded.
Experimental protocol 123
- A detailed description of the experimental protocol and analytical methods can be found 124 elsewhere (McKendry et al., 2016) .
- Thereafter, one-repetition maximum (1RM) strength during leg press and 127 knee extension was assessed (Cybex VR-3, MA, USA).
- The following morning at 7.00 h, participants returned to the 142 laboratory after a 10-12h overnight fast and a cannula was inserted into a forearm vein to obtain 143 a blood sample followed by the fourth and last biopsy, which was obtained from the vastus 144 lateralis of the contralateral leg.
- The participants received three standardised meals for consumption the evening prior to 147 the experimental trial, as well as the afternoon and evening after the experimental trial.
Serum IL-15 and IL-15Rα 154
- After collection, all blood samples were centrifuged for 15 minutes at 1000 g, aliquoted and 155 stored at -80 ºC.
- Two high-sensitivity enzyme-linked immunosorbent assay kits were 156 used to determine the serum concentration of IL-15 and IL-15Rα in duplicates.
Both antibodies were diluted into BSA-blocking buffer containing 4% bovine serum albumin in 175
- Antibody specific labelling was revealed by 176 incubation with an HRP-conjugated goat anti-rabbit (IL-15) or anti-mouse (IL-15Rα) antibodies 177 (1:5000), both diluted in 5% blotto blocking buffer and visualised with ECL Western blotting 178 detection system using a ChemiDoc XRS (Bio-Rad, Copenhagen, Denmark).
- Imaging and band 179 quantification were performed using the Quantity One 1-D Analysis software (Bio-Rad, 180 Copenhagen, Denmark).
- Test samples were run together with a control sample from a subject 181 who did not take part in the study.
- The control sample was loaded in three different lanes and 182 used as an internal control for inter-gel variability.
RNA Isolation and quantitative real-time reverse transcription polymerase chain reaction 187 (qRT-PCR). 188
- Approximately 15-20 mg of skeletal muscle tissue was used for the RNA isolation.
- The RNA 189 was extracted by guanine-phenol-chloroform isothiocyanate procedures using TRIzol 190 (AUC) was determined using trapezoid method and compared between groups using a paired 242 Student's t-test.
- Since no significant differences were observed between the 1-and 5-min 243 recovery, both groups were combined for further analyses.
- To determine time effects of the intervention on serum, protein and mRNA levels of IL-245 15 and IL-15Rα, ANOVA for repeated measures was performed.
- Tukey HSD correction was 246 used as post-hoc test when significant differences were detected.
Skeletal muscle IL-15/IL-15Rα expression and myofibrillar protein synthesis. 306
- This lack of 328 differences could be interpreted as evidence to refute the association between skeletal muscle 329 IL-15/IL-15Rα and MPS.
- Nevertheless, the effect sizes and statistical outputs (P<0.10) indicate 330 that a potential difference between groups may actually exist.
- In agreement, the authors have observed a positive association between serum concentration of 395 IL-15 and IL-15 protein levels in skeletal muscle, suggesting that muscle may be an important 396 source of IL-15 in the basal state.
- In the present study, the authors observed that basal IL-15 protein 397 levels in skeletal muscle were associated with serum concentration immediately post-exercise, 398 also suggesting that the size of the intramuscular pool could determine the magnitude of the 399 increase in serum IL-15 elicited by resistance exercise.
