Month: March 2011

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Electrolytes and overdrinking: Noakes vs. Gatorade

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As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

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We all know by now that drinking too much during exercise can have fatal consequences, because your sodium levels get dangerously diluted (hence the name of the condition: hyponatremia, meaning too little sodium). So it seems logical to think that drinking beverages containing sodium, rather than plain water, would mitigate this risk. That’s certainly what sports-drink makers want you to think.

But some evidence suggests otherwise — and that has led to an explosive scientific debate. The latest blow comes from a paper in the British Journal of Sports Medicine by Tim Noakes, in which he takes data from an earlier Gatorade-funded study [full text freely available] and reanalyzes it to reach essentially the opposite conclusion. In typical Noakes fashion, he pulls no punches about what he believes is causing the confusion: the title of his paper is “Changes in body mass alone explain almost all of the variance in the serum sodium concentrations during prolonged exercise. Has commercial influence impeded scientific endeavour?”

It is instructive to review the industrial connections of those who wrote the 2007 ACSM Position Stand [Noakes writes]. Of the six authors, four – Drs. Maughan, Burke, Eichner and Stachenfeld – have direct and longstanding involvement with Gatorade and the Gatorade Sports Science Institute (GSSI), but only three (Drs Maughan, Eichner and Stachenfeld) deemed it necessary to disclose in the Position Stand the existence of that relationship. The two remaining authors – Drs. Sawka and Montain – are employed by the United States Army Research Institute for Environmental Medicine (USARIEM)… It is perhaps surprising that given the large number of experts available to it, the ACSM should consistently choose the authors of its influential Position Stands from such a narrow selection of group thinkers.

Leaving aside the politics, what about the evidence? Noakes argues that the sodium content of your drinks makes little difference; what matters, rather, is how much you drink. If you drink too much, your sodium levels will drop, perhaps dangerously. If you don’t, they won’t. As evidence, he replots the data from Lindsay Baker (formerly of Penn State, now working for Gatorade)’s 2008 paper:

What’s clear here is that how much you drink (which determines the change in body mass) is the dominant factor in where you sodium levels end up. If you drink enough to gain weight, your sodium levels are going to drop no matter how much sodium you ingest. There are some small differences between the drinks (which is why the three dots in each cluster aren’t right on top of each other), but they seem pretty minor. Even Baker, in her original paper, acknowledges this:

[Sodium] consumption attenuated the decline in [serum sodium levels] from pre- to postexperiment during the 0% and +2%?BM trials, but the differences among beverages Na+0, Na+18, and Na+30 were not statistically significant…

Which makes it a little odd that when she summarizes her conclusions, she neglects to mention that the results weren’t statistically significant:

[C]ompared with [sodium]-free beverages, consumption of beverages with [sodium] attenuates the decline in [serum sodium levels] from pre- to postexercise…

So, Baker concludes in this study funded by the Gatorade Sports Science Institute, endurance athletes should consume sports drinks containing electrolytes.

Personally, I don’t think the case is as clear-cut as Noakes suggests. After all, there are some differences between the drinks, as you can see in the graph above. But I also think he’s right to question why a study that failed to find statistically significant differences between drinks with different sodium levels would conclude that athletes should consume drinks with sodium. Maybe it’s true, maybe it isn’t — but the conclusions should follow from the data.

[Thanks to Joe Baker at York for pointing out the paper to me!]

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Wait, maybe thermostat settings really do affect weight

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As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

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I can’t resist posting this follow-up to last month’s discussion of a paper proposing that one of the reasons we’re getting fatter is that we heat our houses too much. Where’s the evidence, you demanded? Ask and you shall receive…

Peter Janiszewski over at Obesity Panacea recently had an interesting post describing a prospective study that followed 1,597 people for six years, looking for “relatively unexplored” factors that might predict who becomes obese and who doesn’t. One of the factors they looked at was the temperature people kept their homes at:

[A] twofold increased risk for both incident obesity and hyperglycemia was estimated in subjects living at an indoor temperature >20 C.

While there are all sorts of cause-and-effect questions to worry about, I should point out that the 315 people who were obese at the start of study weren’t included in the analysis of what caused obesity; similarly, the 618 people who started with hyperglycemia were excluded from the analysis of what caused hyperglycemia. So it wasn’t just that people who are already obese prefer warmer temperatures (which would be the opposite of what I’d naively expect anyway).

