Antioxidant enzymes and Nrf2/Keap1 in human skeletal muscle: Influence of age, sex, adiposity and aerobic fitness.

Ageing, a sedentary lifestyle, and obesity are associated with increased oxidative stress, while regular exercise is associated with an increased antioxidant capacity in trained skeletal muscles. Whether a higher aerobic fitness is associated with increased expression of antioxidant enzymes and their regulatory factors in skeletal muscle remains unknown. Although oestrogens could promote a higher antioxidant capacity in females, it remains unknown whether a sex dimorphism exists in humans regarding the antioxidant capacity of skeletal muscle. Thus, the aim was to determine the protein expression levels of the antioxidant enzymes SOD1, SOD2, catalase and glutathione reductase (GR) and their regulatory factors Nrf2 and Keap1 in 189 volunteers (120 males and 69 females) to establish whether sex differences exist and how age, VO2max and adiposity influence these. For this purpose, vastus lateralis muscle biopsies were obtained in all participants under resting and unstressed conditions. No significant sex differences in Nrf2, Keap1, SOD1, SOD2, catalase and GR protein expression levels were observed after accounting for VO2max, age and adiposity differences. Multiple regression analysis indicates that the VO2max in mL.kg LLM-1.min-1can be predicted from the levels of SOD2, Total Nrf2 and Keap1 (R = 0.58, P < 0.001), with SOD2 being the main predictor explaining 28 % of variance in VO2max, while Nrf2 and Keap1 explained each around 3 % of the variance. SOD1 protein expression increased with ageing in the whole group after accounting for differences in VO2max and body fat percentage. Overweight and obesity were associated with increased pSer40-Nrf2, pSer40-Nrf2/Total Nrf2 ratio and SOD1 protein expression levels after accounting for differences in age and VO2max. Overall, at the population level, higher aerobic fitness is associated with increased basal expression of muscle antioxidant enzymes, which may explain some of the benefits of regular exercise.

Determinants of the maximal functional reserve during repeated supramaximal exercise by humans: The roles of Nrf2/Keap1, antioxidant proteins, muscle phenotype and oxygenation.

When high-intensity exercise is performed until exhaustion a "functional reserve" (FR) or capacity to produce power at the same level or higher than reached at exhaustion exists at task failure, which could be related to reactive oxygen and nitrogen species (RONS)-sensing and counteracting mechanisms. Nonetheless, the magnitude of this FR remains unknown. Repeated bouts of supramaximal exercise at 120% of VO2max interspaced with 20s recovery periods with full ischaemia were used to determine the maximal FR. Then, we determined which muscle phenotypic features could account for the variability in functional reserve in humans. Exercise performance, cardiorespiratory variables, oxygen deficit, and brain and muscle oxygenation (near-infrared spectroscopy) were measured, and resting muscle biopsies were obtained from 43 young healthy adults (30 males). Males and females had similar aerobic (VO2max per kg of lower extremities lean mass (LLM): 166.7 ± 17.1 and 166.1 ± 15.6 ml kg LLM-1.min-1, P = 0.84) and anaerobic fitness (similar performance in the Wingate test and maximal accumulated oxygen deficit when normalized to LLM). The maximal FR was similar in males and females when normalized to LLM (1.84 ± 0.50 and 2.05 ± 0.59 kJ kg LLM-1, in males and females, respectively, P = 0.218). This FR depends on an obligatory component relying on a reserve in glycolytic capacity and a putative component generated by oxidative phosphorylation. The aerobic component depends on brain oxygenation and phenotypic features of the skeletal muscles implicated in calcium handling (SERCA1 and 2 protein expression), oxygen transport and diffusion (myoglobin) and redox regulation (Keap1). The glycolytic component can be predicted by the protein expression levels of pSer40-Nrf2, the maximal accumulated oxygen deficit and the protein expression levels of SOD1. Thus, an increased capacity to modulate the expression of antioxidant proteins involved in RONS handling and calcium homeostasis may be critical for performance during high-intensity exercise in humans.

A Mango Leaf Extract (Zynamite®) Combined with Quercetin Has Exercise-Mimetic Properties in Human Skeletal Muscle.

