ANN ARBOR—Post-menopausal women who walk for exercise may achieve different health goals depending on their walking speeds, according to a pilot study from the University of Michigan Division of Kinesiology.

“Most people, including health care providers, have assumed that if a woman is in reasonably good health, the harder or faster she exercises, the better off she will be,” said Katarina T. Borer, professor of kinesiology and principal investigator on the study. “However, the clinical patterns in our preliminary findings suggest that women who walk for exercise may achieve their individual health goals more effectively by walking at a targeted pace that triggers a particular physiological response.

“The study sample was small and more research is required, but our findings to date are intriguing and of interest to professionals in women’s health,” she added.

The eight-month study included nine women, ages 50-65, who were in good health but sedentary before the study began. Their average weight was 165 pounds. The women walked three miles a day for a total of 15 miles a week for eight months. Insulin and growth hormone (GH) levels were measured at the beginning, mid-point and end of the study along with body fat and total weight.

Borer found that after eight months, those who walked at a slower, 18-20 minute-a-mile pace became more insulin-sensitive—good news for those at risk for diabetes. The sensitivity to insulin tapered off, however, as walking speed increased among the brisk, 15 minute-a-mile walkers—bad news for those at risk for diabetes.

“On the other hand,” Borer said, “the brisk walkers secreted more pulsatile growth hormone, or GH. Growth hormone, which declines as we age, promotes bone and tissue formation and helps reduce the effects of aging. The GH secretion levels of the slower, relaxed walkers actually declined over the course of the study. With GH, evidently, women must exercise at higher intensities or lose GH as they age.”

The brisk walkers lost slightly more weight overall than the slower walkers but the difference was minimal, Borer added. More notably, the slower walkers lost slightly more body fat compared with the brisk walkers.

Why did the slower walkers lose more body fat? “Because they were walking at an aerobic pace where, after the first 20 minutes, muscles, with the help of oxygen, oxidize fat as well as carbohydrates,” Borer explained. “The brisk walkers were moving at a speedy, anaerobic pace, where muscles are not getting enough oxygen to oxidize fat and must therefore rely on metabolizing carbohydrates.”

Borer presented her findings at the annual summer meetings of the American College of Sports Medicine and the Endocrine Society.

American College of Sports MedicineU-M News and Information ServicesUniversity of Michigan