Ashwagandha Cardiorespiratory Endurance Research

Last updated: October 4, 2026 - Reviewed by Verdant Wellness Editorial Team

Updated with 2024 meta-analysis data | 12-minute read

Table of Contents

• What Is Cardiorespiratory Endurance and Why Does It Matter?
• Ashwagandha and Athletic Performance: A Brief Overview
• The Landmark KSM-66 VO2 Max Study Explained
• Elite Cyclists and Treadmill Testing: The 2011 Data
• What the 2024 Meta-Analysis Reveals
• Does Ashwagandha Help Non-Athletes Too?
• How Long Before You See Results?
• KSM-66 vs. Other Ashwagandha Extracts
• Safety Profile and Side Effects for Endurance Athletes
• How Does Ashwagandha Compare to Other Endurance Supplements?
• Quality of Life Benefits Beyond VO2 Max
• Practical Dosing and Supplementation Guidance
• Bottom Line: Is the Evidence Strong Enough?

If you have spent any time researching natural ways to improve athletic endurance, you have almost certainly come across ashwagandha. Once confined to traditional Ayurvedic medicine, this ancient root has now been the subject of multiple randomized controlled trials, systematic reviews, and meta-analyses specifically targeting cardiorespiratory performance. The results are compelling enough that sports nutritionists, exercise physiologists, and elite athletes are paying close attention.

This post digs into every major piece of ashwagandha cardiorespiratory endurance research published to date, breaks down the statistics in plain language, answers the questions athletes are actually asking, and helps you decide whether the evidence warrants adding this adaptogen to your training protocol.

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What Is Cardiorespiratory Endurance and Why Does It Matter?

Cardiorespiratory endurance refers to the ability of the heart, lungs, and circulatory system to deliver oxygen-rich blood to working muscles during sustained physical activity. It is most commonly measured through VO2 max, the maximum rate at which your body can consume oxygen during incremental exercise. Expressed in milliliters of oxygen per kilogram of body weight per minute (mL/kg/min), VO2 max is widely regarded as the gold standard marker of aerobic fitness.

Why does this number matter so much? Because VO2 max is strongly predictive of performance in virtually every endurance-based sport, from distance running and cycling to triathlon and rowing. It is also one of the strongest independent predictors of cardiovascular health and all-cause mortality in general populations, meaning its relevance extends far beyond competitive athletics.

Improving VO2 max through training alone is effective but slow. It typically requires months of consistent aerobic work, and genetic ceilings place hard limits on how high most people can push that number. This is precisely why the ashwagandha endurance research has attracted such widespread interest: multiple studies now suggest that supplementation with a standardized root extract can meaningfully increase VO2 max in timeframes of 8 to 12 weeks, even in people who are already physically active.

Understanding the quality of that research, the magnitude of the effects, and the specific conditions under which they were observed is essential before drawing any practical conclusions. So let us start from the beginning.

Ashwagandha and Athletic Performance: A Brief Overview

Withania somnifera, commonly known as ashwagandha, is a small shrub native to India, North Africa, and the Mediterranean. Its root has been used in Ayurvedic medicine for over 3,000 years as a rasayana, or rejuvenating tonic, prized for its ability to strengthen the body, reduce fatigue, and improve vitality.

Modern phytochemical analysis has identified the primary bioactive compounds as withanolides, steroidal lactones concentrated in both the root and leaves. These compounds are believed to exert adaptogenic effects, helping the body resist physical and psychological stressors, modulate the HPA axis, reduce inflammatory markers, and potentially enhance mitochondrial function and oxygen utilization.

