Pre-race carbs influence marathon pace

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)

***

Cool field study on carbohydrate loading that I missed when it came out in the International Journal of Sports Performance over the summer, but just noticed on Amby Burfoot’s Twitter feed. Researchers enrolled 257 runners preparing for the 2009 London Marathon in a five-week online study where they entered all sorts of details about their training and diet leading up to the race. The subjects had an average age of 39, and an average finishing time of 4:34.

Needless to say, there were many factors that predicted running time: gender, BMI and training being the most obvious! The most interesting was nutrition:

In addition, although individual differences in race day diet did not strongly influence the marathon performances of recreational athletes, the amount of carbohydrate ingested during the day before race-day was identified as a significant and independent predictor of running speed. Furthermore, those runners who ingested more than 7 g carbohydrate per kg body mass during the day before the event ran faster in general and also maintained their running speed to a greater extent than those participants who consumed lower quantities of carbohydrate.

This may remind you of a study I blogged about a few months ago, showing correlations between in-race carbohydrate intake and Ironman finishing time. In this case, the better predictor is day-before carb intake, not in-race carb intake — perhaps not surprising, since a marathon is much shorter than an Ironman triathlon. Here’s the most interesting data:

The most obvious question here is: Is this correlation or causation? It’s certainly plausible — in fact, it’s probable — that the most serious runners who’ve trained best are also those who realize they should eat a lot of carbs. To address this, the researchers did a matched-pair analysis. There were 30 runners who consumed more than 7 g/kg of carbs. From the rest of the subjects, the researchers extracted another 30 runners pair-matched to the carb eaters so that there was no statistical difference in age, BMI, training data, and marathon experience between those two groups of 30.

In the graph above, the open squares are the carb eaters, and the open circles are the matched group that ate fewer carbs. The finding remains the same: the runners who ate fewer carbs ran slower — and perhaps more importantly, their speed declined more sharply during the race, particularly between 35 and 40K.

Non-randomized observational studies like this need to be treated with caution, needless to say. This isn’t “proof” that eating carbohydrates the day before the race makes you faster. But it certainly fits with our current understanding of endurance physiology, and it offers a tangible target for midpack marathoners: 7 grams of carbohydrate per kilogram of bodyweight (a number that conveniently agrees with studies that have found that a single day at 10 g/kg is enough to fully max out your glycogen stores).

Men’s marathon: how much faster is it getting, and why?

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)

***

Marathoners are getting faster — that’s no secret. Here’s the progression of the fastest men’s marathon in each year between 1969 and 2010:

But looking at the leading time is a somewhat narrow approach, since it just reflects the freakish talents of one individual in each year. So here’s data, from a new analysis by researchers from the University of Milan in the Journal of Strength and Conditioning Research, showing the average of the top 200 times for the same time period:

So the basic trends are similar, but not identical. Look at the last three years, for example. From the top time, you might think marathoners are getting slower; but the second graph shows clearly that — as anyone paying attention to the marathon lately can attest — the depth of fast performances has been increasing steadily and sharply. I’ll bet the 2011 numbers will continue that trend.

The average data also shows a few inflection points where the rate of improvement has changed. There was rapid improvement until 1983, then a leveling off until about 1997; decrease again until 2003, then a little hitch for a few years, and now steady decrease again.

So what explains the changes? We can speculate about the role of money, science, and training… But as Amby Burfoot pointed out in his take on this study, it’s hard to get away from this stat:

[I]n 1997, East Africans nabbed just 29 percent of the top 200 times. For 2010, the corresponding figure was 84 percent.

One other interesting nugget: during this time period, the top time improved by about 5 seconds per year, while the average of the top 200 improved by about 10 seconds per year. So this means that (a) competitive depth is improving, and (b) in another 50 years or so, the 100th ranked marathoner in the world will be faster than the top-ranked marathoner of that year.

Salt intake, and why taste is like a dog whistle

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)

***

I was reading a profile of British historian Lucy Worsley in the New Yorker last night, in which the writer (Lauren Collins) takes part in the authentic re-enactment of the meal eaten by King George on February 6, 1789:

THEIR MAJESTIES DINNER

Soupe barley

4 chickens roasted

3 pullets minced and broiled

7 3/4 mutton collop pyes

6 perch boiled

2 breasts of lamb a la pluck

2 salmic of ducks

13 loin veal smort

(And a partridge in a pear tree, presumably.) The article is both fascinating and funny, but the culinary payoff after an enormous amount of work ends up being a bit anticlimactic:

If every age has its sounds and smells, it also has its flavors. The taste of 1789 can be a dog whistle to modern palates… “You’ve had your tongue burnt off by a Mexican chili, and you’ve been eating sugar cookies since you’ve been able to stand [says Marc Meltonville, co-head of the Historic Kitchens team;] if something’s subtle, sweetened with rose petals, how are you going to be able to taste it?”

