Physical Endurance & Stamina: A Nutrition and Natural-Health Reference
1. Definition and Conceptual Framework
Endurance is the capacity of the body to sustain a moderate-intensity physical effort over a prolonged period of time. Stamina is defined as the ability to resist fatigue — both physical and mental — and maintain a high level of performance quality or intensity as exhaustion begins to set in; it relates less to the total duration of the activity and more to maintaining a high-power output near one's maximum limit. While both terms are used interchangeably in common speech, exercise scientists distinguish them: stamina is the time an activity can be performed at maximum capacity, while endurance is the maximum time a physical activity can be performed.
Physical endurance refers to the capacity to perform submaximal physical work for a long period of time. "Endurance exercises" are activities one performs for an extended period that require less than maximum effort; running, bicycle riding, and swimming for long distances are examples.
Endurance is made up of two primary components: cardiovascular endurance and muscular endurance. Cardiovascular endurance is the ability of the heart and lungs to fuel the body with oxygen, while muscular endurance is the ability of the muscles to work continuously without getting tired.
2. Key Physiological Measures
VO₂ max, or maximal oxygen consumption, refers to the maximum amount of oxygen that an individual can utilize during intense or maximal exercise, and this measurement is generally considered the best indicator of cardiovascular fitness and aerobic endurance. The more oxygen a person can use during high-level exercise, the more energy a person can produce; the muscles need oxygen for prolonged aerobic exercise, and the heart must pump adequate amounts of blood through the circulation to meet the demands of aerobic exercise.
Age, gender, genetics, body composition, training condition, and exercise modality are among the key variables affecting VO₂ max. Much of the aerobic improvement resulting from training comes from an increase in the size of the heart.
3. Body Systems Involved
Physical endurance and stamina are the product of coordinated function across multiple body systems:
- Cardiovascular system: Cardiorespiratory fitness refers to the ability of the circulatory and respiratory systems to provide oxygen to skeletal muscle and is characterized classically by the maximal oxygen consumption (VO₂ max), which may be measured directly during a maximal exercise test or indirectly by a submaximal test.
- Musculoskeletal system: Endurance is closely linked to the muscular system, including muscles, bones, and joints, as well as overall musculoskeletal efficiency.
- Metabolic/energy systems: "The major metabolic consequences of the adaptations of muscle to endurance exercise are a slower utilization of muscle glycogen and blood glucose, a greater reliance on fat oxidation, and less lactate production during exercise of a given intensity."
- Central nervous system: Mental stress and mental fatigue can affect the perception of workload and effort. A 2016 review published in Frontiers in Physiology found that participants under mental stress perceived their workload to be greater than a group performing the same workload in the absence of mental stress.
- Neuroendocrine system: The term "adaptogen" is applied to a herb with phytonutrients that regulate metabolism when a body is perturbed by physical or mental stress, and help the body adapt by normalizing system functions, developing resistance to future stress, and elevating the body's functioning to a higher level of performance.
4. Contributing and Associated Factors
4.1 Training Status and Genetics
Endurance refers to the ability to sustain prolonged physical or mental effort, often influenced by genetic factors that determine traits associated with stamina and performance in athletic contexts. Taking into consideration the morphological and functional changes as a consequence of the training process, VO₂ max values are statistically significantly higher in groups of athletes compared to groups of non-athletes.
4.2 Iron Status
Iron is an essential micronutrient for athletes, intricately linked to their performance by regulating cellular respiration and metabolism; impaired iron levels in the body can significantly hinder athletic performance. The increased demand for iron due to exercise, coupled with potential dietary iron insufficiencies — particularly among endurance athletes — amplifies the risk of iron deficiency. Moreover, prolonged exercise can impact iron absorption, utilization, storage, and overall iron concentrations in an athlete.
Different levels of deficiency can occur in the athlete, resulting in symptoms that range from none to severe fatigue. Iron deficiency without anemia may adversely affect athletic performance. Causes of iron deficiency include poor intake, menstrual losses, gastrointestinal and genitourinary losses due to exercise-induced ischemia or organ movement, foot-strike hemolysis, thermohemolysis, and sweat losses.
4.3 Hydration Status
Dehydrated individuals show a higher rate of perceived exertion (RPE) and had a higher body mass loss during endurance efforts. Exogenous factors such as nutritional and hydration strategies affect fatigue in endurance sports, including factors associated with performance fatigability and perceived fatigability.