From a sports performance standpoint, the theoretical mechanisms by which ashwagandha might improve ashwagandha oxygen capacity include:

• Reduced oxidative stress and inflammation, which may improve recovery and allow for greater training volume
• Enhanced mitochondrial biogenesis and energy production, supporting aerobic metabolism
• Modulation of cortisol and thyroid hormones, which influence metabolic rate and energy substrate utilization
• Improved cardiopulmonary efficiency, potentially through effects on nitric oxide pathways
• Reduced perception of effort and fatigue, allowing athletes to sustain higher intensities for longer

These mechanisms were largely theoretical until researchers began subjecting ashwagandha to rigorous randomized controlled trials with objective physiological endpoints. The withania somnifera VO2 max literature that has emerged over the past decade provides some of the strongest evidence we have for any adaptogen's effect on measurable aerobic performance.

The Landmark KSM-66 VO2 Max Study Explained

The study most frequently cited in ashwagandha cardiorespiratory research discussions is a randomized, double-blind, placebo-controlled trial published in 2015 and widely reported in 2016. This trial, which forms the backbone of much of what we know about KSM-66 athletic performance, examined 50 healthy adults engaged in regular athletic activity and represents one of the most methodologically rigorous investigations into this topic to date.

Study Design

Participants were randomly assigned to receive either 600 mg per day of KSM-66 ashwagandha root extract (a high-concentration, full-spectrum extract standardized to at least 5% withanolides) or a matching placebo. The intervention period was 12 weeks, with assessments conducted at baseline, week 8, and week 12. Primary endpoints included VO2 max, metabolic equivalents (METs), and time to exhaustion on a standardized treadmill protocol.

What the Numbers Show

The results of this KSM-66 treadmill study were striking. At both the 8-week and 12-week timepoints, the ashwagandha group demonstrated significantly greater improvements in VO2 max compared to placebo. Specifically:

• The ashwagandha group experienced approximately a 13.6% increase in VO2 max over the 12-week period
• The placebo group showed a more modest improvement of approximately 4.4 to 5%, likely attributable to the training effect alone
• The between-group difference was statistically significant at P < 0.0001, indicating an extremely low probability that the results were due to chance

This KSM-66 VO2 max study also reported improvements in quality of life scores, recovery, and overall sense of well-being in the ashwagandha group, suggesting that the benefits extended beyond the purely physiological domain.

Why This Study Matters

The statistical threshold of P < 0.0001 is not just technically significant; it represents a robust signal in a relatively small sample. The effect size of nearly 10 percentage points of additional VO2 max improvement above placebo is clinically meaningful for athletes. To put that in practical terms, a trained recreational runner with a VO2 max of 50 mL/kg/min who gained 13.6% improvement would theoretically reach approximately 56.8 mL/kg/min, a difference that could translate to meaningful reductions in race times across distances from 5K to marathon.

The ashwagandha endurance study design also incorporated a standardized treadmill protocol for VO2 max measurement, ensuring that differences in testing methodology did not confound the results. This level of methodological rigor distinguishes it from earlier, more preliminary investigations.

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Elite Cyclists and Treadmill Testing: The 2011 Data

Before the KSM-66 trials, earlier ashwagandha athletic trial research was already producing intriguing results in competitive populations. A 2011 to 2012 study examining elite Indian cyclists provides important complementary evidence about ashwagandha's effects in highly trained individuals, a population where ergogenic gains are notoriously difficult to achieve.

Study Population and Protocol

This trial enrolled elite cyclists, a group with already well-developed aerobic systems and limited room for improvement through supplementation. Participants received ashwagandha supplementation for 8 weeks and were assessed using treadmill-based VO2 max testing alongside measurements of metabolic equivalents and time to exhaustion.

Key Results

The findings were statistically significant across all primary endpoints:

• VO2 max: Increased by approximately 13%, rising from a mean of 46 mL/kg/min to 52 mL/kg/min in the experimental group (t = 5.356; P < 0.001)
• METs: Showed significant improvement (t = 4.483; P < 0.001)
• Time to exhaustion on treadmill: Also significantly improved (t = 4.813; P < 0.001)

The fact that elite athletes, whose VO2 max values are already substantially higher than the general population, showed a 13% improvement is particularly notable. Training-naive individuals often show large VO2 max gains simply from beginning an exercise program, which can inflate apparent supplement effects. Elite athletes, by contrast, are operating close to their trained ceiling, making a 6 mL/kg/min absolute increase a genuinely impressive finding.

