Exercise is a multipotent stimulus that results in large-scale dynamic changes to the systemic molecular profile. Alternative exercise prescriptions and doses would be expected to result in distinct signatures due to differences in duration and intensity. We tested two novel combined endurance and resistance exercise regimens to better understand how differing prescriptions alter the acute metabolomics response at multiple timepoints up to 24h post-exercise. Serum metabolomics for n=37 untrained individuals was analyzed for participants completing traditional combined exercise [TRAD; n = 20 (11M/9F)] or high-intensity tactical training [HITT; n= 17 (8M/9F)] before exercise (pre), and immediately (h0), 3 and 24 h post-exercise (h3 and h24, respectively). We found minimal metabolites had a group by time interaction (2 with FDR < 0.10; 31 with nominal p < 0.05;), but both stimuli resulted in large-scale within-group changes to the circulating metabolome. TRAD consistently had greater numbers of differentially abundant metabolites (FDR < 0.10) as compared to HITT at h0 (431 vs. 333), h3 (435 vs. 331) and h24 (168 vs. 76). The major metabolite classes altered were related to key energy substrates for both groups at h0 (e.g., glucose, pyruvate) and energy replenishment for h3 and h24 (e.g., 12,13 diHOME, palmitoylcarnitine, free fatty acids). In summary, our data are the first to describe the acute changes in the circulating metabolome following combined endurance and resistance exercise. Additionally, we show the two distinct doses of combined exercise led to generally similar patterns of responses, with the longer duration TRAD dose resulting in a higher magnitude of change.

In a randomized, dose-response trial, we used molecular and phenomic profiling to compare responses to traditional (TRAD) endurance plus resistance training and high-intensity tactical training (HITT). Ninety-four participants (18-27 years) completed 12 weeks of TRAD or HITT followed by 4 weeks of detraining. While in vivo phenotype improvements were not dose-dependent, a few dose-dependent ex vivo muscle adaptations were overshadowed by wide-ranging inter-individual response heterogeneity (IRH). To address this, we established minimum clinically important difference (MCID) scores to classify participants by their attainment of MCIDs for functional muscle quality (fMQ) and cardiorespiratory fitness (CRF). Using differential gene expression (DGE) of muscle and exosomal microRNAs (miRs) and higher-order singular value decomposition (HOSVD), we mapped the molecular and phenomic biocircuitry of IRH. Nine miRs emerged as robust features of training adaptability, providing new insights into the integrated biocircuitry driving exercise adaptations and response heterogeneity. ### Competing Interest Statement The authors have declared no competing interest. ### Clinical Trial NCT03380923 ### Funding Statement This study was funded by a US Department of Defense Multidisciplinary University Research Initiative (MURI) awarded and administered via the Office of Naval Research under grant N000141613159. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The Institutional Review Board for Human Use of the University of Alabama at Birmingham gave ethical approval for this work. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors.

Low-carbohydrate, high-fat diets enhance lipid metabolism and decrease reliance on glucose oxidation in athletes, but the associated gene expression patterns remain unclear. The purpose of this study was to determine whether coordinated molecular pathways in skeletal muscle may be revealed by differential expression of genes driven by dietary profile, exercise, and/or their interaction. We investigated the skeletal muscle transcriptome in elite ultra-endurance athletes habitually (~ 20 months) consuming a high-carbohydrate, low-fat (HC, n = 10, 33 ± 6y, VO2max = 63.4 ± 6.2 mL O2•kg-1•min-1) or low-carbohydrate, high-fat (LC, n = 10, 34 ± 7y, VO2max = 64.7 ± 3.7 mL O2•kg-1•min-1) diet. Skeletal muscle gene expression was measured at baseline (BL), immediately-post (H0), and 2 h (H2) after 3 h submaximal treadmill running. Diet induced a coordinated but divergent expression pattern at BL where LC had higher expression of genes associated with lipid metabolism. Exercise resulted in a dynamic but uniform gene response, with no major differences between groups (H0). At H2, gene expression patterns were associated with differential pathway activity, including inflammation/immunity, suggesting a diet-specific influence on early muscle recovery. These results indicate that low-carbohydrate, high-fat diets lead to differences in resting and exercise-induced skeletal muscle gene expression patterns, underlying our previous findings of differential fuel utilization in elite ultra-endurance athletes.

