Tuesday, November 25, 2014

Strong Ankles Fight Off Age-Related Slowdown?

As you get older, various muscles and joints start to work less effectively. But which are the key muscles that matter most when it comes to walking and running? That's the question a group of researchers at the University of Jyväskylä in Finland set out to answer in a study that was recently published in the Journal of the Royal Society: Interface.
To answer the question, they assembled three groups of runners (13 in each group) with average ages of 26, 61, and 78. Then they analyzed their biomechanics while walking, running (at ~4:10 per km / 6:42 per mile), and sprinting all-out, looking for changes in the motion and forces at the ankle, the knee, and the hip. Here's some sample data, showing the average power at the ankle and knee through one stride cycle for walking (top), running (middle), and sprinting (bottom):

If you look first at the knee data, you'll see there are no significant differences between the age groups at any point. That suggests that weakened muscles around the knees don't appear to be a limiting factor for the older runners. The same is mostly true for the hips (data not shown). The ankles, though, reveal a different story. Even when walking, the oldest group isn't able to generate as much power at the ankle; this finding is consistent with previous studies. The difference is even more pronounced in running and walking: the older you get, the less power you're able to deliver at the ankle.
Why is the ankle seemingly unique? One possibility the authors mention has to do with the fact that the muscles around the knee and hips tend to be big and powerful, while the muscles around the ankle are smaller. That means that during walking or running, you're generally using a much higher percentage of your maximum strength at the ankle than at the knee or hip. This means that as you get older and begin to lose muscle throughout the body, the ankle is likely to become a limiting factor much sooner than the other joints.
So what's the answer? An obvious possibility is to spend a little extra time and energy strengthening the muscles that plantarflex (bend toward the ground) your ankle, like calf raises. Of course, it's premature to start designing exercise programs based on one biomechanical study. It will be interesting to see if the researchers follow up with a training study to see what effects ankle strengthening has on mitigating the decline in walking and running speed with age. These are hard studies to do, so I don't expect they'll be available very soon. Still, it's an interesting idea and something to keep in mind.

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