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.
Try to get your crunches in. Iâm far too proud of the lines forming in my tummy to ignore what a good set of crunches can do for the tummy. Yes, regular olâ plain olâ crunches. Some days I add a little weight to my chest to make it more difficult, other days I just go a little longer in my sets.