Expression of titin-linked putative mechanosensing proteins in skeletal muscle after power resistance exercise in resistance-trained men

2020 ◽  
Author(s):  
Stefan G. Wette ◽  
Nigel P. Birch ◽  
Matthias Soop ◽  
Martina Zügel ◽  
Robyn M. Murphy ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Creatine Kinase ◽  
Resistance Exercise ◽  
Vastus Lateralis ◽  
Cytoskeletal Proteins ◽  
Muscle Sample ◽  
Post Exercise ◽  
Protein Levels ◽  
Ankyrin Repeat Proteins ◽  
Muscle Remodeling

Little is known about the molecular responses to power resistance exercise that lead to skeletal muscle remodeling and enhanced athletic performance. We assessed the expression of titin-linked putative mechanosensing proteins implicated in muscle remodeling: muscle ankyrin repeat proteins (Ankrd1, Ankrd2 and Ankrd23), muscle-LIM proteins (MLP), muscle RING-finger protein-1 (MuRF-1), and associated myogenic proteins (MyoD1, myogenin, and myostatin) in skeletal muscle in response to power resistance exercise with or without a post-exercise meal, in fed, resistance-trained men. A muscle sample was obtained from the vastus lateralis of seven healthy men on separate days, 3h after 90 min of rest (Rest) or power resistance exercise with (Ex+Meal) or without (Ex) a post-exercise meal, to quantify mRNA and protein levels. The levels of phosphorylated HSP27 (pHSP27-Ser15) and cytoskeletal proteins in muscle and creatine kinase activity in serum were also assessed. The exercise increased (P≤0.05) pHSP27-Ser15 (~6-fold) and creatine kinase (~50%), whereas cytoskeletal protein levels were unchanged (P>0.05). Ankrd1 (~15-fold) and MLP (~2-fold) mRNA increased, whereas Ankrd2, Ankrd23, MuRF-1, MyoD1, and myostatin mRNA were unchanged. Ankrd1 (~3-fold, Ex) and MLPb (~20-fold, Ex+Meal) protein increased, but MLPa, Ankrd2, Ankrd23, and the myogenic proteins were unchanged. The post-exercise meal did not affect the responses observed. Power resistance exercise, as performed in practice, induced subtle early responses in the expression of MLP and Ankrd1, yet had little effect on the other proteins investigated. These findings suggest possible roles for MLP and Ankrd1 in the remodeling of skeletal muscle in individuals who regularly perform this type of exercise.

The influence of acute resistance exercise on cyclooxygenase-1 and -2 activity and protein levels in human skeletal muscle

2013 ◽  
Vol 305 (1) ◽  
pp. R24-R30 ◽  
Author(s):  
Chad C. Carroll ◽  
Devin T. O'Connor ◽  
Robert Steinmeyer ◽  
Jonathon D. Del Mundo ◽  
David R. McMullan ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Resistance Exercise ◽  
Total Protein ◽  
Human Skeletal Muscle ◽  
Vastus Lateralis ◽  
Knee Extensor ◽  
Protein Levels ◽  
Cyclooxygenase 1 ◽  
Cox 2 ◽  
Cox 1

This study evaluated the activity and content of cyclooxygenase (COX)-1 and -2 in response to acute resistance exercise (RE) in human skeletal muscle. Previous work suggests that COX-1, but not COX-2, is the primary COX isoform elevated with resistance exercise in human skeletal muscle. COX activity, however, has not been assessed after resistance exercise in humans. It was hypothesized that RE would increase COX-1 but not COX-2 activity. Muscle biopsies were taken from the vastus lateralis of nine young men (25 ± 1 yr) at baseline (preexercise), 4, and 24 h after a single bout of knee extensor RE (three sets of 10 repetitions at 70% of maximum). Tissue lysate was assayed for COX-1 and COX-2 activity. COX-1 and COX-2 protein levels were measured via Western blot analysis. COX-1 activity increased at 4 h ( P < 0.05) compared with preexercise, but returned to baseline at 24 h (PRE: 60 ± 10, 4 h: 106 ± 22, 24 h: 72 ± 8 nmol PGH2·g total protein−1·min−1). COX-2 activity was elevated at 4 and 24 h after RE ( P < 0.05, PRE: 51 ± 7, 4 h: 100 ± 19, 24 h: 98 ± 14 nmol PGH2·g total protein−1·min−1). The protein level of COX-1 was not altered ( P > 0.05) with acute RE. In contrast, COX-2 protein levels were nearly 3-fold greater ( P > 0.05) at 4 h and 5-fold greater ( P = 0.06) at 24 h, compared with preexercise. In conclusion, COX-1 activity increases transiently with exercise independent of COX-1 protein levels. In contrast, both COX-2 activity and protein levels were elevated with exercise, and this elevation persisted to at least 24 h after RE.