Background:Cachexia is an extrapulmonary manifestation of Chronic Obstructive Pulmonary Disease (COPD) characterized by weight loss and muscle wasting. Transcriptomic profiling of vastus lateralis biopsies enables profiling of COPD-cachexia relevant dysregulation. As obtaining muscle biopsies is invasive and yields limited tissue, human muscle derived cultures (HMDC) may enable mechanistic research into cachexia. However, questions remain regarding the extent to which HMDC recapitulate transcriptomic signatures of bulk skeletal muscle in COPD-cachexia. To address this gap, we tested whether COPD and COPD-cachexia associated transcriptional dysregulation signatures in bulk skeletal muscle are preserved in derived myoblasts, myocytes, and myotubes. Methods:Vastus lateralis biopsies were collected from 13 (6M/7F, 64±9 years) participants; COPD n=5, COPD-cachexia n=4, and 4 age-matched controls. Cachexia was defined using a composite measure of weight loss coupled with reduced muscle strength, fatigue, anorexia, low muscle mass and/or systemic inflammation. Satellite cells were isolated and differentiated into myoblasts, myocytes, and myotubes. Differential gene expression testing, generated from RNA-sequencing, identified transcripts significantly dysregulated (p>0.05) in bulk tissue. Weighted gene co-expression network analysis (WGCNA) was performed to identify modules of co-expressed genes at the whole-transcriptome and mitochondrial transcriptome levels. Bulk tissue modules were tested for preservation in HMDC (Z-summary >2) and correlated with clinical traits. Gene set enrichment analysis was performed for all modules. Results:1,379 genes were significantly differentially expressed in bulk samples from all COPD participants compared to controls. The top upregulated gene was IL32 (L2FC=4.5, p=1.3×10 - 3 ) and top downregulated CGN (L2FC=-5.8, p=8.8×10 - 3 ). A total of 632 genes were significantly differentially expressed in bulk samples from COPD participants with and without cachexia. The top upregulated gene was SEMA4F (L2FC=5.0, p=6.9×10 - 4 ) and top downregulated ARC (L2FC=-4.9, p=3.1×10 - 2 ). WGCNA generated 9 modules (Modules 1 - 9) at the whole-transcriptome level and 2 modules (Modules A and B) at the mitochondrial transcriptome level. Modules 1, 4, 5, and 9 were significantly correlated with COPD-cachexia. Of these, module 1 was preserved in myoblasts and modules 4, 5 and 9 in myocytes. These modules are enriched with genes involved in metabolic and inflammatory remodeling, catabolic stress and atrophy, and chromatin-driven regeneration. Conclusions:These results provide a foundation for using myocytes and myoblasts as in vitro models of degeneration and repair pathway dysregulation in COPD-cachexia. Several modules were preserved between bulk skeletal muscle and HMDC, suggesting HMDC have utility for studying COPD-cachexia.

Chronic exercise training substantially improves skeletal muscle function and performance. The repeated demands and stressors of each exercise bout drive coordinated molecular adaptations within multiple cell types, leading to enhanced neuromuscular recruitment and contractile function, stem cell activation, myofiber hypertrophy, mitochondrial biogenesis, and angiogenesis, among others. To comprehensively profile molecular changes induced by combined resistance and endurance exercise training, we employed spatial transcriptomics coupled with immunofluorescence and computational approaches to resolve effects on myofiber and mononuclear cell populations in human muscle. By computationally identifying fast and slow myofibers, we identified fiber type-specific, exercise-induced gene expression changes that correlated with muscle functional improvements. Additionally, integration of human muscle single cell RNAseq data identified an exercise-induced shift in interstitial cell populations coincident with angiogenesis. Overall, these data provide a unique spatial molecular profiling resource for exploring muscle adaptations to exercise, and provide a pipeline and rationale for future studies in human muscle.

