Antioxidant supplementation does not alter endurance training adaptation

Reactive oxygen species promote endurance exercise-induced adaptations in skeletal muscles

The discovery that contracting skeletal muscle generates reactive oxygen species (ROS) was first reported over 40 years ago. The prevailing view in the 1980s was that exercise-induced ROS production promotes oxidation of proteins and lipids resulting in muscle damage. However, a paradigm shift occurred in the 1990s as growing research revealed that ROS are signaling molecules, capable of activating transcriptional activators/coactivators and promoting exercise-induced muscle adaptation. Growing evidence supports the notion that reduction-oxidation (redox) signaling pathways play an important role in the muscle remodeling that occurs in response to endurance exercise training. This review examines the specific role that redox signaling plays in this endurance exercise-induced skeletal muscle adaptation. We begin with a discussion of the primary sites of ROS production in contracting muscle fibers followed by a summary of the antioxidant enzymes involved in the regulation of ROS levels in the cell. We then discuss which redox-sensitive signaling pathways promote endurance exercise-induced muscle adaptation and debate the strength of the evidence supporting the notion that redox signaling plays an essential role in muscle adaptation to endurance exercise training. In hopes of stimulating future research, we highlight several important unanswered questions in this field.

Oxidative Stress in Military Missions-Impact and Management Strategies: A Narrative Analysis

This narrative review comprehensively examines the impact of oxidative stress on military personnel, highlighting the crucial role of physical exercise and tailored diets, particularly the ketogenic diet, in minimizing this stress. Through a meticulous analysis of the recent literature, the study emphasizes how regular physical exercise not only enhances cardiovascular, cognitive, and musculoskeletal health but is also essential in neutralizing the effects of oxidative stress, thereby improving endurance and performance during long-term missions. Furthermore, the implementation of the ketogenic diet provides an efficient and consistent energy source through ketone bodies, tailored to the specific energy requirements of military activities, and significantly contributes to the reduction in reactive oxygen species production, thus protecting against cellular deterioration under extreme stress. The study also underlines the importance of integrating advanced technologies, such as wearable devices and smart sensors that allow for the precise and real-time monitoring of oxidative stress and physiological responses, thus facilitating the customization of training and nutritional regimes. Observations from this review emphasize significant variability among individuals in responses to oxidative stress, highlighting the need for a personalized approach in formulating intervention strategies. It is crucial to develop and implement well-monitored, personalized supplementation protocols to ensure that each member of the military personnel receives a regimen tailored to their specific needs, thereby maximizing the effectiveness of measures to combat oxidative stress. This analysis makes a valuable contribution to the specialized literature, proposing a detailed framework for addressing oxidative stress in the armed forces and opening new directions for future research with the aim of optimizing clinical practices and improving the health and performance of military personnel under stress and specific challenges of the military field.

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-CaMKIIδ_D (2-fold, p = 0.007) and Ser⁹-GSK3β (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-CaMKIIδ_D (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.

Antioxidants and Sports Performance

The role of reactive oxygen species and antioxidant response in training adaptations and sports performance has been a large issue investigated in the last few years. The present review aims to analyze the role of reactive oxygen species and antioxidant response in sports performance. For this aim, the production of reactive oxygen species in physical activities, the effect of reactive oxygen species on sports performance, the relationship between reactive oxygen species and training adaptations, inflammation, and the microbiota, the effect of antioxidants on recovery and sports performance, and strategies to use antioxidants supplementations will be discussed. Finally, practical applications derived from this information are discussed. The reactive oxygen species (ROS) production during physical activity greatly influences sports performance. This review concludes that ROS play a critical role in the processes of training adaptation induced by resistance training through a reduction in inflammatory mediators and oxidative stress, as well as appropriate molecular signaling. Additionally, it has been established that micronutrients play an important role in counteracting free radicals, such as reactive oxygen species, which cause oxidative stress, and the effects of antioxidants on recovery, sports performance, and strategies for using antioxidant supplements, such as vitamin C, vitamin E, resveratrol, coenzyme Q10, selenium, and curcumin to enhance physical and mental well-being.

Exercise training remodels inguinal white adipose tissue through adaptations in innervation, vascularization, and the extracellular matrix

Inguinal white adipose tissue (iWAT) is essential for the beneficial effects of exercise training on metabolic health. The underlying mechanisms for these effects are not fully understood, and here, we test the hypothesis that exercise training results in a more favorable iWAT structural phenotype. Using biochemical, imaging, and multi-omics analyses, we find that 11 days of wheel running in male mice causes profound iWAT remodeling including decreased extracellular matrix (ECM) deposition and increased vascularization and innervation. We identify adipose stem cells as one of the main contributors to training-induced ECM remodeling, show that the PRDM16 transcriptional complex is necessary for iWAT remodeling and beiging, and discover neuronal growth regulator 1 (NEGR1) as a link between PRDM16 and neuritogenesis. Moreover, we find that training causes a shift from hypertrophic to insulin-sensitive adipocyte subpopulations. Exercise training leads to remarkable adaptations to iWAT structure and cell-type composition that can confer beneficial changes in tissue metabolism.

Astaxanthin promotes mitochondrial biogenesis and antioxidant capacity in chronic high-intensity interval training

PURPOSE

Reactive oxygen and nitrogen species are required for exercise-induced molecular adaptations; however, excessive exercise may cause cellular oxidative distress. We postulate that astaxanthin (ASX) can neutralize oxidative distress and stimulate mitochondrial biogenesis in high-intensity exercise-trained mice.

METHODS

Six-week-old mice (n = 8/group) were treated with ASX (10 mg/kg BW) or placebo. Training groups participated in 30 min/day high-intensity interval training (HIIT) for 6 weeks. Gastrocnemius muscle was collected and assayed following the exercise training period.

RESULTS

Compared to the HIIT control mice, the ASX-treated HIIT mice reduced malonaldehyde levels and upregulated the expression of Nrf2 and FOXO3a. Meanwhile, the genes NQO1 and GCLC, modulated by Nrf2, and SOD2, regulated by FOXO3a, and GPx4, were transcriptionally upregulated in the ASX-treated HIIT group. Meanwhile, the expression of energy sensors, AMPK, SIRT1, and SIRT3, increased in the ASX-treated HIIT group compared to the HIIT control group. Additionally, PGC-1α, regulated by AMPK and SIRT1, was upregulated in the ASX-treated HIIT group. Further, the increased PGC-1α stimulated the transcript of NRF1 and Tfam and mitochondrial proteins IDH2 and ATP50. Finally, the ASX-treated HIIT mice had upregulations in the transcript level of mitochondrial fusion factors, including Mfn1, Mfn2, and OPA1. However, the protein level of AMPK, SIRT1, and FOXO3a, and the transcript level of Nrf2, NQO1, PGC-1α, NRF1, Mfn1, Mfn2, and OPA1 decreased in the HIIT control group compared to the sedentary control group.

CONCLUSION

Supplementation with ASX can reduce oxidative stress and promote antioxidant capacity and mitochondrial biogenesis during strenuous HIIT exercise in mice.

Targeting the molecular & cellular pillars of human aging with exercise

Biological aging is the main driver of age-associated chronic diseases. In 2014, the United States National Institute of Aging (NIA) sponsored a meeting between several investigators in the field of aging biology, who identified seven biological pillars of aging and a consensus review, "Geroscience: Linking Aging to Chronic Disease," was published. The pillars of aging demonstrated the conservation of aging pathways in diverse model organisms and thus represent a useful framework with which to study human aging. In this present review, we revisit the seven pillars of aging from the perspective of exercise and discuss how regular physical exercise can modulate these pillars to stave off age-related chronic diseases and maintain functional capacity.

Nutritional Compounds to Improve Post-Exercise Recovery

The metabolic and mechanical stresses associated with muscle-fatiguing exercise result in perturbations to bodily tissues that lead to exercise-induced muscle damage (EIMD), a state of fatigue involving oxidative stress and inflammation that is accompanied by muscle weakness, pain and a reduced ability to perform subsequent training sessions or competitions. This review collates evidence from previous research on a wide range of nutritional compounds that have the potential to speed up post-exercise recovery. We show that of the numerous compounds investigated thus far, only two-tart cherry and omega-3 fatty acids-are supported by substantial research evidence. Further studies are required to clarify the potential effects of other compounds presented here, many of which have been used since ancient times to treat conditions associated with inflammation and disease.

