Nutritional Strategies to Improve Post-exercise Recovery and Subsequent Exercise Performance: A Narrative Review

Although carbohydrate intake is the cornerstone of glycogen resynthesis, concomitant intake of protein has been suggested to confer additional benefits, primarily owing to the insulinotropic effects of certain amino acids to reduce muscle protein breakdown [84]. However, this benefit appears to occur only when protein is added to a suboptimal amount of carbohydrate (e.g., 0.3 g·kg⁻¹·h⁻¹ protein and 0.9 g·kg⁻¹⋅h⁻¹ carbohydrate) [85]. Similarly, a meta-analysis confirmed that ingesting sufficient carbohydrate should be the priority when aiming to replenish muscle glycogen stores, reporting that co-ingestion of carbohydrate (0.86 g·kg⁻¹⋅h⁻1) with protein (0.27 g·kg⁻¹⋅h⁻¹) did not increase muscle glycogen re-synthesis more than carbohydrate per se when ingested at 0.95 g·kg⁻¹⋅h⁻¹ during short-term post-exercise recovery (≤ 8 h) [86].

From a performance standpoint, co-ingesting protein with carbohydrate during recovery between two bouts of endurance exercise has shown small to moderate effects on subsequent performance compared with carbohydrate alone (e.g., improvements of ~ 1.6% in mean power output during cycling time trials and 0.6% in competitive running performance [87]. However, even a 1% improvement can be critical in elite sports, potentially making the difference between finishing fourth and securing a podium position in Olympic competitions [88]. Rustad et al. [89] reported that co-ingesting carbohydrate (0.8 g·kg⁻¹·h⁻¹) and protein (0.4 g·kg⁻¹·h⁻¹) during the first 2 h of an 18 h of recovery from strenuous cycling exercise led to ~ 14 min longer subsequent exercise capacity compared with carbohydrate intake alone (1.2 g·kg⁻¹·h⁻¹). Similarly, Dahl et al. [63] observed an ~ 8.5-min increase in exercise capacity during subsequent cycling to exhaustion at 70% peak oxygen consumption (VO_2peak) when protein was co-ingested with carbohydrate within 90 min following 5 h of recovery, attributed to higher muscle glycogen synthesis rates and positive nitrogen balance compared with carbohydrate alone in trained male endurance athletes. In addition, exercise capacity during high-intensity interval cycling was significantly greater with carbohydrate-protein co-ingestion (0.8 g·kg⁻¹·h⁻¹of carbohydrates and 0.4 g·kg⁻¹·h⁻¹ of protein) compared with carbohydrate alone (1.2 g·kg⁻¹·h⁻¹) following a 2-h recovery period [90]. These positive results were mainly attributed to greater muscle glycogen synthesis or positive nitrogen balance mediated by the additional protein [85].

In contrast, recent studies have reported similar improvements in subsequent time-trial performance and high-intensity interval cycling capacity after either carbohydrates alone or carbohydrate–protein co-ingestion during 2–5 h recovery periods in both young and master endurance athletes [91, 92] (Supplementary Material 3). These discrepancies may be attributed to interindividual variations in training status and genetic factors, as well as differences in recovery durations, glycogen depletion protocols, performance tests, amounts and types of protein ingested, and methods of nutrient provision during recovery.

Taken together, combining protein with carbohydrates during recovery periods shorter than 24 h likely has a small, but positive, effect on performance, ranging from 0.6 to 1.6% [87]. Accordingly, it should be recommended as it may confer additional benefits, including positive nitrogen balance leading to increased whole-body muscle protein synthesis [93], increased protein content related to mitochondrial biogenesis [94], reduced muscle damage markers [95], and accelerated post-exercise rehydration [96]. Therefore, co-ingestion of carbohydrates and protein during post-exercise may be advantageous, especially for athletes engaging in multiple daily training sessions or with less than 24 h between bouts.