OBJECTIVE:To characterize the relationship between the frequency of idiopathic osteoarthritis (OA) and characteristics including demographics, comorbidities, military service history, and physical health in a veteran population. METHODS:We performed a cohort study in the Million Veteran Program (MVP) using International Classification of Diseases, 9th and 10th revision codes to define the frequency of site-specific OA across 3 joints or unspecified OA in veterans with respect to demographics (eg, age, sex, race and ethnicity), military service data, detailed electronic health records, military branch, and war era. RESULTS:We validated previous reports of sex- and age-dependent differences in OA frequency, and we identified that unspecified OA was associated with a higher frequency of 16 Deyo-Charlson comorbidities. These associations generally persisted within each isolated joint site-specific OA. Depending on military branch, prior military engagement was differentially associated with the frequency of OA. Prior United States Army and Navy service were associated with higher and lower risk, respectively, of OA across all joint sites; however, multivariable-adjusted models adjusting for a range of covariates, including age, sex, and ancestry, reversed the apparent protective effect of prior Navy service. CONCLUSION:These findings highlight the breadth of factors associated with OA in the MVP veteran population and suggest that physical status may be a modifiable risk factor for OA. This work may help in the design of strategies to optimize appropriate detection, intervention, treatment, and even rehabilitation for OA in veterans and the general population.

We showed that higher resistance training (RT) volume (4-sets) offsets muscle hypertrophy nonresponsiveness to single-set RT (1 set) while enhancing hypertrophic response among responders. Here, we investigated molecular traits underpinning RT-related hypertrophic variability via targeted (ribosome density and biogenesis) and untargeted approaches [RNA-Seq gene ontology (GO) and Pathway-Level Information ExtractoR (PLIER)]. Twenty-seven older (69 ± 3 yr) participants in the parental trial had one leg randomly allocated to 1 set and the contralateral leg allocated to 4-sets of RT for 10-wk, 2 times/week. Pre- and postintervention, participants underwent magnetic resonance imaging (MRI) and muscle biopsies. We selected participants based on quadriceps muscle cross-sectional area (qCSA) changes and used the MRI typical error (2 × TE = 3.27%) to allocate those in distinct hypertrophy phenotype: low responders: blunted hypertrophy, regardless of RT volume; medium responders: hypertrophy only following the higher RT volume; and high responders: hypertrophy following both RT volume. The qCSA was higher for 4-sets compared with 1 set for medium and high responders only. Higher RT volume, regardless of responsiveness groups, was followed by increased Frizzled-1 protein expression. RNA-Seq showed that high responders' robust hypertrophy was followed by up-regulation of pathways linked with protein turnover metabolism, RT-related metabolic response, and protein-folding biological processes. Hypertrophy in medium responders was marked by downregulation of pathways linked with muscle catabolism (proteasome and spliceosome), modulations on distinct RT-related metabolic response, and biological processes associated with hormone- and steroid-related pathways. Low responders, on the other hand, did not show measurable changes in any molecular pathways, regardless of RT volume manipulation. Overall, these finding reveal differential molecular signatures across the spectrum of RT responsiveness among older individuals.NEW & NOTEWORTHY We showed that higher RT volume increased total protein expression of Frizzled-1. High responder's robust hypertrophy was followed by upregulation of pathways linked with protein turnover metabolism and RT-related metabolic response. Hypertrophy in medium responders, on the other hand, was marked by downregulation of pathways associated with proteasome and spliceosome, and upregulation of lipoproteins metabolisms and genes was associated with membrane trafficking and intracellular protein transport. These findings reveal differential molecular signatures across the spectrum of RT responsiveness among older individuals in response to different RT volume manipulations.