Redox signaling regulates skeletal muscle remodeling in response to exercise and prolonged inactivity

Skeletal muscle fibers are malleable and undergo rapid remodeling in response to increased contractile activity (i.e., exercise) or prolonged periods of muscle inactivity (e.g., prolonged bedrest). Exploration of the cell signaling pathways regulating these skeletal muscle adaptations reveal that redox signaling pathways play a key role in the control of muscle remodeling during both exercise and prolonged muscle inactivity. In this regard, muscular exercise results in an acute increase in the production of reactive oxygen species (ROS) in the contracting fibers; however, this contraction-induced rise in ROS production rapidly declines when contractions cease. In contrast, prolonged muscle disuse results in a chronic elevation in ROS production within the inactive fibers. This difference in the temporal pattern of ROS production in muscle during exercise and muscle inactivity stimulates divergent cell-signaling pathways that activate both genomic and nongenomic mechanisms to promote muscle remodeling. This review examines the role that redox signaling plays in skeletal muscle adaptation in response to both prolonged muscle inactivity and endurance exercise training. We begin with a summary of the sites of ROS production in muscle fibers followed by a review of the cellular antioxidants that are responsible for regulation of ROS levels in the cell. We then discuss the specific redox-sensitive signaling pathways that promote skeletal muscle adaptation in response to both prolonged muscle inactivity and exercise. To stimulate future research, we close with a discussion of unanswered questions in this exciting field.

Multi-Ingredient Supplement Supports Mitochondrial Health through Interleukin-15 Signaling in Older Adult Human Dermal Fibroblasts

The macroscopic and microscopic deterioration of human skin with age is, in part, attributed to a functional decline in mitochondrial health. We previously demonstrated that exercise attenuated age-associated changes within the skin through enhanced mitochondrial health via IL-15 signaling, an exercise-induced cytokine whose presence increases in circulation following physical activity. The purpose of this investigation was to determine if these mitochondrial-enhancing effects could be mimicked with the provision of a novel multi-ingredient supplement (MIS). Cultured human fibroblasts isolated from older, sedentary women were treated with control media (CON) or CON supplemented with the following active ingredients to create the MIS: coenzyme Q10, alpha lipoic acid, resveratrol, curcumin, zinc, lutein, astaxanthin, copper, biotin, and vitamins C, D, and E. Outcomes were determined following 24 or 72 h of treatment. MIS provision to dermal fibroblasts significantly increased the mRNA abundance of mitochondrial biogenesis activators and downstream IL-15 signaling pathways, and proteins for oxidative phosphorylation subunits and antioxidant defenses. These findings were co-temporal with lower cellular senescence and cytotoxicity following MIS treatment. In summary, MIS supplementation led to exercise-mimetic effects on human dermal fibroblasts and their mitochondria by reproducing the molecular and biochemical effects downstream of IL-15 activation.

State of Knowledge on Molecular Adaptations to Exercise in Humans: Historical Perspectives and Future Directions

For centuries, regular exercise has been acknowledged as a potent stimulus to promote, maintain, and restore healthy functioning of nearly every physiological system of the human body. With advancing understanding of the complexity of human physiology, continually evolving methodological possibilities, and an increasingly dire public health situation, the study of exercise as a preventative or therapeutic treatment has never been more interdisciplinary, or more impactful. During the early stages of the NIH Common Fund Molecular Transducers of Physical Activity Consortium (MoTrPAC) Initiative, the field is well-positioned to build substantially upon the existing understanding of the mechanisms underlying benefits associated with exercise. Thus, we present a comprehensive body of the knowledge detailing the current literature basis surrounding the molecular adaptations to exercise in humans to provide a view of the state of the field at this critical juncture, as well as a resource for scientists bringing external expertise to the field of exercise physiology. In reviewing current literature related to molecular and cellular processes underlying exercise-induced benefits and adaptations, we also draw attention to existing knowledge gaps warranting continued research effort. © 2021 American Physiological Society. Compr Physiol 12:3193-3279, 2022.

Micronutrients and athletic performance: A review

Optimising nutrition intake is a key component for supporting athletic performance and supporting adaption to training. Athletes often use micronutrient supplements in order to correct vitamin and mineral deficiencies, improve immune function, enhance recovery and or to optimise their performance. The aim of this review was to investigate the recent literature regarding micronutrients (specifically iron, vitamin C, vitamin E, vitamin D, calcium) and their effects on physical performance. Over the past ten years, several studies have investigated the impacts of these micronutrients on aspects of athletic performance, and several reviews have aimed to provide an overview of current use and effectiveness. Currently the balance of the literature suggests that micronutrient supplementation in well-nourished athletes does not enhance physical performance. Excessive intake of dietary supplements may impair the body's physiological responses to exercise that supports adaptation to training stress. In some cases, micronutrient supplementation is warranted, for example, with a diagnosed deficiency, when energy intake is compromised, or when training and competing at altitude, however these micronutrients should be prescribed by a medical professional. Athletes are encouraged to obtain adequate micronutrients from a wellbalanced and varied dietary intake.

Nutrition, supplementation and weight reduction in combat sports: a review

Nutrition is the aspect closely connected to physical activity and may affect body composition, sports performance and post-workout regeneration. Using an appropriate diet plan is a proven method to optimize performance improvements in combat sports. In the majority of combat sports athletes are classified according to their body mass in order to minimize differences between competitors. Many athletes induce weight loss in order to gain an advantage over their opponents. The review was undertaken to provide safe, evidence-based protocols helping athletes in weight reduction without negative effects on sports performance. The nutritional requirements for combat sports athletes, sports supplements, gradual and rapid weight reduction strategies are discussed in this review.

Use, Practices and Attitudes of Elite and Sub-Elite Athletes towards Tart Cherry Supplementation

Tart cherry (TC) supplementation can improve exercise recovery and performance; and may also improve sleep duration and quality. This study investigated the use and knowledge of TC supplementation by athletes of all competitive levels. Eighty participants (52.5% elite (international, national, professional), 47.5% sub-elite (semi-professional, state/regional, county level, club level, recreational)) completed an online questionnaire investigating their attitudes towards and use of TC supplementation. Overall, 22.6% of participants were using or had previously used TC supplements, and 12.5% of participants planned to used TC supplements. Improved recovery (71.4%), sleep (32.1%) and immunity and general health (32.1%) were the most frequently indicated goals by respondents using TC supplements. In total, 32.1% of respondents were supplemented with TC chronically, 39.3% acutely and 28.6% used a combination of chronic and acute supplementation. The majority of those employing TC supplementation chronically used TC either over 2-3 days (37.0%) or continuously (37.0%). The most popular TC pre- and post-loading period was one day (34.3% and 41.5%, respectively). There were no significant differences between elite and sub-elite athletes in any parameters assessed (p > 0.05). TC supplementation is not widely used by the athletes surveyed, and athletes using TC supplements showed poor awareness of an evidence-led dosing strategy, regardless of competitive level.

Effect of six weeks 1000 mg/day vitamin C supplementation and healthy training in elderly women on genes expression associated with the immune response - a randomized controlled trial

Background

In this study, we investigated the effects of supplementation and exercise on the expression of genes associated with inflammation like CCL2, CRP, IL1, IL6, IL10 mRNA in elderly women.

Methods

Twenty four participants divided randomly into two groups were subjected to 6 weeks of the same health training program (three times per week). SUP group (supplemented, n = 12, mean age 72.8 ± 5.26 years and mean body mass 68.1 ± 8.3 kg) received 1000 mg of Vitamin C/day during the training period, while CON group (control, n = 12, mean age 72.4 ± 5.5 years and body mass 67.7 ± 7.5 kg) received placebo.

Results

No significant changes in IL-1, IL-6, IL-10 and CRP mRNA were observed within and between groups. However, there was a clear tendency of a decrease in IL-6 (two-way ANOVA, significant between investigated time points) and an increase in IL-10 mRNA noted in the supplemented group. A significant decrease in CCL2 mRNA was observed only in the CON group (from 2^0.2 to 2^0.1, p = 0.01).

