bone density – Sweat Science

October 23, 2011October 23, 2011

Stress fractures: is it weak bones or muscles?

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- Alex Hutchinson (@sweatscience)

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A new study from researchers at the University of Calgary, published in the November issue of Medicine & Science in Sports & Exercise, looks at bone quality and leg muscle strength in a group of 19 women who have suffered stress fractures in their legs, and compares them to a group of matched controls. The basic results:

the women who got stress fractures had thinner bones;
at certain key locations, the quality of the bone was lower in the stress fracture group;
the stress fracture group also had weaker leg muscles, particularly for knee extension (lower by 18.3%, statistically significant) and plantarflexion (lower by 17.3%, though not statistically significant).

Now, this sounds very similar to the results of a University of Minnesota study published a couple of years ago. Here‘s how I summed up the conclusions reached by those researchers:

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.

What I don’t understand is that, in the new Calgary study, even though they mention the Minnesota study repeatedly in their discussion, they don’t discuss at all this idea that it’s the lower muscle strength that dictates the reduced bone size and thus the stress fracture risk — even though that was the primary conclusion of the Minnesota study. Instead, they say “the role of muscle weakness in [stress fractures] is unclear from previous studies,” and suggest that weaker knee extension might change running form to produce a “stiffer” running stride or somehow alter the direction of forces on the bone during running — both of which seem like unnecessarily complex and speculative ideas compared to the straightforward link between muscle strength and bone strength.

It’s entirely possible that I’m missing something here, because the paper is quite complex. But what I take away from it is, once again, that strengthening your legs is likely (though not yet proven in a prospective trial) to reduce your stress fracture risk.

March 2, 2011March 6, 2011

Cyclists: adjusting saddle height and maintaining bone density

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- Alex Hutchinson (@sweatscience)

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Two studies in the March issue of the Journal of Strength and Conditioning Research that may be of interest to cyclists:

First (and simplest), another study about cyclists and bone density. Lots of previous cross-sectional studies have found that cyclists seem to have lower bone density than non-athletes and people who do impact activities like running. This one, from UC San Diego, actually followed 19 male masters cyclists and 18 matched non-athletes for seven years. Sure enough, the cyclists started with lower bone density, and declined faster during the study. By the end of the study (when both groups had an average age of 57), 17 of the cyclists had osteopenia and six had more serious osteoporosis; in the control group, 11 had osteopenia and one had osteoporosis. The message: get some impact activity, do some strength training, and get your bone density checked periodically.

Second is a study about optimizing saddle height (using “saddle” rather than “seat” makes me snicker, but that’s what they use in the paper, so I’ll stick with it!) for both performance and injury prevention. Apparently there are two standard, well-studied approaches to setting saddle height. The Hamley method, based on research in the 1960s, recommends setting the distance between pedal and saddle as 109% of inseam, measured from ischium (hip bone) to floor. That’s based on optimizing performance. The Holmes method, on the other hand, suggests setting knee angle at the bottom of the stroke to between 25 and 35 degrees to avoid injury.

A useful aside in the paper, derived from the Holmes research: pain in the front of the knee usually means the saddle is too high low, pain in the back of the knee means it’s too low high. [Update March 6: Thanks to commenter Phil for catching the fact that the journal article had it backwards!]

Anyway, the problem is that these two methods don’t always coincide, mainly because people have very different ratios of upper leg to lower leg length. In this study, setting the seat at 109% of inseam led to knee angles ranging from 19 to 44 degrees, and only three of the 11 subjects (who were well-trained cyclists) fell into the 25-35 degree injury reduction zone. So which is best?

The researchers looked at anaerobic power (30 second sprints) and economy (15-minutes at 70% VO2max) for three different settings: 109% inseam, 25 degree knee angle, and 35 degree knee angle. Surprisingly, the 25 degree knee outperformed 35 degrees AND 109%, particularly for economy. These results in well-trained cyclists echoed earlier studies by the same group in casual cyclists. So they conclude that 25 degree knee angle is the best way to set saddle height, since it’s within the “minimize injury” range and also appears to optimize performance. Obviously if you’re a Tour de France racer, you’re going to optimize bike position in a much more sophisticated way, but this seems like a useful rule of thumb for the rest of us.

October 6, 2010

What does a nutritionist do at an international Games?

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- Alex Hutchinson (@sweatscience)

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I went to the Delhi 2010 Athletes Village for the first time yesterday (generally lovely, if a little rough around the edges in places), to chat with Jon Kolb, the head of sports science for the Canadian team here, and Trent Stellingwerff, the member of Kolb’s team responsible for nutrition. We had a really interesting talk about the kinds of things they’re up to behind the scenes, which I’ll try to describe in the coming days. To start, here’s a great example of what Trent was doing in the days leading up to the Games.

