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.
Crack, Pop, Crunch..: Yeah. For everyone around you. It's annoying- and makes you look nervous or uncomfortable. It's like cracking your gum all the time. And yes, it can put chronic strain on the joint capsules and lead to laxity and maybe even some arthritis down the line. Every now and then, OK (like once or twice an hour; or just before a fight).