Rehydration after exercise is another key aspect of recovery. Exercising in a dehydrated state is well-established to negatively affect both performance and health [97, 98]. During strenuous exercise in a hot or humid environment, athletes may lose more than 2 L of sweat per hour, accompanied by substantial electrolyte, extracellular, and intracellular water loss that may negatively affect processes such as the rate of post-exercise glycogen and muscle protein resynthesis [44, 99]. Therefore, re-establishing water and electrolyte balance during the post-exercise recovery period is important [100].

Rehydration is particularly important before subsequent training or competition when limited time is available between exercise bouts in environmentally challenging conditions [101, 102]. Understanding pre- and intra-exercise fluid recommendations is fundamental before addressing post-exercise hydration. Athletes are generally recommended to slowly ingest 5–7 mL·kg⁻¹ fluids (via food and liquids) at least 4 h before exercise/competition [103]. Attempts to correct fluid loss induced by exercise should consider the sweat rate, which can vary from 0 to over 2 L·h⁻¹, depending on factors such as environmental conditions, intensity, duration, genetics, fitness level, acclimatization to the environment, and clothing [104, 105]. Although intra-exercise hydration can mitigate fluid loss during exercise, post-exercise hydration is critical for conditions involving subsequent competitions.

If rapid recovery (< 24 h) is the aim or severe hypohydration (> 5% body mass loss) is observed, intensive intake of fluids and electrolytes should be advised to enhance recovery before subsequent competition [106]. For example, daily water and sodium losses can vary significantly and be in the range of 4–10 L and 3.5–7.0 g, respectively, in active athletes under heat stress; thus, both need to be replaced to re-establish normal total body water (i.e., achieve euhydration) [106]. Beginning subsequent exercise in a dehydrated state may impair exercise performance. Therefore, rehydration strategies between exercise bouts recommend that athletes drink fluids equivalent to 125–150% of their body mass lost during exercise [107, 108].

Maughan et al. tested different beverages using the beverage hydration index (BHI), which compares the fluid retention capacity 2 h post-ingestion compared with an equal volume of water [109], finding oral rehydration solutions, skimmed milk, whole milk, and orange juice had higher BHI values compared with water. Notably, beverages such as cola (regular and diet), tea (hot and iced), coffee, lager, sparkling water, and sports drinks did not differ from water in terms of BHI, suggesting that the volume of consumed liquid is more important than its source for hydration. Therefore, it is reasonable to use water or a mix of other beverages as post-exercise hydrational strategies, tailored to individual hydration needs and personal preferences [109].

Oral rehydration solutions and sports drinks are common strategies to improve fluid retention owing to their balanced carbohydrate and electrolyte content [110]. However, studies have observed no differences in fluid retention between post-exercise consumption of oral rehydration solutions and sports drinks following exercise-induced dehydration, even in hot conditions [111, 112] or in subsequent endurance performance [113]. Recent systematic reviews have found that dairy milk leads to a similar net fluid balance compared with carbohydrate-electrolyte sports drinks and water when consumed ad libitum and provides a higher net fluid balance when consumed in similar volumes [114, 115]. Milk-based beverages have also led to greater exercise capacity in subsequent exercise performance when compared with both noncaloric and energy-matched beverages, likely due to simultaneously increasing glycogen resynthesis and stimulating muscle protein synthesis [114]. Interestingly, nonalcoholic beer has been studied as a post-hydration drink, since it is rich in water, carbohydrates, and some minerals. However, as with other beverages, nonalcoholic beer could be considered on the basis of individual preference, but more studies are needed owing to insufficient evidence [115].

