molecule. 1  Chemistry, Physics. the smallest physical unit of an element or compound, consisting of one or more like atoms in an element and two or more different atoms in a compound. 2  Chemistry. a quantity of a substance, the weight of which, measured in any chosen unit, is numerically equal to the molecular weight; gram molecule.
When I do crunches my neck starts to tighten up and it makes me have to rest before doing another set of crunches.
Crunch Correctly. To maximize the benefits of the crunch, it's important to perform them with correct form. Lie on your back on an exercise mat, bend your knees and put your feet flat on the mat. Put your hands behind your head or just behind your ears, then flare your elbows out to the sides. Tighten your stomach muscles and pull your belly button toward your spine.