When it comes to burning calories, the ladies in the shallow end of the pool may be on to something. According to a new study at the University of Utah, walking in water is just as effective for weight loss as strolling on land. Women who hoofed it on dry ground or in waist-high H2O for 40 minutes, four times a week, lost an average of 13 pounds and nearly 4 percent body fat in three months. You can't walk as fast in the pool, but the extra resistance forces your body to work harder, which ticks off the calories. Jump in to change up your routine or if you have an injury that makes weight-bearing exercise like walking or running painful. No matter what your impetus is, don't let water-workout naysayers put a damper on your exercise plans. They're all wet.

Q: I've heard that metabolism slows in your 30s and keeps going downhill. Does exercise prevent it?

A: Yes, to a certain degree. Your muscle mass naturally peaks at age 25, and from then on it drops 4 percent per decade if you're physically active. If you're sedentary, you'll lose about 1 percent of your muscle mass a year, says Betsy Keller, an exercise physiologist in Ithaca, New York. "Exercise increases your body's production of growth hormone, which will rev up your metabolism and help keep pounds at bay." Notable drops in your metabolism--which may be due to a decrease in estrogen--don't occur until your 40s and 50s. So if you've added pounds in your 30s, you're likely not exercising enough. To keep your engine from slowing, do three to five cardio workouts and three total-body strength-training sessions each week.