Muscle Damage, Stanley Salmons (Ed.), (ISBN 0-19-262753-8, Oxford University Press, 198 Madison Ave., New York, NY 10016), 243 pp., $65.00. The 11 chapters in this book were written by experts in the field who offer different perspectives on causes and consequences of muscle damage. The book draws together research on muscle damage that has been published across a variety of disciplines. Dr. Salmons developed this book from a special issue of the journal Basic and Applied Myology (Vol. 4, 1994) that he had organized. With permission and encouragement from the journal editor, Dr. Salmons revised, updated, and refurbished the material in the original publication. Additional chapters were commissioned, and the articles were re-edited for stylistic consistency. Among topics included are muscle damage elicited from exercise or simulated-exercise models, damage due to myopathies, damage from sport injury, rehabilitation of injured muscle, and clinical aspects of muscle damage. An abundance of information is presented on the possible cellular and molecular mechanisms to explain the damage and regeneration process, and several new theories are proposed. Many chapters describe the authors' current research which sometimes can be viewed as “works in progress” because the authors offer novel and often untested explanations for their findings. This insight is of critical importance in furthering research in the field. Perhaps one shortcoming is the absence of a chapter that integrates the variety of mechanisms offered to explain the damage process. There is also little information on exercise-induced muscle damage in humans, although the chapters that do cover this have done a fine job. Also, a chapter integrating the research on humans with information on myopathies and sport related strain injures would have been a useful addition. However, integrating the material may be a welcome and instructive challenge for the reader, especially the diligent student or young investigator. There is probably no aspect of muscle damage overlooked in this book. Drug-induced muscle damage, pharmacological treatments as well as other treatments of muscle pain, damage at the muscle tendon junction, free radical damage, various techniques to assess damage at the cellular and molecular level, and satellite cell involvement in regeneration are covered briefly. Of particular note is the chapter entitled “Damage in Functional Graphs of Skeletal Muscle”; which presents a new and exciting technology for therapeutic application. The information here will be most useful for those who are studying or have an interest in muscle damage, muscle soreness, muscle strain injuries, and clinical applications of the damage/regeneration process. The book is likely to be used primarily as a reference for academics but could also serve as a supplemental text for courses in muscle physiology or as a reference for clinicians for understanding management of damaged or injured muscle. Overall, this book makes a significant contribution to our understanding of muscle damage and provides a wealth of timely and relevant information. Reviewed by: Priscilla M. Clarkson, Department of Exercise Science, University of Massachusetts; Amherst, MA

Resistance exercise can stimulate new bone formation and result in changes to circulating markers of bone metabolism, but the relationship between the bone metabolic response to resistance exercise and bone morphological phenotypes is unknown. This study compared circulating bone biomarker responses to acute ballistic resistance exercise between groups characterized by bone phenotypes. Fuzzy c-means clustering (n = 287, 47% women) of tibial HR-pQCT parameters and micro finite element analysis (both 4% and 30% sites) determined bone phenotypes. Biomarkers of bone formation (PINP, ALP), resorption (βCTx, TRAP5b), mechanical sensing (sclerostin), and systemic anabolism (IGF-I) were assessed by ELISA before and after an acute ballistic lower body resistance exercise test (AET). DXA assessed body composition. Linear mixed-effects modeling analyzed biomarker responses between clusters, controlling for sex, age, and total lean mass with participants as random intercepts. Clustering revealed two phenotypes (C1 n = 150, 78% women; C2 n = 137, 14% women, p < 0.001), with C2 having wider, denser, and stronger bones with more trabeculae. C2 had higher lean mass (mean difference = 9.1 kg, p < 0.001) than C1. Interaction effects showed IGF-I increased in C2 (p = 0.019) versus no change in C1 (p = 0.999), and TRAP5b decreased to a greater extent in C2 (p < 0.001) compared to C1 (p = 0.029) post-AET. Time effects showed ALP (p = 0.001) and βCTx (p < 0.001) decreased while sclerostin increased (p < 0.001) post-AET overall. Individuals with wider, denser bones exhibit post-exercise biomarker responses potentially conducive to osteogenic adaptation, although the effects on bone structure remain unclear. Unsupervised machine learning derived bone phenotypes provides a novel approach to investigate bone health.