What This Tells Us About the Mechanism

The consistency between the elite cyclist data and the later KSM-66 trials suggests that the ashwagandha endurance effect is not merely an artifact of baseline fitness level or training status. The approximately 13% VO2 max improvement appeared in both highly trained cyclists and recreationally active healthy adults, hinting at a genuine physiological mechanism rather than a confounded result.

What the 2024 Meta-Analysis Reveals

The Meta-Analysis Findings

This 2024 analysis focused specifically on withania somnifera VO2 max outcomes in athletes and found:

• Ashwagandha supplementation significantly improved VO2 max by 4.09 mL/kg/min compared to placebo
• The 95% confidence interval ranged from 2.55 to 5.63 mL/kg/min, a range that does not cross zero, confirming statistical significance
• The overall p-value was < 0.001, indicating high confidence in the pooled effect
• Heterogeneity was substantial at I² = 92%, meaning there was considerable variability in the magnitude of effects across individual studies

Interpreting the Heterogeneity

An I² of 92% is high, and it is worth addressing this directly rather than glossing over it. High heterogeneity in a meta-analysis means that the included studies vary considerably in their results, which can reflect differences in:

• Extract type and standardization (KSM-66 versus other preparations)
• Dosage (ranging from 300 mg to 600 mg per day across studies)
• Population (elite athletes versus recreational exercisers versus sedentary individuals)
• Study duration (8 weeks versus 12 weeks)
• Testing protocols (different treadmill incremental tests, cycle ergometry, field tests)

The high heterogeneity does not invalidate the pooled effect estimate, but it does mean that the 4.09 mL/kg/min average improvement should be interpreted as a central tendency across variable conditions rather than a precisely predictable outcome for any individual. Some populations and protocols appear to show larger effects, others smaller ones.

Why the Meta-Analysis Still Strengthens the Case

Despite the heterogeneity caveat, the fact that a pooled analysis across multiple independent trials found a statistically significant, clinically meaningful improvement in VO2 max is powerful. It means the effect is not a product of a single well-designed trial that happened to produce favorable results. The ashwagandha cardiorespiratory research base has now reached a level of breadth and consistency that positions it firmly above the threshold of preliminary or speculative.

Does Ashwagandha Help Non-Athletes Too?

One of the most common questions surrounding ashwagandha endurance research is whether the benefits are exclusive to trained athletes or whether recreational exercisers and relatively sedentary individuals can also expect meaningful improvements.

The short answer, based on the available evidence, is that benefits appear across the fitness spectrum, though the absolute magnitude may differ.

Evidence in Non-Athletic Populations

The primary KSM-66 RCT included "healthy athletic adults" rather than elite competitors, suggesting the sample was closer to the well-trained recreational exerciser population than to professional athletes. The 13.6% VO2 max improvement observed in this trial is therefore relevant to a broad population.

Other studies have examined ashwagandha oxygen capacity in less trained populations and have generally found positive signals, though often with smaller absolute effect sizes. This is consistent with the general principle in exercise science that less trained individuals have more room to improve and may respond more robustly to both training and ergogenic interventions in terms of absolute gains, but may show smaller percentage improvements if they are starting from a lower baseline.

The Practical Implication

For someone who is not a competitive athlete but wants to improve their cardiovascular health, increase their stamina for recreational activities, or perform better in a sport they play casually, the ashwagandha athletic trial data provides a reasonable basis for expecting some degree of benefit. The effect does not appear to be gated behind a minimum fitness threshold.

How Long Before You See Results?

Duration of supplementation is a critical variable in any ergogenic intervention, and the ashwagandha endurance study literature provides some useful guidance here.

