Survival at the gait

One of our most basic abilities—one that kept cavemen alive—may predict our longevity even today

From an evolutionary standpoint, there’s no doubt that mobility dictates survival. Just think about it. If a mountain lion decides to pursue you and your tribe, which one will end up as a tasty meal? The slowest one.

But even now, though we don’t live in a world in which we need to outrun predators (at least not literally) in order to survive, mobility still matters a great deal. Researchers are now finding that gait speed is a great predictor of survival in older adults. But before I explain the recent findings, let’s take a look at why humans walk the way we do.

Setting ourselves apart

The ability to walk upright on two legs is a distinctly human trait. It’s in large part what has set us apart from other animals—freeing our hands so that we could express our creativity and productivity to build the “man- made” world that we all live in today, for better or worse.

Another important factor in setting us apart is our larger brain. But that’s sometimes at odds with our ability to walk upright. Here’s why. In order to walk and run efficiently on two legs, those legs need to be close together. So a more narrow pelvis, especially at the hips, is better for walking and running. On the other hand, our larger brains mean women need to have wider hips to allow the infant to pass safely through the birth canal. That explains why humans are the only animals who have such potentially difficult childbirth—and why we call it “labor.”

At the same time, women’s hips couldn’t be too wide, or they wouldn’t be able to walk and run efficiently. So over time, human infants were born at earlier and earlier stages of development, while the brain is still immature. It means our young are immature and dependent on their parents for longer than other animals. (One look at the most recent generation will confirm that beyond a shadow of a doubt!)

So there has been a grand evolutionary biological compromise between upright posture, freeing the hands, and having bigger brains. Being able to walk efficiently for long distances, and being able to run fast, has been a key to human survival.

The many factors at play

Now when it comes to the opposite end of the age spectrum, scientists are finding that gait speed in older adults may help account for differences in longevity.

It takes several important capacities to be able to walk efficiently and quickly. First you need balance, which comes from your brain’s ability to process input from your eyes (visual), inner ear (vestibular), and limbs (proprioceptive). Your eyes orient you to your position in space. Your inner ear is like a little gyroscope, sensing the position of your head against gravity. Your limbs send signals to the brain about pressure, heat, vibration, and other signals about the ground under your feet. Maintaining balance requires your brain to rapidly process and integrate all this information to keep you upright and on your feet. Even more so when you’re moving.

Gait predicts longevity

Back to that research I mentioned. It turns out that—probably because of all these different faculties needed to walk efficiently—gait speed can tell doctors a lot about your health. In fact, it’s as accurate a predictor of longevity as any other factor— including age, gender, use of medical devices, chronic conditions, smoking history, blood pressure, BMI, and history of hospitalizations!

A 2011 study published in JAMA followed more than 17,500 people ages 65 or older for 6 to 21 years.1

Their gait speed (how fast you can walk) was associated with better survival in every group of older adults studied. There was a direct correlation between how fast you can walk and your longevity across a full range of speeds.

So, for a real measure of “anti- aging” ask your doctor to measure your gait speed. And the next time someone advises you to “slow down” as you get older, think again.

I’ll tell you more about the importance of gait and your skeletal structure in next month’s issue.

Sources:
1. “Gait speed and survival in older adults,” JAMA 2011; 305(1): 50-58