Exercising regularly promotes health, but these benefits are complicated by acute inflammation induced by exercise. A potential source of inflammation is cell-free DNA (cfDNA), yet the cellular origins, molecular causes, and immune system interactions of exercise-induced cfDNA are unclear. To study these, 10 healthy individuals were randomized to a 12-wk exercise program of either high-intensity tactical training (HITT) or traditional moderate-intensity training (TRAD). Blood plasma was collected pre- and postexercise at weeks 0 and 12 and after 4 wk of detraining upon program completion. Whole-genome enzymatic methylation sequencing (EM-seq) with cell-type proportion deconvolution was applied to cfDNA obtained from the 50 plasma samples and paired to concentration measurements for 90 circulating cytokines. Acute exercise increased the release of cfDNA from neutrophils, dendritic cells (DCs), and macrophages proportional to exercise intensity. Exercise training reduced cfDNA released in HITT participants but not TRAD and from DCs and macrophages but not neutrophils. For most participants, training lowered mitochondrial cfDNA at rest, even after detraining. Using a sequencing analysis approach we developed, we concluded that rapid ETosis, a process of cell death where cells release DNA extracellular traps, was the likely source of cfDNA, demonstrated by enrichment of nuclear DNA. Further, several cytokines were induced by acute exercise, such as IL-6, IL-10, and IL-16, and training attenuated the induction of only IL-6 and IL-17F. Cytokine levels were not associated with cfDNA induction, suggesting that these cytokines are not the main cause of exercise-induced cfDNA. Overall, exercise intensity and training modulated cfDNA release and cytokine responses, contributing to the anti-inflammatory effects of regular exercise.

In a randomized, dose-response trial, we used molecular and phenomic profiling to compare responses with traditional moderate-intensity endurance and resistance training (TRAD) versus high-intensity tactical training (HITT) that encompassed explosive whole-body interval training and high-intensity resistance training. Ninety-four participants (18-27 yr) completed 12 wk of TRAD or HITT followed by 4 wk of detraining. Although similar performance and body composition improvements were observed in response to HITT and TRAD, some dose-dependent differences were observed for: 1) ex vivo muscle tissue changes in myofiber size, capillarization, satellite cell frequency, and mitochondrial function and 2) differential gene expression (DGE) of muscle and serum exosomal miRNAs (miRs). However, these dose-dependent ex vivo muscle adaptations were overshadowed by wide-ranging interindividual response heterogeneity (IRH). We therefore explored response heterogeneity by first establishing minimum clinically important difference (MCID) scores to classify each participant based on MCIDs for functional muscle quality (fMQ) and cardiorespiratory fitness (CRF) and then modeling all data based on MCID classification. Using higher-order singular value decomposition (HOSVD), we established multidimensional biocircuitry linked to interindividual response heterogeneity that identified the most influential features across lifestyle, body composition, performance, ex vivo muscle tissue, and miRNA mapping domains. Via cross-comparison of MCID-linked miRs identified via DGE and HOSVD, nine miRs emerged as robust features of training adaptability, providing new insights into the integrated biocircuitry driving IRH.NEW & NOTEWORTHY We examined in vivo and ex vivo adaptations to traditional moderate-intensity endurance and resistance training (TRAD) versus high-intensity tactical training (HITT; explosive whole-body interval training and high-intensity resistance training). TRAD and HITT improved physiological performance and body composition, and induced ex vivo muscle adaptations, with remarkable interindividual response heterogeneity (IRH) in improvements. We leveraged multidimensional modeling to identify interindividual response heterogeneity biocircuitry that integrates deep phenotyping and miR transcriptomics (serum exosomes and skeletal muscle).

