How L-carnitine affects performance and recovery for running, OCR, and endurance sports
Thomas Solomon, PhD.
Updated onReading time approx 7 minutes (1400 words).
What you’ll learn:
L-carnitine is a compound your muscles use to shuttle fatty acids (fats) into mitochondria — the cell’s power plants — so it can be “burned” to produce ATP (energy).
For healthy athletes, L-carnitine probably won’t move the needle on performance. A different form, propionyl-L-carnitine, does help people with peripheral artery disease walk farther — useful medically, but not proof of a performance boost for healthy runners.
Some small, mixed-quality studies suggest a possible benefit for high-intensity work (80% V̇O2maxV̇O2max is the maximal rate of oxygen consumption your body can achieve during exercise. It is a measure of cardiorespiratory fitness and indicates the size of your engine, i.e., your maximal aerobic power, which contributes to endurance performance. or higher), but the evidence isn’t strong.
Curious about the how and why? Scroll down for the details, the nuances, and the nerdy bits.
The information I provide is not medical advice. L-carnitine can have side effects and might interact with other drugs, nutrients, and medical conditions (see here). If you are unsure, always consult your doctor to ensure that a specific supplement is safe for you to use.
What is L-carnitine?
Carnitine is an amino acid predominantly found in muscle tissue, but it isn’t a building block of protein and it’s not coded by your genes. Your body can make it from lysine and methionine, and if you eat meat you’ll also get a chunk from food. Its job: to move fatty acids into mitochondria so they can be oxidized for energy. The gatekeeper for that process is the carnitine palmitoyltransferase system, which helps fat enter the mitochondria and then feed into beta-oxidation — a process that produces lots of ATP (energy). And, this is important because during rest and low to moderate-intensity exercise, the body predominantly “burns” fatty acids to produce energy (ATP).
In the world of medicine, carnitine is sometimes used in people with peripheral artery disease to help treat a symptom called “intermittent claudication” — jargon for achy calf pain during walking that eases when the person stops — which occurs because of poor blood flow and energy metabolism (muscle carnitine deficiency, which reduces fat metabolism). Several meta-analysesA meta-analysis quantifies the overall effect size of a treatment by compiling effect sizes from all known studies of that treatment. (see here, here, here, & here) show that oral or intravenous administration of either L-carnitine or propionyl-L-carnitine (a derivative) can help treat intermittent claudication and improve walking capacity in folks with peripheral artery disease.
In people with peripheral artery disease and in healthy folks, supplementing with L-carnitine or propionyl-L-carnitine can raise carnitine levels in muscle (see here). Propionyl-L-carnitine can also form propionyl-CoA, which can be turned into succinyl-CoA and drop into the Krebs cycle to help produce extra energy (ATP). Furthermore, because people with peripheral artery disease often walk farther after taking it, athletes reasonably ask: “does this help running performance too?”. Carnitine certainly gained some notoriety for that purpose because it was one of the “supplements” that played a starring role in the Alberto Salazar–Mo Farah saga. But…
What is the scientific evidence on L-carnitine’s impact on athletic performance?
L-carnitine and propionyl-L-carnitine are generally considered to be safe to consume (see here, here, here, and here).
Short-term doses before exercise or daily use might help during high-intensity efforts (80% of V̇O2maxV̇O2max is the maximal rate of oxygen consumption your body can achieve during exercise. It is a measure of cardiorespiratory fitness and indicates the size of your engine, i.e., your maximal aerobic power, which contributes to endurance performance. or higher), but the evidence is limited and not super consistent.
Only a few studies have tested moderate-intensity work (below 80% of V̇O2max), and the study designs differ so much that it's hard to tell what’s truly going on.
Most tests were done when participants were fresh. We don’t know if the same effects show up when people are already fatigued — for example, a performance test after a long run.
There’s also very little data in trained athletes: we need more high-quality trials.
There are also two unanswered questions, and high-quality randomised controlled trialsThe “gold standard” approach for determining whether a treatment has a causal effect on an outcome of interest. In such a study, a sample of people representing the population of interest is randomised to receive the treatment or a no-treatment placebo (control), and the outcome of interest is measured before and after exposure to the treatment and control. are needed to answer them:
Does orally taken carnitine actually reach the muscles’ mitochondria in useful amounts?
Is propionyl-L-carnitine the better choice for performance?
