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.
Stretching the abs right after you do a round of crunches can bring fast, effective relief. Roll over onto your stomach and stretch your legs straight behind the body, keeping them about hip-width apart. Place your hands, palms down, next to your shoulders and push up, lifting the chest and hips off the floor.