Resistance exercise augments circulating extracellular vesicle (EV) and metabolite signalling in manners that assist musculoskeletal and systemic adaptations. Women are often underrepresented in exercise research and recent attention has focused on whether hormonal fluctuations during the menstrual cycle and use of hormonal contraception (HC) impact exercise performance and adaptation. We investigated if menstrual phase (follicular and luteal) or HC usage (oral contraceptive pill and hormonal intrauterine device) impact the EV and metabolite response to exercise. Overall, we observed an exercise-induced response across all four groups for EV microRNAs and circulating metabolites. Women in the follicular phase had baseline differences in the most abundant miRNAs and exercise-relevant miRNAs and had the greatest miRNA response to exercise compared to other groups. Relevant metabolites were observed in EVs, but the overall response to exercise was minimally influenced by group among annotated metabolites. Multi-omic analysis showed potential presence of molecular signatures based on circulating hormone concentrations, but trends were not differentiated enough to suggest clear phenotypic differences. Overall, our data highlights unique miRNA profiles at baseline in follicular phase women but does not support the notion that circulating EV and metabolite responses to exercise are heavily influenced by menstrual cycle phase or HC use.Trial Registration: ClinicalTrials.gov identifier: NCT06972862

We investigated effects of three aerobic exercise interventions, varying in amount and intensity with durations of 8-9-months on small RNA (smRNA) expression and regulatory pathways in skeletal muscle and plasma from 120 participants. Using untargeted smRNA sequencing focused on miRNAs and piRNAs, adjusting for demographics and bodyweight, we identified 124 muscle smRNAs altered by exercise amount and 15 by intensity, and 47 plasma smRNAs altered by intensity and one by amount. These smRNAs were enriched in metabolic, transcriptional, translational, and cell cycle pathways. Exercise-induced changes in several smRNAs-six from muscle and five from plasma-and exercise-induced reduction in body weight, aligned with improvement in insulin sensitivity (p<0.05). These findings demonstrate tissue-specific regulation of smRNAs by exercise and identify potential candidates for exercise mimetics to modulate muscle insulin sensitivity.

Understanding how exercise improves whole-body insulin sensitivity (Si) involves complex molecular signaling. This study examines skeletal muscle gene expression changes related to Si, considering sex differences, exercise amount, and intensity to identify pharmacologic targets mimicking exercise benefits. Fifty-three participants from STRRIDE (Studies of Targeted Risk Reduction Interventions through Defined Exercise) I and II completed eight months of aerobic training. Gene expression was assessed via Affymetrix and Illumina technologies, and Si was measured using intravenous glucose tolerance tests. A novel discovery protocol integrating literature-derived and data-driven modeling identified causal pathways and direct transcriptional targets. In women, exercise amount primarily influenced transcription factor targets, which were generally inhibitory, while in men, exercise intensity drove activating targets. Common transcription factors included ATF1, CEBPA, BACH2, and STAT1. Si-related transcriptional targets included TACR3 and TMC7 for intensity-driven effects, and GRIN3B and EIF3B for amount-driven effects. Two key pathways mediating Si improvements were identified: estrogen signaling and protein kinase C (PKC) signaling, both converging on the epidermal growth factor receptor (EGFR) and other relevant targets. The molecular pathways underlying Si improvements varied by sex and exercise parameters, highlighting potential skeletal muscle-specific drug targets such as EGFR to replicate the metabolic benefits of exercise.

Purpose: This study defines correlative and causal relationships between muscle strength and size before and after unilateral resistance training (RT) in a large cohort of healthy adults, focusing on sex differences within these relationships. Methods: Results from 1233 participants (504 males and 729 females) in a retrospective analysis were included. Maximal voluntary isometric contraction strength (MVC), one-repetition maximum strength (1RM), biceps cross-sectional area (CSA) and elbow flexor volume (VOL) measures of the non-dominant and dominant arm were evaluated from baseline and after 12-wk RT twice per week. Correlations of MVC and VOL and 1RM and VOL were calculated in the whole cohort and within each sex independently. Causal analysis modeling was used to infer mechanistic relationships among variables. Results: Absolute muscle strength and size related to one another both at baseline and following training, however correlation strength in each sex were weak. After RT, MVC relative change and VOL relative change correlations were correlated for the whole cohort (r=0.16; p<0.001) and females (r=0.18; p<0.001), but not in males (r=0.11; p=0.07). No significant correlations for relative change in 1RM and VOL were observed for the whole cohort or within sex. Causal discovery determined that change in VOL caused significant change in 1RM (but not MVC) and age was identified as a potential cause. Conclusions: Sex differences occur in muscle size and strength relationship adaptations following resistance training, most notably the absence of significant relationships between relative size and strength changes in men. Simpson's paradox bias, where assessing the combined data of males and females (also affecting overall sample size) affects identifies patterns differently than assessing relationships within each sex, may partially explain our findings.

