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Low carbohydrate availability during recovery from aerobic exercise alters skeletal muscle microRNA (miRNA) profiles, which may mechanistically regulate exercise recovery. However, its impact on circulating miRNA (c-miRNA) profiles remains unclear. This study aimed to determine the effects of low versus adequate carbohydrate availability on c-miRNA profiles during recovery from aerobic exercise. Nine males (22 ± 4 yr, 1.81 ± 0.09 m, 83.9 ± 11.9 kg, 25.7 ± 2.3 kg/m2, means ± SD) completed this randomized, crossover study comprising two glycogen depletion trials, followed by 24 h of isocaloric refeeding to induce low (LOW; 1.5 g/kg carbohydrate, 3.0 g/kg fat) or adequate (AD; 6.0 g/kg carbohydrate, 1.0 g/kg fat) carbohydrate availability. Total c-miRNA was extracted from serum 24 h following glycogen depletion exercise. Data were log-transformed and analyzed as fold change relative to AD. Bioinformatics was conducted on significant c-miRNA and associated pathways (miRTarBase/KEGG). Follow-up transfection of miR-375-3p mimic or inhibitor into C2C12 cells assessed metabolic, inflammatory, and catabolic pathways at the gene and protein levels. Of the 84 miRNAs assessed, miR-335-5p (–0.49 ± 0.60; P = 0.04) and miR-375-3p (–1.57 ± 1.25; P = 0.01) were significantly lower, and miR-214-3p (1.76 ± 1.85; P = 0.02) was significantly higher in AD versus LOW. In vitro experiments indicated that miR-375-3p regulates catabolic pathways at the gene and protein level. Low carbohydrate availability alters c-miRNA profiles, particularly miR-375-3p, which targets proteostasis and metabolism 24 h into recovery from aerobic exercise. These findings identify unique c-miRNA targets as potential biomarkers for the mechanistic effects of low carbohydrate availability on exercise recovery. NEW & NOTEWORTHY: Low carbohydrate consumption (LOW) 24 h in recovery from aerobic exercise elicits a distinct circulating miRNA profile compared with adequate carbohydrate consumption (AD). MicroRNA 375-3p was the most significantly different between the LOW and AD treatments. Follow-up in vitro experiments suggest that AD carbohydrate availability blunts catabolic signaling during postexercise recovery. [ABSTRACT FROM AUTHOR]

Strenuous physical training increases total blood volume (BV) through expansion of plasma volume (PV) and red cell volume (RCV). In contrast, exogenous erythropoietin (EPO) treatment increases RCV but decreases PV, rendering BV stable or slightly decreased. This study aimed to determine the combined effects of strenuous training and EPO treatment on BV and markers of systemic and muscle iron homeostasis. In this longitudinal study, eight healthy nonanemic males were treated with EPO (50 IU/kg body mass, three times per week, sc) across 28 days of strenuous training (4 days/wk, exercise energy expenditures of 1,334 ± 24 kcal/day) while consuming a controlled, energy-balanced diet providing 39 ± 4 mg/day iron. Before (PRE) and after (POST) intervention, BV compartments were measured using carbon monoxide rebreathing, and markers of iron homeostasis were assessed in blood and skeletal muscle (vastus lateralis). Training + EPO increased (P < 0.01) RCV (13 ± 6%) and BV (5 ± 4%), whereas PV remained unchanged (P = 0.86). The expansion of RCV was accompanied by a large decrease in whole body iron stores, as indicated by decreased (P < 0.01) ferritin (−77 ± 10%) and hepcidin (−49 ± 23%) concentrations in plasma. Training + EPO decreased (P < 0.01) muscle protein abundance of ferritin (−25 ± 20%) and increased (P < 0.05) transferrin receptor (47 ± 56%). These novel findings illustrate that strenuous training combined with EPO results in both increased total oxygen-carrying capacity and hypervolemia in young healthy males. The decrease in plasma and muscle ferritin suggests that the marked upregulation of erythropoiesis alters systemic and tissue iron homeostasis, resulting in a decline in whole body and skeletal muscle iron stores. NEW & NOTEWORTHY: Strenuous exercise training combined with erythropoietin (EPO) treatment increases blood volume, driven exclusively by red cell volume expansion. This hematological adaptation results in increased total oxygen-carrying capacity and hypervolemia. The marked upregulation of erythropoiesis with training + EPO reduces whole body iron stores and circulating hepcidin concentrations. The finding that the abundance of ferritin in muscle decreased after training + EPO suggests that muscle may release iron to support red blood cell production. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This study investigated the effects of EPO on hemoglobin (Hgb) and hematocrit (Hct), time trial (TT) performance, substrate oxidation, and skeletal muscle phenotype throughout 28 days of strenuous exercise. Eight males completed this longitudinal controlled exercise and feeding study using EPO (50 IU/kg body mass) 3×/week for 28 days. Hgb, Hct, and TT performance were assessed PRE and on Days 7, 14, 21, and 27 of EPO. Rested/fasted muscle obtained PRE and POST EPO were analyzed for gene expression, protein signaling, fiber type, and capillarization. Substrate oxidation and glucose turnover were assessed during 90‐min of treadmill load carriage (LC; 30% body mass; 55 ± 5% V̇O2peak) exercise using indirect calorimetry, and 6‐6‐[2H2]‐glucose PRE and POST. Hgb and Hct increased, and TT performance improved on Days 21 and 27 compared to PRE (p < 0.05). Energy expenditure, fat oxidation, and metabolic clearance rate during LC increased (p < 0.05) from PRE to POST. Myofiber type, protein markers of mitochondrial biogenesis, and capillarization were unchanged PRE to POST. Transcriptional regulation of mitochondrial activity and fat metabolism increased from PRE to POST (p < 0.05). These data indicate EPO administration during 28 days of strenuous exercise can enhance aerobic performance through improved oxygen carrying capacity, whole‐body and skeletal muscle fat metabolism. [ABSTRACT FROM AUTHOR]

Exogenous glucose oxidation is reduced 55% during aerobic exercise after three days of complete starvation. Whether energy deficits more commonly experienced by athletes and military personnel similarly affect exogenous glucose oxidation and what impact this has on physical performance remains undetermined. This randomized, longitudinal parallel study aimed to assess the effects of varying magnitudes of energy deficit (DEF) on exogenous glucoseoxidation and physical performance compared to energy balance (BAL). Participants consumed a4-day BAL diet, followed by a 6-day 20% ( n =10), 40% ( n =10), or 60% ( n =10) DEF diet. At the end of each energy phase participants performed 90-min of steady-state cycle ergometry (56±3% V̇O 2peak ) while consuming a glucose drink (80 g), followed by a time to exhaustion (TTE) performance test. Substrate oxidation (g/min) was determined by indirect calorimetry and 13 C glucose. Muscle glycogen (mmol/kg dry weight) and transcript accumulation were assessed in rested fasted muscle collected before exercise in each phase. Muscle glycogen was lower ( P = 0.002) during DEF (365±179) than BAL (456±125), regardless of group. Transcriptional regulation of glucose uptake ( GLUT4 italic> and IRS2 ) and glycogenolysis ( HKII and PKM ) were lower ( P < 0.05) during DEF than BAL, independent of group. Regardless of group, exogenous glucose oxidation was 10% lower ( P < 0.001) during DEF (0.38±0.08) than BAL (0.42±0.08). There was no evidence of a difference in TTE between BAL and DEF or between groups. In conclusion, despite modest reduction in exogenous glucose oxidative capacity during energy deficit, physical performance was similar compared with balance.