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 (P I O 2 : 143 mmHg) and severe acute hypoxia (P I O 2 : 73 mmHg). CaMKII and AMPKα phosphorylation were similarly induced in both conditions. Enhanced Nrf2 signalling was achieved by raising Nrf2 total protein and Ser 40 Nrf2 phosphorylation, accompanied by a reduction of Keap1. Keap1 protein degradation is facilitated by the phosphorylation of p62/SQSTM1 at Ser 349 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 O 2 -dependent.

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.

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 h thereafter for 24 h, 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 h 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.

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.

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.

No abstract

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. VO2max 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 %), VO2max per kg of legs lean mass (VO2max‐LLM) and age (p = 0.47). Multiple regression analysis showed that the fat % (β = 0.47) is the main predictor of the variability in ACE2 protein expression in skeletal muscle, explaining 5.2% of the variance. VO2max‐LLM had also predictive value (β = 0.09). There was a significant fat % by VO2max‐LLM interaction, such that for subjects with low fat %, VO2max‐LLM was positively associated with ACE2 expression while as fat % increased the slope of the positive association between VO2max‐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.

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.