BACKGROUND:Understanding the causal pathways, systems, and mechanisms through which exercise impacts human health is complex. This study explores molecular signaling related to whole-body insulin sensitivity (Si) by examining changes in skeletal muscle gene expression. The analysis considers differences by biological sex, exercise amount, and exercise intensity to identify potential molecular targets for developing pharmacologic agents that replicate the health benefits of exercise. METHODS:The study involved 53 participants from the STRRIDE I and II trials who completed eight months of aerobic training. Skeletal muscle gene expression was measured using Affymetrix and Illumina technologies, while pre- and post-training Si was assessed via an intravenous glucose tolerance test. A novel gene discovery protocol, integrating three literature-derived and data-driven modeling strategies, was employed to identify causal pathways and direct causal factors based on differentially expressed transcripts associated with exercise intensity and amount. RESULTS:In women, the transcription factor targets identified were primarily influenced by exercise amount and were generally inhibitory. In contrast, in men, these targets were driven by exercise intensity and were generally activating. Transcription factors such as ATF1, CEBPA, BACH2, and STAT1 were commonly activating in both sexes. Specific transcriptional targets related to exercise-induced Si improvements included TACR3 and TMC7 for intensity-driven effects, and GRIN3B and EIF3B for amount-driven effects. Two key signaling pathways mediating aerobic exercise-induced Si improvements were identified: one centered on estrogen signaling and the other on phorbol ester (PKC) signaling, both converging on the epidermal growth factor receptor (EGFR) and other relevant targets. CONCLUSIONS:The signaling pathways mediating Si improvements from aerobic exercise differed by sex and were further distinguished by exercise intensity and amount. Transcriptional adaptations in skeletal muscle related to Si improvements appear to be causally linked to estrogen and PKC signaling, with EGFR and other identified targets emerging as potential skeletal muscle-specific drug targets to mimic the beneficial effects of exercise on Si.

BACKGROUND:Resistance training confers numerous health benefits that are mediated in part by circulating factors. Toward an enhanced molecular understanding, there is growing interest in a class of signaling biomarkers called extracellular vesicles (EV). EVs support physiological adaptations to exercise by transporting their cargo (e.g., microRNA (miRNA)) to target cells. Previous studies of changes in EV cargo have focused on aerobic exercise, with limited data examining the effects of resistance exercise. We examined the effect of acute resistance exercise on circulating EV miRNAs and their predicted target pathways. METHODS:Ten participants (5 men; age, 26.9 ± 5.5 yr; height, 173.4 ± 10.5 cm; body mass, 74.0 ± 11.1 kg; body fat, 25.7% ± 11.6%) completed an acute heavy resistance exercise test (AHRET) consisting of six sets of 10 repetitions of back squats using 75% one-repetition maximum. Pre-/post-AHRET, EVs were isolated from plasma using size exclusion chromatography, and RNA sequencing was performed. Differentially expressed miRNAs between pre- and post-AHRET EVs were analyzed using Ingenuity Pathway Analysis to predict target messenger RNAs and their target biological pathways. RESULTS:Overall, 34 miRNAs were altered by AHRET ( P < 0.05), targeting 4895 mRNAs, with enrichment of 175 canonical pathways ( P < 0.01), including 12 related to growth/metabolism (p53, IGF-I, STAT3, PPAR, JAK/STAT, growth hormone, WNT/β-catenin, ERK/MAPK, AMPK, mTOR, and PI3K/AKT) and 8 to inflammation signaling (TGF-β, IL-8, IL-7, IL-3, IL-6, IL-2, IL-17, IL-10). CONCLUSIONS:Acute resistance exercise alters EV miRNAs targeting pathways involved in growth, metabolism, and immune function. Circulating EVs may serve as significant adaptive signaling molecules influenced by exercise training.

