Burpees can be modified for beginners, as good form is an important part of making this bodyweight exercise work. But burpees are the ultimate in terms of hitting just about every major area of the body: arms, abs, glutes, hamstrings, quads, and calves. And it works the heart and lungs as well. Start with a squat, dropping your hands to the ground. Kick back both legs into a plank position, drop down into a pushup, then jump legs back toward your hands; stand and jump, then repeat. Work in small sets (5-10 to start) and add more as your strength and endurance improve.