scholarly journals The Effects of a Protease Enzyme Blend on Post-Resistance Exercise Intramuscular Anabolic Signaling

2020 ◽  
Vol 4 (Supplement_2) ◽  
pp. 1767-1767
Author(s):  
Jeremy Townsend ◽  
Jaclyn Morimune ◽  
Megan Jones ◽  
Laurel Littlefield ◽  
Stephen Heffington ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Resistance Exercise ◽  
Whey Protein ◽  
Repeated Measures ◽  
Vastus Lateralis ◽  
Mapk Signaling ◽  
Controlled Study ◽  
Post Exercise ◽  
Protease Enzyme ◽  
Main Effect

Abstract Objectives Protease supplementation has been reported to decrease inflammation and indices of muscle damage while increasing functional recovery following strenuous resistance exercise compared to a placebo. While various mechanisms have been proposed, the effects of protease supplementation on the resistance exercise induced anabolic signaling response has not been reported in the literature. To examine the effects of a protease enzyme blend added to whey protein on post-resistance exercise intramuscular anabolic signaling. Methods Ten resistance-trained males (24.4 ± 4.1yrs, 1.79 ± 0.86 m, 92.6 ± 10.4 kg) were enrolled in this double-blind, cross-over, placebo controlled study and engaged in three separate bouts of resistance exercise. Each participant completed 4 sets of leg presses and leg extensions for 8–10 repetitions at 75% of their 1-repetition maximum with 90 seconds of rest between each set. Immediately following the resistance exercise protocol, participants consumed either 250 mg of a protease enzyme blend + 26 g of whey protein (PW), 26 g whey alone (W), or non-caloric control (CON) in a counterbalanced fashion. Skeletal muscle microbiopsies were obtained from the vastus lateralis pre-exercise (PRE), 1-hour (1H), and 3-hours (3H) post-exercise. Multiplex signaling assay kits were used to quantify the phosphorylation status of proteins specific to the mTOR (AKT, mTOR, p70S6K) and MAPK (ERK1/2, JNK, p38) signaling pathways using the MAGPIX® (Luminex, Austin, TX, USA). A 2-way repeated measures analysis of variance (ANOVA) was used to identify differences between treatments over time. Results A main effect for time (p &lt; 0.05) revealed phosphorylation of AKT was decreased at 1H (p &lt; 0.001), mTOR was increased at 1H (P = 0.025) and 3H (P = 0.009) post-exercise, while p70S6K remained unchanged (P &gt; 0.05) from PRE. A main effect for time (p &lt; 0.05) was found with increased phosphorylation at 1H for JNK (P = 0.001), and decreased phosphorylation at 3H for ERK 1/2 (P = 0.022) with respect to baseline. Additionally, there were no differences in any mTOR nor MAPK signaling proteins observed between treatments. Conclusions These data suggest that acute protease supplementation may not alter mTOR or MAPK signaling in skeletal muscle following acute resistance exercise. Funding Sources Deerland Enzymes, Kennesaw, GA.

scholarly journals High Carbohydrate Diet Increased Glucose Transporter Protein Levels in Jejunum but Did Not Lead to Enhanced Post-Exercise Skeletal Muscle Glycogen Recovery

