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.
However, taking breaks will go a long way toward preventing stress-related neck pain. Take frequent stretch breaks to loosen up tight neck or back muscles, get up for a short walk around the office, or fill up your water glass every 30-45 mins. Adjust your car seat.