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Talking of walking in three easy pieces

MAR 2011

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Gait speed, hiking poles, and footwear.

Walking is one of the simplest, least expensive, and most effective things you can do for your health. It strengthens bones, tunes up the cardiovascular system, and, psychologically, can clear a cluttered mind. Hundreds of studies have documented its benefits. Here are three pieces about some interesting research into this most pedestrian activity.

1. Gait speed

As we get older, the stroll that was once a walk in the park may get difficult for any number of reasons: angina, arthritis, bad balance, failing vision. In the latter decades, walking becomes as much an indicator of health as a promoter of it.

Researchers at the University of Pittsburgh have shown that walking may also serve as something of a prognosticator. Results of their research, published in the Jan. 5, 2011, issue of The Journal of the American Medical Association, show that after about age 65, how fast we walk may predict how long we have to live.

Walking, or gait, speed has long been recognized as a proxy for overall health and vitality and has been measured in many research projects. The University of Pittsburgh researchers didn't conduct a new study, but used some sophisticated statistical techniques to pool the results of nine that had already been done. They standardized the disparate ways gait speed had been measured in those studies — no small feat — and then did some further analysis to see how gait speed correlated with how long people lived.

What they found was a remarkably consistent association between faster gait speed and longer life that was true for both men and women ages 65 and older. More precisely, each increase of 0.1 meter per second in gait speed was associated with a 12% reduction in the risk of dying during a study's follow-up period (the follow-up periods varied). They also calculated that people with gait speeds of 1 meter per second or faster lived longer than would be expected given their age or gender. (One meter per second is equivalent to 2.2 miles per hour and just a bit slower than the speed needed to cross the street at most timed traffic lights.) When the researchers factored in body mass index, blood pressure, prior hospitalization, and several other factors, the relationship between gait speed and longevity didn't change much. In other words, walking speed seemed to be independently associated with life expectancy, not just a marker for other conditions that would affect it.

More number crunching produced interesting correlations between gait speed and five- and 10-year survival rates that make some easy comparisons possible. For example, just 15% of the men ages 75 to 84 with a very slow gait speed of less than 0.4 meters per second (imagine someone shuffling) lived for another 10 years. In contrast, half of those with a speedier gait of 1.2 meters per second or faster lived at least 10 years. Women live longer than men, so the survival rates were longer at both slow and fast speeds for them, but the pattern was the same: faster walkers had much better five- and 10-year survival rates than slower ones.

So does this mean that if you're older and you work on improving your walking speed, you'll live longer? No, you can't draw that kind of a cause-and-effect conclusion from this study, which is based on statistical associations in observational studies. On the other hand, countless other studies have shown associations between physical activity and better health and longer life. For the vast majority of people at any age, regular walking improves health.

The University of Pittsburgh re searchers envision a day when standardized measures of gait speed, along with other information, might be a low-tech way for doctors and other clinicians to assess the overall health and life expectancy of their patients. In fact, you could do it yourself at home. All that's needed is a reliable watch that keeps track of seconds and some tape to mark off four meters in a hallway or large room. A slow gait could trigger action to improve modifiable risk factors or, in a very old person, to avoid certain interventions — say, certain types of surgery — because life expectancy is too short. Clinicians would also be a position to give their fast-walking patients the good news about their health and life expectancy prospects.

2. Hiking poles

Hiking poles are similar to ski poles but are designed to be used while walking. Bipedalism has its advantages, but requires balance and can be hard on the legs. Hiking poles, which cost about $100, permit upright walking and get all four limbs involved.

Research confirms that hikers probably can benefit from using hiking poles — trekking poles, if you want to use the sportier name. Ascents may be the more satisfying and metabolically challenging part of hiking, but descents are physically more difficult in many ways. Going downhill is much harder on the hip and leg muscles and puts compressive forces on the knees that are three or four times higher than the forces experienced when walking on level ground. A variety of biomechanical experiments done in carefully controlled lab conditions have shown that hiking poles can significantly reduce those forces, as well as movement in the joints that creates strain. Other studies have shown that hiking poles keep people more upright while hiking, help with stability, and are associated with a reduced risk of ankle fracture. In 2010, British researchers reported results of a study that compared 19 novice hikers who used trekking poles with a control group of 18 who did not. After climbing and descending 3,400-foot Mount Snowdon in Wales, the people who used trekking poles reported less muscle soreness and recovered faster than those who made the 7-mile round-trip hike without poles. Many hikers would have predicted that.

