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Does caffeine REALLY help exercise performance?

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My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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We all know caffeine helps exercise performance. Long, short, power, endurance, whatever. I wrote a Jockology column on it for the Globe back in 2008; Gretchen Reynolds had a round-up of the latest research in the New York Times a couple of days ago. So what more is there to say?

Well, if you want to get into the nitty-gritty, there’s a really interesting round-table discussion in the current issue of (wait for it) the Journal of Caffeine Research. It’s freely available online, and it’s not a research paper or a study — it just brings together a bunch of the leading researchers and practitioners in this area from around the world (like Terry Graham from the University of Guelph and Greg Cox from the Australian Institute of Sport) and gets them to air their opinions, thoughts, suspicions and doubts about how and in what contexts caffeine really works.

It turns out things are quite a bit more complicated than you might think. For example, Reynolds in the Times writes:

Caffeine has been proven to increase the number of fatty acids circulating in the bloodstream, which enables people to run or pedal longer (since their muscles can absorb and burn that fat for fuel and save the body’s limited stores of carbohydrates until later in the workout).

However, in the roundtable discussion, Graham disagrees with that statement. In fact, he makes a very broad argument:

I would take the controversial position that the ergogenic effect is not because of an alteration in either blood flow or alteration in delivery of blood-borne metabolites (fuels).

Instead, he believes the evidence points to effects in the muscle itself enhancing contractions, which would explain why it seems to work for virtually every sport. And the others appear to agree.

Interestingly, the editor-in-chief of the journal, Jack James of the National University of Ireland, proposes a totally contrary position. What if the supposed “ergogenic” effects of caffeine are really just due to the fact that, in virtually every study of caffeine, the subjects come to the lab in a state of withdrawal from not having had their usual morning dose? That, apparently, is what the evidence now suggests in studies of caffeine’s mental effects:

What we are talking about here arises from the fact that almost the entire population is exposed to caffeine on a regular basis, and studies show that decrements in psychomotor performance and mood are detectable after as little as 6–8 hours after caffeine was last ingested. Standard double-blind trials involve a brief pre-test period of caffeine abstinence, typically involving overnight abstinence to coincide with usual caffeine consumption patterns. By morning, participants are in the early stages of withdrawal and are experiencing negative withdrawal effects on cognitive performance and mood. When caffeine is then re-ingested under laboratory conditions, participants typically show improvements in performance and mood. However, studies that have controlled for withdrawal effects have repeatedly shown that the observed improvements are due to the reversal of withdrawal effects. That is, for cognitive performance, there is  little or no genuine net effect of caffeine over and above reversal of the negative effects caused by caffeine withdrawal. As such, can we be satisfied that this source of confounding has been adequately controlled in studies of physical performance?

It’s an interesting question. There are lots of other interesting nuggets in the discussion, on topics like dosage, responders vs. non-responders, whether habitually consuming caffeine reduces its ergogenic effects (Graham says no), and so on. In all cases, what you realize is that the literature is far less clear than we might have thought. The book on caffeine isn’t quite closed yet after all.

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Mental effort increases physical fatigue, reduces HR variability

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My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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A pretty neat study just appeared online at European Journal of Applied Physiology, looking at the links between mental effort and physical fatigue. This is a topic I’ve touched on previously, and find really interesting. The new study, from researchers at Michigan Technological University and Virginia Tech, adds some new wrinkles.

The protocol is quite complex, but basically a bunch of volunteers did fatiguing shoulder exercises while doing mental arithmetic (“Here’s a number, multiply it by three… now multiply it by three again…” etc.). The researchers measured how quickly the subjects’ shoulders fatigued, and how quickly they recovered and returned to full strength in the 15 minutes after the exercise bout. As you can probably guess, the subjects doing mental arithmetic lost strength and reached failure more quickly than the controls.

Why does this happen? Well, the researchers discuss some previous work suggesting that mental activity triggers stress which triggers low-level muscular contractions, which can lead to premature fatigue. But I actually find another explanation more convincing:

It has been shown that fatiguing contractions require high attentional demands due to changes in the excitability of motor cortex. As such, it could be argued that additional mental demand in the current study may have reduced available attentional resources needed to increase the drive to motor neurons to maintain the required force levels, resulting in early task failure (i.e., shorter endurance times).

In other words, it takes focus and mental effort to push to your limits, and those are finite quantities that can be squandered thinking about other things. That seems like the simplest explanation to me, and it would fit with the research by Samuele Marcora that I mentioned above.

A neat additional observation: the mental arithmetic resulted in lower “heart rate variability” (HRV). Basically, you measure the time between successive heart beats — if that time is always identical, you have low HRV; if it fluctuates, you have higher HRV. This tells you something about the balance between sympathetic and parasympathetic nervous systems; when you’re under stress, the sympathetic system ramps up and release norepinephrine (aka noradrenaline), which elevates your heart rate but reduces heart rate variability. The result: it takes longer for your heart rate to settle back to normal — which is exactly what the researchers observed in the subjects doing the mental arithmetic.

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More data on cryotherapy

THANK YOU FOR VISITING SWEATSCIENCE.COM!

My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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Another study on whole-body cryotherapy (or “cryosaunas,” or whatever you want to call them), from the same group at the French National Institute of Sport that published a similar study last summer. The full text is freely available online, along with a press release.

The study took nine well-trained runners, and had them perform three “hilly” treadmill runs, each time with a different recovery routine:

  1. Cryotherapy (3 minutes at -110 C), taken immediately, 24 hours, and 48 hours after the run;
  2. Far infrared therapy, also taken at the same three intervals;
  3. Nothing (“passive”).

