If you normally end your workouts with a few minutes of ab workouts, you're not alone. But if you're always saving something like a core workout (or other body-part-specific move) until the very end, you may be sabotaging your routine. "[At the end of your workout], your energy levels are lower, which means higher risk of injury and less intensity. And if you’re running late on time, you’re going to skip what's at the end," says celebrity trainer Gunnar Peterson. Instead, build a circuit workout that keeps you moving from one body part to the next, so you're working all areas throughout your workout. Try these fast total-body workout ideas to get started.