Days Of Endurance Training Research Articles

The Impact of Heat Acclimation on Gastrointestinal Function following Endurance Exercise in a Hot Environment

To determine the effects of heat acclimation on gastrointestinal (GI) damage and the gastric emptying (GE) rate following endurance exercise in a hot environment. Fifteen healthy men were divided into two groups: endurance training in hot (HOT, 35 °C, n = 8) or cool (COOL, 18 °C, n = 7) environment. All subjects completed 10 days of endurance training (eight sessions of 60 min continuous exercise at 50% of the maximal oxygen uptake (V·O2max). Subjects completed a heat stress exercise tests (HST, 60 min exercise at 60% V·O2max) to evaluate the plasma intestinal fatty acid-binding protein (I-FABP) level and the GE rate following endurance exercise in a hot environment (35 °C) before (pre-HST) and after (post-HST) the training period. We assessed the GE rate using the 13C-sodium acetate breath test. The core temperature during post-HST exercise decreased significantly in the HOT group compared to the pre-HST (p = 0.004) but not in the COOL group. Both the HOT and COOL groups showed exercise-induced plasma I-FABP elevations in the pre-HST (p = 0.002). Both groups had significantly attenuated exercise-induced I-FABP elevation in the post-HST. However, the reduction of exercise-induced I-FABP elevation was not different significantly between both groups. GE rate following HST did not change between pre- and post-HST in both groups, with no significant difference between two groups in the post-HST. Ten days of endurance training in a hot environment improved thermoregulation, whereas exercise-induced GI damage and delay of GE rate were not further attenuated compared with training in a cool environment.

Effect Of Low Energy Availability During Three Consecutive Days Of Endurance Training On Gastrointestinal Damage In Male Long-distance Runners

Effect Of Low Energy Availability During Three Consecutive Days Of Endurance Training On Gastrointestinal Damage In Male Long-distance Runners

Heat acclimation does not attenuate hepcidin elevation after a single session of endurance exercise under hot condition.

PurposeWe sought to determine the effects of heat acclimation on endurance exercise-induced hepcidin elevation under hot conditions.MethodsFifteen healthy men were divided into two groups: endurance training under hot conditions (HOT, 35 °C, n = 8) and endurance training under cool conditions (CON, 18 °C, n = 7). All subjects completed 10 days of endurance training (8 sessions in total), consisting of 60 min of continuous exercise at 50% of maximal oxygen uptake (dot{V}{text{O}}_{2max }) under their assigned environment condition. Subjects completed a heat stress exercise test (HST, 60 min exercise at 60% dot{V}{text{O}}_{2max }) to evaluate the exercise-induced thermoregulatory and hepcidin responses under hot conditions (35 °C) before (pre-HST) and after (post-HST) the training period.ResultsCore temperature during exercise in the post-HST decreased significantly in the HOT group compared to pre-HST (P = 0.004), but not in the CON group. The HOT and CON groups showed augmented exercise-induced plasma interleukin-6 (IL-6) elevation in the pre-HST (P = 0.002). Both groups had significantly attenuated increases in exercise-induced IL-6 in the post-HST; however, the reduction of exercise-induced IL-6 elevation was not different significantly between both groups. Serum hepcidin concentrations increased significantly in the pre-HST and post-HST in both groups (P = 0.001), no significant difference was observed between both groups during each test or over the study period.Conclusion10 days of endurance training period under hot conditions improved thermoregulation, whereas exercise-induced hepcidin elevation under hot conditions was not attenuated following the training.

Impact of Three Consecutive Days of Endurance Training Under Hypoxia on Muscle Damage and Inflammatory Responses.