The basic results, according to the paper: cryotherapy “accelerates recovery from exercise-induced muscle damage to a greater extent than far infrared or passive modalities.” That’s based on better results for perceived pain and maximal voluntary muscle contraction. Here’s the muscle data:

So yeah, one hour after the run, the cryotherapy allowed the runners to clench a little harder, and those results appeared to more or less persist for a couple of days. But these aren’t placebo-proof, since the runners weren’t blinded to the modality. What about a more placebo-proof measure of recovery? Well, not so good. Creatine kinase levels in the blood weren’t improved. In fact, if you look at the data and squint a bit, you might conclude that far infrared is the best choice! Uh oh.

Seriously, this study is a good start, but cryotherapy still has a ways to go. I would have liked to see it compared to conventional ice-bath therapy (which itself seems to produce more ambiguous results than you’d expect when it’s tested). Because surely we’re hoping that this therapy is actually an improvement on the current standard-of-care (which is not far infrared), rather than just a way to save seven minutes after a game or workout.

was the best recovery modality to hasten recovery from EIMD by limiting the torque loss and subjective sensations of pain
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Book suggestions for Christmas

THANK YOU FOR VISITING SWEATSCIENCE.COM!

My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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‘Tis the season, so a few quick thoughts:

  • Top choice: Which Comes First, Cardio or Weights? A wonderful page-turner crammed with no-nonsense summaries of the latest scientific research on 111 common (and uncommon) questions about fitness, training, health and nutrition… Why yes, I did happen to write it. But seriously, for readers who are new to Sweat Science: the book came out at the end of May, and aims to cover in greater depth and detail the kinds of topics discussed here on the blog. Read reviews here, check out the table of contents (which lists all 111 questions addressed in the book) in the sneak preview on Amazon, and find links to order here.
  • Blogger friends: Brian Martin of Running Technique Tips has a new e-book out called (surprise) Running Technique, which explores the theory and practice of developing good running form, along with plenty of suggested exercises and training methods. Brian is a thoughtful, balanced voice in the raging debate on what constitutes good form, so his thoughts are worth checking out. Also Jimson Lee of SpeedEndurance has a new book — well, actually, a new/old book: a revised edition of Bud Winter’s 1964 classic The Rocket Sprint Start on 1960 Olympic 100-metre champ Armin Hary’s legendary start, with Lee offering updates and comparison to the starts of the current crop of Jamaican sprinters.
  • Totally unrelated non-fiction: While I’m at it, two of the best non-fiction books I read this year. Charlotte Gill‘s first-hand look at the culture of tree-planting in Canada, Eating Dirt, has been garnering award nominations left, right and centre (most recently the $40,000 B.C. Prize; also the Globe 100 best-of-the-year, and the Weston Prize). The nominations are well-deserved: captivating topic, beautifully written. And Andrew Westoll‘s new book, The Chimps of Fauna Sanctuary, was a total surprise to me: not a topic that I expected to grab me, but it did. Pick up a copy of either of these books, and you (or your giftee!) won’t be disappointed.
  • Looking ahead: Okay, these books won’t be available this Christmas. But I was excited to hear recently that Pete Larson of Runblogger and Yoni Freedhoff of Weighty Matters have inked book deals. Among the sanest and wisest voices in the blogosphere — can’t wait to read the books.
  • And lastly: Did I mention Which Comes First, Cardio or Weights?
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Antioxidants are more complicated than we thought

THANK YOU FOR VISITING SWEATSCIENCE.COM!

My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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I wrote last month about emerging evidence that taking antioxidant supplements may actually be counterproductive, especially for athletes. There’s an interesting paper coming up in Cell Metabolism that casts further doubt on the whole basis of our belief that (a) oxidative stress is what causes aging and other cellular damage, and (b) antioxidants can counteract these effects (press release here; abstract here).

What’s new about the study is that they didn’t use the typical indirect methods to guess about levels of reactive oxygen species (ROS – the bad guys) and antioxidants, averaged over the entire body. Using transgenic fruit flies, they were able to measure ROS activity directly and in real time, in different parts of the body. There are a whole bunch of surprising results in this study that fly in the face of the conventional antioxidant theory. A few of the key ones:

  • If oxidation is linked to aging, we’d expect to see more ROS as the flies get older. In fact, ROS levels stay constant throughout the aging process except in the intestine. Only the intestine shows gradually increasing levels of oxidation.
  • Even in the intestine, the flies who lived longest had ROS levels that increased more quickly than the flies who died earliest — exactly the opposite of what we’d expect if oxidative stress is linked to aging and eventual death.
  • When the flies were fed an antioxidant, their production of ROS increased in response.

This last point, of course, is most interesting from the perspective of supplementation. It suggests that there’s a homeostatic response that attempts to preserve the balance between oxidants and antioxidants at a roughly constant level. So if you take a lot of antioxidants, your body simply ramps up its level of oxidants in response — with who knows what effect!

Let me emphasize: this is a study of fruit flies. Fruit flies are not humans. Still, the results suggest that our basic understanding of the real-time dynamics of oxidant-antioxidant interactions is far from complete. Now, I’d happily ignore all this cell biology stuff if there were lots of controlled trials showing increased health or performance from antioxidants. If it works, who cares about the mechanism? But since (a) we have no consistent evidence that antioxidants work, and (b) it’s increasingly clear that we don’t even understand how or why they should work, or what supposed problem they’re supposed to fix, I still think a balanced diet with lots of brightly coloured fruits and veggies in the way to go. Not powders, and not pills.