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University of Birmingham
Skeletal muscle IL-15/IL-15R and myofibrillar protein
synthesis after resistance exercise
Pérez López, Alberto; McKendry, James; Martin-Rincon, Marcos ; Morales-Alamo, David;
Pérez-Köhler, Bárbara ; Valadés, David; Buján, Julia ; Calbet, Jose; Breen, Leigh
DOI:
10.1111/sms.12901
License:
None: All rights reserved
Document Version
Peer reviewed version
Citation for published version (Harvard):
Pérez López, A, McKendry, J, Martin-Rincon, M, Morales-Alamo, D, Pérez-Köhler, B, Valadés, D, Buján, J,
Calbet, J & Breen, L 2017, 'Skeletal muscle IL-15/IL-15R and myofibrillar protein synthesis after resistance
exercise', Scandinavian Journal of Medicine and Science in Sports. https://doi.org/10.1111/sms.12901
Link to publication on Research at Birmingham portal
Publisher Rights Statement:
Checked for eligibility: 27/04/2017
"This is the peer reviewed version of the following article: Pérez-López A, McKendry J, Martin-Rincon M, et al. Skeletal muscle IL-15/IL-15R
and myofibrillar protein synthesis after resistance exercise. Scand J Med Sci Sports. 2017, which has been published in final form at
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PROOF
Skeletal muscle IL
-
15
/IL
-
15Rα and myofibrillar protein
synthesis after resistance exercise
Journal:
Scandinavian Journal of Medicine and Science in Sports
Manuscript ID
SJMSS-O-694-16.R2
Manuscript Type:
Original Article
Date Submitted by the Author:
27-Mar-2017
Complete List of Authors:
Pérez-López, Alberto; University of Alcalá, Medicine and Medical
Specialties. Faculty of Medicine and Health Sciences. Biomedical Research
Networking Centre on Bioengineering, Biomaterials and Nanomedicine
(CIBER-BBN); University of Alcalá, Biomedical Sciences. Faculty of
Medicine and Health Sciences; University of Birmingham, School of Sport,
Exercise and Rehabilitation Sciences; University of Las Palmas de Gran
Canaria, Department of Physical Education. Faculty of Physical Education
McKendry, James; University of Birmingham, School of Sport, Exercise and
Rehabilitation Sciences; University of Birmingham, MRC-ARUK Centre for
Musculoskeletal Ageing Research
Martin-Rincon, Marcos; University of Las Palmas de Gran Canaria,
Department of Physical Education. Faculty of Physical Education; University
of Las Palmas de Gran Canaria, Research Institute of Biomedical and
Health Sciences (IUIBS)
Morales-Alamo, David; University of Las Palmas de Gran Canaria,
Department of Physical Education. Faculty of Physical Education; University
of Las Palmas de Gran Canaria, Research Institute of Biomedical and
Health Sciences (IUIBS)
Pérez-Köhler, Bárbara; University of Alcalá, Department of Medicine and
Medical Specialities. Faculty of Medicine and Health Sciences. Biomedical
Research Networking Centre on Bioengineering, Biomaterials and
Nanomedicine (CIBER-BBN)
Valadés, David; University of Alcalá, Department of Biomedical Sciences.
Faculty of Medicine and Health Sciences.
Buján, Julia; University of Alcalá, Department of Medicine and Medical
Specialities. Faculty of Medicine and Health Sciences. Biomedical Research
Networking Centre on Bioengineering, Biomaterials and Nanomedicine
(CIBER-BBN)
Calbet, Jose; University of Las Palmas de Gran Canaria, Department of
Physical Education. Faculty of Physical Education; University of Las Palmas
de Gran Canaria, Research Institute of Biomedical and Health Sciences
(IUIBS)
Breen, Leigh; University of Birmingham, School of Sport, Exercise and
Rehabilitation Sciences; University of Birmingham, MRC-ARUK Centre for
Musculoskeletal Ageing Research
Keywords:
Myokines, IL-15/IL-15Rα axis, strength training, muscle protein
synthesis/breakdown
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PROOF
1
Skeletal muscle IL-15/IL-15Rα and myofibrillar protein synthesis after resistance 1
exercise 2
3
Alberto Pérez-López
1,2,3,4
, James McKendry
3,5
, Marcos Martin-Rincon
4,6
, David Morales-4
Alamo
4,6
, Bárbara Pérez-Köhler
1
, David Valadés
2
, Julia Buján
1
, Jose A. L. Calbet
4,6
and 5
Leigh Breen
3,5
.6
7
1
Department of Medicine and Medical Specialities. Faculty of Medicine and Health Sciences. 8
University of Alcalá, Madrid, Spain. Biomedical Research Networking Centre on 9
Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), Madrid, Spain. 10
2
Department of Biomedical Sciences. Faculty of Medicine and Health Sciences. University of 11
Alcalá, Madrid, Spain. 12
3
School of Sport, Exercise and Rehabilitation Sciences. University of Birmingham, 13
Birmingham, UK. 14
4
Department of Physical Education. Faculty of Physical Education. University of Las Palmas 15
