Keep your lower back on the floor to exclude its muscles from work
Crunches are great. Well, not always but they’re a potent exercise for those who wants to build a pack. There are two problems with them though. Crunches absolutely do not spot reduce, meaning no matter how hard or how long or often you crunch, your abs will hide under a layer of fat till you lose it through diet and cardio. Another problem is much bigger and more serious. Doing crunches incorrectly and often can lead to lower back problems. So if you think you know how to do crunches, read on. You may be in for a surprise.
Since there are many crunch variations out there let’s first breakdown the basic floor crunch every newbie starts with regardless of experience or gym membership. Lying with back on the floor, bend legs at the knees and place your arms behind your head or cross on your chest (a bit harder). Start moving towards your knees by lifting your shoulder blades but keeping your lower back firmly on the floor. The crunching motion should happen in your chest area rather than your lower back. Try to feel the tension in your abdominis rectus and make sure not to pull yourself by the neck if you’re keeping hands behind your head.
Keeping your lower back pinned is important. You don’t want your pelvic muscles engage into work, just abs. You also don’t want to put strain on your neck and pulling a muscle there while you crunch. The circular crunching motion should happen in the chest area.
Keeping this principle in mind will help you do the crunches right whether you’re doing them on the floor, a reclined bench, or a crossover trainer. You only need six months to build solid muscle in your ab area and crunches are great for that but if you want some deep core conditioning there are far better and safer exercises out there to help you. Once your newbie phase is done it’s safer to ditch the crunches altogether.