Of course, I should include the disclaimer from the paper:

It might be hypothesized that metabolic processes are favorably affected by an ambient temperature within the thermal neutral zone, that is, not requiring energy expenditure to be allocated to maintaining a constant body temperature. However, no evidence exists to support this and socioeconomic factors might confound these associations.

As Peter noted (rather forcefully!) in his blog post, this idea is way out there on the fringe. And no one, including me, is suggesting that it’s a dominant factor in causing obesity. But perhaps it’s actually worth considering as one of the elements in an “obesogenic environment.”

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Early rehab after knee surgery pays off

THANK YOU FOR VISITING SWEATSCIENCE.COM!

As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

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Back in 2009, I wrote about the trend to move from passive rehabilitation to active rehabilitation — that instead of “RICE” (rest, ice, compression and elevation), we should think in terms of “MICE” (movement, ice, compression and elevation). In that light, I was interested to see a new Spanish study that tested when rehab should begin after knee replacement surgery. They took 300 patients and randomly assigned them to begin rehab either within 24 hours of surgery or 48 to 72 hours after surgery. The results were clear:

On average, those beginning treatment earlier stayed in hospital two days less than the control group and had five fewer rehabilitation sessions before they were discharged. An early start also lead to less pain, a greater range of joint motion both in leg flexion and extension, improved muscle strength and higher scores in tests for gait and balance.

Obviously they weren’t doing jumping jacks or anything like that on day one:

The post-operative treatment began with a series of leg exercises, breathing exercises, and tips on posture. By the second day walking short distances with walking aids was added, and in subsequent days this was built up towards adapting to daily life activities, such as beginning to climb stairs on day four.

Anyway, just thought it was an interesting data point — that even for something as major as a knee replacement, lying around and staying immobilized is no longer seen as the optimal way to promote healing.

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The physiology of aquafit (and pool running)

THANK YOU FOR VISITING SWEATSCIENCE.COM!

As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

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This week’s Jockology column looks at the physiological differences between land- and water-based exercise — aquafit, water running and activities where you’re vertical in the water rather than horizontal like swimming:

[…] The differences between water and land might seem obvious, but there are some subtleties. For example, the pressure exerted by water against your body is strongest at the bottom of the pool, where your feet are, and weakest at the top. This pressure gradient helps push blood back towards your heart, making its job easier. [Read the whole article…]

The article focuses mainly on the advantages of water-based exercise for people with balance, joint or weight concerns that make land-based exercise more difficult. But there’s a special bonus for pool-running aficionados: a brutal 60-minute workout that Canadian mile record-holder Kevin Sullivan used when he had a stress fracture in his sacrum. He got it from 1984 Olympic bronze medalist (and fellow Michigan alum) Brian Diemer, who relied on it to stay in shape prior the 1984 Olympic Trials — Diemer apparently had a stress fracture and came out of the pool only three weeks before the Trials, but was still fit enough to make the team and go on to medal later that summer.

I did it myself, every third day, when I had a sacral stress fracture in 2004. There’s something about the symmetry of the workout that I love — I’m always surprised when all those parts manage to add up to exactly 59:55.

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Protein during exercise: good for strength not endurance training

THANK YOU FOR VISITING SWEATSCIENCE.COM!

As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

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Does adding a bit of protein to a carb-heavy sports drink improve performance? That’s the claim of drinks like Accelerade, which boast a 4:1 ratio of carbohydrate to protein. But the research showing any performance advantage has been controversial. There’s a new study in the American Journal of Physiology: Endocrinology and Metabolism that put this to the test once again (hat tip to Amby Burfoot for pointing it out).

The study is quite complex, but basically it involved putting 12 cyclists through a two-hour cycling test at 55% maximum power while ingesting either a carbohydrate drink (at a rate of 1 gram per kilogram of body weight per hour) or a 4:1 carb-protein drink. They did a whole bunch of tests, including repeated muscle biopsies, to evaluate whether the protein boosted rates of muscle protein synthesis during exercise. The result: it didn’t.

An interesting wrinkle: the same group (from Maastricht University in the Netherlands) did an similar study on resistance training. In that case, adding protein did boost protein synthesis rates. The researchers speculate that muscle protein synthesis is blocked during actual exercise, but can take place in the short rests between sets of a strength training routine. Thus, the protein only helps for intermittent exercise.

Two final notes. First, this wasn’t a performance study, so it certainly doesn’t prove anything either way — that debate will continue, though my sense is that dominant current opinion is that protein during exercise doesn’t help endurance. Second, we’re only talking about drinks ingested during exercise; it’s clear that protein is very important after exercise.