de Gran Canaria, Las Palmas de Gran Canaria, Spain. 16
5
MRC-ARUK Centre for Musculoskeletal Ageing Research. University of Birmingham, 17
Birmingham, UK. 18
6
Research Institute of Biomedical and Health Sciences (IUIBS). Las Palmas de Gran Canaria, 19
Spain. 20
21
Address for correspondence: 22
Alberto Pérez-López 23
Department of Medicine and Medical Specialties. 24
Faculty of Medicine and Health Sciences, University of Alcalá. 25
Ctra. Madrid-Barcelona km 33,600 26
28871 Alcalá de Henares, Madrid (Spain) 27
E-mail: Alberto_perez-lopez@hotmail.com
28
Phone: (+34) 636 710 130 29
30
Running head: IL-15/IL-15Rα in Resistance Exercise
31
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ABSTRACT 32
In vitro and in vivo studies described the myokine IL-15 and its receptor IL-15Rα as 33
anabolic/anti-atrophy agents, however the protein expression of IL-15Rα has not been measured 34
in human skeletal muscle and data regarding IL-15 expression remain inconclusive. The 35
purpose of the study was to determine serum and skeletal muscle IL-15 and IL-15Rα responses 36
to resistance exercise session and to analyse their association with myofibrillar protein synthesis 37
(MPS). Fourteen participants performed a bilateral leg resistance exercise composed of 4 sets of 38
leg press and 4 sets of knee extension at 75% 1RM to task failure. Muscle biopsies were 39
obtained at rest, 0, 4 and 24h post-exercise and blood samples at rest, mid-exercise, 0, 0.3, 1, 2, 40
4 and 24h post-exercise. Serum IL-15 was increased by ~5.3-fold immediately post-exercise, 41
while serum IL-15Rα decreased ~75% over 1h post-exercise (P<0.001). Skeletal muscle IL-42
15Rα mRNA and protein expression were increased at 4h post-exercise by ~2-fold (P<0.001) 43
and ~1.3-fold above rest (P=0.020), respectively. At 24h post-exercise IL-15 (P=0.003) and IL-44
15Rα mRNAs increased by ~2-fold (P=0.002). Myofibrillar fractional synthetic rate between 0-45
4h was associated with IL-15Rα mRNA at rest (r=0.662, P=0.019), 4h (r=0.612, P=0.029) and 46
24h post-exercise (r=0.627, P=0.029). Finally, the muscle IL-15Rα protein up-regulation was 47
related to Leg press 1RM (r=0.688, P=0.003) and total weight lifted (r=0.628, P=0.009). In 48
conclusion, IL-15/IL-15Rα signalling pathway is activated in skeletal muscle in response to a 49
session of resistance exercise. 50
Keywords: Myokines, IL-15/IL-15Rα axis, strength training, muscle protein 51
synthesis/breakdown. 52
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Citations
More filters
••
TL;DR: Pre‐clinical and clinical studies investigating whether physical exercise would improve muscle performance and whether this improvement would translate in a clinically meaningful benefit for patients with cancer, in terms of survival and quality of life are summarized.
Abstract: Cachexia is a syndrome characterized by involuntary weight loss and wasting of skeletal muscle mass. It is associated with worse overall survival and quality of life. The cancer‐induced systemic inflammation and the consequent host derived catabolic stimuli, trigger cachexia by inhibiting muscle protein synthesis and enhancing muscle catabolism. The muscle itself may further promote chronic inflammation, introducing a vicious catabolic circle. Nutritional support alone plays a limited role in the treatment of cancer cachexia and should be combined with other interventions. Physical exercise lowers systemic inflammation and promotes muscle anabolism. It also attenuates the age‐related physical decline in elderly and it might counteract the muscle wasting induced by the cancer cachexia syndrome. This review describes how cancer‐induced systemic inflammation promotes muscle wasting and whether physical exercise may represent a suitable treatment for cancer‐induced cachexia, particularly in patients with non‐small cell lung cancer. We summarized pre‐clinical and clinical studies investigating whether physical exercise would improve muscle performance and whether this improvement would translate in a clinically meaningful benefit for patients with cancer, in terms of survival and quality of life. Moreover, this review describes the results of studies investigating the interplay between physical exercise and the immune system, including the role of the intestinal microbiota.
10 citations
••
TL;DR: During intense muscle contraction, a reduced PO2 and glycolytic rate, and possibly, an attenuated RONS generation may facilitate IL-15 production, accompanied by STAT3 activation, in a process that does not require AMPK phosphorylation.