Zynamite PX®, a mango leaf extract combined with quercetin, enhances exercise performance by unknown molecular mechanisms. Twenty-five volunteers were assigned to a control (17 males) or supplementation group (8 males, receiving 140 mg of Zynamite® + 140 mg quercetin/8 h for 2 days). Then, they performed incremental exercise to exhaustion (IE) followed by occlusion of the circulation in one leg for 60 s. Afterwards, the cuff was released, and a 30 s sprint was performed, followed by 90 s circulatory occlusion (same leg). Vastus lateralis muscle biopsies were obtained at baseline, 20 s after IE (occluded leg) and 10 s after Wingate (occluded leg), and bilaterally at 90 s and 30 min post exercise. Compared to the controls, the Zynamite PX® group showed increased basal protein expression of Thr287-CaMKIIδD (2-fold, p = 0.007) and Ser9-GSK3ß (1.3-fold, p = 0.005) and a non-significant increase of total NRF2 (1.7-fold, p = 0.099) and Ser40-NRF2 (1.2-fold, p = 0.061). In the controls, there was upregulation with exercise and recovery of total NRF2, catalase, glutathione reductase, and Thr287-CaMKIIδD (1.2-2.9-fold, all p < 0.05), which was not observed in the Zynamite PX® group. In conclusion, Zynamite PX® elicits muscle signaling changes in resting skeletal muscle resembling those described for exercise training and partly abrogates the stress kinases responses to exercise as observed in trained muscles.

Angiotensin-Converting Enzyme 2 (SARS-CoV-2 receptor) expression in human skeletal muscle.

The study aimed to determine the levels of skeletal muscle angiotensin-converting enzyme 2 (ACE2, the SARS-CoV-2 receptor) protein expression in men and women and assess whether ACE2 expression in skeletal muscle is associated with cardiorespiratory fitness and adiposity. The level of ACE2 in vastus lateralis muscle biopsies collected in previous studies from 170 men (age: 19-65 years, weight: 56-137 kg, BMI: 23-44) and 69 women (age: 18-55 years, weight: 41-126 kg, BMI: 22-39) was analyzed in duplicate by western blot. VO2 max was determined by ergospirometry and body composition by DXA. ACE2 protein expression was 1.8-fold higher in women than men (p = 0.001, n = 239). This sex difference disappeared after accounting for the percentage of body fat (fat %), VO2 max per kg of legs lean mass (VO2 max-LLM) and age (p = 0.47). Multiple regression analysis showed that the fat % (ß = 0.47) is the main predictor of the variability in ACE2 protein expression in skeletal muscle, explaining 5.2% of the variance. VO2 max-LLM had also predictive value (ß = 0.09). There was a significant fat % by VO2 max-LLM interaction, such that for subjects with low fat %, VO2 max-LLM was positively associated with ACE2 expression while as fat % increased the slope of the positive association between VO2 max-LLM and ACE2 was reduced. In conclusion, women express higher amounts of ACE2 in their skeletal muscles than men. This sexual dimorphism is mainly explained by sex differences in fat % and cardiorespiratory fitness. The percentage of body fat is the main predictor of the variability in ACE2 protein expression in human skeletal muscle.

Functional reserve and sex differences during exercise to exhaustion revealed by post-exercise ischaemia and repeated supramaximal exercise.

KEY POINTS: Females have lower fatigability than males during single limb isometric and dynamic contractions, but whether sex-differences exist during high-intensity whole-body exercise remains unknown. This study shows that males and females respond similarly to repeated supramaximal whole-body exercise, and that at task failure a large functional reserve remains in both sexes. Using post-exercise ischaemia with repeated exercise, we have shown that this functional reserve depends on the glycolytic component of substrate-level phosphorylation and is almost identical in both sexes. Metaboreflex activation during post-exercise ischaemia and the O2 debt per kg of active lean mass are also similar in males and females after supramaximal exercise. Females have a greater capacity to extract oxygen during repeated supramaximal exercise and reach lower PETCO2 , experiencing a larger drop in brain oxygenation than males, without apparent negative repercussion on performance. Females had no faster recovery of performance after accounting for sex differences in lean mass. ABSTRACT: The purpose of this study was to ascertain what mechanisms explain sex differences at task failure and to determine whether males and females have a functional reserve at exhaustion. Exercise performance, cardiorespiratory variables, oxygen deficit, and brain and muscle oxygenation were determined in 18 males and 18 females (21-36 years old) in two sessions consisting of three bouts of constant-power exercise at 120% of V̇O2max until exhaustion interspaced by 20 s recovery periods. In one of the two sessions, the circulation of both legs was occluded instantaneously (300 mmHg) during the recovery periods. Females had a higher muscle O2 extraction during fatiguing supramaximal exercise than males. Metaboreflex activation, and lean mass-adjusted O2 deficit and debt were similar in males and females. Compared to males, females reached lower PETCO2 and brain oxygenation during supramaximal exercise, without apparent negative consequences on performance. After the occlusions, males and females were able to restart exercising at 120% of V̇O2max , revealing a similar functional reserve, which depends on glycolytic component of substrate-level phosphorylation and its rate of utilization. After ischaemia, muscle O2 extraction was increased, and muscle V̇O2 was similarly reduced in males and females. The physiological response to repeated supramaximal exercise to exhaustion is remarkably similar in males and females when differences in lean mass are considered. Both sexes fatigue with a large functional reserve, which depends on the glycolytic energy supply, yet females have higher oxygen extraction capacity, but reduced PETCO2 and brain oxygenation.