8 Weeks vs. 12 Weeks

The KSM-66 RCT measured outcomes at both 8 and 12 weeks, and reported that improvements in VO2 max were already statistically significant by week 8, with further gains at week 12. This suggests:

• Meaningful effects can emerge within 8 weeks of consistent daily supplementation
• Continued supplementation beyond 8 weeks may produce additional gains, though the incremental improvement from week 8 to week 12 appears smaller than the initial effect from baseline to week 8

The elite cyclist study also used an 8-week protocol and found significant improvements, further supporting the view that 8 weeks represents a reasonable minimum timeframe for observing cardiorespiratory benefits.

What This Means for Athletes

Athletes preparing for a key competition or training block should plan supplementation at least 8 to 12 weeks in advance to maximize the likelihood of seeing measurable improvements in ashwagandha oxygen capacity. Short-term supplementation of 2 to 4 weeks is unlikely to produce the magnitude of effects seen in the clinical trials.

KSM-66 vs. Other Ashwagandha Extracts

A legitimate and important question in interpreting ashwagandha cardiorespiratory research is whether the results are specific to KSM-66 or can be generalized to other ashwagandha preparations.

What Makes KSM-66 Distinctive

KSM-66 is a proprietary, full-spectrum root extract manufactured by Ixoreal Biomed. It is standardized to contain at least 5% withanolides and is produced using a patented process that maintains the natural balance of the root's constituent compounds. Crucially, it is the extract used in the most frequently cited and methodologically rigorous KSM-66 VO2 max study, giving it the strongest direct evidence base.

Other Clinically Studied Extracts

Sensoril is another well-characterized ashwagandha extract, standardized from both root and leaf, that has been studied for stress and cognitive outcomes but has a thinner evidence base specifically for KSM-66 athletic performance-type endpoints. Some studies in the broader ashwagandha endurance literature have used non-proprietary root powder preparations, which may have variable withanolide content and bioavailability.

The Honest Assessment

The strongest, most consistent evidence for VO2 max improvement is linked to KSM-66 and to high-quality standardized root extracts more broadly. Cheap, non-standardized ashwagandha root powder purchased from bulk suppliers may not deliver the same concentrations of active compounds used in the trials and therefore cannot be assumed to produce equivalent results.

When evaluating any product claiming to support ashwagandha endurance, looking for a standardized extract with defined withanolide content is the most important quality criterion.

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Safety Profile and Side Effects for Endurance Athletes

No discussion of ergogenic supplementation is complete without a thorough examination of safety. Athletes in particular need to consider both short-term tolerability and any potential long-term concerns.

General Safety Profile

Ashwagandha has a well-established safety record in the general population. Multiple clinical trials at doses of 300 to 600 mg per day have reported adverse event rates comparable to placebo, with the most commonly noted issues being mild gastrointestinal discomfort, particularly when taken on an empty stomach.

The ashwagandha athletic trial literature specifically has not identified any performance-relevant adverse effects. In the KSM-66 endurance trials, no significant safety signals were reported at the 600 mg per day dose used throughout the 12-week study period.

Specific Considerations for Athletes

• Thyroid function: Ashwagandha has documented effects on thyroid hormones, particularly thyroid-stimulating hormone and T4. Athletes with thyroid conditions or those taking thyroid medications should consult a healthcare provider before supplementing
• Autoimmune conditions: As an immune-modulating adaptogen, ashwagandha may theoretically stimulate immune activity, which could be relevant for athletes with autoimmune conditions
• Drug interactions: Potential interactions with sedatives, immunosuppressants, and thyroid medications warrant caution
• Anti-doping considerations: Ashwagandha is not currently on the World Anti-Doping Agency (WADA) prohibited list, making it permissible for competitive athletes subject to drug testing. However, athletes should always verify their specific federation's regulations and use third-party tested products

Pregnancy and Long-Term Use

High-dose ashwagandha is generally contraindicated in pregnancy due to its traditional use as an emmenagogue. Long-term safety data beyond 12 weeks at high doses remains limited, though the available evidence does not raise red flags for cycle-based use consistent with training blocks.