Abstract: Interleukin (IL)-15 stimulates mitochondrial biogenesis, fat oxidation, glucose uptake and myogenesis in skeletal muscle. However, the mechanisms by which exercise triggers IL-15 expression remain to be elucidated in humans. This study aimed at determining whether high-intensity exercise and exercise-induced RONS stimulate IL-15/IL-15Rα expression and its signaling pathway (STAT3) in human skeletal muscle. Nine volunteers performed a 30-s Wingate test in normoxia and hypoxia (PIO2=75 mmHg), 2 h after placebo or antioxidant administration (α-lipoic acid, vitamin C and E) in a randomized double-blind design. Blood samples and muscle biopsies (vastus lateralis) were obtained before, immediately after, and 30 and 120 min post-exercise. Sprint exercise upregulated skeletal muscle IL-15 protein expression (ANOVA, P=0.05), an effect accentuated by antioxidant administration in hypoxia (ANOVA, P=0.022). In antioxidant conditions, the increased IL-15 expression at 120 min post-exercise (33%; P=0.017) was associated with the oxygen deficit caused by the sprint (r=–0.54; P=0.020); while, IL-15 and Tyr705-STAT3 AUCs were also related (r=0.50; P=0.036). Antioxidant administration promotes IL-15 protein expression in human skeletal muscle after sprint exercise, particularly in severe acute hypoxia. Therefore, during intense muscle contraction, a reduced PO2 and glycolytic rate, and possibly, an attenuated RONS generation may facilitate IL-15 production, accompanied by STAT3 activation, in a process that does not require AMPK phosphorylation.
9 citations
••
TL;DR: Researchers found that muscle tissues during the contraction are the predominant source of interleukin-6, and muscle damage is not required in order to increase plasma IL-6 during exercise.
Abstract: Cytokines are key modulators of inflammation, participating in acute and chronic inflammation via a complex and sometimes contradictory network of interactions.1 The cytokines and other peptides that are produced, expressed and released by muscle fibers, and exert autocrine, paracrine or endocrine effects, are classified as myokines. Skeletal muscle contains resident immune cell populations and their abundance and type are altered in inflammatory myopathies, endotoxemia or other different types of muscle injury.2 The interleukins (ILs) correspond to class of cytokines released by numerous body tissues to control and coordinate immune responses. There are several isoforms and the most known is interleukin-6 (IL-6), an early-stage myokine that might play important role in exercise-induced muscular growth. IL-6 was first cloned and characterized in the mid-1980s by several independent groups, by assessing immunoglobulin production and acute-phase protein responses in different cell lines.3 IL-6 is a pleiotropic cytokine associated with the control and coordination of immune responses, inflammation, hematopoiesis, and oncogenesis, which regulates cell growth, survival, and differentiation.4 Skeletal muscle cells are a further important source of IL-6 and this cytokine is detected locally at elevated concentrations in actively contracting muscle fibers and after increased workload. Exercise is known to cause major physiological, hormonal, metabolic, and immunological effects. The resistance training acutely upregulates IL-6 by up to 100fold, and the peak of IL-6 level is reached at the end of the exercise or shortly after, about 30 minutes after the exercise, followed by a rapid decrease towards pre-exercise levels.5 Exercise-induced metabolic stress may further stimulate its production.6,7 However, there is a low interaction between muscle damage and increased levels of IL-6, and studies found a low correlation in the time course of IL-6 and creatine kinase.8,9 Therefore, researchers found that muscle tissues during the contraction are the predominant source of IL-6.5 Thus, muscle damage is not required in order to increase plasma IL-6 during exercise.
9 citations
••
TL;DR: The view that pre‐exercise carbohydrate availability does not have a major impact on acute responses of circulating plasma cytokines in humans is supported.
Abstract: Carbohydrate availability is proposed as a potential regulator of cytokine responses. We aimed to evaluate the effect of a preresistance exercise carbohydrate meal versus fat meal on plasma cytokine responses to resistance exercise after an endurance exercise earlier that day. Thirteen young, healthy, recreationally active males performed two experimental days with endurance exercise in the morning and resistance exercise in the afternoon. Either a carbohydrate (110 g carbohydrate, 52 g protein, 9 g fat; ~750 kcal) or an isocaloric fat meal (20 gr carbohydrate, 52 g protein, 51 g fat) was provided 2 h before resistance exercise. Blood was taken at baseline and at regular time intervals to measure circulating plasma cytokine levels (e.g. IL-6, IL-8, IL-10, IL-15, TNFα, ANGPTL4, decorin and MCP-1). Plasma glucose and insulin were higher in the postprandial period before the start of the resistance exercise on the carbohydrate condition, while free fatty acids were reduced. At 2 h postresistance exercise, IL-6 concentrations were higher in the fat condition compared to the carbohydrate condition (P 0.05). There were no differences between conditions on TNFα levels and levels remain constant when compared with baseline (P > 0.05). ANGPTL4, IL-15, Decorin and MCP-1 showed no differences between the fat and carbohydrate condition (P > 0.05). The composition of the pre-exercise meal did in general not influence cytokine responses in the postresistance exercise period, except postresistance exercise circulating plasma IL-6 levels being higher in the fat condition compared with carbohydrate. Our findings support the view that pre-exercise carbohydrate availability does not have a major impact on acute responses of circulating plasma cytokines in humans.