4.4 Glycogen Availability
For almost a century, it has been recognized that consuming a high-carbohydrate diet can enhance endurance performance. The introduction of the muscle biopsy technique in the 1960s revealed that these findings were linked to muscle glycogen availability, and several studies have subsequently confirmed that commencing exercise with low muscle glycogen availability can markedly compromise endurance performance.
4.5 Mental Fatigue
A review published in Frontiers in Physiology found that participants under mental stress perceived workload to be greater than a group performing the same workload in the absence of mental stress, emphasizing the importance of mental balance for endurance performance overall.
4.6 Environmental Conditions
In hot conditions, athletes show significant increases in RPE, heart rate, and skin temperature after endurance tests. No differences were found when athletes were subjected to altitude or cold conditions in the meta-analysis reviewed, though other research on altitude and iron metabolism remains an area of active investigation.
5. Nutritional Factors
5.1 Carbohydrates
In endurance exercise, carbohydrate and fat oxidation are the main sources of substrate metabolism. Exercise intensity and duration play a crucial role in determining the predominant metabolic pathway utilized during physical activity, as variations between low and high intensity result in different rates of fat, protein, and carbohydrate oxidation.
Scientific evidence: A meta-analysis of 34 studies found that carbohydrate (CHO) intake increased time to exhaustion (p < 0.001) and decreased heart rate during endurance tests (p = 0.018). A systematic review found that, for the most part (8 of 12 RCTs included), consumption of carbohydrates can improve performance in endurance exercises, including when associated with other performance-enhancing substances. For recovery, a carbohydrate intake of 1.2–1.5 g·kg⁻¹·hr⁻¹ during short-term recovery (≤8 h) appears to be the threshold for maximizing the post-exercise rate of glycogen synthesis.
Low-carbohydrate, high-fat (LCHF) diets have been associated with an impaired ability to perform high-intensity exercise, a reduced carbohydrate oxidative capacity, a lower energy yield per litre of O₂, and reduced mitochondrial respiration, which can explain the absent effects of this diet on performance in elite endurance athletes.
5.2 Protein and Amino Acids
As exercise duration increases beyond 2 hours, the rate of amino acid oxidation increases, equivalent to 6% of the total energy cost of exercise; branched-chain amino acids (isoleucine, leucine, and valine) are oxidized preferentially over other amino acids.
Scientific evidence: Previous meta-analysis evidence shows that the combined intake of protein and carbohydrates improves exhaustion time by an average of 9%. This combination stimulates the synthesis rate of skeletal muscle protein in the human body and improves the net protein balance of the whole body. The mean effect of BCAAs on immediate performance is small; however, sustained supplementation (≥5 g per dose for >7 days) can significantly lower serum creatine kinase and delayed-onset muscle soreness, thereby shortening the recovery window — effects particularly valuable when total protein intake is suboptimal or recovery demands are heavy.
5.3 Iron
Iron is a micronutrient that plays an important role in oxygen transport and energy metabolism. Iron is an essential component of hemoglobin, which is required for oxygen transport in red blood cells; therefore, iron deficiency reduces the oxygen transport capacity of active muscles, leading to a decline in athletic performance.
Scientific evidence: Iron deficiency negatively affects endurance performance by 3–4%. However, endurance performance improved by 2–20% when iron-deficient athletes were treated with 100 mg/day of elemental iron for up to 56 days via oral supplementation. Iron-deficient non-anemic athletes with low serum ferritin stores may be predisposed to reduced maximal aerobic capacity; however, maximal aerobic capacity improved by 6–15% following 16–100 mg/day of elemental iron for 36–126 days. Iron deficiency in athletes is common due to several mechanisms, including increased losses of iron during training caused by micro-ischemia, hemolysis, and sweating; women are more prone than men because of menstrual bleeding.
5.4 Magnesium
Magnesium helps muscles contract and relax and supports normal nerve signaling. If this input is running low, the result can manifest as fatigue, brain fog, or reduced exercise capacity. Evidence for magnesium supplementation specifically improving performance in already-replete individuals is considered preliminary; the primary benefit documented in the literature is the correction of a deficiency state.
5.5 Dietary Nitrates (Beetroot)
Findings show that beetroot-derived nitrates can improve endurance, oxygen efficiency, muscular power, recovery, and cardiovascular function, particularly in recreationally active or moderately trained individuals.
Scientific evidence: In 2009, it was shown that beetroot ingestion of 5.5 mmol NO₃⁻ per day for 6 days improved time to exhaustion during intense cycling exercise in eight young, healthy men compared with placebo (675 ± 203 s vs. 585 ± 145 s, p < 0.05). A double-blind placebo-controlled crossover trial in 11 recreationally fit men and women found that during the last 1.8 km of a 5-km run, running velocity was 5% faster in the beetroot trial, and rating of perceived exertion was lower with beetroot.
