This is excellent stuff. Notice that the low back remains stable throughout the movement and the abs are flat and not domed. Notice also how he stresses that the abs work throughout the movement -down as well as up.
Essentially an ab crunch is a roll up and down of the upper back. At the highest point, the shoulders blades just leave the ground. When performed well, it is quite clear that the action is happening directly over the stomach. The head, neck and shoulders just ride up and down, being moved by the tummy muscles. The whole abdominal area feels crunched inwards throughout. And you can breathe!
Things that go wrong.
The commonest mistake is doing ‘neck-ups’. This is just poking your head up off the floor and results in neck ache. Ab crunches are hard work and require a reasonable degree of ab strength before they can be done. A good place to start ab strengthening is the plank rather than ab crunches.
Andy is instructed to ‘hold an orange’ under his chin – but note that Andy is looking forwards as he comes up and not upwards. The curl in the upper back includes curling the neck. It will also help to press the tongue onto the roof of the mouth, since this helps the deep neck flexors (muscles that tuck the chin in) to activate.
If you cannot get your low back flat on the floor, then this means the muscles that lift your thighs, the hip flexors, are very tight and your low back muscles are over active. If this is the case, then for now roll a towel up sufficiently to just fill the gap and work over that, maintaining steady pressure on the towel. This would also be the case if a disc bulge has been diagnosed or suspected.
There is huge disagreement as to whether your back should be flat on the floor or slightly off the floor in this movement. From personal experience and from training many people, I emphatically think the back should easily flatten on to the floor and if it won’t, then remedial action should be taken to stretch out the tight muscles mentioned above that hinder this.
If your abs are doming, then this means you are not engaging the deepest abdominal muscle, the transversus abdominis. This is the muscle that wraps around the abdominal contents like a corset and is turned off when foods like wheat are eaten, if the guts are generally unhappy, eg constipated, after abdominal surgery or if the back aches. Breathing out as Andy was instructed helps. But the problem lies not in misunderstanding the instructions, but rather as to what is or isn’t going on inside the guts.
Hand and leg positions.
The hands can be behind the head as instructed or they can be placed on the abs. This is an excellent place to feel what is going on there. If your abs are contracting properly and you have a good head position, your head should not need supporting. The hands can also be crossed on the chest or held overhead.
When you lift the feet off the floor, usually knees are bent to 90°, then the hip flexor group should be more disabled, so the abs themselves get no assistance. To really ensure the hip flexors are disabled, then it helps to put the heels on a bench and press them into the bench, making the back of the legs and the bottom contract.
Why not to do this exercise.
People are rightly obsessed with tummy fat and mistakenly believe that doing hundreds of ab crunches will miraculously make that fat disappear. When you exercise a muscle, the muscle does not grow little teeth to gobble up the overlying fat. Tummy fat is the result of too much stress and eating the wrong things. It is reduced by eating well, sleeping well, reducing stress and getting stronger overall to increase the daily calorie demand.
Although ab crunches do have a place in ab strengthening, there are many other exercises like the plank and variations that have great carry over to sport and everyday life. Also if you learn how to do resistance work ((ie shoving heavy things about in the gym with your arms or your legs)) well, then you will be engaging your abs to a surprising degree, and this too has great carry over to sports and every day activity.