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.
No, endless crunches aren't the secret to a flat belly. Crunches, sit ups and planks may strengthen the muscles that lie underneath excess belly fat, but they don't burn it off. Cardio exercise that raises your heart rate for an extended period of time is more likely to help you slim down that muffin top.