Nutrients ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 2140
Author(s):  
Yumiko Takahashi ◽  
Yutaka Matsunaga ◽  
Hiroki Yoshida ◽  
Terunaga Shinya ◽  
Ryo Sakaguchi ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Glucose Transporter ◽  
High Carbohydrate Diet ◽  
Oral Glucose ◽  
Carbohydrate Diet ◽  
Post Exercise ◽  
Glucose Administration ◽  
Protein Levels ◽  
High Carbohydrate ◽  
Glucose Transporter 2

We examined the effect of dietary carbohydrate intake on post-exercise glycogen recovery. Male Institute of Cancer Research (ICR) mice were fed moderate-carbohydrate chow (MCHO, 50%cal from carbohydrate) or high-carbohydrate chow (HCHO, 70%cal from carbohydrate) for 10 days. They then ran on a treadmill at 25 m/min for 60 min and administered an oral glucose solution (1.5 mg/g body weight). Compared to the MCHO group, the HCHO group showed significantly higher sodium-D-glucose co-transporter 1 protein levels in the brush border membrane fraction (p = 0.003) and the glucose transporter 2 level in the mucosa of jejunum (p = 0.004). At 30 min after the post-exercise glucose administration, the skeletal muscle and liver glycogen levels were not significantly different between the two diet groups. The blood glucose concentration from the portal vein (which is the entry site of nutrients from the gastrointestinal tract) was not significantly different between the groups at 15 min after the post-exercise glucose administration. There was no difference in the total or phosphorylated states of proteins related to glucose uptake and glycogen synthesis in skeletal muscle. Although the high-carbohydrate diet significantly increased glucose transporters in the jejunum, this adaptation stimulated neither glycogen recovery nor glucose absorption after the ingestion of post-exercise glucose.

A single bout of exercise activates matrix metalloproteinase in human skeletal muscle

2007 ◽  
Vol 102 (6) ◽  
pp. 2346-2351 ◽  
Author(s):  
E. Rullman ◽  
H. Rundqvist ◽  
D. Wågsäter ◽  
H. Fischer ◽  
P. Eriksson ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Matrix Metalloproteinase ◽  
Vastus Lateralis ◽  
Tissue Expression ◽  
Tissue Inhibitor Of Metalloproteinase ◽  
Vastus Lateralis Muscle ◽  
Protein Levels ◽  
Single Bout ◽  
Exercise Induced ◽  
Muscle Biopsies

The aims of this study were 1) to characterize changes in matrix metalloproteinase (MMP), endostatin, and vascular endothelial growth factor (VEGF)-A expression in skeletal muscle in response to a single bout of exercise in humans; and 2) to determine if any exchange of endostatin and VEGF-A between circulation and the exercising leg is associated with a change in the tissue expression or plasma concentration of these factors. Ten healthy males performed 65 min of cycle exercise, and muscle biopsies were obtained from the vastus lateralis muscle at rest and immediately and 120 min after exercise. In the muscle biopsies, measurements of mRNA expression levels of MMP-2, MMP-9, MMP-14, and tissue inhibitor of metalloproteinase; VEGF and endostatin protein levels; and MMP activities were performed. Femoral arterial and venous concentrations of VEGF-A and endostatin were determined before, during, and 120 min after exercise. A single bout of exercise increased MMP-9 mRNA and activated MMP-9 protein in skeletal muscle. No measurable increase of endostatin was observed in the skeletal muscle or in plasma following exercise. A concurrent increase in skeletal muscle VEGF-A mRNA and protein levels was induced by exercise, with no signs of peripheral uptake from the circulation. However, a decrease in plasma VEGF-A concentration occurred following exercise. Thus 1) a single bout of exercise activated the MMP system without any resulting change in tissue endostatin protein levels, and 2) the increased VEGF-A protein levels are due to changes in the skeletal muscle tissue itself. Other mechanisms are responsible for the observed exercise-induced decrease in VEGF-A in plasma.

