Sylvester Stallone, age 75, works out relentlessly on weight machines, using hand weights, and using his own body weight. Serena Williams, 40, does an intense array of arm, glute, and core/leg exercises designed to increase her metabolism and endurance.

Good for them. But it turns out that over-the-top routines aren't necessary to reap one of the most important benefits of physical activity — preventing cancer.

A report from the American Cancer Society says 46,000 cancer cases annually in the U.S. could be avoided if people got just five hours of physical activity per week.

And we're not talking running stairs or bench pressing 200 pounds. What's needed is five hours of moderate-intensity activity, such as brisk walking, water aerobics, riding a bike, playing doubles tennis, pushing a lawn mower, hiking, or rollerblading.

The report, published in the journal Medicine & Science in Sports & Exercise, shows that 16.9% of stomach cancers, 11.9% of endometrial cancers, 11% of kidney cancers, 9.3% of colon cancers, 8.1% of esophageal cancers, 6.5% of female breast cancers, and 3.9% of urinary bladder cancers are associated with lack of exercise.

So opt for working out for one hour, five days a week. But remember all activity counts — and adds up — as you aim for even more benefits from 10,000 steps a day or the equivalent.

If you can find seven hours a day to stare at a screen (that's U.S. adults' average), you can find an hour a day to live younger, longer, stronger.