A 2025 umbrella review concluded that acute (2–3 h pre-exercise) and chronic (≥3 days) supplementation with beetroot juice to achieve nitrate levels of 8.3–16.4 mmol (515–1017 mg/day) are recommended to enhance physical performance; beetroot juice shows population-specific effects, improving muscular strength in professional athletes and aerobic endurance in non-athletes. Results are mixed in elite athletes, likely due to their already optimized nitric oxide utilization. A meta-analysis on muscle damage found that beetroot juice accelerated isometric strength recovery 72 hours post-exercise (SMD: 0.54, p = 0.01) and countermovement jump performance 24–72 hours post-exercise. Some trials testing lower doses (~4–6 mmol) still observed improvements in heart rate, oxygen cost, or muscular endurance; higher doses (>15 mmol) did not provide clear additional benefits.
5.6 Caffeine
Caffeine (1,3,7-trimethylxanthine) is one of the most widely consumed performance-enhancing substances in sport due to its well-established ergogenic effects; its use is more common in aerobic-based sports due to the ample evidence endorsing the benefits of caffeine supplementation on endurance exercise.
Scientific evidence: Caffeine improves central arousal and neuromuscular drive via adenosine-receptor antagonism, consistently enhancing endurance, sprinting, and sport-specific skill execution while lowering ratings of perceived exertion and pain/soreness at 3–6 mg/kg ingested 30–60 min pre-exercise; co-ingestion with carbohydrate may also facilitate post-exercise muscle glycogen resynthesis. Recent systematic reviews and meta-analyses further support these findings, indicating that acute caffeine ingestion (3–6 mg·kg⁻¹) can enhance sport-specific actions as well as maximal strength and muscular endurance across multiple sports.
5.7 Beta-Alanine
Beta-alanine is a non-essential amino acid that is commonly used to improve exercise performance; it can influence the buffering of hydrogen ions produced during intense exercise and delay fatigue, providing a substrate for increased synthesis of intramuscular carnosine.
Scientific evidence: A 2024 systematic review and meta-analysis found that of 18 individual studies analyzed in 331 participants, 14 of the 18 studies showed beta-alanine supplementation having a beneficial effect on maximal exercise. One study showed an improvement of 13.9% in ventilatory threshold; another reported that beta-alanine supplementation for 28 days enhanced sub-maximal endurance performance by delaying the onset of blood lactate accumulation. Evidence is considered moderate-to-strong for high-intensity efforts lasting 1–10 minutes but is less consistent for longer, lower-intensity exercise.
5.8 Creatine
Creatine is a popular dietary supplement purported to enhance exercise performance. It is synthesized endogenously primarily in the kidneys, liver, and pancreas via a two-step process involving the amino acids arginine, glycine, and methionine. It is difficult to saturate creatine stores within muscles through diet alone.
Scientific evidence: Given creatine's ability to enhance anaerobic work capacity and performance through repeated surges in intensity, creatine supplementation may be beneficial for sports such as cross-country skiing, mountain biking, cycling, and triathlon, as well as for short-duration events where end-spurts are critical for performance, such as rowing, kayaking, and track cycling. Creatine is a pleiotropic molecule that has been shown to influence several metabolic, hormonal, and physiological factors that may impact endurance performance. Evidence for pure aerobic endurance improvement is more limited than for strength and power; creatine's primary endurance-relevant role is facilitating repeated high-intensity efforts within longer events.
5.9 Coenzyme Q10 (CoQ10)
Coenzyme Q10 (CoQ10) is a natural substance that plays a fundamental role in the mitochondria, the parts of the cell that produce energy from food. On this basis, it has been proposed as a performance enhancer for athletes; however, most clinical trials have found no significant improvement in performance with the use of CoQ10.
Scientific evidence: A systematic review of 16 studies found that after CoQ10 supplementation, a decrease in oxidative stress markers was observed, followed by higher antioxidant activity; lower levels of liver damage markers were identified; and a reduction in fatigue indicators such as creatine kinase and an increase in anaerobic performance were noted. Oral CoQ10 at 30–300 mg was able to potentiate plasma antioxidant activity and anaerobic performance, reducing markers linked to oxidative stress in athletes aged 17 and older. Evidence for direct aerobic endurance improvement remains mixed, and the primary documented benefit is in recovery and antioxidant capacity rather than performance enhancement.