Conclusions

It can be concluded, that 6 weeks of supplementation and exercise was too short to obtain significant changes in gene expression in leukocytes, but supplementation of 1000 mg vitamin C positively affected IL-6 and IL-10 expression – which are key changes in the adaptation to training. However, changes in body mass, IL1 and CCL2 were positive in CON group. It is possible that Vitamin C during 6 weeks of supplementation could have different effects on the expression of individual genes involved in the immune response.

Trial registration

Retrospectively registered. 

The Role of Vitamin C in Two Distinct Physiological States: Physical Activity and Sleep

This paper is a literature overview of the complex relationship between vitamin C and two opposing physiological states, physical activity and sleep. The evidence suggests a clinically important bidirectional association between these two phenomena mediated by different physiological mechanisms. With this in mind, and knowing that both states share a connection with oxidative stress, we discuss the existing body of evidence to answer the question of whether vitamin C supplementation can be beneficial in the context of sleep health and key aspects of physical activity, such as performance, metabolic changes, and antioxidant function. We analyze the effect of ascorbic acid on the main sleep components, sleep duration and quality, focusing on the most common disorders: insomnia, obstructive sleep apnea, and restless legs syndrome. Deeper understanding of those interactions has implications for both public health and clinical practice.

Redox-dependent regulation of satellite cells following aseptic muscle trauma: Implications for sports performance and nutrition

Skeletal muscle satellite cells (SCs) are indispensable for tissue regeneration, remodeling and growth. Following myotrauma, SCs are activated, and assist in tissue repair. Exercise-induced muscle damage (EIMD) is characterized by a pronounced inflammatory response and the production of reactive oxygen species (ROS). Experimental evidence suggests that SCs kinetics (the propagation from a quiescent to an activated/proliferative state) following EIMD is redox-dependent and interconnected with changes in the SCs microenvironment (niche). Animal studies have shown that following aseptic myotrauma, antioxidant and/or anti-inflammatory supplementation leads to an improved recovery and skeletal muscle regeneration through enhanced SCs kinetics, suggesting a redox-dependent molecular mechanism. Although evidence suggests that antioxidant/anti-inflammatory compounds may prevent performance deterioration and enhance recovery, there is lack of information regarding the redox-dependent regulation of SCs responses following EIMD in humans. In this review, SCs kinetics following aseptic myotrauma, as well as the intrinsic redox-sensitive molecular mechanisms responsible for SCs responses are discussed. The role of redox status on SCs function should be further investigated in the future with human clinical trials in an attempt to elucidate the molecular pathways responsible for muscle recovery and provide information for potential nutritional strategies aiming at performance recovery.

Antioxidants and Exercise Performance: With a Focus on Vitamin E and C Supplementation

Antioxidant supplementation, including vitamin E and C supplementation, has recently received recognition among athletes as a possible method for enhancing athletic performance. Increased oxidative stress during exercise results in the production of free radicals, which leads to muscle damage, fatigue, and impaired performance. Despite their negative effects on performance, free radicals may act as signaling molecules enhancing protection against greater physical stress. Current evidence suggests that antioxidant supplementation may impair these adaptations. Apart from athletes training at altitude and those looking for an immediate, short-term performance enhancement, supplementation with vitamin E does not appear to be beneficial. Moreover, the effectiveness of vitamin E and C alone and/or combined on muscle mass and strength have been inconsistent. Given that antioxidant supplements (e.g., vitamin E and C) tend to block anabolic signaling pathways, and thus, impair adaptations to resistance training, special caution should be taken with these supplements. It is recommended that athletes consume a diet rich in fruits and vegetables, which provides vitamins, minerals phytochemicals, and other bioactive compounds to meet the recommended intakes of vitamin E and C.

Vitamin C and E Treatment Blunts Sprint Interval Training-Induced Changes in Inflammatory Mediator-, Calcium-, and Mitochondria-Related Signaling in Recreationally Active Elderly Humans

Sprint interval training (SIT) has emerged as a time-efficient training regimen for young individuals. Here, we studied whether SIT is effective also in elderly individuals and whether the training response was affected by treatment with the antioxidants vitamin C and E. Recreationally active elderly (mean age 65) men received either vitamin C (1 g/day) and vitamin E (235 mg/day) or placebo. Training consisted of nine SIT sessions (three sessions/week for three weeks of 4-6 repetitions of 30-s all-out cycling sprints) interposed by 4 min rest. Vastus lateralis muscle biopsies were taken before, 1 h after, and 24 h after the first and last SIT sessions. At the end of the three weeks of training, SIT-induced changes in relative mRNA expression of reactive oxygen/nitrogen species (ROS)- and mitochondria-related proteins, inflammatory mediators, and the sarcoplasmic reticulum Ca²⁺ channel, the ryanodine receptor 1 (RyR1), were blunted in the vitamin treated group. Western blots frequently showed a major (>50%) decrease in the full-length expression of RyR1 24 h after SIT sessions; in the trained state, vitamin treatment seemed to provide protection against this severe RyR1 modification. Power at exhaustion during an incremental cycling test was increased by ~5% at the end of the training period, whereas maximal oxygen uptake remained unchanged; vitamin treatment did not affect these measures. In conclusion, treatment with the antioxidants vitamin C and E blunts SIT-induced cellular signaling in skeletal muscle of elderly individuals, while the present training regimen was too short or too intense for the changes in signaling to be translated into a clear-cut change in physical performance.

Exercise Training and Vitamin C Supplementation Affects Ferritin mRNA in Leukocytes without Affecting Prooxidative/Antioxidative Balance in Elderly Women

Physical training and antioxidant supplementation may influence iron metabolism through reduced oxidative stress and subsequent lowering of mRNA levels of genes that are easily induced by this stress, including those responsible for iron homeostasis. Fifteen elderly women participated in our 12-week experiment, involving six weeks of training without supplementation and six weeks of training supported by oral supplementation of 1000 mg of vitamin C daily. The participants were divided into two groups (n = 7 in group 1 and n = 8 in group 2). In group 1, we applied vitamin C supplementation in the first six weeks of training, while in group 2 during the remaining six weeks of training. In both phases, the health-related training occurred three times per week. Training accompanied by vitamin C supplementation did not affect prooxidative/antioxidative balance but significantly decreased ferritin heavy chain (FTH) and ferritin light chain (FTL) mRNA in leukocytes (for FTH mRNA from 2^64.24 to 2^11.06, p = 0.03 in group 1 and from 2^60.54 to 2^16.03, p = 0.01 in group 2, for FTL mRNA from 2^20.22 to 2^4.53, p = 0.01 in group 2). We concluded that vitamin C supplementation might have caused a decrease in gene expression of two important antioxidative genes (FTH, FTL) and had no effect on plasma prooxidative/antioxidative balance.

Effects of Dietary Supplements on Adaptations to Endurance Training

Endurance training leads to a variety of adaptations at the cellular and systemic levels that serve to minimise disruptions in whole-body homeostasis caused by exercise. These adaptations are differentially affected by training volume, training intensity, and training status, as well as by nutritional choices that can enhance or impair the response to training. A variety of supplements have been studied in the context of acute performance enhancement, but the effects of continued supplementation concurrent to endurance training programs are less well characterised. For example, supplements such as sodium bicarbonate and beta-alanine can improve endurance performance and possibly training adaptations during endurance training by affecting buffering capacity and/or allowing an increased training intensity, while antioxidants such as vitamin C and vitamin E may impair training adaptations by blunting cellular signalling but appear to have little effect on performance outcomes. Additionally, limited data suggest the potential for dietary nitrate (in the form of beetroot juice), creatine, and possibly caffeine, to further enhance endurance training adaptation. Therefore, the objective of this review is to examine the impact of dietary supplements on metabolic and physiological adaptations to endurance training.