Role of CaMKII and sarcolipin in muscle adaptations to strength training with different levels of fatigue in the set.

Strength training promotes a IIX-to-IIA shift in myosin heavy chain (MHC) composition, likely due to changes in sarcoplasmic [Ca2+ ] which are sensed by CaMKII. Sarcoplasmic [Ca2+ ] is in part regulated by sarcolipin (SLN), a small protein that when overexpressed in rodents stimulates mitochondrial biogenesis and a fast-to-slow fiber type shift. The purpose of this study was to determine whether CaMKII and SLN are involved in muscle phenotype and performance changes elicited by strength training. Twenty-two men followed an 8-week velocity-based resistance training program using the full squat exercise while monitoring repetition velocity. Subjects were randomly assigned to two resistance training programs differing in the repetition velocity loss allowed in each set: 20% (VL20) vs 40% (VL40). Strength training caused muscle hypertrophy, improved 1RM and increased total CaMKII protein expression, particularly of the δD isoform. Phospho-Thr287 -CaMKII δD expression increased only in VL40 (+89%), which experienced greater muscle hypertrophy, and a reduction in MHC-IIX percentage. SLN expression was increased in VL20 (+33%) remaining unaltered in VL40. The changes in phospho-Thr287 -CaMKII δD were positively associated with muscle hypertrophy and the number of repetitions during training, and negatively with the changes in MHC-IIX and SLN. Most OXPHOS proteins remained unchanged, except for NDUFB8 (Complex I), which was reduced after training (-22%) in both groups. The amount of fatigue allowed in each set critically influences muscle CaMKII and SLN responses and determines muscle phenotype changes. With lower intra-set fatigue, the IIX-to-IIA MHC shift is attenuated.

Regulation of Nrf2/Keap1 signalling in human skeletal muscle during exercise to exhaustion in normoxia, severe acute hypoxia and post-exercise ischaemia: Influence of metabolite accumulation and oxygenation.

The Nrf2 transcription factor is induced by reactive oxygen and nitrogen species and is necessary for the adaptive response to exercise in mice. It remains unknown whether Nrf2 signalling is activated by exercise in human skeletal muscle. Here we show that Nrf2 signalling is activated by exercise to exhaustion with similar responses in normoxia (PIO2: 143 mmHg) and severe acute hypoxia (PIO2: 73 mmHg). CaMKII and AMPKα phosphorylation were similarly induced in both conditions. Enhanced Nrf2 signalling was achieved by raising Nrf2 total protein and Ser40 Nrf2 phosphorylation, accompanied by a reduction of Keap1. Keap1 protein degradation is facilitated by the phosphorylation of p62/SQSTM1 at Ser349 by AMPK, which targets Keap1 for autophagic degradation. Consequently, the Nrf2-to-Keap1 ratio was markedly elevated and closely associated with a 2-3-fold increase in Catalase protein. No relationship was observed between Nrf2 signalling and SOD1 and SOD2 protein levels. Application of ischaemia immediately at the end of exercise maintained these changes, which were reverted within 1 min of recovery with free circulation. While SOD2 did not change significantly during either exercise or ischaemia, SOD1 protein expression was marginally downregulated and upregulated during exercise in normoxia and hypoxia, respectively. We conclude that Nrf2/Keap1/Catalase pathway is rapidly regulated during exercise and recovery in human skeletal muscle. Catalase emerges as an essential antioxidant enzyme acutely upregulated during exercise and ischaemia. Post-exercise ischaemia maintains Nrf2 signalling at the level reached at exhaustion and can be used to avoid early post-exercise recovery, which is O2-dependent.

