Archive for February, 2011

Stride rate, running speed, and “cruise control” for runners

February 16th, 2011

A press release from Simon Fraser University in Vancouver reported a few days ago that a pair of biomedical physiologists have invented a “cruise control” device for runners. As far as I can tell, it’s basically a metronome that provides a beat for you to synchronize your strides with; it measures your speed (presumably via GPS) and increases the cadence if you’re going slower than your desired speed, and slows it down if you’re going too fast. Right now, it’s basically a clunky backpack prototype, but future versions might be, say, an iPhone app that provides music with a “sliding tempo” to keep you on pace.

Okay, so not a device I’d feel much need for, but I can see a potential market. One hesitation, though. The entire device is predicated on the following assumption:

“We know that for higher running speeds humans prefer higher step frequencies,” says Snaterse. “This relationship can be inverted – for higher step frequencies, humans prefer higher speeds. The cruise control for runners uses this principle.”

Is that really true? There’s a lot of dogma floating around the running world that running speed is essentially independent of stride rate — if you go for a jog and gradually pick up speed until you’re nearly sprinting, your stride length will get longer and longer but your stride rate will stay essentially unchanged. For example, check out this recent post from Amby Burfoot’s blog about the potential benefits of shortening your stride:

Most of us, when we increase pace, increase stride length much more than stride rate. So our stride rate stays roughly the same at different paces, slow and fast.

Now, that doesn’t necessarily mean the reverse is true. It’s possible that when you increase speed, your stride rate stays the same, but when you increase stride rate, you speed up. And there’s some evidence that other effects might crop up when people exercise while listening to music — for example, I wrote about a study where British researchers secretly sped up and slowed down workout music by 10% and people on exercise bikes sped up and slowed down without realizing what was happening. If we’re dealing with a cruise control that, by design, is intended to make only small corrections to your pace, maybe a small effect like that is sufficient.

What does the actual research say? It’s harder to dig up than I expected, partly because it’s such an “old” question that some of the relevant studies aren’t online. Here a description of an older (1974) study from a 2009 paper:

Saito et al. [27] showed that trained runners increased their speed to 7 m/s [2:22/km, 3:50/mile] by lengthening their stride, whereas untrained runners increased stride length only up to 5.5 m/s [3:02/km, 4:53/mile]; any further increase in running speed was achieved primarily by increasing stride rate.

In other words, you have to be sprinting pretty darn fast before you start increasing stride rate instead of stride length. Still there must be some better and more recent data out that show the typical relationship between speed and stride rate — if anyone knows where I should be looking, please let me know!


Evidence-based guidelines for sedentary behaviour

February 16th, 2011
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I’ve written a few times recently about the newly emerging dangers of sitting too much (as opposed to exercising too little). Today, the Canadian Society for Exercise Physiology announced the release of the first-ever guidelines for sedentary behaviour for children and youth. How bad is the problem?

“Canadian children and youth spend sixty-two per cent of their waking hours in sedentary pursuits, with six to eight hours per day of screen time as the average for school-aged kids,” said Dr. Mark Tremblay, Director, Healthy Active Living and Obesity Research (HALO) at the CHEO Research Institute.

There are still no precise answers (yet) to questions like how many hours you can stay motionless before damaging changes in your muscles begin. But the guidelines do a nice job of setting reasonable goals and providing common-sense strategies for keeping kids from spending too long in a zombiefied state — even if, much like the companion guidelines for physical activity, the goals are likely to be somewhat aspirational for many parents. Goals like “Indoors, help children and youth stay active by having them help with meal preparation and other household chores” are well-meaning. But really, if parents aren’t already doing that, it’s probably not just because they didn’t know it was a good idea.

Anyway, the guidelines for children aged 5-11 are available here, and for youth aged 12-17 here. Take a look at them, even if you’re an adult — it might give you some good ideas.

Not running will ruin your knees

February 14th, 2011

The annual meeting of the American Academy of Orthopaedic Surgeons is taking place right now, and a press release describes five studies looking at the link between obesity and knee arthritis. There’s nothing particularly earth-shattering here, but I just like to highlight news like this because I still sometimes hear people who say they’d like to run but don’t want to ruin their knees — an idea that has been pretty firmly debunked.

“Other studies have looked at the effect that a combination of weight loss, diet and exercise had on knee arthritis, but it was difficult to say which of these factors contributed the most to reducing knee pain,” says Christopher Edwards, co-investigator and a fourth year medical student at the Penn State College of Medicine. “Our study should send a message to patients, health care providers, and payers that weight loss is an important consideration in the treatment of knee arthritis.”