Although water is one of the most common and accessible options for post-exercise rehydration, drinking water alone may not optimize hydration status, as it has a low BHI value owing to the absence of osmotic nutrient content such as electrolytes, carbohydrate, and protein [109]. Therefore, water alone may not be the best choice to maximize subsequent exercise capacity [92, 116], especially considering that other nutrients are also essential for recovery. Conversely, factors such as an athlete’s eating behavior, thirst, palatability, and gastrointestinal comfort may influence the volume of other beverages consumed, leading to different recovery outcomes [117]. Studies examining the co-ingestion of various foods with beverages ad libitum during 2–4 h of recovery from exercise-induced dehydration have indicated that, regardless of beverage choice, similar recovery fluid balance [117, 118] and subsequent exercise performance [118] can be achieved using milk-based formulations, sports drinks, or water along with different solid meals in both males and females, despite varying dietary behaviors [117–119]. The mechanism behind this may be related to delayed gastric emptying and increased plasma osmolality, which reduces urine output and enhances fluid retention [117] (Supplementary Material 4, 5).

Sodium bicarbonate (NaHCO₃) supplementation before exercise is widely recognized for enhancing extracellular buffering capacity when administered at doses of 0.2–0.4 g·kg⁻¹ body mass (BM) 1–3 h prior to activity [120]. This strategy can improve high-intensity exercise performance lasting approximately 30 s to 10 min [121]. The performance enhancements observed with NaHCO₃ supplementation are attributed to increased extracellular buffering capacity, lowered extracellular potassium (K⁺) levels, elevated sodium (Na⁺) levels before exercise, and a potential reduction in cellular oxidative stress responses [122–124]. Another mechanism that may explain the ergogenic effect of post-exercise NaHCO₃ ingestion is its hyperhydration effect, leading to an ~ 8% increase in blood volume through increased sodium availability in the blood [125].

The lack of performance enhancement in some studies may be due to intraindividual variability in the time required to reach peak HCO₃⁻ levels and the occurrence of gastrointestinal discomfort [127, 132, 133]. De Oliveira et al. [121] established a threshold increase of 4–6 mmol/L for circulating HCO₃⁻ levels to determine the ergogenic potential of NaHCO₃ supplementation. This threshold depends on the time needed for circulating HCO₃⁻ levels to rise and is influenced by factors such as the dosage and timing of ingestion [134], supplement form (i.e., solution versus capsules) [123, 135], potential adverse effects, genetic factors related to hydrogen ion (H⁺) transporters, the individual’s training status, and exercise type [136].

Taken together, administration of NaHCO₃ after exercise can expedite the restoration of acid–base equilibrium following intense physical activity, potentially improving performance during subsequent exercise sessions if an adequate recovery period of 30–90 min is provided [124, 129, 137]. For athletes with longer recovery periods (> 90 min) who are more susceptible to severe gastrointestinal symptoms, new forms of NaHCO₃ such as enteric-coated, delayed-release capsules and mini-tablet NaHCO₃ hydrogels could be considered as they may mitigate gastrointestinal discomfort [138–140]. In addition, administering NaHCO₃ before exercise can promote acid–base restoration and improve subsequent exercise performance, particularly when the recovery period between sessions is less than 40 min [141]. However, further research is needed to examine the effects of different NaHCO₃ supplementation forms and their impact on HCO₃⁻ kinetics during recovery between exercise sessions. More research is needed to assess the impact of post-exercise NaHCO₃ supplementation in brief, high-intensity exercise bouts such as combat sports.

Creatine (α-methyl-guanidinoacetic acid) is a widely used nutritional supplement that has been extensively researched over the past two decades [142]. It is well-documented that creatine supplementation can enhance adaptations to resistance training, including increases in strength, power, and muscular endurance [143]. In addition, creatine supplementation may positively affect muscle glycogen storage in the days following glycogen-depleting exercise [144].