Purpose: The purpose of this study was to determine the effect of 3 consecutive days of endurance training under hypoxia on muscle damage, inflammation, and performance responses.Methods: Nine active healthy males completed two trials in different periods, consisting of either 3 consecutive days of endurance training under hypoxia [fraction of inspired oxygen (Fio2): 14.5%, HYP] or normoxia (Fio2: 20.9%, NOR). They performed daily 90-min sessions of endurance training consisting of high-intensity endurance interval pedaling [10 × 4-min pedaling at 80% of maximal oxygen uptake () with 2 min of active rest at 30% of ] followed by 30-min continuous pedaling at 60% of during 3 consecutive days (days 1–3). Venous blood sample, muscular performance of lower limb, and score of subjective feelings were determined every morning (days 1–4) to evaluate muscle damage and inflammation. On day 4, subjects performed an incremental exercise test (IET) to evaluate the performance response.Results: Pedaling workload during daily endurance training was significantly lower in the HYP trial (interval exercise: 166 ± 4 W) than in the NOR trial (194 ± 8 W; P < 0.0001). Serum creatine kinase (CK) and high-sensitivity C-reactive protein (hsCRP) concentrations did not significantly change during days 1–4 in either trial. Maximal voluntary contraction (MVC) of knee extension (P < 0.0001) and drop jump (DJ) index (P = 0.004) were significantly decreased with training in both trials, with no significant difference between trials. The muscle soreness and fatigue scores significantly increased in both trials (P < 0.0001). However, the HYP trial showed a significantly lower score of fatigue on day 4 compared with the NOR trial (P = 0.004). Maximal aerobic power output during IET on day 4 did not significantly differ between trials.Conclusion: Three consecutive days of endurance training under hypoxia induced comparable levels of muscle damage, inflammation, and performance responses compared with the same training under normoxia.

Hepcidin response to three consecutive days of endurance training in hypoxia.

The purpose of this study was to determine the effects of 3 consecutive days of endurance training in hypoxia on hepcidin responses. Nine active healthy males completed two trials, consisting of 3 consecutive days of endurance training in either hypoxia [fraction of inspired oxygen (FiO2): 14.5%) or normoxia (FiO2: 20.9%). On days 1-3, participants performed one 90min session of endurance training per day, consisting of high-intensity endurance interval exercise [10 × 4min of pedaling at 80% of maximal oxygen uptake ([Formula: see text]O2max) with 2min of active rest at 30% of [Formula: see text]O2max] followed by 30min of continuous exercise at 60% of [Formula: see text]O2max. Venous blood samples were collected prior to exercise each day during the experimental period (days 1-4) to determine serum hepcidin, iron, ferritin, haptoglobin, and ketone body concentrations. Serum iron (p < 0.0001), ferritin (p = 0.005) and ketone body (p < 0.0001) concentrations increased significantly in both trials on days 2-4 compared with day 1, with no significant differences between trials. No significant changes in serum haptoglobin concentrations were observed throughout the experimental period in either trial. Serum hepcidin concentrations also increased significantly on days 2-4 compared with day 1 in both trials (p = 0.004), with no significant differences observed between trials. 3 consecutive days of endurance training in hypoxia did not affect hepcidin concentrations compared with endurance training in normoxia.

The Impact Of Three Consecutive Days Of Endurance Training In Hypoxia On Hepcidin Responses.

Endurance exercise in hypoxia resulted in similar hepcidin elevation compared with exercise in normoxia (Govus et al. 2014; Goto et al. 2017). However, how consecutive days of endurance training in hypoxia affects hepcidin elevation remains unclear. PURPOSE: The purpose of the present study was to determine the effect of three consecutive days of endurance training in hypoxia on hepcidin response. METHODS: Nine active healthy males completed two trials on different days, consisting of either three consecutive days of endurance training in hypoxia (FiO2: 14.5%) or normoxia (FiO2: 20.9%). They performed 90-min sessions of endurance training consisting of high-intensity endurance interval exercise (10 × 4 min pedaling at 80% of VO2max with 2 min of active rest at 30% of VO2max) followed by 30 min continuous pedaling at 60% of VO2max during three consecutive days (days 1-3). Venous blood samples were collected after an overnight fast during experimental periods (days 1-4) to determine the serum hepcidin, iron, ferritin and haptoglobin concentrations. RESULTS: Pedaling workload during endurance training were significantly lower in the HYP (interval exercise: 166 ± 4.3 W) than in the NOR (194 ± 7.6 W, P < 0.0001). Serum iron (P < 0.0001) and ferritin (P = 0.005) concentrations on days 2-4 significantly increased in both trials, whereas there was no significant difference between the two trials. Serum haptoglobin concentrations did not significantly change throughout the experimental periods in either trial. Moreover, NOR showed significantly greater serum hepcidin elevation on the days 2-4 compared with day 1 (day1: 13.9 ± 8.6 ng/mL, day2: 30.4 ± 9.9 ng/mL, P = 0.004). However, no significant difference was observed in serum hepcidin concentrations between the NOR and HYP. CONCLUSION: Three consecutive days of endurance training in hypoxia did not affect further hepcidin elevation compared with endurance training in normoxia.