Antioxidant supplements and endurance exercise: Current evidence and mechanistic insights

Antioxidant supplements are commonly consumed by endurance athletes to minimize exercise-induced oxidative stress, with the intention of enhancing recovery and improving performance. There are numerous commercially available nutritional supplements that are targeted to athletes and health enthusiasts that allegedly possess antioxidant properties. However, most of these compounds are poorly investigated with respect to their in vivo redox activity and efficacy in humans. Therefore, this review will firstly provide a background to endurance exercise-related redox signalling and the subsequent adaptations in skeletal muscle and vascular function. The review will then discuss commonly available compounds with purported antioxidant effects for use by athletes. N-acetyl cysteine may be of benefit over the days prior to an endurance event; while chronic intake of combined 1000 mg vitamin C + vitamin E is not recommended during periods of heavy training associated with adaptations in skeletal muscle. Melatonin, vitamin E and α-lipoic acid appear effective at decreasing markers of exercise-induced oxidative stress. However, evidence on their effects on endurance performance are either lacking or not supportive. Catechins, anthocyanins, coenzyme Q10 and vitamin C may improve vascular function, however, evidence is either limited to specific sub-populations and/or does not translate to improved performance. Finally, additional research should clarify the potential benefits of curcumin in improving muscle recovery post intensive exercise; and the potential hampering effects of astaxanthin, selenium and vitamin A on skeletal muscle adaptations to endurance training. Overall, we highlight the lack of supportive evidence for most antioxidant compounds to recommend to athletes.

The Association between Dietary Antioxidant Quality Score and Cardiorespiratory Fitness in Iranian Adults: a Cross-Sectional Study

The association between dietary antioxidant quality score (DAQS) and cardiovascular risk factors such as low cardiovascular fitness (CRF) and elevated blood pressure (BP) has rarely been investigated. To investigate the association between DAQS, CRF, and BP. This cross-sectional study was conducted on 270 adult subjects living in Tehran, Iran. Dietary intake was evaluated using a validated food frequency questionnaire. The DAQS was calculated using antioxidant-nutrient intake. Socio-economic status, anthropometric measures, and BP were recorded by a trained interviewer, using standard methods. A significant increase was found in maximal oxygen uptake (p value = 0.01) across tertiles of DAQS. After adjusting for confounders, the association remained unchanged (p value = 0.02). Participants in the highest tertile of DAQS had higher systolic BP (SBP) (p value = 0.01) and diastolic BP (DBP) (p value = 0.03), although adjustment for confounding factors attenuated the results (p value = 0.3 for DBP and p value = 0.6 for SBP). Our results revealed that higher DAQS is associated with better CRF in Iranian adults. Further studies are needed to establish the veracity of our results.

Nutrition and Athlete Immune Health: New Perspectives on an Old Paradigm

Respiratory and gastrointestinal infections limit an athlete's availability to train and compete. To better understand how sick an athlete will become when they have an infection, a paradigm recently adopted from ecological immunology is presented that includes the concepts of immune resistance (the ability to destroy microbes) and immune tolerance (the ability to dampen defence yet control infection at a non-damaging level). This affords a new theoretical perspective on how nutrition may influence athlete immune health; paving the way for focused research efforts on tolerogenic nutritional supplements to reduce the infection burden in athletes. Looking through this new lens clarifies why nutritional supplements targeted at improving immune resistance in athletes show limited benefits: evidence supporting the old paradigm of immune suppression in athletes is lacking. Indeed, there is limited evidence that the dietary practices of athletes suppress immunity, e.g. low-energy availability and train- or sleep-low carbohydrate. It goes without saying, irrespective of the dietary preference (omnivorous, vegetarian), that athletes are recommended to follow a balanced diet to avoid a frank deficiency of a nutrient required for proper immune function. The new theoretical perspective provided sharpens the focus on tolerogenic nutritional supplements shown to reduce the infection burden in athletes, e.g. probiotics, vitamin C and vitamin D. Further research should demonstrate the benefits of candidate tolerogenic supplements to reduce infection in athletes; without blunting training adaptations and without side effects.

Fruit-Derived Polyphenol Supplementation for Athlete Recovery and Performance

Polyphenols are characterised structurally by two or more hydroxyl groups attached to one or more benzene rings, and provide the taste and colour characteristics of fruits and vegetables. They are radical scavengers and metal chelators, but due to their low concentration in biological fluids in vivo their antioxidant properties seem to be related to enhanced endogenous antioxidant capacity induced via signalling through the Nrf2 pathway. Polyphenols also seem to possess anti-inflammatory properties and have been shown to enhance vascular function via nitric oxide-mediated mechanisms. As a consequence, there is a rationale for supplementation with fruit-derived polyphenols both to enhance exercise performance, since excess reactive oxygen species generation has been implicated in fatigue development, and to enhance recovery from muscle damage induced by intensive exercise due to the involvement of inflammation and oxidative damage within muscle. Current evidence would suggest that acute supplementation with ~ 300 mg polyphenols 1–2 h prior to exercise may enhance exercise capacity and/or performance during endurance and repeated sprint exercise via antioxidant and vascular mechanisms. However, only a small number of studies have been performed to date, some with methodological limitations, and more research is needed to confirm these findings. A larger body of evidence suggests that supplementation with > 1000 mg polyphenols per day for 3 or more days prior to and following exercise will enhance recovery following muscle damage via antioxidant and anti-inflammatory mechanisms. The many remaining unanswered questions within the field of polyphenol research and exercise performance and recovery are highlighted within this review article.

Redox basis of exercise physiology

Redox reactions control fundamental processes of human biology. Therefore, it is safe to assume that the responses and adaptations to exercise are, at least in part, mediated by redox reactions. In this review, we are trying to show that redox reactions are the basis of exercise physiology by outlining the redox signaling pathways that regulate four characteristic acute exercise-induced responses (muscle contractile function, glucose uptake, blood flow and bioenergetics) and four chronic exercise-induced adaptations (mitochondrial biogenesis, muscle hypertrophy, angiogenesis and redox homeostasis). Based on our analysis, we argue that redox regulation should be acknowledged as central to exercise physiology.

Application of Molecular Hydrogen as a Novel Antioxidant in Sports Science

Molecular hydrogen (H₂) is a colorless, tasteless, odorless, and minimal molecule with high flammability. Although H₂ has been thought to be an inert gas in living bodies for many years, an animal study reported that inhalation of H₂ gas decreased oxidative stress and suppressed brain injury caused by ischemia and reperfusion injury due to its antioxidant action. Since then, the antioxidant action of H₂ has attracted considerable attention and many studies have reported on its benefits. Most studies have reported the effects of H₂ on diseases such as cancer, diabetes, cerebral infarction, and Alzheimer's disease. However, little is known regarding its effects on healthy subjects and exercise. Thus far, including our study, only 6 studies have explored the effect of H₂ on exercise. H₂ is the smallest molecule and therefore can easily penetrate the cellular membrane and rapidly diffuse into organelles. H₂ is thought to be able to selectively reduce hydroxyl radicals and peroxynitrite and does not affect physiologically reactive species. H₂ can be supplied to the body through multiple routes of administration, such as oral intake of H₂ water and H₂ bathing. Therefore, H₂ may be a potential alternative strategy for conventional exogenous antioxidant interventions in sports science. The purpose of this review is to provide evidence regarding the effects of H₂ intake on changes in physiological and biochemical parameters, centering on exercise-induced oxidative stress, for each intake method. Furthermore, this review highlights possible future directions in this area of research.

The Effects of Strength Training Combined with Vitamin C and E Supplementation on Skeletal Muscle Mass and Strength: A Systematic Review and Meta-Analysis

Intense muscle contractile activity can result in reactive oxygen species production in humans. Thus, supplementation of antioxidant vitamins has been used to prevent oxidative stress, enhance performance, and improve muscle mass. In this sense, randomized controlled studies on the effect of vitamin C and E supplementation combined with strength training (ST) on skeletal muscle mass and strength have been conducted. As these studies have come to ambiguous findings, a better understanding of this topic has yet to emerge. The purpose of the present review is to discuss the current knowledge about the effect of vitamin C and E supplementation on muscle mass and strength gains induced by ST. Search for articles was conducted in the following databases: PubMed/Medline, Web of Science, Scopus, Cochrane Central Register of Controlled Trials, and Google Scholar. This work is in line with the recommendations of the PRISMA statement. Eligible studies were placebo-controlled trials with a minimum of four weeks of ST combined with vitamin C and E supplementation. The quality of each included study was evaluated using the Physiotherapy Evidence Database Scale (PEDro). 134 studies were found to be potentially eligible, but only seven were selected to be included in the qualitative synthesis. A meta-analysis of muscle strength was conducted with 3 studies. Findings from these studies indicate that vitamins C and E has no effect on muscle force production after chronic ST. Most of the evidence suggests that this kind of supplementation does not potentiate muscle growth and could possibly attenuate hypertrophy over time.