While the exact physiological mechanisms by which creatine augments post-exercise muscle glycogen storage are not fully understood, several plausible mechanisms have been proposed. Creatine may enhance the abundance of glucose transporter (GLUT) 4, facilitating greater glucose uptake into muscle cells [145]. It may also mitigate post-exercise inflammation, reducing markers of muscle damage and soreness [146]. This is important because exercise-induced muscle damage (EIMD) can impede muscle glycogen replenishment for up to 10 days [147], suggesting that creatine could facilitate glycogen resynthesis by alleviating EIMD. Furthermore, as an osmotically active compound, creatine can increase intracellular fluid volume [148], which may be beneficial because cell swelling has been identified as a potent stimulus for muscle glycogen synthesis [149]. However, creatine does not appear to affect muscle glycogen recovery within the initial 6 h following exercise but has been shown to increase glycogen storage over a 5-day period [144]. Other research has shown that creatine supplementation, combined with a high carbohydrate diet, led to 82% greater glycogen resynthesis within 24 h following exhaustive exercise compared with placebo [150]. Moreover, Van Loon et al. [151] observed an 18% increase in muscle glycogen content following 5 days of creatine loading (20 g·day^–1), underscoring a notable glycogen storage boost without significant impacts on fasting plasma insulin levels or GLUT-4 mRNA/protein content. In addition, research by Nelson et al. [152] demonstrated that a moderate carbohydrate intake post-creatine loading could enhance muscle glycogen stores by 53% compared with a high-carbohydrate diet alone, further indicating the efficacy of creatine supplementation in enhancing glycogen storage, although the exact mechanism remains unclear. However, an individual’s training status may influence creatine’s efficacy regarding glycogen storage, as two studies focusing on highly trained athletes did not show significant enhancements in muscle glycogen levels following creatine supplementation [153, 154]. Specifically, trained individuals might experience reduced benefits from creatine supplementation in enhancing glycogen storage owing to their already optimized glycogen resynthesis capabilities following exercise, compared with untrained individuals [155] (Supplementary Material 7). Collectively, this evidence highlights the potential benefits and mechanisms of creatine supplementation in athletic performance and recovery, although the impact of simultaneous creatine and carbohydrate consumption on subsequent exercise performance remains debated.

In summary, the simultaneous ingestion of creatine and carbohydrate can effectively augment muscle glycogen storage, particularly after the initial 6-h post-exercise period. Despite these findings, further research is necessary to determine the impact of creatine and carbohydrate co-ingestion on endurance performance in subsequent activities, with a special focus on weight-bearing sports. It is also important to note that most studies referenced involve male subjects. Given that creatine metabolism exhibits sex-specific differences [156], there is a need for a better understanding of creatine supplementation’s effects across sex and levels of athletic training.

Caffeine (1,3,7-trimethylxanthine) is one of the most extensively researched performance-enhancing supplements and is known to enhance exercise performance when consumed before [157] and during prolonged exercise [158]. Recent evidence suggests caffeine could also positively affect post-exercise recovery owing to its ability to decrease muscle soreness [159] and, when paired with carbohydrates, accelerate muscle glycogen replenishment [160]. Loureiro et al. [161] proposed that caffeine might enhance muscle glycogen synthesis by activating molecular pathways related to either energy sensing or muscle contraction. Specifically, caffeine co-ingestion could lead to higher activation of adenosine monophosphate-activated protein kinase (AMPK), possibly through enhanced activation of the Ca²⁺-calmodulin-dependent protein kinase (CaMK) and the phosphorylation of acetyl-CoA carboxylase (ACC), which could collectively induce translocation of GLUT4 to the cell membrane and promote muscle glucose uptake [162, 163].