Effect of low energy availability during three consecutive days of endurance training on iron metabolism in male long distance runners.

We investigated the effect of low energy availability (LEA) during three consecutive days of endurance training on muscle glycogen content and iron metabolism. Six male long distance runners completed three consecutive days of endurance training under LEA or neutral energy availability (NEA) conditions. Energy availability was set at 20 kcal/kg fat‐free mass (FFM)/day for LEA and 45 kcal/kg FFM/day for NEA. The subjects ran for 75 min at 70% of maximal oxygen uptake ( V˙O2max) on days 1–3. Venous blood samples were collected following an overnight fast on days 1–4, immediately and 3 hr after exercise on day 3. The muscle glycogen content on days 1–4 was evaluated by carbon‐magnetic resonance spectroscopy. In LEA condition, the body weight and muscle glycogen content on days 2–4, and the FFM on days 2 and 4 were significantly lower than those on day1 (p < .05 vs. day1), whereas no significant change was observed throughout the training period in NEA condition. On day 3, muscle glycogen content before exercise was negatively correlated with serum iron level (immediately after exercise, 3 hr after exercise), serum hepcidin level immediately after exercise, and plasma IL‐6 level immediately after exercise (p < .05). Moreover, serum hepcidin level on day 4 was significantly higher in LEA condition than that in NEA condition (p < .05). In conclusion, three consecutive days of endurance training under LEA reduced the muscle glycogen content with concomitant increased serum hepcidin levels in male long distance runners.

Do Antioxidant Vitamins Prevent Exercise-Induced Muscle Damage? A Systematic Review.

Free radicals produced during exercise play a role in modulating cell signaling pathways. High doses of antioxidants may hamper adaptations to exercise training. However, their benefits are unclear. This review aims to examine whether vitamin C (VitC) and/or vitamin E (VitE) supplementation (SUP) prevents exercise-induced muscle damage. The PubMed, Web of Science, Medline, CINAHL, and SPORTDiscus databases were searched, and 21 articles were included. Four studies examined the effects of acute VitC SUP given pre-exercise: in one study, lower CK levels post-exercise was observed; in three, no difference was recorded. In one study, acute VitE SUP reduced CK activity 1 h post-exercise in conditions of hypoxia. In three studies, chronic VitE SUP did not reduce CK activity after an exercise session. Chronic VitE SUP did not reduce creatine kinase (CK) concentrations after three strength training sessions, but it was effective after 6 days of endurance training in another study. Chronic SUP with VitC + E reduced CK activity post-exercise in two studies, but there was no such effect in four studies. Finally, three studies described the effects of chronic VitC + E SUP and long-term exercise, reporting dissimilar results. To conclude, although there is some evidence of a protective effect of VitC and/or VitE against exercise-induced muscle damage, the available data are not conclusive.

Muscle Glycogen Content during Endurance Training under Low Energy Availability

The present study investigated the effects of three consecutive days of endurance training under conditions of low energy availability (LEA) on the muscle glycogen content, muscle damage markers, endocrine regulation, and endurance capacity in male runners. Seven male long-distance runners (19.9 ± 1.1 yr, 175.6 ± 4.7 cm, 61.4 ± 5.3 kg, maximal oxygen uptake [V˙O2max]: 67.5 ± 4.3 mL·kg·min) completed two trials consisting of three consecutive days of endurance training under LEA (18.9 ± 1.9 kcal·kg FFM·d) or normal energy availability (NEA) (52.9 ± 5.0 kcal·kg FFM·d). The order of the two trials was randomized, with a 2-wk interval between trials. The endurance training consisted of 75 min of treadmill running at 70% of V˙O2max. Muscle glycogen content, respiratory gas variables, and blood and urine variables were measured in the morning for three consecutive days of training (days 1-3) and on the following morning after training (day 4). As an indication of endurance capacity, time to exhaustion at 19.0 ± 0.8 km·h to elicit 90% of V˙O2max was evaluated on day 4. During the training period, body weight, fat-free mass, and skeletal muscle volume were significantly reduced in LEA (P = 0.02 for body weight and skeletal muscle volume, P = 0.01 for fat-free mass). Additionally, muscle glycogen content was significantly reduced in LEA (~30%, P < 0.001), with significantly lower values than those in NEA (P < 0.001). Time to exhaustion was not significantly different between the two trials (~20 min, P = 0.39). Three consecutive days of endurance training under LEA decreased muscle glycogen content with lowered body weight. However, endurance capacity was not significantly impaired.

