What It Works: Glutes, quadriceps, core How To Do It: Position your legs just wider than shoulder-width apart with your feet pointed forward and slightly out. Raise your arms up by your ears and hold them there throughout the duration of the exercise. Keeping your feet planted, sit back to 90 degrees as if there's a chair beneath you, and then come up. To prevent injury, make sure your knees never go past your toes, and don't worry if you can't sit back to 90 degrees on your first try. Depending on your joints and muscles, your range may vary, Wood says. Start with three sets of eight to 12 reps. This is an effective amount of work for conditioning. As you gain strength, you can try out the exercise with 7.5- to 10-pound dumbbells, one in each hand. Ultimately, you can work up to holding a barbell or Olympic bar on your shoulders.