Good back exercises using only your body weight.
Start: Get down on your hands and knees. Keeping your back flat.
Finish: Take a deep breath, allowing your belly to pooch out. Then forcibly exhale and round your back like an angry cat as you lift your navel up toward your spine. When you can exhale no more, keep your back rounded and your navel in as you purse your lips and take shallow breaths through your nose for several seconds. That's 1 repetition; it should take 20 to 30 seconds. Inhale as you flatten your back to the starting position.
Start: Lie facedown with your legs straight and your arms stretched straight in front of you, with your hands on the floor.
Finish: Lift your arms, head, chest, and lower legs off the floor simultaneously. Hold this position for 1 to 5 seconds, keeping your head and neck at the same height as your shoulders throughout the movement. Return to the starting position.
Start: Lie with your abs and chest on the ball, your back rounded, and your legs straight behind you, braced against the base of a wall. Fold your arms across the ball.
Finish: Uncoil your torso and lift your chest a couple of inches off the ball.
Start: Start on all fours, with your knees and toes on the floor and your palms facedown in front of you.
Finish: Pull in your abs, then straighten one arm and the opposite leg, extending both limbs parallel to the floor while keeping your torso and hips in a straight line. Hold for 1 to 5 seconds, then lower your working limbs and repeat with the opposite arm and leg. That's 1 rep.