How Does Ashwagandha Compare to Other Endurance Supplements?

Athletes considering ashwagandha endurance supplementation naturally want to know how it stacks up against established ergogenic aids. Here is a brief evidence-based comparison.

Beetroot/Dietary Nitrate

Dietary nitrate from beetroot juice is perhaps the most extensively studied natural ergogenic for endurance performance. Its mechanism, converting nitrate to nitric oxide, directly reduces the oxygen cost of exercise and has been shown in numerous trials to improve time trial performance and VO2 max. The evidence base is larger and more consistent than for ashwagandha, and effects can be observed acutely within hours of ingestion, unlike ashwagandha which requires weeks of supplementation.

Beta-Alanine

Beta-alanine improves muscular endurance through buffering of intramuscular acid, but its primary benefits are in high-intensity efforts of 1 to 4 minutes rather than pure aerobic endurance. The mechanisms are complementary rather than overlapping with withania somnifera VO2 max effects.

Caffeine

Caffeine remains the most evidence-backed acute ergogenic aid for endurance performance, reducing perceived effort and improving time to exhaustion. Unlike ashwagandha, it works acutely but requires cycling to prevent tolerance development.

Where Ashwagandha Fits

Ashwagandha occupies a somewhat unique position in the ergogenic landscape. Its adaptogenic mechanism means it addresses underlying physiological stress, recovery capacity, and potentially mitochondrial function over time, rather than providing an acute performance boost. This makes it potentially valuable as a foundation supplement that enhances training adaptation, complementing rather than competing with acute ergogenics like caffeine and nitrate.

The KSM-66 endurance research supports it as one of the better-evidenced natural supplements for improving baseline aerobic capacity over an 8 to 12 week training block.

Quality of Life Benefits Beyond VO2 Max

The ashwagandha cardiorespiratory research trials have consistently measured outcomes beyond pure physiological performance, and the quality-of-life data deserves attention in its own right.

Fatigue and Recovery

Multiple studies in the ashwagandha endurance study literature have reported significant reductions in perceived fatigue and improvements in self-reported recovery quality. For athletes, the ability to train harder and recover faster is arguably as important as direct improvements in VO2 max, because it determines the quality and volume of training load that can be sustained over time.

Stress and Cortisol

Ashwagandha's most consistent finding across its entire research literature is its ability to support healthy cortisol levels and perceived stress. Chronic training stress elevates cortisol, which can impair recovery, suppress immune function, and ultimately reduce training adaptation. By moderating the cortisol response, ashwagandha may create a more favorable hormonal environment for endurance adaptation.

Sleep Quality

Several trials have reported improvements in sleep quality with ashwagandha supplementation, including reductions in time to fall asleep and improvements in sleep efficiency. Since sleep is the primary period of physiological recovery and adaptation, this benefit could compound over weeks of training to produce meaningful performance gains.

Muscle Strength and Recovery

While outside the core focus of ashwagandha oxygen capacity research, several trials have also noted improvements in muscle strength and recovery markers, suggesting a broad anabolic and anti-catabolic profile that supports overall athletic adaptation.

Practical Dosing and Supplementation Guidance

Based on the totality of the ashwagandha cardiorespiratory research, the following practical guidance can be offered.

Dose

The most frequently used and best-studied dose for endurance-related outcomes is 600 mg per day of a standardized root extract. This was the dose used in the landmark KSM-66 trials and falls within the range consistently supported by the meta-analytic evidence. Some studies have used 300 mg twice daily as a split dose, which may improve tolerability and is functionally equivalent in total daily dose.

Timing

There is no strong evidence that the time of day of ashwagandha supplementation materially affects its endurance-related benefits, given that effects accumulate over weeks rather than occurring acutely. Many users prefer taking it with meals to minimize any gastrointestinal discomfort. Taking it in the evening may offer additional sleep quality benefits for some individuals.