However, the evidence regarding enhanced post-exercise glycogen synthesis with caffeine co-ingestion is mixed. For example, no positive effect was observed when combining caffeine (6 mg·kg^–1) with glucose (~ 1 g·kg^–1⋅h^–1) on muscle glycogen replenishment rates during a 5-h recovery period after exhaustive cycling [164]. In contrast, another study reported that muscle glycogen restoration was ~ 66% higher during 4 h of recovery with a very high dose of caffeine (8 mg·kg^–1) and moderate carbohydrate intake (1 g·kg^–1·h^–1) compared with carbohydrate ingestion alone in trained endurance athletes [160]. However, both studies used carbohydrate doses below the optimal 1.2 g·kg⁻¹·h⁻¹ recommended for maximal glycogen resynthesis [160, 164]. Another study examined the effect of caffeine co-ingestion with a more optimal carbohydrate dose, finding no significant differences in glycogen resynthesis when 1.7 mg·kg⁻¹·h⁻¹ of caffeine was co-ingested with 1.2 g·kg⁻¹·h⁻¹ of carbohydrates (1:1 glucose and maltodextrin) during a 6-h recovery period, compared with carbohydrates alone. The authors concluded that an optimal carbohydrate dose of 1.2 g·kg⁻¹·h⁻¹ is sufficient to maximize glycogen replenishment rates, with no additional benefits from caffeine co-ingestion [165]. Recently, Loureiro et al. investigated the impact of caffeine co-ingestion through coffee combined with milk containing 1.2 g·kg⁻¹ of carbohydrates and 0.3 g·kg⁻¹ of protein on muscle glycogen resynthesis, finding that the addition of caffeine to milk resulted in approximately 153% higher rates of muscle glycogen synthesis compared with milk alone [166] (Supplementary Material 8). However, while the carbohydrate dose was considered optimal, the carbohydrate composition (milk sugars) was not, as recent evidence suggests that galactose–glucose mixtures are inferior as compared with glucose-based carbohydrates when provided at a dose of 1.2 g·kg^–1·h^–1 [24] (Fig. 2). Therefore, the positive effects of caffeine on muscle glycogen synthesis rates might be due to suboptimal amount or type of carbohydrate provision.

Further studies are warranted to investigate caffeine and glucose or glucose plus fructose combinations with different doses. Nevertheless, these results support the hypothesis that components within coffee could stimulate enzymes associated with muscle glycogen synthesis [161]. The positive effects of caffeine seem most apparent when muscle glycogen stores are very low and/or carbohydrate availability is suboptimal. Inconsistencies across studies may be attributed to differences in exercise protocols, glycogen depletion methods, recovery durations, dosages, and timing of carbohydrate and caffeine provision.

While caffeine–carbohydrate co-ingestion post-exercise may enhance muscle glycogen repletion, its impact on subsequent exercise performance is unclear. For instance, Taylor et al. [167] found that caffeine (6 mg·kg^–1) combined with carbohydrate (1.2 g·kg^–1·h^–1 glucose) improved exercise capacity in an intermittent shuttle run test compared with carbohydrate alone (~ 48 min versus 32 min). Conversely, Andrea-Souza et al. [168] did not observe significant performance enhancements in soccer players following co-ingestion of caffeine (6 mg·kg⁻¹) and carbohydrates (1.2 g·kg⁻¹·h⁻¹), possibly owing to insufficient glycogen depletion in the testing protocol. Similarly, Barzegar et al. [169] found no performance benefit with combined caffeine (6 mg·kg^–1) and carbohydrate (0.6 g·kg^–1) intake compared with carbohydrate alone or a placebo during a 5 × 500 m kayak test conducted 24 h after a 20-km time-trial paddle used for glycogen depletion. Moreover, caffeine ingestion alone is sufficient to enhance performance in subsequent sessions for shorter, high-intensity exercises such as wrestling [170] (Supplementary Material 9).

In summary, consuming caffeine alongside carbohydrates during the initial post-exercise recovery hours may benefit athletes who have multiple competitions in a single day or who employ training sessions with low carbohydrate availability, such as the “sleep low, train low” thought to maximize training adaptations [171]. Efficient repletion of glycogen stores after a low carbohydrate-availability exercise session is crucial for subsequent training, especially those involving high-intensity efforts [167]. It is important to note that excessive caffeine intake can lead to adverse effects, including tachycardia, anxiety, headaches, gastrointestinal issues, and a heightened risk of overnight insomnia [172, 173]. Therefore, further research focusing on glycogen storage measurements and involving larger sample sizes is necessary to clarify the impact of caffeine–carbohydrate co-ingestion on recovery and performance.