Supplementation with a Mango Leaf Extract (Zynamite®) in Combination with Quercetin Attenuates Muscle Damage and Pain and Accelerates Recovery after Strenuous Damaging Exercise.

Prolonged or unusual exercise may cause exercise-induced muscle damage (EIMD). To test whether Zynamite®, a mango leaf extract rich in the natural polyphenol mangiferin, administered in combination with quercetin facilitates recovery after EIMD, 24 women and 33 men were randomly assigned to two treatment groups matched by sex and 5 km running performance, and ran a 10 km race followed by 100 drop jumps to elicit EIMD. One hour before the competition, and every 8 hours thereafter for 24 hours, they ingested placebo (728 mg of maltodextrin) or 140 mg of Zynamite® combined with 140 mg of quercetin (double-blind). Although competition times were similar, polyphenol supplementation attenuated the muscle pain felt after the competition (6.8 ± 1.5 and 5.7 ± 2.2 a.u., p = 0.035) and the loss of jumping performance (9.4 ± 11.5 and 3.9 ± 5.2%, p = 0.036; p = 0.034) and mechanical impulse (p = 0.038) 24 hours later. The polyphenols attenuated the increase of serum myoglobin and alanine aminotransferase in men, but not in women (interaction p < 0.05). In conclusion, a single dose of 140 mg Zynamite® combined with 140 mg of quercetin, administered one hour before competition, followed by three additional doses every eight hours, attenuates muscle pain and damage, and accelerates the recovery of muscle performance.

Sarcolipin expression in human skeletal muscle: Influence of energy balance and exercise.

Sarcolipin (SLN) is a SERCA uncoupling protein associated with exercise performance and lower adiposity in mice. To determine SLN protein expression in human skeletal muscle and its relationship with adiposity, resting energy expenditure (REE), and performance, SLN was assessed by Western blot in 199 biopsies from two previous studies. In one study, 15 overweight volunteers underwent a pretest followed by 4 days of caloric restriction and exercise (45-minute one-arm cranking + 8-hour walking), and 3 days on a control diet. Muscle biopsies were obtained from the trained and non-exercised deltoid, and vastus lateralis (VL). In another study, 16 men performed seven sessions of 4-6 × 30-sec all-out sprints on the cycle ergometer with both limbs, and their VL and triceps brachii biopsied pre- and post-training. SLN expression was twofold and 44% higher in the VL than in the deltoids and triceps brachii, respectively. SLN was associated with neither adiposity nor REE, and was not altered by a severe energy deficit (5500 kcal/day). SLN and cortisol changes after the energy deficit were correlated (r = .38, P = .039). SLN was not altered by low-intensity exercise in the overweight subjects, whereas it was reduced after sprint training in the other group. The changes in SLN with sprint training were inversely associated with the changes in gross efficiency (r = -.59, P = .016). No association was observed between aerobic or anaerobic performance and SLN expression. In conclusion, sarcolipin appears to play no role in regulating the fat mass of men. Sprint training reduces sarcolipin expression, which may improve muscle efficiency.

Exercise Mitigates the Loss of Muscle Mass by Attenuating the Activation of Autophagy during Severe Energy Deficit.

The loss of skeletal muscle mass with energy deficit is thought to be due to protein breakdown by the autophagy-lysosome and the ubiquitin-proteasome systems. We studied the main signaling pathways through which exercise can attenuate the loss of muscle mass during severe energy deficit (5500 kcal/day). Overweight men followed four days of caloric restriction (3.2 kcal/kg body weight day) and prolonged exercise (45 min of one-arm cranking and 8 h walking/day), and three days of control diet and restricted exercise, with an intra-subject design including biopsies from muscles submitted to distinct exercise volumes. Gene expression and signaling data indicate that the main catabolic pathway activated during severe energy deficit in skeletal muscle is the autophagy-lysosome pathway, without apparent activation of the ubiquitin-proteasome pathway. Markers of autophagy induction and flux were reduced by exercise primarily in the muscle submitted to an exceptional exercise volume. Changes in signaling are associated with those in circulating cortisol, testosterone, cortisol/testosterone ratio, insulin, BCAA, and leucine. We conclude that exercise mitigates the loss of muscle mass by attenuating autophagy activation, blunting the phosphorylation of AMPK/ULK1/Beclin1, and leading to p62/SQSTM1 accumulation. This includes the possibility of inhibiting autophagy as a mechanism to counteract muscle loss in humans under severe energy deficit.

