Caffeine & Exercise… In The Heat?

Caffeine is generally considered a performance-enhancing drug that’s (for most people) safe, legal, not even banned in sports competitions, and even somewhat encouraged by sports scientists.

See: International society of sports nutrition position stand: caffeine and exercise performance

Depending on the rate at which you metabolize caffeine (there are genes for this), the effects will come/go earlier/later, but as a general rule of thumb, caffeine should work within about 20 minutes, and will peak in effect 1–2 hours after consumption:

Nutrition Supplements to Stimulate Lipolysis: A Review in Relation to Endurance Exercise Capacity

We covered this and more, in more detail, here:

What To Eat, Take, And Do Before A Workout

So, does hot weather change this?

It is reasonable to wonder whether it’s really a good idea to take a vasoconstrictive stimulant in conditions when your body is under threat of overheating if it’s not already.

Most of the time for most people, the benefits of caffeine outweigh the risks: Caffeine: Cognitive Enhancer Or Brain-Wrecker?

We may also wonder about “isn’t caffeine dehydrating?” and the answer is that it is diuretic (so you will pee more). Now, even if you are not peeing while you are working out (and let us for the sake of science assume that you are not), this is still somewhat an issue, since fluids that have been dispatched by your kidneys to your bladder cannot be reclaimed directly from there; at that point, it’s already gone in every way that matters.

However, when the body is overheating (even if subclinically, i.e. not to the extent of being a medical crisis, but just “the room is warm” or “the weather is hot today” or “we’ve worked up a sweat due to exercise”), then the body is sending little or no fluid to the bladder, because the kidneys “know” that the water is needed to cool down the body—hence the sweating. Which means if you’re sweating, then whether or not you took a diuretic shouldn’t make a big difference as your body won’t usually prepare to pee it out if you’re already sweating it out (unless you are overhydrated, which is rarer but perfectly possible—again, not an issue though, because this is your homeostatic system doing exactly the job it’s supposed to do to keep your body well).

See also: Things Many People Forget When It Comes To Hydration

And for that matter: When To Take Electrolytes (And When We Shouldn’t!)

Researchers (Dr. Akira Katagiri et al.) studied whether caffeine taken during exercise improves performance in heat without worsening physiological strain.

And the answer is… Yes it does:

• The starting position: they noted that pre-exercise caffeine can impair performance in hot conditions due to hyperthermia, excessive breathing, and reduced brain blood flow.
• Their hypothesis: in-exercise caffeine intake will delay peak blood caffeine levels, potentially enhancing late-stage performance and minimizing adverse effects.
• How they tested it: the participants exercised in 35°C (95°F) heat, first at moderate intensity, then at high intensity until exhaustion, after ingesting a high dose of caffeine (5 mg/kg) or placebo, 5 minutes into the session. Then the intervention and control groups switched places (randomized controlled double-blind crossover).
• Did it help? Yes, when consumed during exercise, caffeine levels rose slowly, improving endurance in later high-intensity activity and reducing perceived exertion.
• Did it hurt? No (with one caveat*), as it didn’t worsen overheating-induced overbreathing or result in further reduced brain blood flow.

*The caveat: while performance improved, caffeine led to slightly higher cardiorespiratory and temperature strain… At the very end of exercise. In other words, you remember when we said that it improved endurance? That means that it improved the duration before exhaustion, which means that the slightly higher cardiorespiratory and temperature strain occurred after the time point at which the non-caffeine group had met exhaustion and stopped exercising.

You can find the paper itself here: In-Exercise Caffeine Improves Exercise Performance in the Heat Without Exacerbating Hyperventilation and Brain Hypoperfusion

Before you grab your workout clothes and an energy drink, though, do also consider that sometimes exercise is best deferred whether or not you have caffeine.

See: Sun, Sea, And Sudden Killers To Avoid: Stay Safe From Heat Exhaustion & Heatstroke!

Want to take it further?

For the most empoweringly refreshing workout drink, check out the science for how:

Beetroot Juice & Caffeine Work Better Than Either Alone

Enjoy!