That being said, it’s not as simple and obvious as you might think. The additional weight of being obese certainly puts extra load on joints — but there’s also evidence that fat tissue secretes inflammatory hormones that make joint problems worse. My wife is actually doing some research in this area at the moment… so if there are any big breakthroughs, I’ll keep you posted!

More muscle tension: there is research

February 13th, 2011

A few thoughts following up on the post about Steve Magness’s muscle tension article in Running Times. Steve was kind enough to send me a copy of Marius Bakken‘s medical school thesis, which consisted of two documents: a detailed literature review on efforts to characterize and measure muscle tension, and a clinical trial investigating whether regular cross-friction massage can reduce muscle tension. It’s still a very young field of study, but it turns out there is some literature devoted to the ideas discussed in Steve’s article.

What Steve is talking about here is what you might call “passive” muscle tension — the tension that remains in your muscles even when they’re completely relaxed (i.e. receiving no neural instructions to contract). Bakken adopts the definition of “resting muscle tone” from a 1998 journal paper, which is:

the elastic and/or the viscoelastic stiffness in the absence of contractile activity.

So how do you measure this tension? Most simply, you relax your muscle and press into it to see how stiff it is. This is, obviously, a pretty crude measurement. Bakken is now using a tool developed by an Estonian company called Myoton (shown above), which measures the frequency and damping of muscle oscillations to determine muscle tone, elasticity and stiffness. That’s the tool he used for his massage study, in which five athletes received 20 minutes of massage once a week for four weeks. The Myoton showed that their resting muscle tone decreased by an average of 3.3%, and EMG measurements of nerve signals showed that the decrease was unrelated to changes in active muscle contraction.

If you poke through the references in Bakken’s literature search, you find various interesting hints — e.g. links between overtraining and muscle tension in cross-country skiers in a 2002 study. There are still some pretty big pieces missing from the puzzle, for example showing a link between resting muscle tone and performance. And the mechanisms responsible for this resting tone are still being debated (is it extracellular water pressure? cross-bridges between contractile proteins?). But the documents made for an interesting read, and show that there is some serious science behind these ideas. I’ll be following further developments in this field with interest.

Dynamic warm-up routine for runners

February 11th, 2011

I’ve written quite a bit about the growing pile of evidence that static stretching before exercise is a bad idea — which may leave you wondering what you are supposed to do to warm-up. The current buzzword is “dynamic warm-up,” but that means a lot of different things to different people. I just noticed that Canadian Running magazine had an article a few months ago by Olympic 5,000-metre runner (and physical therapist) Megan Wright, who shared her own eight-part dynamic warm-up routine, complete with pictures of the various moves. It’s definitely worth checking out if you’re looking for ideas for your own warm-up routine.

Manipulating muscle tension to run faster

February 11th, 2011

[UPDATE Feb. 13: more detailed info on muscle tension research in this post.]

Steve Magness has an article in next month’s Running Times magazine called “Managing Running Tension,” in which he argues that we should aim to have loose, floppy muscles during easy runs to enhance recovery, and tight, tense muscles during hard workouts and races to get more “pop” in the legs. He suggests several ways to increase tension (sprinting, ice baths, running on hard surfaces, etc.) and several ways to decrease it (jogging, massage, warm baths, running on soft surfaces, etc.).

Runner’s World’s Amby Burfoot offers his take on the article on his Peak Performance blog: the take-away message, he believes, is that when you’re tapering before before a race, you should be wary of doing all your runs on soft surfaces lest you’re left with sub-par tension, and thus dead legs on race day.

It’s an interesting idea. Certainly, I’ve always marvelled at how incredibly dead my legs tend to feel on race mornings — a reaction I’ve always assumed was mental rather than physical, as my brain becomes hypersensitive to sensations of effort in anticipation of the supreme effort to come. Could muscle tension have something to do with it? I don’t know. I’d like to see some evidence to support the story. Do we know how to objectively measure muscle tension? Has anyone measured how it changes in response to things like running surface? I’d welcome pointers if anyone knows — because it sure would be nice to learn how to avoid that dead-leg feeling!

How much compression do socks need?

February 9th, 2011

Over the past few years, there’s been a ton of research into the effects of various types of compression gear, with conflicting results. Some studies show improved performance, others don’t; some studies show changes in physiological markers, others don’t. One of the big problems is fit: no one really know exactly how tight the garments should be.

