4. "Change your choice of cardio. Always hop on the treadmill? Go on the stair climber. Or test-drive my absolute favorite, the often-overlooked rowing machine — it’s actually the biggest heart rate booster. Start by rowing a total of 500 meters (it’ll say how far you’ve gone on the screen) and then, try to increase that distance by 250 meters, little by little, every week." — DK