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.
How to fix those clicking and cracking sounds in our neck. Over the last few months, my neck muscles have been super stiff. And my range of motion is not like it used to be. Even worse, I have been hearing a grinding (or crunching) noise whenever I turn my neck.