The Effects of Endurance Training Under Low Energy Availability on Muscle Glycogen Contents

PURPOSE:Some previous studies demonstrated that acute bout of exercise suppressed appetite and reduced energy intake among athletes. However, the accumulative effects of reduced energy intake during consecutive days of training period remains unclear. The purpose of the present study was to investigate the influences of 3 days of endurance training under low energy availability on muscle glycogen content, endocrine responses and endurance capacity. METHODS:Seven male long distance runners (19.9 ± 0.4 years, 175.6 ± 1.8 cm, 61.4 ± 2.0 kg, 67.5 ± 1.6 ml/kg/min) completed 3 consecutive days of endurance training under low energy availability trial (LEA, 18.9 ± 0.7 kcal/kg FFM/day) and normal energy availability trial (NEA, 52.9 ± 1.9 kcal/kg FFM/day). The order of two trials was randomized with two weeks interval between trials. The experiment consisted of 3 consecutive days of endurance training (days 1-3) and exercise performance test on the following morning (day 4). The endurance training consisted of 75 min of treadmill running at 70% of maximal oxygen uptake (VO2max) in both trials. Muscle glycogen contents, respiratory gas variables, subjective parameters, blood and urinal variables were evaluated in the morning during 3 days of training periods (day 1-day 3) and on the following morning after the training (day 4). As an indication of endurance capacity, time to exhaustion during submaximal running test was determined on day 4. RESULTS:LEA trial showed that body weight, free fat mass and skeletal muscle volume were significantly reduced during training period (P < 0.05). Also, muscle glycogen contents were significantly decreased in LEA (P < 0.001) with significant lower values than those in NEA trial (P < 0.001). Blood glucose, serum free testosterone and insulin like growth factor-1 concentrations were significant lowered with training under LEA (P < 0.05). On the other hand, serum leptin concentration did not change significantly in LEA trial during training period (P > 0.05). Time to exhaustion during submaximal running test evaluated on day 4 was not significantly different between LEA trial (1170 ± 127 s) and NEA trial (1361 ± 196 s, P > 0.05). CONCLUSION:Three consecutive days of endurance training under Low EA reduced muscle glycogen content. However, endurance capacity was not attenuated.

Expression Pattern of Angiogenic Factors in Healthy Heart in Response to Physical Exercise Intensity.

Recently, many studies showing the regeneration potential of both cardiac and hematopoietic stem cells in adult heart following injury were definitively retracted by the literature. Therefore, stimulating myocardial angiogenesis becomes to be important for preventing cardiovascular diseases. Regular endurance exercise has been reported to induce capillary growth in healthy and diseased myocardium resulting in cardioprotective phenotype. Previously, we demonstrated a significantly increased capillary proliferation in mouse hearts following 30 and 45 days of endurance training. In the present study, we examined the localization and expression pattern of vascular endothelial growth factor receptors (VEGFR-1/Flt-1 and VEGFR-2/Flk-1), hypoxia-inducible factor-1α (HIF-1α), and inducible nitric oxide synthase (iNOS) in heart neocapillarization in response to a mild, moderate, and high intensity of endurance training. Sixty-three Swiss male mice were divided into four untrained control groups and three groups trained for 15 (T15), 30 (T30), and 45 (T45) days with a gradually increasing intensity on a treadmill. We observed the localization of studied proteins with immunostaining and their expression level with Western blot analyses. We found that VEGFR-2/Flk-1 expression progressively increased in trained groups compared with controls, while VEGFR-1/Flt-1 and HIF-1α were higher in T15 than in controls, T30, and T45 animals. Differently, iNOS levels enhanced after 15 and 30 days of exercise. The localization of these factors was not altered by exercise. The results showed that the expression of VEGFR-1/Flt-1, VEGFR-2/Flk-1, HIF-1α, and iNOS is differently regulated in cardiac angiogenesis according to the exercise intensity. VEGFR-1/Flt-1 and HIF-1α are upregulated by a mild intensity exercise, while VEGFR-2/Flk-1 progressively enhances with increasing workload. Differently, iNOS protein is modulated by a moderate intensity exercise. VEGF pathway appears to be involved in exercise-related angiogenesis in heart and VEGF might act in a paracrine and endocrine manner. Understanding this relationship is important for developing exercise strategies to protect the heart by insults.

