Believe it or not, many of the abdominal exercises that instructors choose for classes (or meatheads use in the gym) tend to work other muscles more than the actual abdominals. Sit-ups, leg lifts, hanging leg raises, etc. anatomically have little to do with the core. Raising your legs (or raising your body to meet your legs) is the responsibility of the hip flexors, a group of muscles which attach between the lower back and the top of the femur. The rectus abdominis (the main ab muscle) attaches from the ribs to the pelvis and is responsible for spinal flexion.
That’s not to say that the abs have nothing to do with leg lifts and other hip flexor movements, but they are not the prime movers.* They are instead used isometrically as stabilizers to keep the spine from extending as the legs come toward the torso. Lower back problems can result as these stabilizers tend to fatigue before the end of the set which results in arching and spinal compression. Sit ups, especially are “no bueno” for this reason.
So how do we help our class (and ourselves) get the universally desired 6-pack? (It actually should be called an 8-pack, but that’s a whole other discussion.)
True core strengthening moves can actually help relieve lower back pain. Some examples include:
These are just a few examples of ab-working exercises. Most moves that bring the chest closer to the hips will work. Also, leg lifts and other exercises can still be used in class, but it’s a good idea to use those moves as the exception and not the rule. Your class will thank you.
*The prime mover, or agonist, is the main muscle involved in a specific movement or action.