Alterations in Skeletal Muscle Repair in Young Adults with Type 1 Diabetes Mellitus

2021 ◽  
Author(s):  
Athan G. Dial ◽  
Grace K. Grafham ◽  
Cynthia MF. Monaco ◽  
Jennifer Voth ◽  
Linda Brandt ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Skeletal Muscle ◽  
Type 1 Diabetes ◽  
Young Adults ◽  
Gene Networks ◽  
Vastus Lateralis ◽  
Post Exercise ◽  
Ultrastructural Damage ◽  
The Impact

Though preclinical models of type 1 diabetes (T1D) exhibit impaired muscle regeneration, this has yet to be investigated in humans with T1D. Here we investigated the impact of damaging exercise (eccentric quadriceps contractions) in eighteen physically-active young adults with and without T1D. Pre- and post-exercise (48h and 96h), participants provided blood samples, vastus lateralis biopsies and performed maximal voluntary quadriceps contractions (MVC). Skeletal muscle sarcolemmal integrity, extracellular matrix content (ECM), and satellite cell (SC) content/proliferation were assessed by immunofluorescence. Transmission electron microscopy was used to quantify ultrastructural damage. MVC was comparable between T1D and controls before exercise. Post-exercise, MVC was decreased in both groups, but T1D subjects exhibited moderately lower strength recovery at both 48h and 96h. Serum creatine kinase, an indicator of muscle damage, was moderately higher in T1D participants at rest, and exhibited a small elevation 96h post-exercise. T1D participants showed lower SC content at all timepoints and demonstrated a moderate delay in SC proliferation after exercise. A greater number of myofibers exhibited sarcolemmal damage (disrupted dystrophin) and increased ECM (laminin) content in participants with T1D despite no differences between groups in ultrastructural damage as assessed by electron microscopy. Finally, transcriptomic analyses revealed dysregulated gene networks involving RNA translation and mitochondrial respiration, providing potential explanations for previous observations of mitochondrial dysfunction in similar T1D cohorts. Our findings indicate that skeletal muscle in young adults with moderately-controlled T1D is altered after damaging exercise; suggesting that longer recovery times following intense exercise may be necessary.

scholarly journals Antioxidants Facilitate High–intensity Exercise IL–15 Expression in Skeletal Muscle

2018 ◽  
Vol 40 (01) ◽  
pp. 16-22 ◽  
Author(s):  
Alberto Pérez-López ◽  
Marcos Martin-Rincon ◽  
Alfredo Santana ◽  
Ismael Perez-Suarez ◽  
Cecilia Dorado ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Expression ◽  
High Intensity ◽  
Human Skeletal Muscle ◽  
Vastus Lateralis ◽  
Acute Hypoxia ◽  
High Intensity Exercise ◽  
Oxygen Deficit ◽  
Post Exercise ◽  
Sprint Exercise

AbstractInterleukin (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.

scholarly journals Mammalian Tribbles homolog 3 impairs insulin action in skeletal muscle: role in glucose-induced insulin resistance

2010 ◽  
Vol 298 (3) ◽  
pp. E565-E576 ◽  
Author(s):  
Jiarong Liu ◽  
Xuxia Wu ◽  
John L. Franklin ◽  
Joseph L. Messina ◽  
Helliner S. Hill ◽  
...  
Keyword(s):  
Insulin Resistance ◽  
Skeletal Muscle ◽  
Glucose Transporter ◽  
Vastus Lateralis ◽  
Glucose Deprivation ◽  
Muscle Cells ◽  
Diabetic Rats ◽  
Glucose Disposal ◽  
Insulin Resistant ◽  
Protein Levels