Systematic Physical Exercise and Spirulina maxima Supplementation Improve Body Composition, Cardiorespiratory Fitness, and Blood Lipid Profile: Correlations of a Randomized Double-Blind Controlled Trial

Cardiovascular diseases are part of the highly preventable chronic diseases associated with changes in lifestyle. Within them, physical activity, low-fat and high-fiber diets are distinguished as the main support for prevention, even when supplementation with nutraceuticals has become a very common practice. Fifty-two young sedentary men with excess body weight (body mass index (BMI) ≥ 25 kg·m-2) were enrolled in a randomized-crossover controlled trial [six weeks of a systematic physical exercise with Spirulina maxima or placebo supplementation (4.5 g·day-1)]. Body composition, blood lipid profile, and maximal oxygen uptake were determined pre/post intervention. Pairwise comparisons showed a significant improvement (p < 0.01) on blood lipid profile in the group of exercise plus Spirulina maxima. Moreover, correlations of absolute changes of BMI, body fat percentage, blood lipids and maximal oxygen uptake were statistically significant (p < 0.01). These results indicate that the Spirulina maxima supplementation could be acting in a synergistic way with exercise due to the enhanced effects on body composition, cardiorespiratory fitness, and blood lipid profile. This phenomenon should be considered to reduce risk of cardiovascular disorders. Trial registration: Clinical Trials, NCT02837666 (July 19, 2016).

High-Dose Astaxanthin Supplementation Suppresses Antioxidant Enzyme Activity during Moderate-Intensity Swimming Training in Mice

Exercise-induced reactive oxygen and nitrogen species are increasingly considered as beneficial health promotion. Astaxanthin (ASX) has been recognized as a potent antioxidant suitable for human ingestion. We investigated whether ASX administration suppressed antioxidant enzyme activity in moderate-intensity exercise. Seven-week-old male C57BL/6 mice (n = 8/group) were treated with ASX (5, 15, and 30 mg/kg BW) combined with 45 min/day moderate-intensity swimming training for four weeks. Results showed that the mice administrated with 15 and 30 mg/kg of ASX decreased glutathione peroxidase, catalase, malondialdehyde, and creatine kinase levels in plasma or muscle, compared with the swimming control group. Beyond that, these two (15 and 30 mg/kg BW) dosages of ASX downregulated gastrocnemius muscle erythroid 2p45 (NF-E2)-related factor 2 (Nrf2). Meanwhile, mRNA of Nrf2 and Nrf2-dependent enzymes in mice heart were also downregulated in the ASX-treated groups. However, the mice treated with 15 or 30 mg/kg ASX had increased constitutive nitric oxidase synthase and superoxide dismutase activity, compared with the swimming and sedentary control groups. Our findings indicate that high-dose administration of astaxanthin can blunt antioxidant enzyme activity and downregulate transcription of Nrf2 and Nrf2-dependent enzymes along with attenuating plasma and muscle MDA.

TGF-β2 is an exercise-induced adipokine that regulates glucose and fatty acid metabolism

Exercise improves health and well-being across diverse organ systems, and elucidating mechanisms underlying the beneficial effects of exercise can lead to new therapies. Here, we show that transforming growth factor-β2 (TGF-β2) is secreted from adipose tissue in response to exercise and improves glucose tolerance in mice. We identify TGF-β2 as an exercise-induced adipokine in a gene expression analysis of human subcutaneous adipose tissue biopsies after exercise training. In mice, exercise training increases TGF-β2 in scWAT, serum, and its secretion from fat explants. Transplanting scWAT from exercise-trained wild type mice, but not from adipose tissue-specific Tgfb2−/− mice, into sedentary mice improves glucose tolerance. TGF-β2 treatment reverses the detrimental metabolic effects of high fat feeding in mice. Lactate, a metabolite released from muscle during exercise, stimulates TGF-β2 expression in human adipocytes. Administration of the lactate-lowering agent dichloroacetate during exercise training in mice decreases circulating TGF-β2 levels and reduces exercise-stimulated improvements in glucose tolerance. Thus, exercise training improves systemic metabolism through inter-organ communication with fat via a lactate-TGF-β2-signaling cycle.

Antioxidants in Personalized Nutrition and Exercise

The present review highlights the idea that antioxidant supplementation can be optimized when tailored to the precise antioxidant status of each individual. A novel methodologic approach involving personalized nutrition, the mechanisms by which antioxidant status regulates human metabolism and performance, and similarities between antioxidants and other nutritional supplements are described. The usefulness of higher-level phenotypes for data-driven personalized treatments is also explained. We conclude that personally tailored antioxidant interventions based on specific antioxidant inadequacies or deficiencies could result in improved exercise performance accompanied by consistent alterations in redox profile.

Training-Induced Changes in Mitochondrial Content and Respiratory Function in Human Skeletal Muscle

A sedentary lifestyle has been linked to a number of metabolic disorders that have been associated with sub-optimal mitochondrial characteristics and an increased risk of premature death. Endurance training can induce an increase in mitochondrial content and/or mitochondrial functional qualities, which are associated with improved health and well-being and longer life expectancy. It is therefore important to better define how manipulating key parameters of an endurance training intervention can influence the content and functionality of the mitochondrial pool. This review focuses on mitochondrial changes taking place following a series of exercise sessions (training-induced mitochondrial adaptations), providing an in-depth analysis of the effects of exercise intensity and training volume on changes in mitochondrial protein synthesis, mitochondrial content and mitochondrial respiratory function. We provide evidence that manipulation of different exercise training variables promotes specific and diverse mitochondrial adaptations. Specifically, we report that training volume may be a critical factor affecting changes in mitochondrial content, whereas relative exercise intensity is an important determinant of changes in mitochondrial respiratory function. As a consequence, a dissociation between training-induced changes in mitochondrial content and mitochondrial respiratory function is often observed. We also provide evidence that exercise-induced changes are not necessarily predictive of training-induced adaptations, we propose possible explanations for the above discrepancies and suggestions for future research.

Exercise-Induced Oxidative Stress and the Effects of Antioxidant Intake from a Physiological Viewpoint

It is well established that the increase in reactive oxygen species (ROS) and free radicals production during exercise has both positive and negative physiological effects. Among them, the present review focuses on oxidative stress caused by acute exercise, mainly on evidence in healthy individuals. This review also summarizes findings on the determinants of exercise-induced oxidative stress and sources of free radical production. Moreover, we outline the effects of antioxidant supplementation on exercise-induced oxidative stress, which have been studied extensively. Finally, the following review briefly summarizes future tasks in the field of redox biology of exercise. In principle, this review covers findings for the whole body, and describes human trials and animal experiments separately.

Mitochondria-Targeted Antioxidants and Skeletal Muscle Function

One of the main sources of reactive oxygen species (ROS) in skeletal muscle is the mitochondria. Prolonged or very high ROS exposure causes oxidative damage, which can be deleterious to muscle function, and as such, there is growing interest in targeting antioxidants to the mitochondria in an effort to prevent or treat muscle dysfunction and damage associated with disease and injury. Paradoxically, however, ROS also act as important signalling molecules in controlling cellular homeostasis, and therefore caution must be taken when supplementing with antioxidants. It is possible that mitochondria-targeted antioxidants may limit oxidative stress without suppressing ROS from non-mitochondrial sources that might be important for cell signalling. Therefore, in this review, we summarise literature relating to the effect of mitochondria-targeted antioxidants on skeletal muscle function. Overall, mitochondria-targeted antioxidants appear to exert beneficial effects on mitochondrial capacity and function, insulin sensitivity and age-related declines in muscle function. However, it seems that this is dependent on the type of mitochondrial-trageted antioxidant employed, and its specific mechanism of action, rather than simply targeting to the mitochondria.