This made me think of the long-running and bitter debate about the “right” amount of salt consumption, and how tastes are formed. Just this morning, the New York Times reported on a neat new study suggesting that the amount of salt you’re fed as an infant determines your taste for it in later life. But taste for salt is also somewhat plastic. When my wife and I started eating together, her taste for salt was dramatically higher than mine. Now, a few years later, our tastes have sort of met in the middle. She no longer adds as much salt to food as she used to; but when I visit my parents, I find that I now need to add salt to dishes that I loved for many years with no added salt.

And I still struggle to reconcile all this with the widespread message that we’re eating wayyy more salt now than we used to (and thus salt is responsible for the current epidemic of hypertension). As I wrote last year about a study by Harvard’s Walter Willett:

He and a colleague reviewed studies between 1957 and 2003 that measured sodium excretion in urine — a very accurate way of determining salt intake that gets around the difficulties in figuring out exactly how much salt is in your food. They found two main things: (a) sodium intake averaged about 3,700 mg per person per day, which is way higher than the upper recommended limit of 2,300; and (b) it essentially hasn’t changed in the half-century studied.

Interestingly, these results agree almost exactly with similar reviews of studies from 33 different countries: salt intake is high, and it hasn’t changed in recent memory.

And Henry VIII, according to Worsley in the New Yorker piece, ate 20 grams of salt each day!

How neutrophils boost (or weaken) your immune system after exercise

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)

***

Exercise boosts your immune system — up to a point. A neat new paper in Medicine & Science in Sports & Exercise digs a little deeper into this complicated relationship between exercise and immune function. Specifically, it looks into the response of neutrophils:

When infection occurs, neutrophils rapidly migrate to the infection site (chemotaxis) and ingest the pathogens (phagocytosis).

So how does exercise affect these neutrophils? Well, that depends on what kind of exercise you do. For regular, moderate exercise (“CME,” or “chronic moderate exercise,” consisting of 30 minutes of moderate cycling daily for two months), here are the results:

“DT” is “detraining.” So you can clearly see that regular, moderate exercise boosts the ability of the neutrophils to get to infection sites quickly (chemotaxis) and attack the bad guys (phagocytosis). And in fact, the neutrophils are still ultra-alert for a couple of months after you stop training. In addition, the researchers found that regular exercise extended the life of the neutrophils.

On the other hand, the effects of  “acute severe exercise” (an incremental test to exhaustion) had more mixed results. Chemotaxis was enhanced, but phagocytosis wasn’t, and the lifespan of the neutrophils was shortened — not so good for immune function.

So is this a surprise? Not really — it’s been clear for a long time that exercise has a J-shaped influence on immune function. Some is good, more is better, but beyond a certain point, too much is bad. Run a marathon, you’ll have a slightly elevated risk of catching a cold (or at least suffering from some sort of respiratory symptoms) afterward. But studies like this are needed to understand what exactly is happening in the body, so that eventually we’ll have a better idea of exactly where the curve in the J starts — and possibly figure out some ways to extend the sweet spot of the curve.

Standing desks, sedentary behaviour, and the need for motion

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)

***

My Jockology column in this week’s Globe and Mail takes a look at the surge of interest in standing desks:

Now that we’ve accepted the surprising truth about sedentary behaviour – that sitting at a desk all day wreaks havoc on your health, no matter how much you exercise before or after work – the standing desk is having a moment. Desk jockeys everywhere are rising up.

The cashiers of the world, meanwhile, must be scratching their heads.

“Ask anyone who works in a shop whether they feel good standing all day, or whether they need to periodically sit,” says Alan Hedge, who directs the Human Factors and Ergonomics program at Cornell University in Ithaca, N.Y.

Indeed, prolonged standing has been linked to a long list of health problems over the years: most commonly varicose veins, but also night cramps, clogged arteries, back pain and even (according to one study) “spontaneous abortions” – enough to make you think twice before throwing away your chair. But striking the right balance in your cubicle isn’t necessarily about the furniture, researchers say – it’s about how you use it… [READ THE WHOLE ARTICLE]