The bridge works the glutes (butt), hamstrings, and core. Lying on your back with knees bent and feet hip-width apart, peel your spine off the floor, starting at the tailbone, forming a diagonal line from knees down to shoulders. Slowly return to the starting position. For an extra challenge: Target your triceps by holding light weights, lifting your arms toward the ceiling as you raise your hips. Bend your elbows to lower the weights towards the floor. Do 10 times.