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

Acute supplementation with a curcuminoid-based formulation fails to enhance resting or exercise-induced NRF2 activity in males and females

Purpose: Exercise and (poly)phenols may activate nuclear factor erythroid 2-related factor 2 (NRF2), a transcription factor that coordinates antioxidant synthesis. The purpose of this study was to determine whether curcuminoid supplementation augments resting and exercise-induced NRF2 activity. Methods: In a double-blinded, randomised, between-subjects design, 14 males and 12 females performed plyometric exercise (100 drop jumps, 50 squat jumps) following 4 d supplementation with a curcuminoid-based formulation (CUR + EX; n = 13; ∼200 mg d-1 curcuminoids) or a placebo (PLA + EX; n = 13). NRF2/DNA binding in peripheral blood mononuclear cells, plasma glutathione peroxidase (GPX), and plasma cytokines (interleukin-6 [IL-6], tumour necrosis factor-alpha [TNF-α]) were measured pre-, post-, 1, 2 h post-exercise. Curcuminoid metabolites were measured 0, 1, 2 h post-administration of a single bolus. Results: Total area under the curve for total curcuminoid metabolites was greater in CUR + EX (p < 0.01), with bioavailability peaking at 2 h post administration (CUR + EX: [0 h] 80.9 ± 117 nM [1 h] 76.6 ± 178.5 nM [2 h] 301.1 ± 584.7 nM; PLA + EX: [0 h] 10.4 ± 1.6 [1 h] 8.5 ± 2.6 [2 h] 10.6 ± 2.1). NRF2 activity did not increase in PLA + EX (p = 0.78) or CUR + EX (p = 0.76); however, curcuminoid metabolite concentrations did positively predict NRF2/DNA binding (R2 = 0.39; p = 0.02). Exercise increased IL-6 (p = 0.03) but TNF-α was unresponsive (p = 0.97) and lower across PLA + EX (p = 0.03). GPX activity was higher in CUR + EX (p < 0.01) but not in PLA + EX (p = 0.94). Conclusion: Supplementation with a curcuminoid-based formulation failed to augment resting or exercise-induced NRF2/DNA binding; however, higher concentrations of curcuminoid metabolites predicted NRF2/DNA binding response, suggesting effects may be dependent on bioavailability.

Sex differences in human performance

Sex as a biological variable is an underappreciated aspect of biomedical research, with its importance emerging in more recent years. This review assesses the current understanding of sex differences in human physical performance. Males outperform females in many physical capacities because they are faster, stronger and more powerful, particularly after male puberty. This review highlights key sex differences in physiological and anatomical systems (generally conferred via sex steroids and puberty) that contribute to these sex differences in human physical performance. Specifically, we address the effects of the primary sex steroids that affect human physical development, discuss insight gained from an observational study of 'real-world data' and elite athletes, and highlight the key physiological mechanisms that contribute to sex differences in several aspects of physical performance. Physiological mechanisms discussed include those for the varying magnitude of the sex differences in performance involving: (1) absolute muscular strength and power; (2) fatigability of limb muscles as a measure of relative performance; and (3) maximal aerobic power and endurance. The profound sex-based differences in human performance involving strength, power, speed and endurance, and that are largely attributable to the direct and indirect effects of sex-steroid hormones, sex chromosomes and epigenetics, provide a scientific rationale and framework for policy decisions on sex-based categories in sports during puberty and adulthood. Finally, we highlight the sex bias and problem in human performance research of insufficient studies and information on females across many areas of biology and physiology, creating knowledge gaps and opportunities for high-impact studies.

Unlocking peak performance: The role of Nrf2 in enhancing exercise outcomes and training adaptation in humans

Since the discovery of the nuclear factor erythroid-derived 2-like 2 (Nrf2) transcription factor thirty years ago, it has been shown that it regulates more than 250 genes involved in a multitude of biological processes, including redox balance, mitochondrial biogenesis, metabolism, detoxification, cytoprotection, inflammation, immunity, autophagy, cell differentiation, and xenobiotic metabolism. In skeletal muscle, Nrf2 signalling is primarily activated in response to perturbation of redox balance by reactive oxygen species or electrophiles. Initial investigations into human skeletal muscle Nrf2 responses to exercise, dating back roughly a decade, have consistently indicated that exercise-induced ROS production stimulates Nrf2 signalling. Notably, recent studies employing Nrf2 knockout mice have revealed impaired skeletal muscle contractile function characterised by reduced force output and increased fatigue susceptibility compared to wild-type counterparts. These deficiencies partially stem from diminished basal mitochondrial respiratory capacity and an impaired capacity to upregulate specific mitochondrial proteins in response to training, findings corroborated by inducible muscle-specific Nrf2 knockout models. In humans, baseline Nrf2 expression in skeletal muscle correlates with maximal oxygen uptake and high-intensity exercise performance. This manuscript delves into the mechanisms underpinning Nrf2 signalling in response to acute exercise in human skeletal muscle, highlighting the involvement of ROS, antioxidants and Keap1/Nrf2 signalling in exercise performance. Furthermore, it explores Nrf2's role in mediating adaptations to chronic exercise and its impact on overall exercise performance. Additionally, the influence of diet and certain supplements on basal Nrf2 expression and its role in modulating acute and chronic exercise responses are briefly addressed.

Physiological and molecular predictors of cycling sprint performance

The study aimed to identify novel muscle phenotypic factors that could determine sprint performance using linear regression models including the lean mass of the lower extremities (LLM), myosin heavy chain composition (MHC), and proteins and enzymes implicated in glycolytic and aerobic energy generation (citrate synthase, OXPHOS proteins), oxygen transport and diffusion (myoglobin), ROS sensing (Nrf2/Keap1), antioxidant enzymes, and proteins implicated in calcium handling. For this purpose, body composition (dual-energy X-ray absorptiometry) and sprint performance (isokinetic 30-s Wingate test: peak and mean power output, Wpeak and Wmean ) were measured in young physically active adults (51 males and 10 females), from which a resting muscle biopsy was obtained from the musculus vastus lateralis. Although females had a higher percentage of MHC I, SERCA2, pSer16 /Thr17 -phospholamban, and Calsequestrin 2 protein expressions (all p < 0.05), and 18.4% lower phosphofructokinase 1 protein expression than males (p < 0.05), both sexes had similar sprint performance when it was normalized to body weight or LLM. Multiple regression analysis showed that Wpeak could be predicted from LLM, SDHB, Keap1, and MHC II % (R 2  = 0.62, p < 0.001), each variable contributing to explain 46.4%, 6.3%, 4.4%, and 4.3% of the variance in Wpeak , respectively. LLM and MHC II % explained 67.5% and 2.1% of the variance in Wmean , respectively (R 2  = 0.70, p < 0.001). The present investigation shows that SDHB and Keap1, in addition to MHC II %, are relevant determinants of peak power output during sprinting.