Fat is primarily stored as triacylglycerol (TG) in adipose tissue, with smaller amounts inside muscle fibers (intramyocellular TG; IMTG) [174]. IMTG stores are used as an energy source mainly during early stages of endurance exercise, with the reliance on them diminishing as exercise duration extends in favor of plasma-derived substrate oxidation [175]. IMTG are also utilized as a fuel source in the post-exercise recovery window [176]. However, their availability does not seem to play a role in performance as interventions aimed at increasing IMTG have resulted in either no differences [177] or worsened [178] performance in exercise trials lasting 20–140 min. In addition, there is no to very little net utilization of IMTG during high-intensity intermittent exercise [179], which calls into question the necessity for replenishing stores prior to a competitive event. Although a low-fat diet can attenuate repletion of IMTG following exercise [180], post-exercise plasma fatty acid availability is increased independently of post-exercise dietary ingestion, mainly due to the hormonal response that stimulates adipose tissue lipolysis and skeletal muscle blood flow during the recovery period [181]. However, there is a lack of evidence to support targeted replenishment of IMTG to improve subsequent exercise performance lasting less than 3 h, but future research in the context of repeated daily ultra-endurance performance is warranted.

Ingestion of specific types of fats may have the potential to aid in the recovery of muscle function and/or influence post-exercise glycogen resynthesis. Omega-3 fatty acids, specifically eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are types of fats that have reported anti-inflammatory properties and the capacity for reducing EIMD and enhancing muscle function following exercise [182], providing additional rationale for their recommended use in aiding exercise recovery in a dose- and duration-dependent manner [183].

Conjugated linoleic acid (CLA) refers to a mixture of polyunsaturated fatty acids that exists as various isomers of linoleic acid (18:2), and chronic supplementation may positively influence glycogen resynthesis after exercise [184]. Dietary sources include dairy and meat from ruminant animals, which are primarily found as the cis-9 trans-11 isomer; however, synthetic isomers have also been studied [185]. While most commonly studied in the context of body composition, humans have also shown an increase in post-exercise muscle GLUT4 protein expression and post-exercise muscle glycogen resynthesis rates following 8 weeks of 3.8 g⋅day⁻¹ of trans-10 cis-12 and cis-9 trans-11 CLA supplementation [184]. A study in rats supports these findings and provides some more mechanistical evidence for these findings, namely showing increased muscle glycogen synthase activity with a mixture of isomers (cis-9 trans-11, cis-10 trans-12), but not with cis-9 trans-11 isomer, suggesting physiological effects are likely isomer-specific [186]. Although consuming dietary fat in the post-exercise meal can prolong gastric emptying times [187], in the context of adequate carbohydrate ingestion, glycogen resynthesis is not influenced by the addition of fat and protein in the 3-h [188] or 24-h [189] post-exercise period. Therefore, athletes can include protein and high-quality fat in the post-exercise window without sacrificing muscle glycogen synthesis, bearing in mind that very high-fat intakes in the post-exercise window may attenuate some, but not all, signaling markers [190].

Micronutrients consumed prior to exercise, including vitamins, minerals, and phytonutrients, also have the potential to affect muscle recovery and therefore impact subsequent exercise performance. This occurs primarily via reductions in EIMD and reductions in reactive oxygen and nitrogen species (RONS) leading to improved muscle contractile function.

