Barring an injury, if you are experiencing discomfort in your lower back when performing abdominal exercises then it may be that your core as a whole needs to be strengthened. The abdominal muscles are just one component of your core; the rest consists of the hips, pelvis and lower back. The various muscle groups of the core work together to support your posture, protect your spine and provide you with agility, balance and power. Core exercises can help to strengthen your abs and protect your back at the same time.
Warm up with five to 10 minutes of cardiovascular exercise such as jogging, cycling or jumping rope.
Improve your balance and strengthen your entire core with the bird-dog exercise. Come to your hands and knees on an exercise mat or padded surface. Place your hands directly beneath your shoulders and your knees beneath your hips. Pull your abdominal muscles in, engage your glutes, flatten your lower back and slide your shoulder blades down your upper back. Lift your right hand off the floor and extend the arm straight in front of you at shoulder height. Simultaneously lift your left knee and extend the leg behind you at hip height. Continue to engage your abs and glutes to remain stable. Hold the lift for one count and then return to starting position. Repeat on the other side by lifting the left arm and right leg. Continue to alternate sides for five to 10 full rounds.
Tone your abs while strengthening your lower back with plank pose, which is also the top of the pushup position. Position yourself on your hands and knees on an exercise mat, with your hands directly beneath your shoulders. Tuck your toes under and lift your knees until your legs are straight. Flatten out your body so there is one straight line from your shoulders to the heels. Press your hands into the floor for stability and keep your abs activated. Maintain a neutral neck to avoid looking up or down. Hold plank pose for 30 to 60 seconds and then release your knees to the floor.
Increase the challenge of plank pose to further improve your core strength and stability with side plank. Position your body in plank pose. Lift your left hand off of the ground as you shift your body sideways, coming onto the outside edge of your right foot; the right hand remains on the floor. Stack your left foot, hip and shoulder over their right counterparts. Lift your left arm toward the ceiling while keeping it in line with your shoulder. Stay here for 15 to 30 seconds or go one step further, if you feel stable, by lifting your left leg toward the ceiling, as high as possible. Release the pose by returning the left hand to the floor and coming onto your knees. Repeat on the other side.