Tribbles homolog 3 (TRIB3) was found to inhibit insulin-stimulated Akt phosphorylation and modulate gluconeogenesis in rodent liver. Currently, we examined a role for TRIB3 in skeletal muscle insulin resistance. Ten insulin-sensitive, ten insulin-resistant, and ten untreated type 2 diabetic (T2DM) patients were metabolically characterized by hyperinsulinemic euglycemic glucose clamps, and biopsies of vastus lateralis were obtained. Skeletal muscle samples were also collected from rodent models including streptozotocin (STZ)-induced diabetic rats, db/db mice, and Zucker fatty rats. Finally, L6 muscle cells were used to examine regulation of TRIB3 by glucose, and stable cell lines hyperexpressing TRIB3 were generated to identify mechanisms underlying TRIB3-induced insulin resistance. We found that 1) skeletal muscle TRIB3 protein levels are significantly elevated in T2DM patients; 2) muscle TRIB3 protein content is inversely correlated with glucose disposal rates and positively correlated with fasting glucose; 3) skeletal muscle TRIB3 protein levels are increased in STZ-diabetic rats, db/db mice, and Zucker fatty rats; 4) stable TRIB3 hyperexpression in muscle cells blocks insulin-stimulated glucose transport and glucose transporter 4 (GLUT4) translocation and impairs phosphorylation of Akt, ERK, and insulin receptor substrate-1 in insulin signal transduction; and 5) TRIB3 mRNA and protein levels are increased by high glucose concentrations, as well as by glucose deprivation in muscle cells. These data identify TRIB3 induction as a novel molecular mechanism in human insulin resistance and diabetes. TRIB3 acts as a nutrient sensor and could mediate the component of insulin resistance attributable to hyperglycemia (i.e., glucose toxicity) in diabetes.

Effect of Capsinoids Supplementation on Fat Oxidation and Muscle Glycogen Restoration During Post-exercise Recovery in Humans

2020 ◽  
Vol 26 ◽  
Author(s):  
Su-Fen Liao ◽  
Mallikarjuna Korivi ◽  
Jung-Piao Taso ◽  
Chun-Ching Huang ◽  
Chia-Chen Chang ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Young Adults ◽  
Muscle Glycogen ◽  
Vastus Lateralis ◽  
Recovery Period ◽  
Fat Oxidation ◽  
Exercise Recovery ◽  
Post Exercise ◽  
Glycogen Resynthesis ◽  
Post Exercise Recovery

Background: Capsinoids (CSN), the novel non-pungent capsaicin analogs have been reported to promote metabolic health and exercise tolerance. However, the effect of CSN on fat oxidation and changes in skeletal muscle glycogen levels during post-exercise recovery has not been investigated in humans. Purpose: We examined the effect of CSN supplementation on energy reliance, glycogen resynthesis and molecular proteins in the skeletal muscle of young adults during post-exercise recovery. Methods: In this crossover-designed study, nine healthy adult male volunteers (aged 21.4±0.2 years, BMI 21.9±1.3 kg/m2 ) completed a 60-min cycling exercise at 70% VO2max. Participants consumed either CSN (12 mg, single dosage) or placebo capsules with a high-carbohydrate meal (2 g carb/kg bodyweight) immediately after exercise. Biopsied muscle samples (vastus lateralis), blood and gaseous samples were obtained during 3h post-exercise recovery period. Results: We found that oral CSN supplementation right after exercise significantly altered the energy reliance on fat oxidation during recovery. This was evidenced by lower respiratory exchange ratio (RER) and higher fat oxidation rate in CSN trial. Despite, acute CSN dosage does not contribute to enhance the glycogen replenishment in skeletal muscle during 3h recovery. We identified no significant differences in postprandial glucose and insulin area under the curve in both trials. Western blot data showed increased muscle GLUT4 expression, but no significant response of p-Akt/Akt ratio with CSN during post-exercise recovery. Conclusion: Our findings conclude that acute CSN intake could change energy reliance on fat oxidation, but unable to enhance muscle glycogen resynthesis during post-exercise recovery. Thus, ergogenic properties of CSN in relevance to muscle glycogen restoration following exercise needs to be further investigated in young adults.