Differential effects of vitamin C or protandim on skeletal muscle adaptation to exercise

Maintaining proteostasis is a key mechanism for preserving cell function. Exercise-stimulated proteostasis is regulated, in part, by redox-sensitive signaling. Several studies suggest that supplementation with exogenous antioxidants blunts exercise-induced cellular adaptations, although this conclusion lacks consensus. Our group uses a fundamentally different approach to maintain redox balance by treatment with bioactive phytochemicals to activate the transcription factor nuclear factor (erythroid-derived 2)-like 2 and downstream endogenous antioxidant pathways. We hypothesized that vitamin C (VitC) would interfere with redox-sensitive proteostatic mechanisms in skeletal muscle, whereas phytochemical treatment would permit proteostatic maintenance. We measured protein and DNA synthesis in skeletal muscle from high-volume voluntary wheel-running rats. Whereas phytochemical treatment permitted mitochondrial and other proteostatic adaptations to exercise, VitC treatment did not. During an in vitro oxidative challenge, phytochemical treatment helped maintain proteostasis, including the mitochondrial fraction while VitC did not. Our findings support the conclusion that VitC can blunt some of the beneficial adaptations to exercise. We propose that regulation of endogenous antioxidants represents a novel approach to maintain redox balance while still permitting redox-sensitive proteostatic adaptations. NEW & NOTEWORTHY Whether vitamin C blocks aerobic exercise adaptions lacks consensus, perhaps because of approaches that only assess markers of mitochondrial biogenesis. By directly measuring mitochondrial biogenesis, we demonstrate that vitamin C blunts exercise-induced adaptations. Furthermore, we show that treatment with Protandim, a purported nuclear factor (erythroid-derived 2)-like 2 activator that upregulates endogenous antioxidants, permits mitochondrial biogenesis. We confirm that vitamin C blunts aerobic exercise adaptions, whereas Protandim does not, suggesting targeting the endogenous antioxidant network facilitates adaptations to exercise.

Inhibition of Oxidative Stress by Antioxidant Supplementation Does Not Limit Muscle Mitochondrial Biogenesis or Endurance Capacity in Rats

The objective of the present study was to analyze the activation and expression patterns of upstream and downstream factors of PGC-1α to determine whether antioxidant (AO) supplementation inhibits mitochondrial biogenesis in skeletal muscles as an adaptation to endurance training, as well as to analyze changes in endurance capacity based on such findings. For this objective, 24 male Sprague-Dawley (SD) rats were allocated into 4 groups (vehicle-sedentary, V-Sed; vehicle-exercise, V-EX; antioxidant-sedentary, AO-Sed; antioxidant-exercise, AO-EX) of 6 rats each. The rats were then treated with vitamin C (500 mgkg^-1 body weightd^-1) or a placebo for 8 wk, and a swimming program was implemented in some rats during the last 4 wk of this period. Immediately after the last training session, blood was collected from the tail of each rat, and TBARS was measured to test the effect of vitamin C as an AO. As a result, increased oxidative stress from exercise was inhibited by vitamin C supplementation. Analysis of whether reduced oxidative stress by vitamin C supplementation also inhibited mitochondrial biogenesis within skeletal muscles showed that phosphorylation of p38 MAPK and AMPK, along with levels of PGC-1α, NRF-1, mtTFA, and mitochondrial electron transport enzymes, increased after endurance training in spite of vitamin C supplementation. Moreover, running time, distance, and total work increased significantly in the exercise group as compared to those in the sedentary group, regardless of vitamin C supplementation. These results indicate that mitochondrial biogenesis and endurance capacity increase as a result of endurance training, regardless of AO supplementation.

Antioxidant-rich foods and response to altitude training: A randomized controlled trial in elite endurance athletes

High doses of isolated antioxidant supplements such as vitamin C and E have demonstrated the potential to blunt cellular adaptations to training. It is, however, unknown whether intake of high doses of antioxidants from foods has similar effects. Hence, the aim of the study was to investigate whether intake of antioxidant-rich foods affects adaptations to altitude training in elite athletes. In a randomized controlled trial, 31 national team endurance athletes (23 ± 5 years) ingested antioxidant-rich foods (n = 16) or eucaloric control foods (n = 15) daily during a 3-week altitude training camp (2320 m). Changes from baseline to post-altitude in hemoglobin mass (Hb_mass ; optimized CO rebreathing), maximal oxygen uptake (VO_2max ; n = 16) or 100 m swimming performance (n = 10), and blood parameters were compared between the groups. The antioxidant group significantly increased total intake of antioxidant-rich foods (~118%) compared to the control group during the intervention. The total study population improved VO_2max by 2.5% (1.7 mL/kg/min, P = .006) and Hb_mass by 4.7% (48 g, P < .001), but not 100 m swimming performance. No difference was found between the groups regarding changes in Hb_mass , VO_2max or swimming performance. However, hemoglobin concentration increased more in the antioxidant group (effect size = 0.7; P = .045) with a concomitantly larger decrease in plasma and blood volumes compared to control group. Changes in ferritin and erythropoietin from pre- to post-altitude did not differ between the groups. Doubling the intake of antioxidant-rich foods was well tolerated and did not negatively influence the adaptive response to altitude training in elite endurance athletes.

The effect of Opuntia ficus-indica juice supplementation on oxidative stress, cardiovascular parameters, and biochemical markers following yo-yo Intermittent recovery test

The aim of the study was to investigate the effect of a flavonoid-rich fresh fruit juice on cardiovascular, oxidative stress, and biochemical parameters during the yo-yo intermittent recovery test (YYIRT). Twenty-two healthy males subjects participated in this study divided into two groups: An experimental group (EG: n = 11) who consumed the antioxidant supplement and a control group (CG: n = 11). All participants performed two test sessions at 07:00 hr before and after 2 weeks of supplementation with Opuntia ficus-indica juice. Blood samples were taken before (P1) and immediately (P2) after the YYIRT. Our results showed that following the 2,2-diphenyl-1- picrylhydrazyl (DPPH ●) test, the Opuntia ficus-indica juice has an antioxidant capacity for capturing free radicals (p < .05) and reducing oxidative stress related to exercise. Concerning biochemical and cardiovascular parameters, our results showed a significant increase on total cholesterol (TC) (p < .01), triglycerides (TG) (p < .05), high-density lipoprotein (HDL) (p < .01), low-density lipoprotein (LDL) (p < .01), creatine kinase (CK) (p < .01), lactate deshydrogenase (LDH) (p < .01), glucose (GLC) (p < .01), systolic (SBP), and diastolic blood pressure (DBP) (p < .01) immediately after exercise. However, TC (p < .05), TG (p < .05) and LDL (p < .05), the maximal heart rate (HRmax), the CK (p < .05), and LDH (p < .01) as well as the malondialdehyde (MDA) (p < .01) demonstrated a significant decrease after supplementation of Opuntia ficus-indica juice before and immediately after YYIRT. However, no significant effect on HDL (p > .05), GLC (p > .05) levels nor the SBP and DBP (p > .05) was observed after supplementation with Opuntia ficus-indica juice. The supplementation leads to an improvement on YYIRT performance (The total distance covered during the YYIRT,VO 2max, VMA) and the rating of perceived exertion (RPE). Opuntia ficus-indica juice has a potent antioxidant activity that reduces total and LDL-cholesterol with only a moderate lowering of HDL-cholesterol and oxidative stress. Moreover, supplementation decreases muscle damage caused by the endurance exercise.