9 citations
Cites background from "Skeletal muscle IL-15/IL-15Rα and m..."
...We were especially interested in circulating IL-6, IL-8, IL-15, decorin and MCP-1, since elevations of these cytokines may contribute or reflect adaptations of skeletal muscle (Catoire and Kersten 2015; Perez-Lopez et al. 2017)....
[...]
••
TL;DR: Results support the claim that resistance training combined with cold exposure modified muscle strength through modulation of myostatin and IL-15 concentrations and induced a positive and likely significant improvement of isokinetic muscle strength.
Abstract: The study aimed to determine whether combining cryostimulation with resistance training would effectively increase muscle strength, and if so, whether this adaptation would be related to changes in circulating levels of exerkines (i.e., mediators of systemic adaptation to exercise). Twenty-five students completed 12 sessions of resistance training, each followed by either cryostimulation (n = 15, 3 min exposure at -110 °C) or passive recovery (n = 10). Prior to and post this intervention, participants performed two eccentric cycling bouts (before and after training). At these points, serum concentrations of muscle damage marker (myoglobin), exerkines (interleukin 6 (IL-6), interleukin 15 (IL-15), irisin, brain-derived neurotrophic factor), hypertrophy-related factors (myostatin, insulin-like growth factor 1), and muscle strength were measured. The applied procedure reduced the physiological burden of the second eccentric cycling bout and myoglobin concentrations only in the group subject to cryostimulation. The same group also exhibited decreased levels of myostatin (from 4.7 ± 1.7 to 3.8 ± 1.8 ng·mL-1, p < 0.05). A significant and large interaction between the group × time was noted in IL-15 concentration (p = 0.01, ηp2=0.27). Training and cryostimulation induced a positive and likely significant improvement of isokinetic muscle strength. Altogether, obtained results support the claim that resistance training combined with cold exposure modified muscle strength through modulation of myostatin and IL-15 concentrations.
8 citations
Cites background from "Skeletal muscle IL-15/IL-15Rα and m..."
...They also observed that the activation of this signaling pathway supported myofibrillar protein synthesis [52]....
[...]
References
More filters
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TL;DR: A cytokine was identified that stimulated the proliferation of T lymphocytes, and a complementary DNA clone encoding this new T cell growth factor was isolated, indicating that IL-15 uses components of the IL-2 receptor.
Abstract: A cytokine was identified that stimulated the proliferation of T lymphocytes, and a complementary DNA clone encoding this new T cell growth factor was isolated. The cytokine, designated interleukin-15 (IL-15), is produced by a wide variety of cells and tissues and shares many biological properties with IL-2. Monoclonal antibodies to the beta chain of the IL-2 receptor inhibited the biological activity of IL-15, and IL-15 competed for binding with IL-2, indicating that IL-15 uses components of the IL-2 receptor.
1,441 citations
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TL;DR: It is concluded that exercise resulted in an increase in muscle net protein balance that persisted for up to 48 h after the exercise bout and was unrelated to the type of muscle contraction performed.
