Archive for November, 2009

Bone density: are muscles or gravity more important?

November 5th, 2009

Earlier this year, I wrote a series of posts about bone density (see here, here and here), as well as a Jockology column on the topic. I started out with the assumption that maintaining strong bones is all about weight-bearing activity (which clearly makes no sense for, say, your arm bones), but after talking to some researchers, I learned that it’s our muscles, in fact, that place the greatest stress on our bones (which explains why our arm bones don’t wither away). But there were still a lot of conflicting studies about what type of activity is most important for bone health — whether, for instance, the smooth motion of an elliptical trainer or bicycle can help as much as the jarring motion of running.

So I was interested to see in the latest issue of Medicine & Science in Sports & Exercise a series of papers debating this very question, under the heading “Muscle Forces or Gravity–What Predominates Mechanical Loading on Bone?” (Intro here.) Basically, the answer is that we don’t know, and researchers are still arguing about it. It seems that gravity was long assumed to be the key, dating back to studies of bed rest in the 1920s and studies astronauts in the 1960s and 1970s. But there was a big shift in the 1980s:

Since 1987 when Harold Frost first proposed the “mechanostat theory” and began to assert that “Bone strength and ‘mass’ normally adapt to the largest voluntary loads on bones. The loads come from muscles, not body weight,” the notion has increasingly pervaded the literature.

Now, apparently, there’s a bit of a backlash from researchers arguing that gravitational loading — and in particular, sudden jarring like you get from hopping — is more important than previously suspected. I’m afraid there isn’t a nice, neat take-home message here. The researchers still don’t know the optimal way to stimulate bone growth, but it looks increasingly as if both muscular strength and weight-bearing activity have a role to play. So for now, cover your bases by doing both!

Group exercise produces more endorphins

November 2nd, 2009

A few months ago, I wrote about some research showing that people in “spinning” classes tended to exercise wayyy harder than if they’d just hopped on an exercise bike by themselves. In fact, many spinners were reaching intensities higher than the “maximum” predicted by researchers! With that in mind, I was interested to see a recent study in Biology Letters from researchers at Oxford University about the chemical effects of group workouts. As a BBC report put it:

Exercising together appears to increase the level of the feel-good endorphin hormones naturally released during physical exertion, a study suggests. A team from Oxford University carried out tests on 12 rowers after a vigorous workout in a virtual boat. Those who trained alone withstood less pain – a key measure of endorphins – than those who exercised together.

It’s worth noting that they didn’t simply measure rowing performance, where the motivational effects of being in a group might have helped the subjects push harder. They actually subjected them to a torture test: after the rowing, they inflated a blood-pressure sleeve around the subjects’ arms to cut off circulation, and timed how long they could withstand the pain. (Resistance to pain is a proxy for endorphin production.) Sure enough, the solo exercisers couldn’t last as long as the group exercisers, indicating that there was something going on inside the body during the group workout.

The researchers speculate that this mechanism may be the key to other social activities (“such as laughter, music-making and dancing”). More importantly, from our point of view, it’s good to have a reason to seek out training partners!