A Single Dose of The Mango Leaf Extract Zynamite® in Combination with Quercetin Enhances Peak Power Output During Repeated Sprint Exercise in Men and Women.

The mango leaf extract rich in mangiferin Zynamite® improves exercise performance when combined with luteolin or quercetin ingested at least 48 h prior to exercise. To determine whether a single dose of Zynamite® administered 1 h before exercise increases repeated-sprint performance, 20 men and 20 women who were physically active were randomly assigned to three treatments following a double-blind cross-over counterbalanced design. Treatment A, 140 mg of Zynamite®, 140 mg of quercetin, 147.7 mg of maltodextrin, and 420 mg of sunflower lecithin; Treatment B, 140 mg of Zynamite®, 140 mg of quercetin, and 2126 mg of maltodextrin and Treatment C, 2548 mg of maltodextrin (placebo). Subjects performed three Wingate tests interspaced by 4 min and a final 15 s sprint after ischemia. Treatments A and B improved peak power output during the first three Wingates by 2.8% and 3.8%, respectively (treatment x sprint interaction, p = 0.01). Vastus Lateralis oxygenation (NIRS) was reduced, indicating higher O2 extraction (treatment × sprint interaction, p = 0.01). Improved O2 extraction was observed in the sprints after ischemia (p = 0.008; placebo vs. mean of treatments A and B). Blood lactate concentration was 5.9% lower after the ingestion of Zynamite® with quercetin in men (treatment by sex interaction, p = 0.049). There was a higher Vastus Lateralis O2 extraction during 60 s ischemia with polyphenols (treatment effect, p = 0.03), due to the greater muscle VO2 in men (p = 0.001). In conclusion, a single dose of Zynamite® combined with quercetin one hour before exercise improves repeated-sprint performance and muscle O2 extraction and mitochondrial O2. consumption during ischemia. No advantage was obtained from the addition of phospholipids.

Enhancement of Exercise Performance by 48 Hours, and 15-Day Supplementation with Mangiferin and Luteolin in Men.

The natural polyphenols mangiferin and luteolin have free radical-scavenging properties, induce the antioxidant gene program and down-regulate the expression of superoxide-producing enzymes. However, the effects of these two polyphenols on exercise capacity remains mostly unknown. To determine whether a combination of luteolin (peanut husk extract containing 95% luteolin, PHE) and mangiferin (mango leave extract (MLE), Zynamite®) at low (PHE: 50 mg/day; and 140 mg/day of MLE containing 100 mg of mangiferin; L) and high doses (PHE: 100 mg/day; MLE: 420 mg/day; H) may enhance exercise performance, twelve physically active men performed incremental exercise to exhaustion, followed by sprint and endurance exercise after 48 h (acute effects) and 15 days of supplementation (prolonged effects) with polyphenols or placebo, following a double-blind crossover design. During sprint exercise, mangiferin + luteolin supplementation enhanced exercise performance, facilitated muscle oxygen extraction, and improved brain oxygenation, without increasing the VO2. Compared to placebo, mangiferin + luteolin increased muscle O2 extraction during post-exercise ischemia, and improved sprint performance after ischemia-reperfusion likely by increasing glycolytic energy production, as reflected by higher blood lactate concentrations after the sprints. Similar responses were elicited by the two doses tested. In conclusion, acute and prolonged supplementation with mangiferin combined with luteolin enhances performance, muscle O2 extraction, and brain oxygenation during sprint exercise, at high and low doses.

Mangifera indica L. Leaf Extract in Combination With Luteolin or Quercetin Enhances VO2peak and Peak Power Output, and Preserves Skeletal Muscle Function During Ischemia-Reperfusion in Humans.

