running – Page 11 – Sweat Science

February 11, 2010March 24, 2010

Stretching is bad for power… and endurance running

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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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[UPDATE – March 24, 2010: for further info on this study, including an interview with the author, see this post.]

Among the latest batch of papers accepted for future publication in the Journal of Strength and Conditioning Research is one on the effect static stretching during warm-up on jumping performance, by researchers from the University of Milan. It shows that stretching before exercise makes you jump lower, more slowly, and with less force. Ho-hum, right? Anyone who cares about this stuff has seen these studies before.

(For the record, what’s new in this latest study is that it looks at different joint angles. We already knew that power from full knee extension — e.g. in sprinting from starting blocks or playing football — was reduced. Now we know other angles, like you might encounter in swimming, basketball, soccer and so on, are also compromised.)

But for many people, these studies don’t carry much weight. The typical attitude is summed up by running guru Steve Boyd on his excellent blog:

Although I hedge my bets by not making a religion of stretching, I count myself among those millions who are convinced on the pure level of “feel” that flexibility work enables them to run further and faster, and cope with injuries better. And I think one day science will discover the secret of what many runners “know” deep in their fibers.

And to be fair, most of the existing studies look at explosive power rather than endurance. So I was definitely interested to see another study on the JSCR site that, for the first time, focuses on the effect of static stretching on endurance performance. (There was a study last year that found that less-flexible runners tend to have higher running economy, but it didn’t look explicitly at stretching.)

Lo and behold, stretching before a run makes you run more slowly and less efficiently.

The basic details of the study, which comes from Florida State University: 10 trained distance runners performed two one-hour runs, once with stretching before (four 30-second reps of five basic stretching exercises) and once without. The one-hour runs consisted of 30 minutes at a set pace (65% of VO2max) during which running economy was measured, then 30 minutes going as fast as they could to see how much distance they could cover. The non-stretchers burned ~5% fewer calories in the first part of the experiment, and ran 3.4% farther in the second part of the experiment.

I won’t get into the debate about what causes this. It may have to do with the energy storage abilities of floppy tendons, or the torque-producing capabilities of stretched muscles fibres; this study doesn’t address that. I’m also not making any pronouncements about the role of stretching in general — after all, it’s still very possible (though highly controversial) that a regular stretching program might reduce injury rates.

But I will say this. Static stretching may feel good (possibly in part because so many of us were brought up believing in it), but given the steady accumulation of evidence, you’d be a fool to keep it as part of your warm-up routine before a race. Or any type of athletic competition, for that matter, other that those where range of motion is a key factor, like gymnastics or hockey goaltending.

January 22, 2010January 27, 2010

Mark Plaatjes on barefoot/minimalist running

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- Alex Hutchinson (@sweatscience)

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[1/27: For more on this debate, see here.]

Mark Plaatjes, the marathon gold medalist at the 1993 world championships and longtime physical therapist to running stars in Boulder, has posted his thoughts about the current fad for barefoot/minimalist running on Facebook. It’s an interesting read. He starts with five facts that (he says) no one would dispute:

1. Running barefoot/minimalist strengthens the intrinsic or postural muscles in the feet and lower leg.
2. Running barefoot/minimalist increases proprioceptive awareness and balance.
3. Running barefoot/minimalist forces a change in mechanics to adapt to the forces on the feet.
4. There are no clinical trials that show an effect of barefoot/minimalist running for a prolonged period of time.
5. There are no research studies that prove that wearing traditional running shoes increases injuries or that barefoot/minimalist running reduces injuries.

I’d agree with these statements.

He then discusses the distinction between “good” and “bad” heel-striking. People who overstride come crashing down on their heels, braking with each stride. This is bad. But it doesn’t necessarily follow that ALL heel-striking is bad — if you’re running with a short enough stride, so that your centre of gravity is above your heel when you land, that’s a perfectly good stride, Plaatjes says. In other words, not everybody has to become a forefoot striker, despite the claims made by minimalist advocates.

After that, the article starts to ramble a bit, and I’m less clear what his point is. He does make an interesting claim: that 65 to 75% of people are unable to run barefoot because they have inadequate foot structure and mechanics (and he can tell by looking at their feet). He starts to lose me here, since he doesn’t back up this statistic. But I think his first five points (which I quoted above) are a good starting point for any discussion of this issue — because if you disagree (particularly with points 4 and 5), you’ve probably bought some snake oil.

January 21, 2010

When is it too hot to run a marathon?

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- Alex Hutchinson (@sweatscience)

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Ever since the sun-baked fiasco of the 2007 Chicago Marathon, there’s been renewed discussion about how to figure out when it’s unsafe to hold a major road race. In the February issue of Medicine & Science in Sports & Exercise, the medical director of the Twin Cities Marathon, University of Minnesota med school prof William O. Roberts, has an interesting analysis of this question — and he ends up with pretty conservative recommendations.