One trial directly compared the two forms and found propionyl-L-carnitine led to better exercise capacity than L-carnitine (see Brevetti et al. 1992), but that was in people with peripheral artery disease, not athletes.
If you choose to use L-carnitine / propionyl-L-carnitine, a reasonable dose is:
3 to 4 grams about 60 to 90 minutes before exercise, or 2 to 3 grams per day for 9 to 24 weeks. These are doses used in studies, not a personal prescription.
Taking more doesn’t necessarily mean a bigger effect.
When supplementation is stopped, we don’t yet know how fast muscle levels fall back to baseline.
Can L-carnitine enhance athletic performance?
Moderate quality of evidenceA moderate quality of evidence means that, in general, studies in this field have some limitations. This could be due to somewhat inconsistent effects between studies, a moderate range of effect sizes between studies, and/or a moderate risk of bias (caused by a small to medium number of studies, small to medium numbers of participants, poorly described randomization processes, some missing data, some inappropriate methods/statistics). When the quality of evidence is moderate, there is some doubt and only moderate confidence in the overall effect of an intervention, and future studies could change overall conclusions. The best way to improve the quality of evidence is for scientists to conduct large, well-controlled, high-quality randomized controlled trials. shows that propionyl-L-carnitine is likely to improve walking distance in people with peripheral artery disease. However, this medical benefit does not automatically apply to trained athletes.
Although some evidence shows that L-carnitine taken daily or pre-session might help in high-intensity efforts, but overall it’s unlikely to boost performance in a meaningful way.
Due to insufficient research, it is unclear whether these effects are similar between trained athletes and untrained folks or between males and females.
Because there is not a high quality meta-analysisA meta-analysis quantifies the overall effect size of a treatment by compiling effect sizes from all known studies of that treatment., the overall effect sizeAn effect size is a standardized measure of the magnitude of an effect of an intervention. Unlike p-values, effect sizes show how large the effect is and indicate how meaningful it might be. Common effect size measures include standardised mean difference (SMD), Cohen’s d, Hedges’ g, eta-squared, and correlation coefficients. is currently uncertain.
Keep in mind: there is also high heterogeneityHeterogeneity shows how much the results in different studies in a meta-analysis vary from each other. It is measured as the percentage of variation (the I2 value). A rule of thumb: if I2 is roughly 25%, that indicates low heterogeneity (good), 50% is moderate, and 75% indicates high heterogeneity (bad). High heterogeneity means there’s more variability in effects between studies and, therefore, a less precise overall effect estimate. (variability) in effects between studies, moderate/high risk of biasRisk of bias in a meta-analysis refers to the potential for systematic errors in the studies included in the analysis. Such errors can lead to misleading/invalid results, and unreliable conclusions. This can arise because of issues with the way participants are selected (randomisation), how data is collected and analysed, and how the results are reported., and possible publication biasPublication bias in meta-analysis occurs when studies with significant results are more likely to be published than those with non-significant findings, leading to distorted conclusions. This bias can inflate effect sizes and misrepresent the true effectiveness of interventions, making it crucial to identify and correct for it in research.. So, the overall certainty of evidenceCertainty of evidence tells us how confident we are that the results reflect the true effect. It’s based on factors like study design, risk of bias, consistency, directness, and precision. Low certainty means more doubt and less confidence, and that future studies could easily change the conclusions. High certainty means that the current evidence is so strong and consistent that future studies are unlikely to change conclusions. is lowA low quality of evidence means that, in general, studies in this field have several limitations. This could be due to inconsistency in effects between studies, a large range of effect sizes between studies, and/or a high risk of bias (caused by inappropriate controls, a small number of studies, small numbers of participants, poor/absent randomisation processes, missing data, inappropriate methods/statistics). When the quality of evidence is low, there is more doubt and less confidence in the overall effect of an intervention, and new studies could easily change overall conclusions. The most effective way to enhance the quality of evidence is for scientists to conduct large, well-controlled, high-quality randomised controlled trials.. Therefore, additional high-quality randomised controlled trialsThe “gold standard” approach for determining whether a treatment has a causal effect on an outcome of interest. In such a study, a sample of people representing the population of interest is randomised to receive the treatment or a no-treatment placebo (control), and the outcome of interest is measured before and after exposure to the treatment and control. are needed.