Effect Of Low Energy Availability During Three Consecutive Days Of Endurance Training On Muscle Glycogen Contents And Serum Hepcidin Levels In Male Long Distance Runners.

Effect Of Low Energy Availability During Three Consecutive Days Of Endurance Training On Muscle Glycogen Contents And Serum Hepcidin Levels In Male Long Distance Runners.

Iron Supplementation during Three Consecutive Days of Endurance Training Augmented Hepcidin Levels.

Iron supplementation contributes an effort to improving iron status among athletes, but it does not always prevent iron deficiency. In the present study, we explored the effect of three consecutive days of endurance training (twice daily) on the hepcidin-25 (hepcidin) level. The effect of iron supplementation during this period was also determined. Fourteen male endurance athletes were enrolled and randomly assigned to either an iron-treated condition (Fe condition, n = 7) or a placebo condition (Control condition; CON, n = 7). They engaged in two 75-min sessions of treadmill running at 75% of maximal oxygen uptake on three consecutive days (days 1–3). The Fe condition took 12 mg of iron twice daily (24 mg/day), and the CON condition did not. On day 1, both conditions exhibited significant increases in serum hepcidin and plasma interleukin-6 levels after exercise (p < 0.05). In the CON condition, the hepcidin level did not change significantly throughout the training period. However, in the Fe condition, the serum hepcidin level on day 4 was significantly higher than that of the CON condition (p < 0.05). In conclusion, the hepcidin level was significantly elevated following three consecutive days of endurance training when moderate doses of iron were taken.

Iron Supplementation During 3 Consecutive Days Of Endurance Training Augmented Hepcidin Concentration

PURPOSE: Several physiological mechanisms have been proposed to explain impaired iron status, such as gastrointestinal bleeding, hemolysis, lack of iron in dietary diet and losses in sweat. However, detailed mechanisms underlying exercise-induced iron deficiency among athletes remain unclear. Hepcidin, the 25-amino acid peptide hormone, is a key mediator of iron homeostasis and it may represent another mechanism for iron deficiency in response to exercise training.The present study was designed to investigate impact of consecutive days of strenuous endurance training on hepcidin concentration. The influence of iron supplementation during training period was also determined. METHODS: Fourteen male endurance athletes (long distance runners, triathletes) participated (mean ± standard error, age: 19-22 yrs ; height: 1.68 ± 0.01m ; body mass: 57.3 ± 1.6 kg; maximal oxygen uptake (VO2max): 59.6 ± 0.8 ml/kg/min). Subjects were randomly assigned to either an iron treatment group (Fe group, n=7) or a placebo group (CON group, n=7). All subjects completed 3 consecutive days of endurance training, consisting of two bouts of 75 min of treadmill running at 75 % of VO2max, separated with 3h of rest between bouts. In the Fe group, 12 mg of iron was provided using flavor drink twice a day (24 mg/day), whereas the subjects in the CON group took the same flavor drink without iron. Venous blood samples were collected in early morning on days1-4 and 3h after second bout of exercise on day1. Serum hepcidin, ferritin, iron, myoglobin and plasma IL-6 concentrations were evaluated. RESULTS: The Fe and CON groups showed acute elevations of serum hepcidin, myoglobin and plasma IL-6 concentrations 3h after exercise (P < 0.05 vs. baseline). After 3 days of training period (day4), serum hepcidin concentration was significantly higher in Fe group than in CON group (11.0 ± 2.5 ng/mL vs. 5.9 ± 1.6 ng/mL, P < 0.05). Moreover, serum iron concentration was decreased only in Fe group on day 4 (91.3 ± 13.5 in the Fe group vs. 129.7 ± 7.4 μg/dL in the CON group). CONCLUSIONS: Three consecutive days of endurance training increased hepcidin concentration at baseline when the iron was supplemented.