6. Herbs and Botanical Ingredients
6.1 Ashwagandha (Withania somnifera)
Traditional use: Both modern medical literature and traditional Ayurveda writings report many potential health benefits of ashwagandha, also known as Indian Ginseng or Winter Cherry, under the rubrics of anti-stress effects, neuroprotective effects, immunomodulatory effects, and rejuvenating effects, via the herb's interplay with the nervous system, the endocrine system, the cardiopulmonary system, the energy production system, and the immune system. Ashwagandha is a member of the family of herbs referred to as "adaptogens," a term applied to a herb with phytonutrients that regulate metabolism when a body is perturbed by physical or mental stress, and help the body adapt by normalizing system functions, developing resistance to future stress, and elevating the body's functioning to a higher level of performance.
Scientific evidence: Ashwagandha is considered a potent adaptogen and anti-stress agent that could have potential to improve physical performance. A PRISMA-based systematic review and Bayesian meta-analysis aimed to evaluate clinical trials regarding the effect of ashwagandha supplementation on physical performance in healthy individuals. A total of 13 studies met the requirements of this systematic review, although only 12 were included in the quantitative analysis. One 8-week double-blind trial evaluated the efficacy of 300 mg of ashwagandha root extract capsules (twice daily) in enhancing cardiorespiratory endurance (VO₂ max) and recovery among athletes. Another trial assessing the effectiveness of 500 mg capsules of aqueous ashwagandha root taken twice daily for eight weeks in elite cyclists revealed a significant improvement in various anaerobic parameters. Evidence quality is rated low-to-moderate overall due to varying populations and outcome measures across studies.
6.2 Rhodiola rosea
Traditional use: Rhodiola rosea is grown at high altitudes and northern latitudes. Due to its purported adaptogenic properties, it has been studied for its performance-enhancing capabilities in healthy populations and its therapeutic properties in a number of clinical populations. Historically, it has been used in Scandinavian and Russian traditional medicine as a tonic against fatigue and cold stress, and by Soviet-era researchers as an adaptogen for athletes and cosmonauts.
Scientific evidence: A 2025 systematic review and meta-analysis including 26 RCTs with 668 healthy participants found that RR supplementation significantly improved endurance-related outcomes, including VO₂ max (11 studies; ES = 0.32, p < 0.01), time to exhaustion (7 studies; ES = 0.38, p < 0.05), and time trial performance. An earlier systematic review found more mixed results: of 206 articles identified in a systematic search, 11 met inclusion criteria; 10 were described as RCTs and one as a CCT, and the conclusion was that research regarding R. rosea efficacy is contradictory. One RCT found that R. rosea significantly lowered CRP levels at 5 hours and 5 days after an exhaustive exercise test (p < 0.05), though CK levels were not significantly different between groups. Overall, evidence is preliminary-to-moderate and heterogeneous, with small-to-medium effect sizes; larger, more standardized trials are warranted.
6.3 Panax Ginseng (Asian/Korean Ginseng)
Traditional use: Herbs have been used throughout history to enhance physical performance, but scientific scrutiny with controlled clinical trials has only recently been applied to study such effects. Ginsengs — including Chinese, Korean, and American ginsengs — are currently used to enhance physical performance regardless of scientific evidence of effect.
Scientific evidence: Controlled studies of Asian ginsengs found improvements in exercise performance when most of the following conditions were met: use of standardized root extracts, study duration greater than 8 weeks, daily dose greater than 1 g dried root or equivalent, large number of subjects, and older subjects. Results across trials have been inconsistent; some well-controlled trials have found no ergogenic effect on graded maximal aerobic exercise. Evidence is rated as mixed and preliminary for performance enhancement, particularly in already-trained individuals.
6.4 Cordyceps (Cordyceps sinensis)
Traditional use: Cordyceps is a parasitic fungus used for centuries in Traditional Chinese Medicine (TCM) as a tonic to support energy, lung function, and physical vitality. It has been described in historical Chinese pharmacopeias as an agent for replenishing qi (vital energy) and strengthening yang.
Scientific evidence: The most investigated medicinal herbs for their adaptogenic activity include Eleutherococcus senticosus, Panax ginseng, Withania somnifera, Schisandra chinensis, and Rhodiola spp. Several human trials have tested Cordyceps in combination with other botanicals such as Rhodiola for endurance and exercise performance. In two RCTs on exercise performance, intervention capsules contained 300 mg of R. rosea (standardized to 3.0% rosavins and 2.5% salidrosides), 1000 mg of Cordyceps sinensis, and 800 mg of a proprietary blend. Isolating the independent effect of Cordyceps is difficult from combination trials. Evidence for Cordyceps as a single agent in human endurance performance is limited; most well-controlled human trials are small and use mixed formulations, making firm conclusions premature.