Background Chronic obstructive pulmonary disease (COPD) is the third leading cause of mortality worldwide. Unintentional weight loss and musculoskeletal comorbidities like cachexia and sarcopenia in COPD have been associated with higher symptom burden, morbidity and mortality. Chronic tissue stress from smoking and COPD drive cachexia and muscle loss. We previously investigated a ferret model of COPD exhibiting that smoke exposure leads to chronic bronchitis, emphysema, and dramatic reduction in weight. Cigarette smoke exposure is the leading cause of COPD, however its effect on gene expression in skeletal muscle and the development of cachexia is unknown. Methods Ten ferrets (6M/4F) were exposed to cigarette smoke for 6 months and compared to 6 controls (3M/3F). Transcriptomics data were generated from tibialis anterior muscle. Single gene and weighted gene correlation network analysis (WGCNA) were conducted on whole-transcriptome data to determine differential expression in smoke exposed and controls. Functional enrichment was performed using FUMA-GWAS. Druggable targets were queried on PHAROS. Results Smoke-exposed ferrets lost significantly more weight than controls (-18±11% vs. +5±7%). Single gene analysis found 39 differentially expressed genes, with adj p > 0.1. Expression of RIPOR2 (logFC= 0.78, adj p= 0.04) and SLC1A4 (logFC=1.8, adj p= 0.04) were significantly higher in smoke-exposed ferrets. SLC1 encodes a norepinephrine transport suggesting that chronic tissue stress drives cachexia and muscle loss. RIPOR2 is required for actin stabilization. WGCNA showed the tan (rtan= 0.8, ptan= 3x10-4) and yellow modules (ryellow= 0.8, pyellow= 3x10-4) were significantly associated with smoke exposure. The tan (rtan= – 0.8, ptan= 4x10-4) and pale turquoise (rpale turquoise= 0.8, ppale turquoise= 6x10-4) modules were significantly associated with percent weight change. Functional enrichment analysis found TMEM9, TNIK, TMEM116, and ZNF385A, to be enriched in the single gene data, from the CAMP_UP. V1_UP oncogenic gene set (adj. p= 6.7x10-3). Both yellow (n=15) and tan (n=4) modules contained genes that were significantly differentially expressed at the single-gene level. Pharmaceutical target molecules were found for 4 of the genes identified, PARP3, KCNA4, SLC6A3 and HDAC9. All of these were overexpressed in smoke exposed organisms with logFC 0.21, 0.94, 0.87, 0.74 respectively. Conclusions This study furthers our understanding of the effect of cigarette smoking on skeletal muscle using the Ferret model of COPD cachexia and provides a foundation for exploration in human cohorts. Functional enrichment analysis of single gene data identified gene sets associated with oncogenic processes including cell adhesion, migration, replication and apoptosis.

RATIONALE. Cachexia (metabolically-driven muscle wasting) is an extrapulmonary consequence of advanced-stage chronic obstructive pulmonary disease (COPD) dramatically interfering with function, independence, and quality of life. Our group previously identified transcriptomic biomarkers of COPD cachexia in whole blood; however, transcriptomic studies of muscle tissue are more representative of the primary pathophysiology of cachexia. Skeletal muscle consists of multinucleated, post-mitotic cells (fibers) arranged in bundles, surrounded by sheaths of connective tissue. Skeletal muscle biopsy is a safe but under-utilized procedure, with collected tissue a limited and valuable resource. While cells isolated from a biopsy can be cultured, whether molecular signatures in mature muscle are preserved in culture is unclear. METHODS. To address this, we collected skeletal muscle biopsy samples from vastus lateralis and generated cells at three differentiation stages (myoblast, myocyte, and myotube) in 13 participants with and without COPD and/or unintentional weight loss (UWL), a hallmark of cachexia. We tested whether transcriptomic modules of co-expressed genes in bulk skeletal muscle were preserved in human cell culture models. Biopsy tissue was either snap-frozen or harvested for quiescent satellite cells (CD56+) for culturing. RNA was isolated from muscle homogenate and from cells at the three differentiation stages. Transcriptome-wide RNA-seq data were collected by Illumina NovaSeq 6000 and analyzed using Weighted Gene Correlation Network Analysis (WGCNA) to construct networks as modules based on pairwise relatedness between genes. Module preservation was defined as a Z-score>2 between mature muscle and each differentiation stage. Gene-set enrichment analysis using FUMA. RESULTS. Adults (6M/7F, 64±9y) were recruited across four study groups: healthy non-smokers(n=2), former smokers(n=2), individuals with COPD(n=6), and those with COPD and cachexia(n=3). Two modules of co-expressed genes, turquoise and blue, from mature muscle tissue were preserved in all three differentiation states. The top genes (membership >80%) in the turquoise modules were enriched with genes involved with infection response and neural development, whereas genes in the blue module were not enriched with genes in any known gene-sets. Three additional modules were preserved between mature muscle tissue and myotubes: pink (containing genes enriched for myogenesis and contractile activity); brown (containing oxidative metabolism genes); and magenta (not enriched with any known gene-sets). CONCLUSIONS. These findings provide evidence transcriptional networks are preserved between skeletal muscle tissue and cell culture in COPD and cachexia. The myotube differentiation stage appears to best recapitulate the mature muscle tissue environment. Future work will investigate whether differences across study groups are detectable at each differentiation stage.