What’s interesting about his analysis is that he takes a population-level approach: instead of sticking a few representative subjects on a treadmill, he analyzes two large data sets. First, he looks at eight unexpectedly hot races that results in either mid-race cancellations or “mass casualty events” (where the number of patients overwhelms the medical resources available in a community), and calculates the “wet bulb globe temperature” (WBGT) at start time. He finds that WBGT above about 21 C (70 F) is an indicator of serious trouble for marathons at northern latitudes with participants who haven’t acclimatized to the unexpectedly hot weather.

Then he does a more specific analysis for the Twin Cities marathon, plotting the percentage of marathon starters who were either unable to finish or required medical attention as a function of WBGT. (The graph, along with the full text of the paper, is available here.) In this case, he finds that a start WBGT above 20.5 C (69 F) is trouble.

These conclusions contrast with American College of Sports Medicine guidelines allowing starts with WBGT up to 28-30 C (82-86 F) — guidelines based on tests of young military recruits. The key problems are (a) the average recreational marathon runner is not G.I. Joe, and (b) the participants in a northern (latitude greater than 40 degrees) marathon will be less prepared for a hot day than people who live in hot places.

This probably isn’t welcome news for race directors — no matter how hot it is, few participants are going to take kindly to a decision to cancel something they’ve spent months training for. But knowledge is good — and even if a race isn’t cancelled, this is the kind of information that runners themselves should take into account when they’re facing adverse weather conditions.

(A note on WBGT: it’s a scale that takes into account the effects of humidity and solar radiation, as well as air temperature, on humans. As a very rough rule of thumb, if humidity is above about 50%, WBGT will be higher than air temperature; if humidity is below 50%, WBGT will be less than air temperature.)

December 23, 2009December 23, 2009

How to run up and down hills

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- Alex Hutchinson (@sweatscience)

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You lose more time running up a hill than you gain by running back down the same hill — that’s a basic observation that runners quickly learn from experience, in the same way that a tailwind never helps you as much as a headwind hurts you. Studying this in the lab, though, is challenging, because treadmills don’t let you vary your pace naturally. That’s why I was interested to see a neat little study on hill running in the January issue of Medicine & Science in Sports & Exercise from some Australian researchers at Queensland University of Technology.

What’s neat is that they performed a “field study” of runners on a roughly 10-kilometre time trial, divided into three laps, with one big uphill and one big downhill on each loop. To collect data, the runners wore a portable gas analyzer that measured oxygen consumption, a GPS receiver to measure speed and acceleration, an “activity monitor” that measured stride rate and stride length, and a heart-rate monitor.

As you might imagine, the researchers used all this gear to collect a huge pile of data, and their paper contains quite a lengthy analysis of the various factors affecting running speed. It turns out that the study participants ran 23% slower on uphills, but only 13.8% faster on downhills — so we do lose out on hilly course. Stride rate stays nearly constant while going up and down hills, while stride length varies. And so on.

There are also some practical lessons to be learned. Continue reading “How to run up and down hills”

November 18, 2009

Stress fractures: reducing stride length and the role of muscle

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- Alex Hutchinson (@sweatscience)

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A couple of interesting studies about stress fractures in the December issue of Medicine & Science in Sports & Exercise.

First, researchers from Iowa State University looked at the effect of stride length. Basically, the idea is that if you shorten your stride, you’ll have more footstrikes per mile (and thus more impact jarring your bones) but each footstrike will be a little gentler. So which effect predominates? The researchers had 10 runners run at their normal stride length, and with a 10 percent reduction in stride length, measuring the relevant forces with motion-capture cameras and force plates. They then used a computer model based on bone damage and repair mechanisms to estimate the risk of stress fracture for both groups. The conclusion: shortening your stride length by 10 percent reduces stress fracture risk by three to six percent!

The clinical implications for these results are clear [they write]. Those runners wanting to decrease their likelihood for stress fracture can do so by reducing their stride length by 10%. This reduction would also allow for runners to run an additional 2 miles [per day] and maintain the same [fracture risk].

In general, I’m not a big fan of trying to meddle with your running form, thanks in part to studies like the one I wrote about here. But overstriding is apparently a pretty common issue, and prominent coaches like Jack Daniels have advocated increased cadence (and thus shorter stride) as a way of running more efficiently. So maybe there’s something here…

In the same issue of MSSE, researchers from the University of Minnesota examined the bone strength and body composition of 39 female distance runners, (slightly less than) half of whom had a history of stress fractures. To nobody’s surprise, the tibia bones in the stress fracture group were smaller by seven to eight percent, and weaker by nine to 10 percent. What’s interesting, though, it that the bone differences were exactly in proportion to the size of the muscles in the same area, and there was no difference in bone mineral density. What this suggests is that the best way to avoid stress fractures is to make sure you have enough muscle on your legs — presumably by doing weights and (it goes without saying) eating enough.