Q WHAT’S A GREAT WORKOUT I CAN DO IN HALF AN HOUR TO FRY FAT AND HELP MY HEART?

That two-for-one special calls for a hybrid workout that redlines your ticker and stokes your metabolism. The high-intensity interval circuit on this page, designed by Rachel Cosgrove, owner of Results Fitness in Newhall, California, does that by mixing bursts of rowing with explosive body-weight moves. “Rowing demands more strength than most cardio training does. Plus, it’s great for a guy who sits at a desk because it targets his back muscles. Squat thrusts and split jumps work your entire body.” Each interval is 30 seconds on, 30 off: that’s short enough to max your intensity, yet it also gives you time to recover. Studies show that high-intensity intervals strengthen your heart’s muscles, increase your blood’s ability to carry oxygen, and make your arteries more flexible. They can also increase the size and number of your mitochondria, the powerhouses that burn fat and provide energy to your cells. In fact, a recent study in the Journal of Applied Physiology found that people who did intervals for just two weeks fried 36% more fat in subsequent workouts than those who did traditional exercises.