The Effect of Heat on Ergogenic Aids and Supplements

Ergogenic aids, or performance-enhancing substances, include any substances that enhance performance or recovery. The term encompasses legal substances like caffeine and prohibited substances like anabolic steroids. Interestingly, the research that determined just how ‘sports enhancing’ they could be, was done in controlled laboratory settings rather than real-world scenarios. While controlled settings leave less room for error, they can also only tell us how the substance or supplement preformed in that specific environment. And it turns out, we don’t often compete in labs. Athletes, particularly ultrarunners, compete for long durations (longer than most studies) and in widely different environments, including in high heat and high humidity.

Heat and ergogenic aids

Exercise in the heat creates a unique set of physiological demands. For instance, it creates a heightened competition for blood flow, which can, in turn, limit performance. Essentially, your performance is dictated by your capacity to dissipate heat (move heat into the environment). Modifiable factors that affect heat dissipation include:

1. enhanced skin vasodilation (sending blood to your skin surface)
2. sweating (evaporative heat transfer)
3. lowered metabolic heat production.

We understand how dietary supplements might influence your physiology and performance in thermo-neutral environments (the lab). However, the literature is far less clear on how these same supplements might impact our ability to thermoregulate. This is important because altering our ability to thermoregulate may reduce the efficacy of some supplements in the heat.

Research on Heat and ergogenic aids

In a meta-analysis released in June 2021, researchers grappled with this very question, and what they found surprised me.

Athletes commonly reach for caffeine during training and competition, and it has proven ergogenic effects in thermo-neutral environments. However, in research done in the heat it showed no improvement in performance, or even a negative impact on performance.

Caffeine and Heat

What gives? Well, caffeine binds to adenosine receptors, which increases the amount of circulating dopamine (the ‘feel-good’ neurotransmitter) in the brain. Sounds great, right? Except, the increased dopamine concentration of dopamine that makes you feel good also increases your core temperature. When you combine that with increased metabolic heat production from caffeine ingestion, suddenly we have a recipe for disaster.

Any rise in core temperature decreases heat storage capacity. This leads to an earlier onset of hyperthermic symptoms (blurred vision, dizziness, muscle cramps, etc.) and a subsequent decline in exercise performance. Makes you pause, right?

Branched Chain Amino Acids and Heat

On the other hand, some supplements show more promise in the heat, including branched-chain amino acids (BCAAs), tyrosine, and taurine. While not commonly selected for training and competition, they have been shown to increase time-to-exhaustion in the heat.

The mechanism behind the ergogenic effects of amino acids like BCAAs and tyrosine in the heat is not well understood. A likely theory suggests they may delay the onset of fatigue by competing with tryptophan for transport across the blood-brain barrier. The literature is kind of all over the place on BCAAs and tyrosine. The studies use different exercise protocols, dosages, and timing of ingestion, which appear to be critical for efficacy. In short we need more research.

Taurine and Core Temperature

Finally, perhaps the most interesting nugget of wisdom from the article highlights the sulphur-containing amino acid, taurine. Yep, taurine, an ingredient you’ve likely seen on the label of energy drinks. Evidently, taurine has a large impact on core temperature, in that it may keep core temperature low. This suggests that taurine impacts thermoregulation in a positive way. Again, the mechanism is not entirely understood. One theory suggests that taurine affects thermoregulation by increasing sweat rate, sweat onset, and by enhancing vasodilation.

The Takeaway

The meta-analysis was not conclusive enough to guide decisions related to heat and ergogenic aids. However, it highlights an important idea: study specificity. Just because something worked in a lab, that doesn’t mean it will work in the field. And it really doesn’t mean it will work at hour 12 of your 100-mile endurance race.

I advise caution when turning to supplements for sports performance. Evaluate studies with a critical eye and look at study methodology. How, where, and for how long was the intervention done. Although I’ll still reach for caffeine most mornings and at specific times during races, I will be more cognizant of environmental factors when I do. Similarly, I’ve never been an ultrarunner who slams a taurine-containing energy drink at Mile 80, but based on this new research I might try it on some long training runs.

By Corrine Malcolm,
CTS Expert Coach, Ultrarunning Host for the Trainright Podcast

Reference:

Peel, J.S., McNarry, M.A., Heffernan, S.M. et al. The Effect of Dietary Supplements on Endurance Exercise Performance and Core Temperature in Hot Environments: A Meta-analysis and Meta-regression. Sports Med 51, 2351–2371 (2021). https://doi.org/10.1007/s40279-021-01500-2