Hiking with trekking poles does have minor dangers and drawbacks. If a trail is narrow and hemmed in by vegetation, the poles will get in the way. In rocky terrain, they can get stuck between the rocks and throw a person off balance. Groups like the Appalachian Mountain Club ask hikers to avoid sticking poles too deeply into soft soil because the disruption can lead to erosion.

Using hiking poles on flat land has been dubbed Nordic walking because the motion resembles cross-country skiing and, by some accounts, the practice has a Finnish provenance. Proponents say the poles and the arm movement mean Nordic walking provides a better cardiovascular workout than plain old walking, while also taking some of the load off the knees and other parts of the legs. In places with icy streets and sidewalks, hiking poles can be used just for a little added balance, and a single pole can serve nicely as a sporty alternative to a cane.

Results from several studies (all of them quite small and of questionable quality) show that using hiking poles while walking at a fairly brisk pace does seem to increase cardiovascular workload. Some studies show that people have an increased physiological response but don't feel as though any more exertion is involved, which is quite a combination. One study of people who have pain in their legs while walking because of poor circulation (the medical term is intermittent claudication) found that they were able to walk farther with less pain if they used hiking poles.

But whether the Nordic walker is doing much to spare his or her knees is debatable. The studies are split on whether the poles do much, if anything, to reduce compressive forces on the joint. Researchers at the University of Copenhagen in Denmark published a study in 2010 showing that there was no effect on the knees even when walkers more than doubled the force they were putting on the poles. One of the explanations they offered for their result is that the poles hit the ground at an angle, so that much of the force propels the walker forward but does little to take the load off the knees.

3. Footwear

Pain from arthritic knees makes walking difficult for many people, and shoes with thick, cushiony soles are commonly believed to help. But some research is challenging that conventional wisdom with results that suggest that thinner, more flexible soles — even flip-flops — actually put less load on the knees.

Researchers at Rush University Medical Center in Chicago compared walking barefoot against walking with four types of shoes: clogs, "stability" walking shoes with a thick heel and sole (Brooks Addiction Walkers), walking shoes with a thin heel and sole (Puma H-Street), and flip-flops. Using special camera equipment, they analyzed the gaits of 31 volunteers with symptomatic knee arthritis. The part of the gait cycle they focused on is when knee adduction is highest, which occurs as weight shifts from the outside of the knee (the lateral compartment) to the inside (the medial compartment). Directly measuring loads inside the knee is impractical, so gait researchers have adopted knee adduction as a proxy for loads on the medial compartment. Arthritis is 10 times more common in the medial compartment than in the lateral one, and gaits that put more weight on that region are believed to contribute.

The study results, reported in 2010 in Arthritis Care & Research, showed that walking in clogs or stability walking shoes produced significantly more knee adduction (15%) — and presumably more load on the medial compartment — than did walking in thinner walking shoes or flip-flops, which were both equivalent to walking barefoot.

The researchers offered a couple of possible explanations. Elevated heels increase loads on the medial compartment. Clogs and stability walking shoes don't come to mind when we think about high-heeled shoes, but the models used in this study, which are fairly standard, had heel heights of 1� to 2 inches — an inch or more higher than those of the thin-soled shoes and the flip-flops.

The stiffer soles of the clogs and stability walking shoes may also affect a person's gait, putting more load on the inner part of the knee. The same researchers reported several years ago that walking barefoot is associated with lower knee loads than walking with shoes, perhaps because the unshod foot flexes and pronates (rolls in somewhat, so the arch gives) in a more natural fashion. Flexible soles may allow for a motion that more closely resembles walking barefoot.

This was a tightly controlled experiment, not a real-world test. Perhaps it will lead to more definitive, longer-term trials. Meanwhile, people whose arthritic knees keep them from walking might want to experiment with shoes with flexible soles to see if they help. However, we won't recommend flip-flops, for many reasons unrelated to knee stress.