It remains unknown whether polyphenols such as luteolin (Lut), mangiferin and quercetin (Q) have ergogenic effects during repeated all-out prolonged sprints. Here we tested the effect of Mangifera indica L. leaf extract (MLE) rich in mangiferin (Zynamite®) administered with either quercetin (Q) and tiger nut extract (TNE), or with luteolin (Lut) on sprint performance and recovery from ischemia-reperfusion. Thirty young volunteers were randomly assigned to three treatments 48 h before exercise. Treatment A: placebo (500 mg of maltodextrin/day); B: 140 mg of MLE (60% mangiferin) and 50 mg of Lut/day; and C: 140 mg of MLE, 600 mg of Q and 350 mg of TNE/day. After warm-up, subjects performed two 30 s Wingate tests and a 60 s all-out sprint interspaced by 4 min recovery periods. At the end of the 60 s sprint the circulation of both legs was instantaneously occluded for 20 s. Then, the circulation was re-opened and a 15 s sprint performed, followed by 10 s recovery with open circulation, and another 15 s final sprint. MLE supplements enhanced peak (Wpeak) and mean (Wmean) power output by 5.0-7.0% (P < 0.01). After ischemia, MLE+Q+TNE increased Wpeak by 19.4 and 10.2% compared with the placebo (P < 0.001) and MLE+Lut (P < 0.05), respectively. MLE+Q+TNE increased Wmean post-ischemia by 11.2 and 6.7% compared with the placebo (P < 0.001) and MLE+Lut (P = 0.012). Mean VO2 during the sprints was unchanged, suggesting increased efficiency or recruitment of the anaerobic capacity after MLE ingestion. In women, peak VO2 during the repeated sprints was 5.8% greater after the administration of MLE, coinciding with better brain oxygenation. MLE attenuated the metaboreflex hyperpneic response post-ischemia, may have improved O2 extraction by the Vastus Lateralis (MLE+Q+TNE vs. placebo, P = 0.056), and reduced pain during ischemia (P = 0.068). Blood lactate, acid-base balance, and plasma electrolytes responses were not altered by the supplements. In conclusion, a MLE extract rich in mangiferin combined with either quercetin and tiger nut extract or luteolin exerts a remarkable ergogenic effect, increasing muscle power in fatigued subjects and enhancing peak VO2 and brain oxygenation in women during prolonged sprinting. Importantly, the combination of MLE+Q+TNE improves skeletal muscle contractile function during ischemia/reperfusion.

Skeletal Muscle Pyruvate Dehydrogenase Phosphorylation and Lactate Accumulation During Sprint Exercise in Normoxia and Severe Acute Hypoxia: Effects of Antioxidants.

Compared to normoxia, during sprint exercise in severe acute hypoxia the glycolytic rate is increased leading to greater lactate accumulation, acidification, and oxidative stress. To determine the role played by pyruvate dehydrogenase (PDH) activation and reactive nitrogen and oxygen species (RNOS) in muscle lactate accumulation, nine volunteers performed a single 30-s sprint (Wingate test) on four occasions: two after the ingestion of placebo and another two following the intake of antioxidants, while breathing either hypoxic gas (PIO2 = 75 mmHg) or room air (PIO2 = 143 mmHg). Vastus lateralis muscle biopsies were obtained before, immediately after, 30 and 120 min post-sprint. Antioxidants reduced the glycolytic rate without altering performance or VO2. Immediately after the sprints, Ser293- and Ser300-PDH-E1α phosphorylations were reduced to similar levels in all conditions (~66 and 91%, respectively). However, 30 min into recovery Ser293-PDH-E1α phosphorylation reached pre-exercise values while Ser300-PDH-E1α was still reduced by 44%. Thirty minutes after the sprint Ser293-PDH-E1α phosphorylation was greater with antioxidants, resulting in 74% higher muscle lactate concentration. Changes in Ser293 and Ser300-PDH-E1α phosphorylation from pre to immediately after the sprints were linearly related after placebo (r = 0.74, P < 0.001; n = 18), but not after antioxidants ingestion (r = 0.35, P = 0.15). In summary, lactate accumulation during sprint exercise in severe acute hypoxia is not caused by a reduced activation of the PDH. The ingestion of antioxidants is associated with increased PDH re-phosphorylation and slower elimination of muscle lactate during the recovery period. Ser293 re-phosphorylates at a faster rate than Ser300-PDH-E1α during the recovery period, suggesting slightly different regulatory mechanisms.

Skeletal muscle signaling, metabolism, and performance during sprint exercise in severe acute hypoxia after the ingestion of antioxidants.