Influence of muscle glycogen availability on ERK1/2 and Akt signaling after resistance exercise in human skeletal muscle

2005 ◽  
Vol 99 (3) ◽  
pp. 950-956 ◽  
Author(s):  
Andrew Creer ◽  
Philip Gallagher ◽  
Dustin Slivka ◽  
Bozena Jemiolo ◽  
William Fink ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Resistance Exercise ◽  
Muscle Glycogen ◽  
Human Skeletal Muscle ◽  
Glycogen Content ◽  
Vastus Lateralis ◽  
Akt Signaling ◽  
Cellular Growth ◽  
Muscle Glycogen Content ◽  
Ribosomal S6 Kinase

Two pathways that have been implicated for cellular growth and development in response to muscle contraction are the extracellular signal-regulated kinase (ERK1/2) and Akt signaling pathways. Although these pathways are readily stimulated after exercise, little is known about how nutritional status may affect stimulation of these pathways in response to resistance exercise in human skeletal muscle. To investigate this, experienced cyclists performed 30 repetitions of knee extension exercise at 70% of one repetition maximum after a low (2%) or high (77%) carbohydrate (LCHO or HCHO) diet, which resulted in low or high (∼174 or ∼591 mmol/kg dry wt) preexercise muscle glycogen content. Muscle biopsies were taken from the vastus lateralis before, ∼20 s after, and 10 min after exercise. ERK1/2 and p90 ribosomal S6 kinase phosphorylation increased ( P ≤ 0.05) 10 min after exercise, regardless of muscle glycogen availability. Akt phosphorylation was elevated ( P < 0.05) 10 min after exercise in the HCHO trial but was unaffected after exercise in the LCHO trial. Mammalian target of rapamycin phosphorylation was similar to that of Akt during each trial; however, change or lack of change was not significant. In conclusion, the ERK1/2 pathway appears to be unaffected by muscle glycogen content. However, muscle glycogen availability appears to contribute to regulation of the Akt pathway, which may influence cellular growth and adaptation in response to resistance exercise in a low-glycogen state.

scholarly journals Acute and chronic resistance training downregulates select LINE-1 retrotransposon activity markers in human skeletal muscle

2018 ◽  
Vol 314 (3) ◽  
pp. C379-C388 ◽  
Author(s):  
Matthew A. Romero ◽  
C. Brooks Mobley ◽  
Petey W. Mumford ◽  
Paul A. Roberson ◽  
Cody T. Haun ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Resistance Training ◽  
Resistance Exercise ◽  
Satellite Cell ◽  
Vastus Lateralis ◽  
Future Research ◽  
Resistance Training Program ◽  
Myoblast Proliferation ◽  
Retrotransposon Activity

Herein, we examined if acute or chronic resistance exercise affected markers of skeletal muscle long interspersed nuclear element-1 (LINE-1) retrotransposon activity. In study 1, 10 resistance-trained college-aged men performed three consecutive daily back squat sessions, and vastus lateralis biopsies were taken before (Pre), 2 h following session 1 (Post1), and 3 days following session 3 (Post2). In study 2, 13 untrained college-aged men performed a full-body resistance training program (3 days/wk), and vastus lateralis biopsies were taken before ( week 0) and ~72 h following training cessation ( week 12). In study 1, LINE-1 mRNA decreased 42–48% at Post1 and 2 ( P < 0.05), and reverse transcriptase (RT) activity trended downward at Post2 (−37%, P = 0.067). In study 2, LINE-1 mRNA trended downward at week 12 (−17%, P = 0.056) while LINE-1 promoter methylation increased (+142%, P = 0.041). Open reading frame (ORF)2p protein expression (−24%, P = 0.059) and RT activity (−26%, P = 0.063) also trended downward by week 12. Additionally, changes in RT activity versus satellite cell number were inversely associated ( r = −0.725, P = 0.008). Follow-up in vitro experiments demonstrated that 48-h treatments with lower doses (1 μM and 10 μM) of efavirenz and nevirapine (non-nucleoside RT inhibitors) increased myoblast proliferation ( P < 0.05). However, we observed a paradoxical decrease in myoblast proliferation with higher doses (50 μM) of efavirenz and delavirdine. This is the first report suggesting that resistance exercise downregulates markers of skeletal muscle LINE-1 activity. Given our discordant in vitro findings, future research is needed to thoroughly assess whether LINE-1-mediated RT activity enhances or blunts myoblast, or primary satellite cell, proliferative capacity.

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