If you're trying to get or stay in shape, you've probably heard that walking 10,000 steps a day can do the trick. But maybe you've found that the recommendation, which the American College of Sports Medicine promoted in the 1990s and has since been widely adopted by exercise-promotion campaigns, isn't doable in your busy life — or that it doesn’t raise your heart rate enough to reduce your risk of cardiovascular disease.

Today, you've got additional guidelines to go on that may make whatever walking you do more heart-healthy. Walking 3,000 steps over 30 minutes, five days a week — or 1,000 steps for 10 minutes a day — can get your heart pumping enough to cut your risk of heart disease, according to research in the May issue of the American Journal of Preventive Medicine.

Suffer from inexplicable lower-back pain? Exercise may be the best way to keep it away, according to a new analysis of remedies, including workouts, shoe inserts and support belts. 

"We did an evaluation of high quality studies on the prevention of back problem episodes in adults [and] found that, surprisingly, exercise is the only intervention that works, and other popular interventions don't work," says Stanley Bigos, emeritus professor of orthopedic surgery at the University of Washington in Seattle, and lead author of the analysis published recently in The Spine Journal.

A new study shows that sugar may not be so sweet for the brain – and may lead to memory problems.

Researchers from four universities report in the Annals of Neurology that people who absorb glucose more slowly than those who metabolize it quickly are more forgetful and are more likely to have a faulty dentate gyrus, a pocket in the hippocampus section of the brain. The hippocampus is involved with learning and memory formation. 

The findings were based on glucose testing, memory evaluations and fMRI scans of the brains of 240 healthy people ages 65 and older without dementia, and applied even in those without diabetes, which is characterized by an inability to readily convert sugar into energy.

You might be wondering what science has to do with Thanksgiving. Its only complexity should involve family feuds and kitchen disasters, right? Have we got news for you: there are myths to be shattered about this most American of holidays, including the alleged soporific effects of turkey and the assumption that gratitude has nothing to do with good health.

Our in-depth report on the science of Thanksgiving tackles those and other questions you may be mulling as you prep Tom in your oven. Don’t you want to know what makes the meat on your plate white or dark? The reason is all in the family – the family of turkey genetics, that is. And can you eat turkey without becoming drowsy? We’ve got the answer.

We're psyched about Sunday's ING New York City Marathon — cheering on our friends, that is, not competing. We're not thrilled, however, about the wounds marathoners suffer.

Blackened and missing toenails top the list of marathon injuries compiled by ABCNews.com. 

"We've seen lots of things from lots of blisters, black toenails, in-grown toenails, stress fractures," Bruce Williams, president of the American Academy of Podiatric Sports Medicine, told the Web site today. "Just about everybody is going to get a blister."

Black toenails are caused by pools of blood that accumulate under the nail from repeated bruising. "It never really bothers me; it hurts in the beginning when my toenails turn black and blue," 26-year-old Jessica Horne, who will run her second ING New York City Marathon on Sunday, told ABCNews.com. "Another toenail grows underneath and the black and blue one falls off."

More evidence today that our genes aren't always our destiny — with an inconvenient caveat for couch potatoes: Physically active people who carry gene mutations linked to obesity are no more likely to be overweight than those without the variants — as long as they exercise at least three hours a day.

Scientists monitored the physical activity of 704 Amish men and women for a week with accelerometers, devices worn on the hip that keep tabs on movement. Those who carried two copies of the FTO gene variant, which previously has been shown to increase the risk of obesity, had a 27 percent risk of being fat, compared to a 16 percent risk among those who had no mutations on the gene. But heavy labor such as brisk walking, house-cleaning and gardening canceled out the gene's weight-gaining effect.