The majority of exercise physiology research has been conducted in males, resulting in a skewed biological representation of how exercise impacts the physiological system. Extrapolating male-centric physiological findings to females is not universally appropriate and may even be detrimental. Thus, addressing this imbalance and taking into consideration sex as a biological variable is mandatory for optimization of precision exercise interventions and/or regimens. Our present analysis focused on establishing multiomic profiles in young, exercise-naïve males (n = 23) and females (n = 17) at rest and following acute exercise. Sex differences were characterized at baseline and following exercise using skeletal muscle and extracellular vesicle transcriptomics, whole blood methylomics, and serum metabolomics. Sex-by-time analysis of the acute exercise response revealed notable overlap, and divergent molecular responses between males and females. An exploratory comparison of two combined exercise regimens [high-intensity tactical training (HITT) and traditional (TRAD)] was then performed using singular value decomposition, revealing latent data structures that suggest a complex dose-by-sex interaction response to exercise. These findings lay the groundwork for an understanding of key differences in responses to acute exercise exposure between sexes. This may be leveraged in designing optimal training strategies, understanding common and divergent molecular interplay guiding exercise responses, and elucidating the role of sex hormones and/or other sex-specific attributes in responses to acute and chronic exercise.NEW & NOTEWORTHY This study examined methylomics, transcriptomics, and metabolomics in circulation and/or skeletal muscle of young, healthy, exercise-naïve males and females before and after exposure to either traditional combined exercise (TRAD) and high-intensity tactical training (HITT). Across 40 young adults, we found an overlapping yet considerably sex-divergent response in the molecular mechanisms activated by exercise. These findings may provide insight into optimal training strategies for adaptation when considering sex as a biological variable.

BACKGROUND:Skeletal muscle dysfunction is a common extrapulmonary manifestation of chronic obstructive pulmonary disease (COPD). Alterations in skeletal muscle myosin heavy chain expression, with reduced type I and increased type II myosin heavy chain expression, are associated with COPD severity when studied in largely male cohorts. The objectives of this study were (1) to define an abnormal myofibre proportion phenotype in both males and females with COPD and (2) to identify transcripts and transcriptional networks associated with abnormal myofibre proportion in COPD. METHODS:Forty-six participants with COPD were assessed for body composition, strength, endurance and pulmonary function. Skeletal muscle biopsies from the vastus lateralis were assayed for fibre-type distribution and cross-sectional area via immunofluorescence microscopy and RNA-sequenced to generate transcriptome-wide gene expression data. Sex-stratified k-means clustering of type I and IIx/IIax fibre proportions was used to define abnormal myofibre proportion in participants with COPD and contrasted with previously defined criteria. Single transcripts and weighted co-expression network analysis modules were tested for correlation with the abnormal myofibre proportion phenotype. RESULTS:Abnormal myofibre proportion was defined in males with COPD (n = 29) as <18% type I and/or >22% type IIx/IIax fibres and in females with COPD (n = 17) as <36% type I and/or >12% type IIx/IIax fibres. Half of the participants with COPD were classified as having an abnormal myofibre proportion. Participants with COPD and an abnormal myofibre proportion had lower median handgrip strength (26.1 vs. 34.0 kg, P = 0.022), 6-min walk distance (300 vs. 353 m, P = 0.039) and forced expiratory volume in 1 s-to-forced vital capacity ratio (0.42 vs. 0.48, P = 0.041) compared with participants with COPD and normal myofibre proportions. Twenty-nine transcripts were associated with abnormal myofibre proportions in participants with COPD, with the upregulated NEB, TPM1 and TPM2 genes having the largest fold differences. Co-expression network analysis revealed that two transcript modules were significantly positively associated with the presence of abnormal myofibre proportions. One of these co-expression modules contained genes classically associated with muscle atrophy, as well as transcripts associated with both type I and type II myofibres, and was enriched for genetic loci associated with bone mineral density. CONCLUSIONS:Our findings indicate that there are significant transcriptional alterations associated with abnormal myofibre proportions in participants with COPD. Transcripts canonically associated with both type I and type IIa fibres were enriched in a co-expression network associated with abnormal myofibre proportion, suggesting altered transcriptional regulation across multiple fibre types.

