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.
Good ab workout technique prevents neck pain. You can do abdominal workouts at home without any special equipment. But common mistakes in technique can easily result in neck pain and injury. Poor form is the most likely reason people experience neck pain when performing standard abdominal exercises such as crunches. Pre-workout stretching, careful attention to technique and varying your workout can go far toward reducing the likelihood of neck pain.