BACKGROUND:Despite the benefits of exercise, many individuals are unable or unwilling to adopt an exercise intervention. PURPOSE:The purpose of this analysis was to identify putative genetic variants associated with dropout from exercise training interventions among individuals in the STRRIDE trials. METHODS:We used a genome-wide association study approach to identify genetic variants in 603 participants initiating a supervised exercise intervention. Exercise intervention dropout occurred when a subject withdrew from further participation in the study or was otherwise lost to follow-up. RESULTS:Exercise intervention dropout was associated with a cluster of single-nucleotide polymorphisms with the top candidate being rs722069 (T/C, risk allele = C) (unadjusted p = 2.2 × 10-7, odds ratio = 2.23) contained within a linkage disequilibrium block on chromosome 16. In Genotype-Tissue Expression, rs722069 is an expression quantitative trait locus of the EARS2, COG7, and DCTN5 genes in skeletal muscle tissue. In subsets of the STRRIDE genetic cohort with available muscle gene expression (n = 37) and metabolic data (n = 82), at baseline the C allele was associated with lesser muscle expression of EARS2 (p < .002) and COG7 (p = .074) as well as lesser muscle concentrations of C2- and C3-acylcarnitines (p = .026). CONCLUSIONS:Our observations imply that exercise intervention dropout is genetically moderated through alterations in gene expression and metabolic pathways in skeletal muscle. Individual genetic traits may allow the development of a biomarker-based approach for identifying individuals who may benefit from more intensive counseling and other interventions to optimize exercise intervention adoption. CLINICAL TRIAL INFORMATION:STRRIDE I = NCT00200993; STRRIDE AT/RT = NCT00275145; STRRIDE-PD = NCT00962962.

ABSTRACT Purpose Unaccustomed eccentric (ECC) exercise evokes exercise-induced muscle damage (EIMD). Soreness, strength loss, and serum creatine kinase (CK) are often used to quantify EIMD severity. However, changes in these markers are not fully understood mechanistically. To test the hypothesis that muscle damage markers are associated with unique molecular processes, we correlated gene expression responses with variation in each marker post-ECC. Methods Vastus lateralis biopsies were collected from 35 young men 3 h post-ECC (10 sets of 10 maximal eccentric contractions; contralateral leg [CON] as control). Maximal isometric strength, soreness, and serum CK activity were assessed 24 h preexercise and every 24 h for 5 d post-ECC. Strength was also measured 10 min post-ECC. Over the 5 d after ECC, average peak strength loss was 51.5 ± 20%; average soreness increased from 0.9 ± 1.9 on a 100-mm visual analog scale to 39 ± 19; serum CK increased from 160 ± 130 to 1168 ± 3430 U·L −1 . Muscle RNA was used to generate gene expression profiles. Partek Genomics Suite correlated peak values of soreness, strength loss, and CK post-ECC with gene expression in ECC (relative to paired CON) using Pearson linear correlation ( P < 0.05) and repeated-measures ANOVA used to detect influence of ECC. Results After ECC, 2677 genes correlated with peak soreness, 3333 genes with peak strength loss, and 3077 genes with peak CK. Less than 1% overlap existed across all markers (16/9087). Unique genes included 2346 genes for peak soreness, 3032 genes for peak strength loss, and 2937 genes for peak CK. Conclusions The largely unique molecular pathways associated with common indirect markers of EIMD indicate that each marker of “damage” represents unique mechanistic processes.

Sucralose and acesulfame-potassium consumption alters gut microbiota in rodents, with unclear effects in humans. We examined effects of three-times daily sucralose-and acesulfame-potassium-containing diet soda consumption for 1 (n = 17) or 8 (n = 8) weeks on gut microbiota composition in young adults. After 8 weeks of diet soda consumption, the relative abundance of Proteobacteria, specifically Enterobacteriaceae, increased; and, increased abundance of two Proteobacteria taxa was also observed after 1 week of diet soda consumption compared with sparkling water. In addition, three taxa in the Bacteroides genus increased following 1 week of diet soda consumption compared with sparkling water. The clinical relevance of these findings and effects of sucralose and acesulfame-potassium consumption on human gut microbiota warrant further investigation in larger studies.Clinical trial registration: NCT02877186 and NCT03125356.