Abstract: Mixed muscle protein fractional synthesis rate (FSR) and fractional breakdown rate (FBR) were examined after an isolated bout of either concentric or eccentric resistance exercise. Subjects were eight untrained volunteers (4 males, 4 females). Mixed muscle protein FSR and FBR were determined using primed constant infusions of [2H5]phenylalanine and 15N-phenylalanine, respectively. Subjects were studied in the fasted state on four occasions: at rest and 3, 24, and 48 h after a resistance exercise bout. Exercise was eight sets of eight concentric or eccentric repetitions at 80% of each subject's concentric 1 repetition maximum. There was no significant difference between contraction types for either FSR, FBR, or net balance (FSR minus FBR). Exercise resulted in significant increases above rest in muscle FSR at all times: 3 h = 112%, 24 h = 65%, 48 h = 34% (P < 0.01). Muscle FBR was also increased by exercise at 3 h (31%; P < 0.05) and 24 h (18%; P < 0.05) postexercise but returned to resting levels by 48 h. Muscle net balance was significantly increased after exercise at all time points [(in %/h) rest = -0.0573 +/- 0.003 (SE), 3 h = -0.0298 +/- 0.003, 24 h = -0.0413 +/- 0.004, and 48 h = -0.0440 +/- 0.005], and was significantly different from zero at all time points (P < 0.05). There was also a significant correlation between FSR and FBR (r = 0.88, P < 0.001). We conclude that exercise resulted in an increase in muscle net protein balance that persisted for up to 48 h after the exercise bout and was unrelated to the type of muscle contraction performed.
1,095 citations
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TL;DR: Low and intermediate RM training appears to induce similar muscular adaptations, at least after short-term training in previously untrained subjects, and both physical performance and the associated physiological adaptations are linked to the intensity and number of repetitions performed, and thus lend support to the strength–endurance continuum.
Abstract: Thirty-two untrained men [mean (SD) age 22.5 (5.8) years, height 178.3 (7.2) cm, body mass 77.8 (11.9) kg] participated in an 8-week progressive resistance-training program to investigate the "strength–endurance continuum". Subjects were divided into four groups: a low repetition group (Low Rep, n=9) performing 3–5 repetitions maximum (RM) for four sets of each exercise with 3 min rest between sets and exercises, an intermediate repetition group (Int Rep, n=11) performing 9–11 RM for three sets with 2 min rest, a high repetition group (High Rep, n=7) performing 20–28 RM for two sets with 1 min rest, and a non-exercising control group (Con, n=5). Three exercises (leg press, squat, and knee extension) were performed 2 days/week for the first 4 weeks and 3 days/week for the final 4 weeks. Maximal strength [one repetition maximum, 1RM), local muscular endurance (maximal number of repetitions performed with 60% of 1RM), and various cardiorespiratory parameters (e.g., maximum oxygen consumption, pulmonary ventilation, maximal aerobic power, time to exhaustion) were assessed at the beginning and end of the study. In addition, pre- and post-training muscle biopsy samples were analyzed for fiber-type composition, cross-sectional area, myosin heavy chain (MHC) content, and capillarization. Maximal strength improved significantly more for the Low Rep group compared to the other training groups, and the maximal number of repetitions at 60% 1RM improved the most for the High Rep group. In addition, maximal aerobic power and time to exhaustion significantly increased at the end of the study for only the High Rep group. All three major fiber types (types I, IIA, and IIB) hypertrophied for the Low Rep and Int Rep groups, whereas no significant increases were demonstrated for either the High Rep or Con groups. However, the percentage of type IIB fibers decreased, with a concomitant increase in IIAB fibers for all three resistance-trained groups. These fiber-type conversions were supported by a significant decrease in MHCIIb accompanied by a significant increase in MHCIIa. No significant changes in fiber-type composition were found in the control samples. Although all three training regimens resulted in similar fiber-type transformations (IIB to IIA), the low to intermediate repetition resistance-training programs induced a greater hypertrophic effect compared to the high repetition regimen. The High Rep group, however, appeared better adapted for submaximal, prolonged contractions, with significant increases after training in aerobic power and time to exhaustion. Thus, low and intermediate RM training appears to induce similar muscular adaptations, at least after short-term training in previously untrained subjects. Overall, however, these data demonstrate that both physical performance and the associated physiological adaptations are linked to the intensity and number of repetitions performed, and thus lend support to the "strength–endurance continuum".
1,008 citations
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TL;DR: In this article, a percutaneous needle biopsy of skeletal muscle in Physiological and Clinical Research is described, and the authors present a detailed discussion of the procedure and the results.
Abstract: (1975). Percutaneous Needle Biopsy of Skeletal Muscle in Physiological and Clinical Research. Scandinavian Journal of Clinical and Laboratory Investigation: Vol. 35, No. 7, pp. 609-616.
944 citations
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TL;DR: These complexes on activated monocytes present IL-15 in trans to target cells such as CD8 + T cells that express only IL-2/15Rβ and γc upon cell-cell interaction and contribute to the long survival of T cells expressing IL- 15Rα afterIL-15 withdrawal.
874 citations