Antioxidants and endurance performance: A supplement worth trying?

Mar 11, 2021

In endurance sport, there are a huge number of supplements that are purported to enhance performance, recovery, and adaptation, with very few of these actually living up to the hype. As scientists, we tend to be very sceptical of supplements and their claims, and prefer to wait for a body of literature to emerge supporting the use of a particular supplement. However, as practitioners and athletes, we also know that waiting for the scientific literature to catch-up sometimes risks leaving you missing out on a performance aid that your competitors may have taken advantage of. In this blog, we are going to talk about antioxidant supplementation, which might be one of the most discussed supplementation regimens in endurance sport.

So, what are antioxidants? To understand antioxidants, you first have to understand reactive oxygen species or ROS. ROS accumulates in muscle during high-intensity exercise, and ROS appears to have a fatiguing effect on muscle, possibly through effects on processes related to calcium handling that is critical in muscle contraction (9). Antioxidants are what help ‘mop-up’ ROS in muscle; so if we have more antioxidants, we are more able to manage ROS accumulation during high-intensity exercise. We get antioxidants in our diet – for example, foods containing vitamins C and E – but there is also a huge number of suppliers of antioxidant supplements. In endurance sport, the idea behind antioxidant supplementation is to increase the body’s antioxidants stores, and therefore increase our capacity to mop-up ROS when it accumulates during high-intensity exercise.

Therefore, there is some theoretical rationale for why antioxidant supplementation may be beneficial for improving performance in high-intensity, ROS-generating exercise, and recovery. Indeed, a study from 2012 published in the journal Research in Sports Medicine reported an increase in time-to-exhaustion at 95% of peak power output during an incremental test (i.e. well above threshold) following acute supplementation with an antioxidant containing pycnogenol (2). We should however acknowledge here that the acute effect of antioxidant supplementation has been more mixed when considering the literature as a whole, with many studies not observing a positive effect on performance (10).

However, as long-distance triathletes, it is important to recognise our perspective. Why are we doing high-intensity, ROS-accumulating exercise? This is typically not going to be during a competition, which will occur at much lower intensities. Rather, we perform our high-intensity exercise in training, for purposes of training adaptation. Specifically, the goal of our high-intensity training sessions should be to generate positive adaptations that will make us better long-distance triathletes, rather than maximising performance in those training sessions per se. For example, we may perform these high-intensity training sessions for the purposes of increasing and improving our skeletal muscle mitochondria.

This is where antioxidant supplementation gets interesting, and perhaps a little more complicated. As long-distance triathletes, we should be considering whether antioxidant supplementation improves adaptations to high-intensity training, rather than high-intensity performance. Think about that again for one second, as this really is a key point to understand.

The first point to note here is that ROS accumulation during high-intensity exercise appears to be one of the signals that promote adaptations to endurance training (6). Specifically, a number of oxidative stress markers have been associated with endurance training adaptations in mitochondria (5, 7). This is perhaps unsurprising, as we know that many of the changes that occur in response to high-intensity training send signals to encourage training adaptations (4). So, if we decide to blunt ROS accumulation during high-intensity exercise by supplementing with antioxidants, are we simultaneously going to blunt the ROS-related adaptive response to that session? Indeed, a review from 2016 in the Journal of Physiology reported that whilst not always observed, there was building evidence that antioxidant supplementation can interfere with adaptations to high-intensity training, and, importantly, that there wasn’t any evidence suggesting it would help (8).

Anti-oxidant, reactive oxygen species, muscle soreness, recovery, inflammation, training consistency, supplements

An interesting, and recent, hypothesis is that where the antioxidants are targeted might be important. It is possible that ROS accumulating in the mitochondria of muscle cells has damaging effects, whereas ROS accumulation in other parts of the cell might be important for those adaptive signals we just discussed. Therefore, supplementation with antioxidants that specifically target ROS accumulating in mitochondria, such as ubiquinone (CoQ10) and plastoquinone, may actually be useful for endurance training adaptation, in that they may reduce damaging effects of mitochondrial ROS whilst not blunting the positive adaptive signalling taking place elsewhere in the cell (3). At Endure IQ, our motto is all-around performance, HEALTH, and enjoyment, so taking care of your mitochondria is a key consideration for us (1). It’s just not as simple as caring about only training adaptation and performance. Once thing is for sure, personally, I have weighed toward priorisiting health over performance as I've got older. 

Mitochondria-targeted antioxidants are an interesting and on-going area of research, and we eagerly await data on the adaptive response in endurance-trained athletes!

Some supplements and antioxidants I have tried and might worth checking out:
ModexCurraNZ, LipoVitaminC, Metagenics Vitamin D3 liquid, MitoQ

The Modex is a new supplement (and what inspired this blog), that the team at Modex were kind enough to send me to try. And so far, so good. But it's still early days. I take Vitamin C and Vitamin D (products as above) every day, just to cover my bases. 


  1. Annesley SJ, Fisher PR. Mitochondria in health and disease. Cells 8: 680, 2019.
  2. Bentley DJ, Dank S, Coupland R, Midgley A, Spence I. Acute antioxidant supplementation improves endurance performance in trained athletes. Res Sport Med 20: 1–12, 2012.
  3. Broome SC, Woodhead JST, Merry TL. Mitochondria-targeted antioxidants and skeletal muscle function. Antioxidants 7: 1–12, 2018.
  4. Fiorenza M, Gunnarsson TP, Hostrup M, Iaia FM, Schena F, Pilegaard H, Bangsbo J. Metabolic stress-dependent regulation of the mitochondrial biogenic molecular response to high-intensity exercise in human skeletal muscle. J Physiol 596: 2823–2840, 2018.
  5. Henriquez-Olguin C, Renani LB, Arab-Ceschia L, Raun SH, Bhatia A, Li Z, Knudsen JR, Holmdahl R, Jensen TE. Adaptations to high-intensity interval training in skeletal muscle require NADPH oxidase 2. Redox Biol 24: 101188, 2019.
  6. Irrcher I, Ljubcic V, Hood DA. Interactions between ROS and AMP kinase activity in the regulation of PGC-1alpha transcription in skeletal muscle cells. Am J Physiol - Cell Physiol 296: C116–C123, 2009.
  7. Margaritelis N V., Theodorou AA, Paschalis V, Veskoukis AS, Dipla K, Zafeiridis A, Panayiotou G, Vrabas IS, Kyparos A, Nikolaidis MG. Adaptations to endurance training depend on exercise-induced oxidative stress: exploiting redox interindividual variability. Acta Physiol 222, 2018.
  8. Merry TL, Ristow M. Do antioxidant supplements interfere with skeletal muscle adaptation to exercise training? J Physiol 594: 5135–5147, 2016.
  9. Reid MB. Free radicals and muscle fatigue: Of ROS, canaries, and the IOC. Free Radic Biol Med 44: 169–179, 2008.
  10. Rothschild JA, Bishop DJ. Effects of dietary supplements on adaptations to endurance training. Sports Med 50: 25–53, 2020.


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