BACKGROUND: Exercise results in differential small RNA (smRNA/s) expression. smRNAs are a class of non-coding RNAs 15-35 nt in length, generally acting to suppress gene expression. smRNA associated gene silencing may be one of many mechanisms underpinning adaptation to exercise. We evaluated the effects of amount and intensity of aerobic exercise on smRNA expression quantified through smRNA sequencing. Additionally, we sought to identify signaling pathways associated with smRNA expression patterns. METHODS: RNA isolated from PRE and POST skeletal muscle samples (n = 120 [57 female, 63 male]; mean age: 51 ± 8) collected during the STRRIDE trials underwent smRNA sequencing. Resultant FASTQ files were preprocessed using the Qiagen GeneGlobe platform. Raw reads were filtered for low expressors then TMM normalized followed by analysis using a custom-built linear model applying Benjamini-Hochberg adjustment (FDR) to correct for multiple testing. We controlled for baseline smRNA expression, amount and intensity of exercise, age, race, sex, BMIBaseline, and %Δbody weight. RESULTS: Modeling exercise amount, yielded 65 smRNAs predictors (p ≤ 0.05); with intensity in the model, we identified 90 smRNA predictors of amount that were independent of intensity (p ≤ 0.05). Neither model identified smRNAs that passed FDR ≤ 0.05. Intensity yielded 189 smRNAs (p ≤ 0.05); 29 of these smRNAs passed FDR ≤ 0.05. Accounting for amount, we identified 225 smRNA predictors of intensity that were independent of amount (p ≤ 0.05); 28 of these smRNAs passed FDR ≤ 0.05. Differentially expressed (DE) smRNAs were involved in pathways associated with muscle cell regulation and regeneration, metabolism, and inflammation. Interestingly, we identified 57 smRNAs (22.1%) that overlap between the amount and intensity models. CONCLUSIONS: Collectively, these data show that amount but especially intensity of exercise regulate smRNAs in skeletal muscle. Amount and intensity of aerobic exercise resulted in regulation of different smRNAs. DE smRNAs in response to intensity were involved in proteolysis, regeneration, and neural/cognitive function; DE smRNAs in response to amount were involved in pathways related to cell cycle and translational response Supported by NIH Grants R01AG054840 and R01HL153497

Skeletal muscle fibers regulate surrounding endothelial cells (EC) via secretion of numerous angiogenic factors, including extracellular vesicles (SkM-EV). Muscle fibers are broadly classified as oxidative (OXI) or glycolytic (GLY) depending on their metabolic characteristics. OXI fibers secrete more pro-angiogenic factors and have greater capillary densities than GLY fibers. OXI muscle secretes more EV than GLY, however it is unknown whether muscle metabolic characteristics regulate EV contents and signaling potential. EVs were isolated from primarily oxidative or glycolytic muscle tissue from mice. MicroRNA (miR) contents were determined and endothelial cells were treated with OXI- and GLY-EV to investigate angiogenic signaling potential. There were considerable differences in miR contents between OXI- and GLY-EV and pathway analysis identified that OXI-EV miR were predicted to positively regulate multiple endothelial-specific pathways, compared to GLY-EV. OXI-EV improved in vitro angiogenesis, which may have been mediated through nitric oxide synthase (NOS) related pathways, as treatment of endothelial cells with a non-selective NOS inhibitor abolished the angiogenic benefits of OXI-EV. This is the first report to show widespread differences in miR contents between SkM-EV isolated from metabolically different muscle tissue and the first to demonstrate that oxidative muscle tissue secretes EV with greater angiogenic signaling potential than glycolytic muscle tissue.

Extracellular vesicles (EV) function in cell-cell communication by delivering molecular cargo, such as miRNA, to target cells. miRNA are short, non-coding RNAs that regulate gene expression post-transcriptionally. Resistance exercise is known to promote skeletal muscle hypertrophy and alters EV characteristics and gene expression. The role of EV miRNA in altering resistance exercise-related gene expression remains elusive. PURPOSE: This pilot study aimed to examine the effect of resistance exercise on circulating EV miRNA. METHODS: We collected fasted blood from 10 participants (5 men, 5 women; age: 26.9 ± 5.5 y, height: 1.73 ± 0.11 m, body mass: 74.0 ± 11.1 kg, body fat: 25.7 ± 11.6 %) before (PRE) and immediately after (POST) resistance exercise consisting of six sets of 10 repetitions of back squat using 75% 1RM. We isolated EVs from plasma using size exclusion chromatography and extracted total RNA from EVs using commercially available kits. Illumina NextSeq was used to conduct RNA sequencing. To predict target mRNAs and perform functional analyses, we used Ingenuity Pathway Analysis (IPA) Suite on differentially expressed (DE) miRNAs between PRE- vs POST-EVs (total and by sex). Significance was set at p < 0.05 for DE and p ≤ 0.01 for IPA. RESULTS: We observed 19 DE miRNAs in the total sample from PRE to POST (p < 0.05). IPA revealed 144 gene expression pathways targeted by DE miRNAs, including insulin-like growth factor-I (p = 8.5e-7; gene targets = 31), growth hormone (p = 0.001; gene targets = 18), and androgen signaling (p = 0.002; gene targets = 34) pathways. Examination by sex revealed 29 DE miRNAs in men and 8 in women (p < 0.05 for all), with no overlap between sexes. Fifty gene expression pathways were targeted in men and 4 pathways targeted in women (p < 0.01 for all). mTOR signaling was altered in men (p = 0.01; gene targets = 21) but not in women. CONCLUSION: These data demonstrate that an acute bout of resistance exercise alters EV miRNA that target pathways related to muscle protein turnover. Comparison by sex revealed distinct EV miRNA profiles and targeted pathways. Future work should investigate the mechanistic actions of circulating EV miRNAs in response to resistance exercise and whether these response patterns influence sex-specific phenotypic adaptations.Supported by UK MOD Grant WGCC 5.5.6 - Task 0107