The nice part: carnitine doesn't appear to hurt recovery or performance. So, if you like it and believe it works for you, give it a whirl. But, remember that time and money spent trying to improve your performance with something that has no obvious benefit might be better spent optimising your training load, sleep habits, and dietary/nutritional choices.
To minimise the risk of consuming a supplement that contains prohibited substances, only choose products that have been independently tested (e.g., Informed Sport). And, remember: Supplements do not make athletes and do not replace training; they're just the icing on a very well-baked cake. Before reaching for pills and potions, optimise your training load and dial in your sleep, nutrition, and rest.
How to use this: If you want to self-experiment, keep it simple: try 3 to 4 grams about 60 to 90 minutes before a single key session, or 2 to 3 grams per day for at least a few weeks. Track something that matters to you (time to exhaustion, reps, race splits). If there’s no clear, consistent benefit after a few weeks, save your money and invest in good sleep, healthy nutrition, and ample rest.
Strengthen the fight for clean sport
Remember: You are the only person responsible for what goes in your body! Ignorance is not an excuse! Stay educated. Be informed.
Consult WADA’s prohibited list, cross-check your meds against the Global DRO drug reference list, and only choose supplements that have been tested by an independent body (e.g., Informed Sport or LabDoor).
Information you can trust. All content on Veohtu is meticulously researched and written by Thomas Solomon, PhD. He does not sell supplements, recovery products, or ad space, and he has no sponsorships, brand affiliations, or ambassador roles. Everything you read reflects his independent views, shaped solely by peer-reviewed scientific evidence — and that will never change.
Full list of meta-analyses examining L-carnitine for performance.
Here are the meta-analyses I've summarised above:
Clinical Effects of L-Carnitine Supplementation on Physical Performance in Healthy Subjects, the Key to Success in Rehabilitation: A Systematic Review and Meta-Analysis from the Rehabilitation Point of View. Vecchio et al. (2021) J Funct Morphol Kinesio
Effect of Acute and Chronic Oral l-Carnitine Supplementation on Exercise Performance Based on the Exercise Intensity: A Systematic Review. Mielgo-Ayuso et al. (2021) Nutrients
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Who is Thomas Solomon?
My knowledge has been honed following 20+ years of running, cycling, hiking, cross-country skiing, lifting, and climbing, 15+ years of academic research at world-leading universities and hospitals, and 10+ years advising and coaching in athletic performance and lifestyle change.
I have a BSc in Biochemistry, a PhD in Exercise Science, and over 90 peer-reviewed publications in medical journals.
I'm also an ACSM-certified Exercise Physiologist (ACSM-EP), an ACSM-certified Personal Trainer (ACSM-CPT), a VDOT-certified Distance Running Coach, and a UKVRN Registered Nutritionist (RNutr).
Since 2002, I’ve conducted biomedical research in exercise and nutrition and have taught and led university courses in exercise physiology, nutrition, biochemistry, and molecular medicine.
And, with my personal experience of competing on the track (800m to 10,000m), the road (5 k to marathon), on the trails, and in the mountains, by foot, bicycle, cross-country ski, and during obstacle course races (OCR), I deeply understand what it's like to train and compete — I've been there, done it, and gotten sweat, mud, and tears on my t-shirt.
Disclaimer: I occasionally mention brands and products, but it is important to know that I don't sell recovery products, supplements, or ad space, and I'm not affiliated with / sponsored by / an ambassador for / receiving advertisement royalties from any brands. I have conducted biomedical research for which I’ve received research money from publicly-funded national research councils and medical charities, and also from private companies, including Novo Nordisk Foundation, AstraZeneca, Amylin, the A.P. Møller Foundation, and the Augustinus Foundation. I’ve also consulted for Boost Treadmills and Gu Energy on R&D grant applications, and I provide research and scientific writing services for Examine.com. Some of my articles contain links to information provided by Examine.com but I do not receive any royalties or bonuses from those links. Importantly, none of the companies described above have had any control over the research design, data analysis, or publication outcomes of my work. I research and write my content using state-of-the-art, consensus, peer reviewed, and published scientific evidence combined with my empirical evidence observed in practice and feedback from athletes. My advice is, and always will be, based on my own views and opinions shaped by the scientific evidence available. The information I provide is not medical advice. Before making any changes to your habits of daily living based on any information I provide, always ensure it is safe for you to do so and consult your doctor if you are unsure.