The aim of this study was to determine if reactive oxygen species (ROS) could play a role in blunting Thr172-AMP-activated protein kinase (AMPK)-α phosphorylation in human skeletal muscle after sprint exercise in hypoxia and to elucidate the potential signaling mechanisms responsible for this response. Nine volunteers performed a single 30-s sprint (Wingate test) in two occasions while breathing hypoxic gas ([Formula: see text] = 75 mmHg): one after the ingestion of placebo and another following the intake of antioxidants (α-lipoic acid, vitamin C, and vitamin E), with a randomized double-blind design. Vastus lateralis muscle biopsies were obtained before, immediately after, and 30- and 120-min postsprint. Compared with the control condition, the ingestion of antioxidants resulted in lower plasma carbonylated proteins, attenuated elevation of the AMP-to-ATP molar ratio, and reduced glycolytic rate (P < 0.05) without significant effects on performance or V̇o2 The ingestion of antioxidants did not alter the basal muscle signaling. Thr172-AMPKα and Thr184/187-transforming growth factor-ß-activated kinase 1 (TAK1) phosphorylation were not increased after the sprint regardless of the ingestion of antioxidants. Thr286-CaMKII phosphorylation was increased after the sprint, but this response was blunted by the antioxidants. Ser485-AMPKα1/Ser491-AMPKα2 phosphorylation increased immediately after the sprints coincident with increased Akt phosphorylation. In summary, antioxidants attenuate the glycolytic response to sprint exercise in severe acute hypoxia and modify the muscle signaling response to exercise. Ser485-AMPKα1/Ser491-AMPKα2 phosphorylation, a known mechanism of Thr172-AMPKα phosphorylation inhibition, is increased immediately after sprint exercise in hypoxia, probably by a mechanism independent of ROS.NEW & NOTEWORTHY The glycolytic rate is increased during sprint exercise in severe acute hypoxia. This study showed that the ingestion of antioxidants before sprint exercise in severe acute hypoxia reduced the glycolytic rate and attenuated the increases of the AMP-to-ATP and the reduction of the NAD+-to-NADH.H+ ratios. This resulted in a modified muscle signaling response with a blunted Thr286-CaMKII but similar AMP-activated protein kinase phosphorylation responses in the sprints preceded by the ingestion of antioxidants.

The Physiological Mechanisms of Performance Enhancement with Sprint Interval Training Differ between the Upper and Lower Extremities in Humans.

To elucidate the mechanisms underlying the differences in adaptation of arm and leg muscles to sprint training, over a period of 11 days 16 untrained men performed six sessions of 4-6 × 30-s all-out sprints (SIT) with the legs and arms, separately, with a 1-h interval of recovery. Limb-specific VO2peak, sprint performance (two 30-s Wingate tests with 4-min recovery), muscle efficiency and time-trial performance (TT, 5-min all-out) were assessed and biopsies from the m. vastus lateralis and m. triceps brachii taken before and after training. VO2peak and Wmax increased 3-11% after training, with a more pronounced change in the arms (P < 0.05). Gross efficiency improved for the arms (+8.8%, P < 0.05), but not the legs (-0.6%). Wingate peak and mean power outputs improved similarly for the arms and legs, as did TT performance. After training, VO2 during the two Wingate tests was increased by 52 and 6% for the arms and legs, respectively (P < 0.001). In the case of the arms, VO2 was higher during the first than second Wingate test (64 vs. 44%, P < 0.05). During the TT, relative exercise intensity, HR, VO2, VCO2, VE, and Vt were all lower during arm-cranking than leg-pedaling, and oxidation of fat was minimal, remaining so after training. Despite the higher relative intensity, fat oxidation was 70% greater during leg-pedaling (P = 0.017). The aerobic energy contribution in the legs was larger than for the arms during the Wingate tests, although VO2 for the arms was enhanced more by training, reducing the O2 deficit after SIT. The levels of muscle glycogen, as well as the myosin heavy chain composition were unchanged in both cases, while the activities of 3-hydroxyacyl-CoA-dehydrogenase and citrate synthase were elevated only in the legs and capillarization enhanced in both limbs. Multiple regression analysis demonstrated that the variables that predict TT performance differ for the arms and legs. The primary mechanism of adaptation to SIT by both the arms and legs is enhancement of aerobic energy production. However, with their higher proportion of fast muscle fibers, the arms exhibit greater plasticity.