Cycling

The evidence base for long-term continuous use extends to 12 weeks in the primary trials. Common practice is to supplement for 8 to 12 weeks in alignment with a training block, followed by a 4-week break, though there is limited formal evidence either supporting or refuting this approach. Given the safety data available, short-cycle use presents minimal concern.

Quality Selection

When selecting a product, prioritizing those that:

• Use KSM-66 or another clinically validated standardized extract
• Specify withanolide content (minimum 5%)
• Have undergone third-party testing for purity and potency
• Clearly state the root extract dose rather than a proprietary blend dose that obscures the actual ashwagandha content

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Bottom Line: Is the Evidence Strong Enough?

After reviewing the complete landscape of ashwagandha cardiorespiratory endurance research, a clear picture emerges. This is no longer a supplement supported by a single small pilot study or theoretical mechanisms alone. The evidence base now includes:

• A rigorous double-blind RCT with 50 participants showing a ~13.6% VO2 max improvement over 12 weeks with KSM-66 at 600 mg/day, with P < 0.0001
• An elite cyclist trial showing a 13% VO2 max increase over 8 weeks in already highly trained individuals
• A 2024 meta-analysis pooling data across multiple independent studies and finding a significant 4.09 mL/kg/min improvement in VO2 max versus placebo with P < 0.001

The heterogeneity across studies (I² = 92%) is a legitimate consideration and suggests that the magnitude of benefit will vary based on extract quality, dose, population, and duration. Not everyone will see a 13% VO2 max improvement. But the consistency of the directional finding, that ashwagandha supplementation with a standardized root extract meaningfully improves aerobic capacity in physically active individuals, is now supported by multiple independent lines of evidence.

Who Should Consider It

• Endurance athletes in a structured 8 to 12 week training block looking for safe, legal, evidence-based ergogenic support
• Recreational exercisers wanting to improve cardiovascular fitness alongside a consistent training program
• Athletes experiencing high training loads who may benefit from the adaptogenic and cortisol-moderating effects alongside the direct endurance benefits
• Anyone for whom VO2 max improvement has specific health implications, given the well-established relationship between aerobic capacity and long-term cardiovascular health

Who Should Proceed with Caution

• Individuals with thyroid conditions or autoimmune diseases should consult a healthcare provider first
• Pregnant or breastfeeding individuals should avoid high-dose ashwagandha
• Athletes subject to anti-doping testing should use only certified third-party tested products and verify current prohibited substance lists with their relevant federation

The ashwagandha endurance evidence, taken as a whole, places this adaptogen in a select tier of natural supplements where the clinical data is strong enough to justify its inclusion in an evidence-based supplementation protocol for athletes who want to optimize their cardiorespiratory performance. It is not a magic bullet, and it will not replace consistent training. But the research is clear: for the right individual, taking the right form at the right dose for long enough, ashwagandha cardiorespiratory endurance research now provides a meaningful scientific basis for expecting real, measurable improvements in aerobic capacity.

The information in this article is intended for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider before beginning any new supplementation regimen, particularly if you have pre-existing medical conditions or are taking medications.

References

1. Nutritional Outlook. "Ashwagandha enhances cardiorespiratory endurance, new study." nutritionaloutlook.com (2024).
2. NutraIngredients. "Ashwagandha root extract may boost cardiorespiratory endurance, RCT." nutraingredients.com (2016).
3. Shenoy S, et al. "Effects of eight-week supplementation of ashwagandha on cardiorespiratory endurance in elite Indian cyclists." Journal of Ayurveda and Integrative Medicine (2012).
4. Choudhary B, et al. "Efficacy of ashwagandha (Withania somnifera [L.] Dunal) in improving cardiorespiratory endurance in healthy athletic adults." AYU (2015). PMC4687242.
5. Additional primary trial data as cited within NutraIngredients and Nutritional Outlook reporting.
6. Systematic review and meta-analysis on ashwagandha and sports performance. Published 2024 (VO2max effect: 4.09 mL/min/kg; 95% CI 2.55–5.63; p<0.001; I²=92%).