While the cafeteria at the Village is excellent, many athletes will be too far away when they’re competing to return for lunch. In these cases, it’s standard practice at major Games to order an “athlete venue meal” (AVM) that will be delivered to the venue at a specified time. Given the hot climate and the ever-present risk of “Delhi belly,” Trent decided he’d better check out the AVM system. So, a few days before competition started, he ordered the very first AVM — “AVM 001” — asking that it be delivered at noon to the cycling venue. Then he showed up at the appointed time… and waited.

“It came 30 minutes late, in a warm cooler,” he said. “It was a raw salmon sandwich with mayonnaise — basically the worst possible scenario for food poisoning.” That was enough to convince the team staff. No Canadian athletes are relying on AVMs here — instead, they shipped in some familiar non-perishable food from Canada, and are also bringing easily portable food (e.g. bananas) from the dining hall.

Of course, Trent was left with the dodgy AVM he’d ordered — while the delivery guy, happy to have made his first successful delivery, sat beside him and waited for him to eat it. Trent finally asked for a spoon, and when the delivery guy went to get, he stashed the sandwich in his bag for later disposal!

On the topic of food, here are the first two meals I had in Delhi:

In my defence, my flight arrived at 7 a.m., and by the time I got to my hotel and got checked in, I was jet-lagged and furiously hungry. I went wandering down the street in search of food, and the first place I found was a McDonald’s. I haven’t been in one in years, but I’d heard that McDonald’s in India are quite different because of the lack of beef — so I figured it would be a cultural experience! (The verdict: “special sauce” is indeed interesting when it’s spiced up with curry, but I don’t feel any need to sample it again.)

My second meal, thanks to a suggestion from one of the Games volunteers, was a masala dhosa from Saravana Bhavan — much, much better!

July 13, 2010

More bad news for cyclists on bone density

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- Alex Hutchinson (@sweatscience)

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A new study in the Journal of Strength and Conditioning Research follows up with a group of competitive masters cyclists seven years after the original study showing that they had abnormally low bone density. The cyclists now have an average age of 57, and 89.5% of them meet the criteria for osteopenia or osteoporosis. In comparison, only 61.1% of a group of matched controls meet the same criteria.

It’s still not entirely clear why cyclists seem to have poor bone density. Obviously cycling is a non-weight-bearing, non-impact activity, so they’re not getting any bone benefits from their time in the saddle. But it appears that their cycle training makes them less likely to do any weight-bearing activity even compared to non-athletic controls who don’t do any training at all. Another possibility is that they’re sweating out too much calcium, hindering bone formation and repair. This study doesn’t do much to clear up the mystery, but it does show that this is a real effect, not just an artifact of the general skinniness of cyclists — otherwise the equally skinny control group would show the same effects.

One important note: four of the 19 cyclists in the group started weight training during the seven-year interval, and they were able to slow their rate of bone loss. It’s another reminder to everyone whose main sports is something like cycling or swimming: you need to do something that stresses your bones, either through sharp impacts or the torque applied by strength training.

May 9, 2010

Staying fuelled while cycling helps bone density

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- Alex Hutchinson (@sweatscience)

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I’m not sure if my headline is misleading. There’s a new press release from the University of Missouri titled “Maintaining Energy Balance During Stage Races May Protect Cyclists’ Bones, MU Researcher Says,” but the description of the research is a little confusing (and the journal paper in Applied Physiology, Nutrition and Metabolism has yet to appear).

The new study is by Pam Hinton, who I interviewed last year for a piece on exercise and bone density. That previous study compared running, cycling and weightlifting, and concluded that running was good because of the jarring impacts, weightlifting was good because the added muscle puts stress on bones, but cycling had neither of those benefits.

The new study monitored cyclists during the Tour of Sutherland, a six-day, 10-stage race:

Hinton found significant increases in markers of bone formation and bone breakdown among the athletes whose energy intake matched their energy expenditure throughout the race.

Fortunately, bone formation increased more than bone breakdown, which suggests that everything is fine for those who take in enough calories.

“The findings suggest that participation in stage races might not have negative effects on bone turnover if energy intake matches the energy cost of high-intensity racing over several days,” said Pam Hinton, associate professor in the Department of Nutrition and Exercise Physiology. “The results are consistent with the practical recommendation that elite cyclists should match their energy intake to the high energy demands of stage racing.”

What’s unclear from the press release is whether she actually observed enhanced rates of breakdown in cyclists who weren’t getting enough calories during the race. If so, you’d think they’d mention it. If not, then I’m not sure how the study proves anything about adequate energy intake (though it’s obviously a good idea with or without this study!). I’ll follow up on this when I see the full study.

Anyway, uncertainty aside, the message seems to be: hauling ass during a brutal multi-day stage race won’t have any negative effect on your bones, assuming you’re taking in enough calories.