TUESDAY, Sept. 27 (HealthDay News) -- Older, overweight women have about the same power and strength in their legs as normal-weight women. But when their leg strength and power was assessed relative to their weight, older overweight women performed much worse than those of normal weight, a new study has found.

The finding challenges the belief that thin elderly people are most likely to become disabled due to the loss of muscle mass, according to University of New Hampshire researchers.

Instead, the study authors suggest, carrying all that extra weight over time makes it more difficult to walk and to perform activities of daily living that ward off disability.

Two-thirds of Americans are overweight or obese and the number of elderly people is expected to double by 2030, which means a large part of the population could be at risk for disability due to loss of muscle mass, lead author Dain LaRoche, an assistant professor of kinesiology, explained in a university news release.

Compared to normal-weight older women, those who were overweight had an average of 24 percent less leg strength-to-weight ratio, 38 percent less leg power-to-weight ratio, and they walked 20 percent slower, the investigators found.

"Everything pointed to the fact that it was the extra fat that these people were carrying that was really limiting their mobility," LaRoche said in the news release. "Being of a normal body weight lets you perform activities of daily living and live on your own longer."

He said the findings, published in the October issue of the Journal of Electromyography and Kinesiology, suggest that normal-weight adults should try to maintain their weight and strength as they age.

Overweight older adults can improve their strength-to-weight ratio by either boosting strength or losing weight, LaRoche added.

More information

The U.S. Centers for Disease Control and Prevention has more about strength training for older adults.