Rheumatoid arthritis (RA) T cells drive autoimmune features via metabolic reprogramming that reduces oxidative metabolism. Exercise training improves cardiorespiratory fitness (i.e., systemic oxidative metabolism) and thus may impact RA T cell oxidative metabolic function. In this pilot study of RA participants, we took advantage of heterogeneous responses to a high-intensity interval training (HIIT) exercise program to identify relationships between improvements in cardiorespiratory fitness with changes in peripheral T cell and skeletal muscle oxidative metabolism. In 12 previously sedentary persons with seropositive RA, maximal cardiopulmonary exercise tests, fasting blood, and vastus lateralis biopsies were obtained before and after 10 weeks of HIIT. Following HIIT, improvements in RA cardiorespiratory fitness were associated with changes in RA CD4 + T cell basal and maximal respiration and skeletal muscle carnitine acetyltransferase (CrAT) enzyme activity. Further, changes in CD4 + T cell respiration were associated with changes in naïve CD4 + CCR7 + CD45RA + T cells, muscle CrAT, and muscle medium-chain acylcarnitines and fat oxidation gene expression profiles. In summary, modulation of cardiorespiratory fitness and molecular markers of skeletal muscle oxidative metabolism during exercise training paralleled changes in T cell metabolism. Exercise training that improves RA cardiorespiratory fitness may therefore be valuable in managing pathologically related immune and muscle dysfunction. Trial registration: ClinicalTrials.gov, NCT02528344. Registered on 19 August 2015.

New Findings What is the central question of this study? Is 1 week of exercise training sufficient to reduce local and systemic inflammation? Do obesity and short‐term concurrent aerobic and resistance exercise training alter skeletal muscle extracellular vesicle (EV) contents? What is the main finding and its importance? Obesity alters skeletal muscle small EV microRNAs targeting inflammatory and growth pathways. Exercise training alters skeletal muscle small EV microRNAs targeting inflammatory pathways, indicative of reduced inflammation. Our findings provide support for the hypotheses that EVs play a vital role in intercellular communication during health and disease and that EVs mediate many of the beneficial effects of exercise. Abstract Obesity is associated with chronic inflammation characterized by increased levels of inflammatory cytokines, whereas exercise training reduces inflammation. Small extracellular vesicles (EVs; 30–150 nm) participate in cell‐to‐cell communication in part through microRNA (miRNA) post‐transcriptional regulation of mRNA. We examined whether obesity and concurrent aerobic and resistance exercise training alter skeletal muscle EV miRNA content and inflammatory signalling. Vastus lateralis biopsies were obtained from sedentary individuals with (OB) and without obesity (LN). Before and after 7 days of concurrent aerobic and resistance training, muscle‐derived small EV miRNAs and whole‐muscle mRNAs were measured. Pathway analysis revealed that obesity alters small EV miRNAs that target inflammatory (SERPINF1, death receptor and Gα i ) and growth pathways (Wnt/β‐catenin, PTEN, PI3K/AKT and IGF‐1). In addition, exercise training alters small EV miRNAs in an anti‐inflammatory manner, targeting the IL‐10, IL‐8, Toll‐like receptor and nuclear factor‐κB signalling pathways. In whole muscle, IL‐8 mRNA was reduced by 50% and Jun mRNA by 25% after exercise training, consistent with the anti‐inflammatory effects of exercise on skeletal muscle. Obesity and 7 days of concurrent exercise training differentially alter skeletal muscle‐derived small EV miRNA contents targeting inflammatory and anabolic pathways.