Effect of triiodothyronine (T3) excess on fatty acid metabolism in the soleus muscle from endurance-trained rats.

We studied whether short-term administration of triiodothyronine (T3) for the last 3 days of endurance training would influence the rate of uptake of palmitic acid (PA) as well as metabolism in rat soleus muscle, in vitro. Training per se did not affect the rate of PA uptake by the soleus; however, an excess of T3 increased the rate of this process at 1.5 mmol/L PA, as well as the rate that at which PA was incorporated into intramuscular triacylglycerols (TG). The rate of TG synthesis in trained euthyroid rats was reduced after exercise (1.5 mmol/L PA). The rate of PA oxidation in all of the trained rats immediately after exercise was enhanced by comparison with the sedentary values. Hyperthyroidism additionally increased the rate of this process at 1.5 mmol/L PA. After a recovery period, the rate of PA oxidation returned to the control values in both the euthyroid and the hyperthyroid groups. Examination of the high-energy phosphate levels indicated that elevated PA oxidation after exercise-training in euthyroid rats was associated with stable ATP levels and increased ADP and AMP levels, thus reducing energy cellular potential (ECP). In the hyperthyroid rats, levels of ADP and AMP were increased in the sedentary as well as the exercise-trained rats. ECP levels were high as a result of high levels of ATP and decreased levels of ADP and AMP in hyperthyroid rats after the recovery period. In conclusion, short-term hyperthyroidism accelerates PA utilization in well-trained soleus muscle.

The Acute Effect of Concurrent Training on Running Performance Over 6 Days

Purpose: This study examined the effects of strength training on alternating days and endurance training on consecutive days on running performance for 6 days. Methods: Sixteen male and 8 female moderately trained individuals were evenly assigned into concurrent-training (CCT) and strength-training (ST) groups. The CCT group undertook strength training on alternating days combined with endurance training on consecutive days for 6 days. One week later, the CCT group conducted 3 consecutive days of endurance training only to determine whether fatigue would be induced with endurance training alone (CCT-Con). Endurance training was undertaken to induce endurance-training stimulus and to measure the cost of running (CR), rating of perceived exertion (RPE), and time to exhaustion (TTE). The ST group undertook 3 strength-training sessions on alternating days. Maximal voluntary contraction (MVC), rating of muscle soreness (RMS), and rating of muscle fatigue (RMF) were collected prior to each strength and endurance session. Results: For the CCT group, small differences were primarily found in CR and RPE (ES = 0.17–0.41). However, moderate-to-large reductions were found for TTE and MVC (ES = 0.65–2.00), whereas large increases in RMS and RMF (ES = 1.23–2.49) were found prior to each strength- and endurance-training session. Small differences were found in MVC for the ST group (ES = 0.11) and during CCT-Con for the CCT group (ES = 0.15–0.31). Conclusion: Combining strength training on alternating days with endurance training on consecutive days impairs MVC and running performance at maximal effort and increases RMS and RMF over 6 days.

FoxO transcription factors and endurance training: a role for FoxO1 and FoxO3 in exercise-induced angiogenesis.

FoxO transcription factors and endurance training: a role for FoxO1 and FoxO3 in exercise-induced angiogenesis.

