A new study from Winston-Salem, N.C.-based Wake Forest Baptist Medical Center shows that an increase in fat throughout the thigh is predictive of mobility loss in otherwise healthy older adults.

Lead author Kristen Beavers and colleagues at Wake Forest Baptist say the findings suggest that prevention of age-related declines in walking speed isn't just about preserving muscle mass, but also about preventing fat gain.

Walking speed declines with age, says Beavers, and in older adults, slower walking speed is a predictor of disability, nursing home admission, and even death. As such, she says walking speed represents an important and potentially modifiable predictor of independent living for older adults. Unfortunately, Beavers says, not much is known about what precedes this decline, although change in body composition seemed like a reasonable place to start the research.

"As people age, they are more likely to gain fat in and around their muscles, and we speculated that gaining fat in the leg muscle itself would be related to slowed walking speed," Beavers says.

The researchers used data from the National Institute on Aging's Health, Aging, and Body Composition study, a prospective cohort of several thousand initially well-functioning white and black adults aged 70 to 79. They looked at how changes in fat and lean mass affected walking speed and were interested specifically in whether changes in thigh intermuscular fat or thigh muscle area were more predictive of slowed walking speed.

A study sample of about 2,300 men and women was reviewed, with a mean age of 74.6 years. Walking speed was assessed by measuring the usual time it took participants to complete a 20-minute walk, and they were tested annually during a four-year period. Body composition measures were assessed via computed tomography.

Results, published online ahead of print in theAmerican Journal of Clinical Nutrition, found both increasing thigh intermuscular fat and decreasing thigh muscle area to be significant, independent predictors of walking speed decline. Importantly, Beavers says, older adults who gained the most thigh fat and lost the most thigh muscle were at greatest risk of experiencing a clinically meaningful decline in walking speed.

Beavers says she believes this study is the first of its kind to address the independent association between changes in sophisticated measures of body composition and walking speed.

"As the burden of disability becomes increasingly common and expensive, identification of modifiable contributors to functional decline in older adults is emerging as a significant priority of public health research," Beavers says. "Future studies building on these findings should test whether targeted reductions in thigh intermuscular fat, augmentation of thigh muscle area, or both yield improvements in walking speed and prolonged independence for older adults."

This research was supported by the National Institute on Aging, the National Institute on Nursing Research, the Wake Forest University Claude D. Pepper Older Americans Independence Center, and an individual postdoctoral fellowship. Also, it was supported in part by the Intramural Research Program of the NIH, NIA.