Using a within-subject unilateral design, we demonstrated that increasing resistance training (RT) volume may be a simple, effective strategy to improve muscle hypertrophy and strength gains among older adults who do not respond to low-volume RT. In addition, it could most likely be used to further improve hypertrophic outcomes in responders.

The efficacy of the NASA SPRINT exercise countermeasures program for quadriceps (vastus lateralis) and triceps surae (soleus) skeletal muscle health was investigated during 70 days of simulated microgravity. Individuals completed 6° head-down-tilt bedrest (BR, n = 9), bedrest with resistance and aerobic exercise (BRE, n = 9), or bedrest with resistance and aerobic exercise and low-dose testosterone (BRE + T, n = 8). All groups were periodically tested for muscle (n = 9 times) and aerobic (n = 4 times) power during bedrest. In BR, surprisingly, the typical bedrest-induced decrements in vastus lateralis myofiber size and power were either blunted (myosin heavy chain, MHC I) or eliminated (MHC IIa), along with no change (P > 0.05) in %MHC distribution and blunted quadriceps atrophy. In BRE, MHC I (vastus lateralis and soleus) and IIa (vastus lateralis) contractile performance was maintained (P > 0.05) or increased (P < 0.05). Vastus lateralis hybrid fiber percentage was reduced (P < 0.05) and energy metabolism enzymes and capillarization were generally maintained (P > 0.05), while not all of these positive responses were observed in the soleus. Exercise offsets 100% of quadriceps and approximately two-thirds of soleus whole muscle mass loss. Testosterone (BRE + T) did not provide any benefit over exercise alone for either muscle and for some myocellular parameters appeared detrimental. In summary, the periodic testing likely provided a partial exercise countermeasure for the quadriceps in the bedrest group, which is a novel finding given the extremely low exercise dose. The SPRINT exercise program appears to be viable for the quadriceps; however, refinement is needed to completely protect triceps surae myocellular and whole muscle health for astronauts on long-duration spaceflights.NEW & NOTEWORTHY This study provides unique exercise countermeasures development information for astronauts on long-duration spaceflights. The NASA SPRINT program was protective for quadriceps myocellular and whole muscle health, whereas the triceps surae (soleus) was only partially protected as has been shown with other programs. The bedrest control group data may provide beneficial information for overall exercise dose and targeting fast-twitch muscle fibers. Other unique approaches for the triceps surae are needed to supplement existing exercise programs.

We recently reported that aging increases basal expression of many Toll-like receptors (TLRs) in men and lifelong aerobic exercise does not prevent this effect. In addition, a resistance exercise (RE) challenge increased the expression of many TLRs. Here we show that basal TLR expression is minimally influenced by aging in women and findings support the sexual dimorphism of immunity, with women having greater basal skeletal muscle TLR expression and a differential response to unaccustomed exercise than men.