N-acetylcysteine supplementation increases exercise performance and reduces oxidative stress only in individuals with low levels of glutathione

Most of the evidence indicates that chronic antioxidant supplementation induces negative effects in healthy individuals. However, it is currently unknown whether specific redox deficiencies exist and whether targeted antioxidant interventions in deficient individuals can induce positive effects. We hypothesized that the effectiveness of antioxidant supplements to decrease oxidative stress and promote exercise performance depends on the redox status of the individuals that receive the antioxidant treatment. To this aim, we investigated whether N-acetylcysteine (NAC) supplementation would enhance exercise performance by increasing glutathione concentration and by reducing oxidative stress only in individuals with low resting levels of glutathione. We screened 100 individuals for glutathione levels and formed three groups with low, moderate and high levels (N = 36, 12 per group). After by-passing the regression to the mean artifact, by performing a second glutathione measurement, the individuals were supplemented with NAC (2 × 600mg, twice daily, for 30 days) or placebo using a double-blind cross-over design. We performed three whole-body performance tests (VO₂max, time trial and Wingate), measured two systemic oxidative stress biomarkers (F₂-isoprostanes and protein carbonyls) and assessed glutathione-dependent redox metabolism in erythrocytes (glutathione, glutathione peroxidase, glutathione reductase, superoxide dismutase, catalase and NADPH). The low glutathione group improved after NAC supplementation in VO₂max, time trial and Wingate by 13.6%, 15.4% and 11.4%, respectively. Thirty days of NAC supplementation were sufficient to restore baseline glutathione concentration, reduce systemic oxidative stress and improve erythrocyte glutathione metabolism in the low glutathione group. On the contrary, the 30-day supplementation period did not affect performance and redox state of the moderate and high glutathione groups, although few both beneficial and detrimental effects in performance were observed. In conclusion, individuals with low glutathione levels were linked with decreased physical performance, increased oxidative stress and impaired redox metabolism of erythrocytes. NAC supplementation restored both performance and redox homeostasis.

Short-Term High-Dose Vitamin C and E Supplementation Attenuates Muscle Damage and Inflammatory Responses to Repeated Taekwondo Competitions: A Randomized Placebo-Controlled Trial

Background: Exercise-induced muscle damage during intensive sport events is a very common issue in sport medicine. Therefore, the purpose is to investigate the effects of short-term high-dose vitamin C and E supplementation on muscle damage, hemolysis, and inflammatory responses to simulated competitive Olympic Taekwondo (TKD) matches in elite athletes. Methods: Using a randomized placebo-controlled and double-blind study design, eighteen elite male TKD athletes were weight-matched and randomly assigned into either a vitamin C and E group (Vit C+E; N = 9) or placebo group (PLA; N = 9). Vit C+E or PLA supplements were taken daily (Vit C+E: 2000 mg/d vitamin C; 1400 U/d vitamin E) for 4 days (3 days before and on competition day) before taking part in 4 consecutive TKD matches on a single day. Plasma samples were obtained before each match and 24-hours after the first match for determination of markers of muscle damage, hemolysis, and systemic inflammatory state. Results: Myoglobin was lower in the Vit C+E group, compared to PLA, during the match day (area under curve, AUC -47.0% vs. PLA, p = 0.021). Plasma creatine kinase was lower in the Vit C+E group (AUC -57.5% vs. PLA, p = 0.017) and hemolysis was lower in the Vit C+E group (AUC -40.5% vs. PLA, p = 0.034). Conclusions: We demonstrated that short-term (4-days) vitamin C and E supplementation effectively attenuated exercise-induced tissue damage and inflammatory response during and after successive TKD matches.

Antioxidants for preventing and reducing muscle soreness after exercise

BACKGROUND

Muscle soreness typically occurs after intense exercise, unaccustomed exercise or actions that involve eccentric contractions where the muscle lengthens while under tension. It peaks between 24 and 72 hours after the initial bout of exercise. Many people take antioxidant supplements or antioxidant-enriched foods before and after exercise in the belief that these will prevent or reduce muscle soreness after exercise.

OBJECTIVES

To assess the effects (benefits and harms) of antioxidant supplements and antioxidant-enriched foods for preventing and reducing the severity and duration of delayed onset muscle soreness following exercise.

SEARCH METHODS

We searched the Cochrane Bone, Joint and Muscle Trauma Group Specialised Register, the Cochrane Central Register of Controlled Trials, MEDLINE, Embase, SPORTDiscus, trial registers, reference lists of articles and conference proceedings up to February 2017.

SELECTION CRITERIA

We included randomised and quasi-randomised controlled trials investigating the effects of all forms of antioxidant supplementation including specific antioxidant supplements (e.g. tablets, powders, concentrates) and antioxidant-enriched foods or diets on preventing or reducing delayed onset muscle soreness (DOMS). We excluded studies where antioxidant supplementation was combined with another supplement.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened search results, assessed risk of bias and extracted data from included trials using a pre-piloted form. Where appropriate, we pooled results of comparable trials, generally using the random-effects model. The outcomes selected for presentation in the 'Summary of findings' table were muscle soreness, collected at times up to 6 hours, 24, 48, 72 and 96 hours post-exercise, subjective recovery and adverse effects. We assessed the quality of the evidence using GRADE.

MAIN RESULTS

Fifty randomised, placebo-controlled trials were included, 12 of which used a cross-over design. Of the 1089 participants, 961 (88.2%) were male and 128 (11.8%) were female. The age range for participants was between 16 and 55 years and training status varied from sedentary to moderately trained. The trials were heterogeneous, including the timing (pre-exercise or post-exercise), frequency, dose, duration and type of antioxidant supplementation, and the type of preceding exercise. All studies used an antioxidant dosage higher than the recommended daily amount. The majority of trials (47) had design features that carried a high risk of bias due to selective reporting and poorly described allocation concealment, potentially limiting the reliability of their findings.We tested only one comparison: antioxidant supplements versus control (placebo). No studies compared high-dose versus low-dose, where the low-dose supplementation was within normal or recommended levels for the antioxidant involved.Pooled results for muscle soreness indicated a small difference in favour of antioxidant supplementation after DOMS-inducing exercise at all main follow-ups: up to 6 hours (standardised mean difference (SMD) -0.30, 95% confidence interval (CI) -0.56 to -0.04; 525 participants, 21 studies; low-quality evidence); at 24 hours (SMD -0.13, 95% CI -0.27 to 0.00; 936 participants, 41 studies; moderate-quality evidence); at 48 hours (SMD -0.24, 95% CI -0.42 to -0.07; 1047 participants, 45 studies; low-quality evidence); at 72 hours (SMD -0.19, 95% CI -0.38 to -0.00; 657 participants, 28 studies; moderate-quality evidence), and little difference at 96 hours (SMD -0.05, 95% CI -0.29 to 0.19; 436 participants, 17 studies; low-quality evidence). When we rescaled to a 0 to 10 cm scale in order to quantify the actual difference between groups, we found that the 95% CIs for all five follow-up times were all well below the minimal important difference of 1.4 cm: up to 6 hours (MD -0.52, 95% CI -0.95 to -0.08); at 24 hours (MD -0.17, 95% CI -0.42 to 0.07); at 48 hours (MD -0.41, 95% CI -0.69 to -0.12); at 72 hours (MD -0.29, 95% CI -0.59 to 0.02); and at 96 hours (MD -0.03, 95% CI -0.43 to 0.37). Thus, the effect sizes suggesting less muscle soreness with antioxidant supplementation were very unlikely to equate to meaningful or important differences in practice. Neither of our subgroup analyses to examine for differences in effect according to type of DOMS-inducing exercise (mechanical versus whole body aerobic) or according to funding source confirmed subgroup differences. Sensitivity analyses excluding cross-over trials showed that their inclusion had no important impact on results.None of the 50 included trials measured subjective recovery (return to previous activities without signs or symptoms).There is very little evidence regarding the potential adverse effects of taking antioxidant supplements as this outcome was reported in only nine trials (216 participants). From the studies that did report adverse effects, two of the nine trials found adverse effects. All six participants in the antioxidant group of one trial had diarrhoea and four of these also had mild indigestion; these are well-known side effects of the particular antioxidant used in this trial. One of 26 participants in a second trial had mild gastrointestinal distress.

AUTHORS' CONCLUSIONS

There is moderate to low-quality evidence that high dose antioxidant supplementation does not result in a clinically relevant reduction of muscle soreness after exercise at up to 6 hours or at 24, 48, 72 and 96 hours after exercise. There is no evidence available on subjective recovery and only limited evidence on the adverse effects of taking antioxidant supplements. The findings of, and messages from, this review provide an opportunity for researchers and other stakeholders to come together and consider what are the priorities, and underlying justifications, for future research in this area.