A study from researchers at Massey University in New Zealand, which appeared online in the Journal of Strength and Conditioning Research last week, attempted to answer this question. They had 12 well-trained runners complete four 10K time trials on the track wearing four different socks: a non-compressing control, one low compression (12-15 mm Hg), one medium compression (18-21 mm Hg) and one high compression (23-32 mm Hg). All the socks had graduated compression, with maximum compression at the ankle tapering to no compression at the knee.

The results: no significant difference in 10K time, pre- or post-run lactate, heart rate, or several other measures. Now, I have my doubts about the statistical power and repeatability of a 12-person study with four 10Ks over the course of eight weeks, but take it for what it’s worth.

There was an interesting twist, though, represented in the following graph:

We’re looking at the change in “countermovement jump height” from before the race to after the race. The low compression sock shows a significant improvement compared to the control, and the medium sock has an even bigger improvement, while the tightest sock is roughly the same as the control. This test is basically a measurement of leg power, so the researchers speculate that it’s possible that the subjects might be able to produce a faster finishing sprint in the low and medium socks, though it’s not something they measured. I’m fairly skeptical — I never really had the sense that explosive leg power was the limiting factor in the final stretch of a 10K race. But who knows?

In the end, the study is a perfect microcosm of the greater body of research in this area: it shows that something happens when you put properly fitting socks on, but we still don’t know exactly what and we certainly don’t have evidence that it actually makes you faster. But in other ways, the study is a big step forward, in that it makes a serious attempt to determine what a “proper” fit is — at this point, 18-21 mm Hg is looking pretty good. More studies like this will be needed. And one addition that I would really like to see is a placebo compression sock — perhaps something with non-graduated compression that subjects can’t necessarily distinguish from the “real” socks.

How nitrate (and beets) work, and why mouthwash is bad

February 8th, 2011

The performance-boosting effect of beet juice, attributed to the nitrate it contains, has been one of the biggest sports science stories of the past year. A few days ago, Swedish researchers published a new study in the journal Cell Metabolism (press releases here and here) that answers some questions about how nitrate works — and raises some questions about whether mouthwash might actually hurt your performance. Interestingly, this Swedish group has been publishing results on the performance-boosting effects of nitrate since 2007. It’s only when Andrew Jones’s group at the University of Exeter started publishing results in 2009 using beets instead of isolated nitrate that everyone started paying attention.

The study: a randomized, double-blind crossover trial with 14 subjects given either 0.1 mmol/kg of sodium nitrate or a placebo each day for three days. Since their previous studies have shown that this protocol allows subjects to use less oxygen while cycling at a given intensity, this time they looked for the root cause. They isolated mitochondria (the cellular “power plants” that generate ATP to fuel muscle contractions) in the subjects. Sure enough, the mitochondria from the nitrate group used less oxygen to generate a given amount of ATP. Further (rather complicated) experiments suggested that this is because nitrate leads to lower levels of a protein that causes efficiency-sapping proton leakage across the mitochondrial membrane.

So what does it mean? Well, the researchers suggest that it might be nitrate (which, as they note, “has previously been considered merely as an inert end product of NO metabolism or as a potentially toxic constituent in our diet” — think hot dogs) that is responsible for the well-known but poorly understood health benefits of a diet high in vegetables (particularly leafy green ones). And of course, it’s more evidence that nitrate might be the real deal as an ergogenic aid for endurance athletes.

But what really caught my attention was the following offhand remark in one of the press releases:

As an interesting aside, Weitzberg says that the benefits of dietary nitrates suggest that powerful mouthwashes may have a downside. “We need oral bacteria for the first step in nitrate reduction,” he says. “You could block the effects of inorganic nitrate if you use a strong mouthwash or spit [instead of swallowing your saliva]. In our view, strong mouthwashes are not good if you want this system to work.”

Huh? Here’s a brief explanation from the paper itself about how nitrate is used by the body:

Circulating nitrate, normally derived both from endogenous NO [nitric oxide] production and from dietary intake, is actively taken up by the salivary glands, excreted in saliva, and reduced to nitrite by commensal bacteria in the oral cavity.