6.5 Adaptogens as a Class
The main modes of action of the selected adaptogenic plants are stress modulatory, antioxidant, anti-fatigue, and physical endurance enhancement. Phytochemicals that have demonstrated adaptogenic properties mainly belong to flavonoids, terpenoids, and phenylpropanoid glycosides. The adaptogen family of herbs includes ashwagandha, rhodiola, ginseng, schisandra, and maca. Adaptogens are used commonly for stress relief, brain health, adrenal health, and for ameliorating HPA-axis dysfunction.
7. Dietary and Lifestyle Factors
7.1 Overall Nutritional Quality and Energy Availability
Positions from the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine suggest that optimal nutrition can enhance physical activity, exercise performance, and recovery after exercise. An adequate nutritional approach helps to maximize the capacity to train with intensity, as well as muscle recovery and metabolic adaptations resulting from the practice of physical activity. A link between low energy availability and poor iron status in athletes is likely, as the dietary intake of iron may not be sufficient under restricted energy intake conditions.
7.2 Hydration Strategy
Nutritional and hydration strategies affect fatigue in endurance sports, including factors associated with performance fatigability and perceived fatigability. Maintaining fluid balance before, during, and after sustained activity is consistently identified in the literature as a modifiable determinant of endurance capacity, with even modest dehydration elevating perceived exertion and impairing thermoregulation.
7.3 Carbohydrate Periodization
For almost a century, it has been recognized that consuming a high-carbohydrate diet can enhance endurance performance, whereas consumption of a fat-rich diet reduces time to exhaustion, although it increases fat oxidation at a given sub-maximal exercise intensity. Strategic carbohydrate periodization — manipulating carbohydrate availability across training sessions to promote specific metabolic adaptations — is an active area of research, though systematic reviews note that the overall performance effects in elite athletes require further study.
7.4 Progressive Training and Aerobic Adaptation
Enhancing aerobic capacity by choosing an effective training regimen based on VO₂ max remains critical for athletes aiming to boost their performance. Aerobic exercise improves VO₂ max significantly; interestingly, much of this improvement results from an increase in the size of the heart.
7.5 Sleep and Recovery
Many reports describe athletes presenting with vague complaints of weakness, fatigue, decreased physical endurance, feeling hot or cold, diminished immune response, changes in energy levels, cognitive performance, and behavior when recovery is inadequate. Lack of sleep, infection, liver or chronic disease, inflammation, or intense exercise can have immediate effects on serum ferritin, a key marker of iron stores. Sleep quality is consistently identified in the sports science literature as essential for endurance adaptation, hormonal recovery, and glycogen resynthesis, though a detailed review of sleep intervention trials falls outside the scope of the studies retrieved here.
7.6 Antioxidant-Rich Diet and Polyphenols
Antioxidants, polyphenols, and coenzyme Q10 can mitigate oxidative stress and inflammation, reduce delayed-onset muscle soreness (DOMS), and maintain training availability during congested schedules, but dosing and timing should be managed to avoid blunting training adaptations with chronic high-dose use. Dietary polyphenols from whole foods such as berries, dark leafy greens, and tart cherry are discussed in the literature as potential recovery aids, though the evidence for direct endurance performance improvement remains preliminary.
8. Summary of Evidence Strength
- Strong evidence: Carbohydrate availability and timing; caffeine supplementation (3–6 mg/kg); iron correction in deficient athletes; hydration maintenance.
- Moderate evidence: Dietary nitrates/beetroot juice (particularly in recreationally active, non-elite individuals); beta-alanine for high-intensity efforts of 1–10 minutes; combined carbohydrate–protein intake for recovery.
- Preliminary/mixed evidence: Rhodiola rosea (promising 2025 meta-analysis data; earlier reviews contradictory); ashwagandha (low-to-moderate risk of bias in RCTs; effect size meaningful but studies heterogeneous); creatine for endurance specifically; CoQ10 (antioxidant benefit more consistent than direct performance benefit).
- Insufficient human evidence: Cordyceps as a single agent; magnesium supplementation in replete individuals; most other traditional botanical tonics for exercise performance when studied in isolation under rigorous placebo-controlled conditions.
References
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