Exercise performance and physiological responses: the potential role of redox imbalance

Increases in oxidative stress or decreases in antioxidant capacity, or redox imbalance, are known to alter physiological function and has been suggested to influence performance. To date, no study has sought to manipulate this balance in the same participants and observe the impact on physiological function and performance. Using a single‐blind, placebo‐controlled, and counterbalanced design, this study examined the effects of increasing free radicals, via hyperoxic exposure (F_iO₂ = 1.0), and/or increasing antioxidant capacity, through consuming an antioxidant cocktail (AOC; vitamin‐C, vitamin‐E, α‐lipoic acid), on 5‐kilometer (km) cycling time‐trial performance, and the physiological and fatigue responses in healthy college‐aged males. Hyperoxic exposure prior to the 5 km TT had no effect on performance, fatigue, or the physiological responses to exercise. The AOC significantly reduced average power output (222 ± 11 vs. 214 ± 12 W), increased 5 km time (516 ± 17 vs. 533 ± 18 sec), suppressed ventilation (V_E; 116 ± 5 vs. 109 ± 13 L/min), despite similar oxygen consumption (VO₂; 43.1 ± 0.8 vs. 44.9 ± 0.2 mL/kg per min), decreased V_E/VO₂ (35.9 ± 2.0 vs. 32.3 ± 1.5 L/min), reduced economy (VO₂/W; 0.20 ± 0.01 vs. 0.22 ± 0.01), increased blood lactate (10 ± 0.7 vs. 11 ± 0.7 mmol), and perception of fatigue (RPE; 7.39 ± 0.4 vs. 7.60 ± 0.3) at the end of the TT, as compared to placebo (main effect, placebo vs. AOC, respectively). Our data demonstrate that prior to exercise, ingesting an AOC, but not exposure to hyperoxia, likely disrupts the delicate balance between pro‐ and antioxidant forces, which negatively impacts ventilation, blood lactate, economy, perception of fatigue, and performance (power output and 5 km time) in young healthy males. Thus, caution is warranted in athletes taking excess exogenous antioxidants.

Improvement of obesity-linked skeletal muscle insulin resistance by strength and endurance training

Obesity-linked insulin resistance is mainly due to fatty acid overload in non-adipose tissues, particularly skeletal muscle and liver, where it results in high production of reactive oxygen species and mitochondrial dysfunction. Accumulating evidence indicates that resistance and endurance training alone and in combination can counteract the harmful effects of obesity increasing insulin sensitivity, thus preventing diabetes. This review focuses the mechanisms underlying the exercise role in opposing skeletal muscle insulin resistance-linked metabolic dysfunction. It is apparent that exercise acts through two mechanisms: (1) it stimulates glucose transport by activating an insulin-independent pathway and (2) it protects against mitochondrial dysfunction-induced insulin resistance by increasing muscle antioxidant defenses and mitochondrial biogenesis. However, antioxidant supplementation combined with endurance training increases glucose transport in insulin-resistant skeletal muscle in an additive fashion only when antioxidants that are able to increase the expression of antioxidant enzymes and/or the activity of components of the insulin signaling pathway are used.

Vitamin C and E supplementation does not affect heat shock proteins or endogenous antioxidants in trained skeletal muscles during 12 weeks of strength training

Background

Supplementation with large doses of antioxidants, such as vitamin C and E, has been shown to blunt some adaptations to endurance training. The effects of antioxidant supplementation on adaptations to strength training is sparsely studied. Herein we investigated the effects of vitamin C and E supplementation on acute stress responses to exercise and adaptation to traditional heavy load strength training.

Methods

In a double blind placebo-controlled design, twenty-eight, young, trained males and females were randomly assigned to receive either vitamin C and E (C: 1000 mg, E: 235 mg, per day) or placebo supplements, and underwent strength training for 10 weeks. After five weeks, a subgroup conducted a strength training session to investigate acute stress responses. Muscle samples were obtained to investigate changes in stress responses and in proteins and mRNA related to the heat shock proteins (HSPs) or antioxidant enzymes.

Results

The acute responses to the exercise session revealed activation of the NFκB pathway indicated by degradation of IκBα in both groups. Vitamin C and E supplementation had, however, no effects on the acute stress responses. Furthermore, ten weeks of strength training did not change muscle αB-crystallin, HSP27, HSP70, GPx1 or mnSOD levels, with no influence of supplementation.

Conclusions

Our results showed that although vitamin C and E supplementation has been shown to interfere with training adaptations, it did not affect acute stress responses or long-term training adaptations in the HSPs or antioxidant enzymes in this study.

Electronic supplementary material

The online version of this article (doi:10.1186/s40795-017-0185-8) contains supplementary material, which is available to authorized users.

The Ability of Exercise-Associated Oxidative Stress to Trigger Redox-Sensitive Signalling Responses

In this review, we discuss exercise as an oxidative stressor, and elucidate the mechanisms and downstream consequences of exercise-induced oxidative stress. Reactive oxygen species (ROS) are generated in the mitochondria of contracting skeletal myocytes; also, their diffusion across the myocyte membrane allows their transport to neighbouring muscle tissue and to other regions of the body. Although very intense exercise can induce oxidative damage within myocytes, the magnitudes of moderate-intensity exercise-associated increases in ROS are quite modest (~two-fold increases in intracellular and extracellular ROS concentrations during exercise), and so the effects of such increases are likely to involve redox-sensitive signalling effects rather than oxidative damage. Therefore, the responses of muscle and non-muscle cells to exercise-associated redox-sensitive signalling effects will be reviewed; for example, transcription factors such as Peroxisome Proliferator Activated Receptor-gamma (PPARγ) and Liver X-Receptor-alpha (LXRα) comprise redox-activable signalling systems, and we and others have reported exercise-associated modulation of PPARγ and/or LXRα-regulated genes in skeletal myocyte and in non-muscle cell-types such as monocyte-macrophages. Finally, the consequences of such responses in the context of management of chronic inflammatory conditions, and also their implications for the design of exercise training programmes (particularly the use of dietary antioxidants alongside exercise), will be discussed.

Redox Control of Skeletal Muscle Regeneration

Skeletal muscle shows high plasticity in response to external demand. Moreover, adult skeletal muscle is capable of complete regeneration after injury, due to the properties of muscle stem cells (MuSCs), the satellite cells, which follow a tightly regulated myogenic program to generate both new myofibers and new MuSCs for further needs. Although reactive oxygen species (ROS) and reactive nitrogen species (RNS) have long been associated with skeletal muscle physiology, their implication in the cell and molecular processes at work during muscle regeneration is more recent. This review focuses on redox regulation during skeletal muscle regeneration. An overview of the basics of ROS/RNS and antioxidant chemistry and biology occurring in skeletal muscle is first provided. Then, the comprehensive knowledge on redox regulation of MuSCs and their surrounding cell partners (macrophages, endothelial cells) during skeletal muscle regeneration is presented in normal muscle and in specific physiological (exercise-induced muscle damage, aging) and pathological (muscular dystrophies) contexts. Recent advances in the comprehension of these processes has led to the development of therapeutic assays using antioxidant supplementation, which result in inconsistent efficiency, underlying the need for new tools that are aimed at precisely deciphering and targeting ROS networks. This review should provide an overall insight of the redox regulation of skeletal muscle regeneration while highlighting the limits of the use of nonspecific antioxidants to improve muscle function. Antioxid. Redox Signal. 27, 276-310.

Dietary thiols in exercise: oxidative stress defence, exercise performance, and adaptation

Endurance athletes are susceptible to cellular damage initiated by excessive levels of aerobic exercise-produced reactive oxygen species (ROS). Whilst ROS can contribute to the onset of fatigue, there is increasing evidence that they play a crucial role in exercise adaptations. The use of antioxidant supplements such as vitamin C and E in athletes is common; however, their ability to enhance performance and facilitate recovery is controversial, with many studies suggesting a blunting of training adaptations with supplementation. The up-regulation of endogenous antioxidant systems brought about by exercise training allows for greater tolerance to subsequent ROS, thus, athletes may benefit from increasing these systems through dietary thiol donors. Recent work has shown supplementation with a cysteine donor (N-acetylcysteine; NAC) improves antioxidant capacity by augmenting glutathione levels and reducing markers of oxidative stress, as well as ergogenic potential through association with delayed fatigue in numerous experimental models. However, the use of this, and other thiol donors may have adverse physiological effects. A recent discovery for the use of a thiol donor food source, keratin, to potentially enhance endogenous antioxidants may have important implications for endurance athletes hoping to enhance performance and recovery without blunting training adaptations.