Go to almost any gym and you will see people doing exercises like bench press and leg raises. They think these are the best ab exercises. But they are not, they are strength training exercises.
Here's an experiment to try. Stand up and hold on to something for balance. Place your other hand on your abs. Now raise your knee in front of you. Notice that the ab muscles are not activated.
The muscles that lift the legs are the psoas muscles or hip flexors. They start in the lower back, cross the upper pelvis and attach to the front of the thigh. The sitting position is just a reflection of the leg lift.
The legs stay in place and it is the torso that lifts, also using the hip flexors. The role of the abs in these exercises is simply to act as stabilizers. They do not contract over a range of motion, which is necessary in a primary ab exercise.
Let's take a look at the abs and what they do. The abs attach between the pelvis and the rib cage, and their function, in addition to being stabilizers, is to pull these two body parts together in a "crunch" motion - where the torso rolls or curls forward as if to form a ball.
The main abdominal muscles are:
- The abdominal muscles are located on the front and sides of the lower half of the torso, extending from the rib cage and attaching along the pelvis.
- The rectus abdominis muscle is commonly referred to as the "six-pack" muscle of the abs. Thin bands of connective tissue give it this appearance.
- The transverse abdominis (also called transversus) is the deepest muscle in the trunk (meaning it lies beneath all other muscles). It wraps laterally around the abdominal region.
- The fibers of the External and Internal Obliques run diagonally across the body, allowing for angled movement.
Although you may feel more or less stress in different areas of the abs by performing different movements, there are no different exercises for the upper and lower abs.
So the upper and lower abs work virtually as one unit. The fundamental variation in the effect of an ab exercise comes from whether you contract your abs through a full range of motion, or only a partial range, and the resistance to which you subject these muscles.
Crunch standards
Lie on your back on the floor with your legs resting on a bench in front of you. Place your hands behind your neck. Curl your shoulders and core forward and up toward your knees. Don't try to lift your torso, but roll forward. At the top of the movement, pause and squeeze your abs to achieve a full "max contraction." At this point, slowly, under control, lower your torso back to the starting position.
Twisting crunches
Do the same as above, but do one rep by leaning forward so that your left elbow comes closer to your knees to perform the movement. On the next rep, twist the other way so that your right elbow comes closer to your knees.
Reverse Cunch
In this exercise, the pelvis moves toward the rib cage rather than the other way around.
Lie on your back so that you can reach over and behind yourself and grab something to hold on to - the end of a bench, for example, or the uprights of a weight bench, or anything else to stabilize yourself.
Bring your knees toward your chest. This is the starting point of the movement. Roll your pelvis up so that your knees touch your forehead. Pause, then lower your pelvis back to the starting position, with your knees close to your chest.
Vertical Crunch
This move is too difficult for bodybuilders with really massive legs.
Hold onto a hanging chin-up bar or stand on an upright bench with your elbows and forearms on the padding. Bring your knees in toward your abs. This is the starting point for this exercise.
From this position, curl up so that your knees come up toward your forehead. Pause, then return under control to the starting position with your knees close to your chest. If this is too difficult, do regular reverse crunches instead.
Scissor Crunch
In this exercise, both the pelvis and rib cage move towards each other at the same time.
Sit crosswise on the edge of a bench. Lean your torso back and extend your legs. Crunch forward with your upper body and bring your knees toward your chest at the same time. Pause at the top, perform a maximum contraction by squeezing your abs, then slowly and under control return to the starting position.
Crunch machine
There are plenty of machines that claim to provide primary ab exercises, but many of them hit the hip flexors instead. When using an ab machine, pay attention to whether the rib cage and pelvis are tight together through a full range of motion, or whether the muscles involved are more like hip flexion exercises like sit-ups.
Just because your abs are fatigued by certain exercises doesn't mean you're contracting them properly through a full range of motion, pulling your rib cage and pelvis toward each other. Even when acting as stabilizers, they remain fatigued.