Resistance training (RT) remains the most effective treatment for age-related declines in muscle mass. However, many older adults experience attenuated muscle hypertrophy in response to RT when compared with younger adults. This may be attributed to underlying molecular processes that are dysregulated by aging and exacerbated by improperly prescribed RT weekly volume, intensity, and/or frequency doses. MicroRNAs (miRNAs) are key epigenetic regulators that impact signaling pathways and protein expression within cells, are dynamic and responsive to exercise stimuli, and are often dysregulated in diseases. In this study, we used untargeted miRNA-seq to examine miRNA in skeletal muscle and serum-derived exosomes of older adults (n = 18, 11 M/7 F, 66 ± 1 yr) who underwent three times per wk RT for 30 wk [e.g., high intensity three times/wk (HHH, n = 9) or alternating high-low-high (HLH) intensity (n = 9)], after a standardized 4-wk washin. Within each tissue, miRNAs were clustered into modules based on pairwise correlation using weighted gene correlation network analysis (WGCNA). Modules were tested for association with the magnitude of RT-induced thigh lean mass (TLM) change [as measured by dual-energy X-ray absorptiometry (DXA)]. Although no modules were unique to training dose, we identified miRNA modules in skeletal muscle associated with TLM gains irrespective of exercise dose. Using miRNA-target interactions, we analyzed key miRNAs in significant modules for their potential regulatory involvement in biological pathways. Findings point toward potential miRNAs that may be informative biomarkers and could also be evaluated as potential therapeutic targets as an adjuvant to RT to maximize skeletal muscle mass accrual in older adults.NEW & NOTEWORTHY In this work, we identified a set of microRNAs correlated with thigh lean mass gains in a group of older adults. To our knowledge, this is the first time these microRNAs have been identified as novel predictive biomarkers correlating with lean mass gains in aging adults. As biomarkers, these may help interventionalists identify older individuals that are positively responding to an exercise intervention.

We examined small and long transcriptomics in skeletal muscle and serum-derived extracellular vesicles before and after a single exposure to traditional combined exercise (TRAD) and high-intensity tactical training (HITT). Across 40 young adults, we found more consistent protein-coding gene responses to TRAD, whereas HITT elicited differential expression of microRNA enriched in brain regions. Follow-up analysis revealed relationships and temporal dynamics across transcript networks, highlighting potential avenues for research into mechanisms of exercise response and adaptation.

Background: Ageing of skeletal muscle is characterized in some by muscle fiber type grouping due to denervation-reinnervation cycles, but the severity of fiber type grouping varies widely across individuals of the same chro-nological age. It remains unknown whether fiber type grouping is associated with lower muscle mass and/or reduced physical function in elderly. Therefore, we assessed the relationship between fiber type grouping and indices of muscle mass and physical function in older adults. In addition, we assessed whether fiber type grouping is affected by prolonged resistance training in older adults.Methods: Twenty young (21 +/- 2 y) and twenty older (70 +/- 4 y) healthy men participated in the present study. Body composition (DXA-scan), quadriceps cross-sectional area (CT-scan) and muscle strength (1RM) were assessed at baseline (young and old) and following 12 weeks of resistance training (old only). Percutaneous skeletal muscle biopsies from the vastus lateralis were collected at baseline (young and old) and following exercise training (old only). Immunohistochemical analyses were performed to evaluate type I and type II muscle fiber distribution, size, myonuclear content and grouping.Results: At baseline, type II fibers were significantly (P < 0.05) smaller in older compared with young adults (5366 +/- 1288 vs 6705 +/- 1168 mu m2). Whereas no differences were observed in type I, type II fiber grouping was significantly (P < 0.05) lower in older (18 +/- 18 %) compared with young (32 +/- 25 %) men. No significant correlations were observed between fiber type grouping and muscle mass or physical function. Prolonged resistance training in old men resulted in a significant increase (P < 0.05) in type II fiber size (from 5366 +/- 1288 to 6165 +/- 1484 mu m2) with no significant changes in the proportion of type I muscle fibers found grouped.Conclusion: Muscle fiber type grouping is not associated with lower body strength or muscle mass in healthy, older men. In addition, twelve weeks of resistance exercise training results in type II muscle fiber specific hy-pertrophy but does not affect fiber type grouping.

This is the first study to describe the multiome of skeletal muscle paralyzed by a spinal cord injury (SCI) in mice across the acute and subacute timeframe after injury. We show large-scale changes in the metabolome and transcriptome at 7 days post-injury compared with 28 days. Furthermore, we show that the alkaloid boldine was able to prevent SCI-induced changes in muscle glucose and free amino acid levels at 7 days, but not 28 days, after SCI.