This exercise is terrific for strengthening the glutes and lower back muscles. Get on all fours with your knees on the floor under your hips and your hands under your shoulders, arms straight. Keeping your neck and spine in line, extend your right leg out straight behind you while simultaneously extending your left arm straight ahead, holding both parallel with the floor. Hold for three seconds. Minimize any arch in your back and keep your body from swaying.
Lower both limbs to the floor and repeat with your opposite leg and arm. Do six reps with each pair of limbs extended for a total of 12.