PURPOSE: Novel eccentric (ECC) exercise typically leads to strength loss that persists for several days after exercise, which varies widely between subjects. The mechanisms responsible for this variation are poorly understood. Here, we identified biological processes related to the extent of peak strength loss via global gene expression profiling. METHODS: In a previously published study, vastus lateralis biopsies were collected from 35 young men 3hr post-ECC exercise (100 maximal voluntary eccentric (ECC) actions on isokinetic dynamometer, non-exercised contralateral leg (CON) as a control). Maximal isometric strength of the knee extensors was assessed on a Biodex dynamometer. RNA isolated using the TRIzol method was used to generate global gene expression profiles on the Agilent Whole Genome Microarray platform. The current study is a retrospective analysis of the relationship between gene expression changes and peak strength loss from that previous study (GSE23697). Partek Genomics Suite correlated peak strength loss post-ECC (0-5d) with gene expression in ECC relative to intra-subject paired CON. Correlated genes (p<0.05) were analyzed using Ingenuity Pathway Analysis. RESULTS: Peak strength loss averaged 50.7±20.1% with a range of 9.7% to 96.0%. Pearson linear correlation detected 2333 genes (p<0.05) relating ECC (relative to CON) to peak strength loss, where 2201 and 132 genes were positively and negatively correlated to peak strength loss, respectively. Pathway analysis found 37 canonical pathways (p<0.05) associated with peak strength loss, including: glutamate receptor signaling (14 genes; -log p-value=3.22), serotonin receptor signaling (9 genes; -log p-value=2.22), GABA receptor signaling (18 genes; -log p-value=1.78), and cAMP mediated signaling (27 genes; -log p-value=1.58). CONCLUSION: In a model of moderate exercise-induced muscle damage, we assessed early changes in muscle gene expression and related these changes to variation in peak strength loss. Biological pathways that relate to the extent of muscle dysfunction include several neurotransmitter pathways, as well as cell signaling pathways such as cAMP. Insight into early drivers of strength loss could identify targets to reduce muscle dysfunction and optimize recovery in those prone to dysfunction following exercise.

PURPOSE: Numerous studies have evaluated differential gene expression in skeletal muscle following exercise. Additionally, several studies have sought to analyze the effects of aerobic and/or resistance exercise on muscle microRNA (miR) expression, often using qPCR and/or micro-arrays. miRs are ~15-22 nucleotides in length and generally act to repress gene expression. The purpose of the current study was to evaluate the effects of a 6-month aerobic exercise intervention, of various amounts and intensities, on the expression of skeletal muscle miRs quantified by small-RNA sequencing (smRNAseq). METHODS: PRE and POST intervention muscle obtained from the STRRIDE clinical trials repository (n = 124 [65 male, 59 female]; mean age = 51 ± 8; age range = 25-68) was subjected to RNA isolation using commercially available kits. Following isolation, RNA underwent smRNAseq and resulting FAST-Q files were aligned using the Qiagen Data Services platform. Read counts were normalized and underwent subsequent differential expression analysis using the BioConductor package edgeR; counts of the exercise intervention groups (MILD [mod intensity/low amount]; MOD [vigorous intensity/low amount]; HIGH [vigorous intensity/high amount]) were compared to the control group (CON) that abstained from exercise. Data were analyzed using quasi-likelihood F-tests and Benjamini-Hochberg correction for false-discovery rate (FDR) with a priori significance set at p = 0.01 and an FDR cutoff of q = 0.05. RESULTS: We identified 42 differentially expressed miRs (13 upregulated; 29 downregulated) in the MILD group compared to CON (p < 0.01; q < 0.05). Compared to CON, four miRs were differentially expressed (all upregulated) in the MOD group (p < 0.01; q < 0.05), while 61 miRs were differentially expressed (3 upregulated; 58 downregulated) in the HIGH group (p < 0.01; q < 0.05). CONCLUSION: Our results indicate that aerobic exercise of varying amount and intensity result in various degrees of miR differential expression. Exercise-induced changes in miR expression may impact downstream genetic regulation with downregulated miRs generally resulting in an upregulation of its target mRNA and vice-versa. Critically, further research is needed to elucidate the specific gene/s and pathways these miRs act upon. Supported by NIH Grant R01AG054840