The statement about mouthwash having a negative effect is just speculation at this point, not backed up by any studies. But it’s interesting…

UPDATE Feb. 9: Thanks to Colby for pointing out that the same Swedish group has actually already done a study looking at the effects of mouthwash, published back in 2008. The gist is as follows: the nitrate we take in through our diet is converted first to nitrite then to nitric oxide, which is what has a positive effect on blood pressure, performance and other parameters. But our cells are unable to convert nitrate to nitrite — to make that conversion, we rely almost exclusively on friendly bacteria in our saliva. To test that hypothesis, the researchers fed nitrate (the equivalent of about 300 g of spinach or beets) to volunteers 15 minutes after they gargled with an antibacterial mouthwash (Corsodyl). Here’s what they saw:

Even though nitrate levels in saliva were similar, the bacteria needed to convert nitrate to nitrite was gone in the mouthwash experiments, so nitrite levels in saliva remained flat. As a result, nitrite levels circulating in the blood (which is what’s shown above) increased far less in the mouthwash than the non-mouthwash case.

Unfortunately, this still doesn’t tell us much about timing and chronic effects. If you mouthwash before bed, will your nitrate-to-nitrite conversion still be impaired at dinner the next day? I really don’t know. I’m certainly going to keep mouthwashing — but it might make me think twice about the gratuitous middle-of-the-day extra gargle!

Can sitting too long really hurt your health?

February 7th, 2011

Today’s Jockology column in the Globe and Mail looks at the latest research on the potential dangers of sedentary behaviour. This topic generated a lot of interest when I blogged about it a few weeks ago, so I decided to get in touch with Travis Saunders of Obesity Panacea, whose Ph.D. research is investigating this very question, to find out more:

[…] Two new studies highlight the growing consensus that long bouts of uninterrupted sedentary behaviour carry health risks that can’t be erased even if you’re getting plenty of exercise at other times during the day. Researchers are now rushing to determine exactly what counts as “sedentary,” and how people whose jobs require them to sit at a desk for the majority of their waking hours can mitigate some of these risks… [READ THE WHOLE ARTICLE]

Right now there are more questions than answers in this field, so the advice on what we should do to avoid these risks is necessarily vague. But I loved Travis’s answer to how he deals with the issue while awaiting the results of further studies:

Until then, we’re left with interim solutions – such as the $30 foot-pedal device that Mr. Saunders invested in last fall while preparing for his doctoral exams, when he realized he was spending 14 hours a day sitting at a desk reading about the dangers of sitting at a desk.

“It just sits under my desk and I pedal, I’d say about half [an] hour out of every hour. Very low intensity, but it’s engaging the muscles in my legs and the muscles in my lower back,” he says.

“I have no idea whether or not this is making a difference, but it’s plausible … and in the absence of any other options, I’m going to keep doing it.”

There’s also an interesting graphic by Trish McAlaster that accompanies the print version of the article. It’s not yet posted online, but I’ll link to it here if and when it goes up.

UPDATE Feb. 7: I’ve received a bunch of questions about where to buy an exercise peddler like Travis uses. If you’re in the U.S., it’s simple: you can order from Amazon for $24.08. Unfortunately, they don’t seem to ship to Canada. This is the link Travis sent me for where he bought it, but they appear to have gone out of stock since last week. It looks to me like this site would ship to Canada, but I’m not sure. If anyone finds any leads for shipping to Canada, please let me know!

The more stressed you are, the more exercise keeps you healthy

February 7th, 2011

The standard picture of how exercise affects your immune system is sometimes called the “J-curve hypothesis“: your immune system is strongest at some “moderate” level of physical activity, and gets weaker if you exercise too little or too much. Stress, on the other hand, has a simpler curve: the more stressed you are, the more susceptible to infection. A new study in this month’s Medicine & Science in Sports & Exercise takes a look at how these two factors interact, with some interesting results.

The study, from the Karolinska Institute in Sweden, followed 1,509 adults for four months, recording self-reported levels of stress, physical activity, and upper respiratory tract infections (e.g. cold and flu). They saw the following (the top graph is everyone, middle is men, and bottom is women):

The key point: for men in particular, the more stressed you are, the more exercise helps to keep you healthy. Why is this not the case for women?

The ‘‘fight-or-flight’’ response to stress, although present in both men and women, is proposed to be stronger in men and a ‘‘tend-and-befriend’’ response more common in women in response to stress (35). These response differences could explain why men might benefit more from physical activity while under stress than women.

The researchers also note that the J-curve response isn’t very pronounced in their data, likely because very few of the respondents were exercising at anywhere near the intensity and duration of a marathon runner: “A participant classified as having a high physical activity (>55 MET*h/d) in our study would for example be someone with a sedentary job that goes jogging or to the gym for an hour each day and is moderately active the rest of the day.”