Several supplements may be effective in reducing EIMD, including fruit extracts such as tart cherry [191], beetroot [192], pomegranate [193], blueberry [194], watermelon [195], grape [196], and blackcurrant [197], as well as vitamin E [198], curcumin [199], cacao [200], and vitamin D [201], with the strongest evidence surrounding tart cherry, beetroot, pomegranate, and vitamin D [202, 203]. These benefits are likely due to antioxidant effects and have been observed in both trained and untrained populations [203]. However, most studies have measured indicators of muscle damage/inflammation rather than subsequent performance. Despite reductions in muscle damage and/or inflammation, improvements in performance are not always observed [191, 192].

Antioxidants have the potential to improve recovery and acute performance by reducing RONS, which impair muscle contractile force primarily through alterations in myofibrillar calcium sensitivity [204]. Often used as an umbrella term, antioxidants can exert their influence in different ways. Vitamins C and E share a common mechanism of donating a hydrogen atom to a free radical [205], whereas polyphenols stimulate stress-related cell signaling pathways and increase the expression of genes encoding proteins, such as nuclear respiratory factor 2 (NRF2), as well as pathways in skeletal muscle, leading to increased mitochondrial biogenesis [206]. Over 8000 polyphenols have been identified, including curcumin, resveratrol, quercetin, and catechins [206], and are most commonly consumed in fruits, vegetables, and spices. Although most studies of antioxidants and exercise recovery have focused on markers of oxidative stress and/or muscle damage, rather than subsequent exercise performance, quercetin supplementation for 7 days (1 g⋅day⁻¹) improved time to exhaustion at 75% maximal oxygen consumption (VO_2max) by 21.4% following a 3-h recovery period after 60 min of cycling compared with a placebo and also reduced oxidative stress [207]. In contrast, 8 weeks of green tea extract supplementation (500 mg⋅day⁻¹) had no effect on glycogen resynthesis, despite increases in postexercise fat oxidation and exercise-induced muscle GLUT4 protein content [208].

Free radicals produced via aerobic metabolism contribute both to exercise-induced fatigue as well as the adaptive response to exercise [209]. This means there is potential for high-dose antioxidants to blunt favorable training-induced muscle adaptations. Despite attenuations in markers of metabolic and/or mitochondrial adaptations, no impact on exercise performance outcomes has been observed in human studies when supplementing with vitamins C and/or E during controlled endurance training [210]. However, this finding could be related to small sample sizes in studies. For example, two human studies showing a blunting of some markers of training adaptations also had the largest sample sizes [211, 212], whereas a study showing no statistical effect of vitamin C on increases in VO_2max reported increases of 10.8% in the supplementation group (n = 5) and an increase of 22% in the group (n = 9) without supplementation (Cohen’s d = − 1.1, [95% confidence interval (CI) − 2.2, 0.04]) [213]. Supplementation with (-)-epicatechin impaired training adaptations during 4 weeks of cycling training, as increases in VO_2peak (+ 22.6%) and succinate dehydrogenase activity (+ 59.1%) were seen in the placebo but not the supplement group, although no differences in peak power or citrate synthase activity were observed between groups [214].

Supraphysiological doses of antioxidants may be beneficial for enhancing acute recovery and subsequent performance, particularly during the competition period when adaptation is not the primary focus. However, long-term daily use should be approached with caution, as research is inconclusive regarding the extent of their effects on training adaptations, especially during the muscle adaptation training phase [210]. This could be related to the multiple pathways regulating skeletal muscle adaptations to exercise. Beyond RONS, exercise adaptations are also regulated by contraction-induced changes in mechanical strain, adenosine triphosphate (ATP) turnover, calcium flux, redox balance, and intracellular oxygen pressure [215]. As an alternative to high-dose antioxidant supplementation, whole fruits and fruit-derived juices or extracts can also provide a good source of antioxidants as well as micronutrients [216]. It is possible that interactions may occur when consuming between multiple sources of polyphenols, but practical research is challenged by a large number of active compounds in a whole-food diet and the need for longer-term studies to see meaningful effects. To optimize recovery between exercise bouts, it is recommended to consume > 1000 mg polyphenols per day either from food sources or supplements for at least 3 days [203].