Regulation of miRNAs in human skeletal muscle following acute endurance exercise and short‐term endurance training

The identification of microRNAs (miRNAs) has established new mechanisms that control skeletal muscle adaptation to exercise. The present study investigated the mRNA regulation of components of the miRNA biogenesis pathway (Drosha, Dicer and Exportin-5), muscle enriched miRNAs, (miR-1, -133a, -133b and -206), and several miRNAs dysregulated in muscle myopathies (miR-9, -23, -29, -31 and -181). Measurements were made in muscle biopsies from nine healthy untrained males at rest, 3 h following an acute bout of moderate-intensity endurance cycling and following 10 days of endurance training. Bioinformatics analysis was used to predict potential miRNA targets. In the 3 h period following the acute exercise bout, Drosha, Dicer and Exportin-5, as well as miR-1, -133a, -133-b and -181a were all increased. In contrast miR-9, -23a, -23b and -31 were decreased. Short-term training increased miR-1 and -29b, while miR-31 remained decreased. Negative correlations were observed between miR-9 and HDAC4 protein (r=-0.71; P=0.04), miR-31 and HDAC4 protein (r=-0.87; P=0.026) and miR-31 and NRF1 protein (r=-0.77; P=0.01) 3 h following exercise. miR-31 binding to the HDAC4 and NRF1 3 untranslated region (UTR) reduced luciferase reporter activity. Exercise rapidly and transiently regulates several miRNA species in muscle. Several of these miRNAs may be involved in the regulation of skeletal muscle regeneration, gene transcription and mitochondrial biogenesis. Identifying endurance exercise-mediated stress signals regulating skeletal muscle miRNAs, as well as validating their targets and regulatory pathways post exercise, will advance our understanding of their potential role/s in human health.

HSP60 is muscle fiber-type specific and increases after endurance training: Mice model

Heat shock protein (Hsp) 60 plays a key role in the translocation of proteins and cytoprotection, is primarily localized inside mitochondrial, and its levels increase in skeletal muscle upon exercise (Folkesson et al., 2013). The aim of this study was to examine muscle fiber specificity of HSP60 at rest and after an endurance training program of 45 days. Forth-eight male young (7-weeks old) healthy mice (BALB/c) were subdivided into six groups (8 mice per group). Three groups were trained on a rota-rod, at a gradually increasing duration and speed; while the other three groups did not perform any type of regular physical activity. One group of each condition was sacrificed after 15, 30 and 45 days. Forth-eight hours after the last exercise session all mice were sacrificed by cervical dislocation and posterior muscles group of hindlimb (gastrocnemius, soleus and plantaris) were dissected, weighed and embedded into paraffin or frozen in liquid nitrogen. Immunohystochemistry and immunofluorescence analysis showed that skeletal muscle type I fiber expressed high levels of Hsp60. The western blotting analyses of the entire posterior muscle group did not show any difference in the protein levels after endurance training, while the analysis of soleus muscle (reach in type I fibers) showed an over expression of Hsp60 after 30 and 45 days of endurance training. These data indicated that Hsp60 is muscle fibre type–specific. This may be due to the differences in mitochondrial content between slow and fast fibres. Anyway Hsp60 may be localized also in the cytoplasm, in the outer membrane, in the interstitium and in the blood stream, hence the role of this protein in endurance training need be elucidated.

Alterations in global gene expression patterns resulting from 10 days of endurance training in humans

The gene profile of human skeletal muscle can be altered via chronic increases in contractile activity, leading to alteration in skeletal muscle metabolism and ultra-structure. We investigated how short-term endurance training alters skeletal muscle global gene expression patterns, using H19K oligonucleotide micro-arrays, in response to cycling exercise and training. Seven healthy, sedentary individuals participated in a 10-d intensified endurance training regimen which increased VO2max by 12±8% (P<0.05). Differential gene expression (n=4; P<0.05) of 1.5 fold was determined in from muscle biopsies taken before and 3h after a single bout of cycling exercise (~73% pre-training VO2max) pre-training, (199 genes were differentially expressed (DE); 145 up regulated and 54 down regulated) and post-training (188 genes were DE; 107 up regulated and 81 down regulated). A comparison of pre-exercise gene expression patterns (post- vs. pre-training; 235 genes were DE; 121 up regulated and 114 down regulated). Post exercise (post- vs. pre-training) gene expression patterns revealed 191 genes as DE (69 up regulated and 122 down-regulated). Thus short-term training in previously untrained individuals resulted in marked changes in skeletal muscle global gene expression profiles, with genes like peroxisome proliferator-activated receptor α (PPAR-α), calsyphosine (CAPS), glucose-6-phosphate dehydrogenase (G6PD), kaptin (KPTN), and sarcomeric muscle protein (SARCOSIN) responding to cycle exercise and training.