1| STEP-UPS WITH SPRINGS
Holding a five-to-ten-pound dumbbell in each hand, arms at your sides, face a 12-to-18-inch-high box, bench, or step. Step up with your right foot, then explode up onto your toes while driving your left knee up in front of you as high as you can. Lower back down to the floor and repeat. Switch legs and repeat to complete one set.
2| EXPLOSIVE LUNGES
With a ten-pound dumbbell in each hand, lunge forward until your front leg reaches a 90-degree angle, keeping your feet pointing forward. Push off hard with the front foot and return to starting position. Repeat, alternating feet with each rep.
Hold a barbell on your shoulders. With feet shoulder width apart, squat until your thighs are parallel to the ground, keeping your abs tight, back straight, and knees over your toes. Stand and repeat.
4| BICYCLE CRUNCHES
With your hands laced behind your head, lower back flat on the floor, and legs extended, lift your upper body off the floor while pulling your left knee toward your chest. Twist, touching right elbow to left knee while extending your right leg. Lie back. Alternate sides with every crunch. Do 20 reps, then roll over and do a Superman.
Lie flat on your stomach with arms extended overhead, legs straight and shoulder width apart. Lift both ends of your body six inches to a foot off the ground. Hold forfive seconds, then relax and roll back over for more crunches. (Cycle through the core exercises this way for five minutes.)