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.
When the sides of the neck are tight, the muscles are in a state of contraction and can pull on the shoulders, causing pain and discomfort. Relaxing the sides of the neck helps the shoulders relax. Sit or stand up straight. Relax your shoulders and square them forward. Place your right on the left side of your head. Pull your head toward your right shoulder, stopping when you feel tension in the left side of your neck. Place your left fingers on your left shoulder and press down gently to deepen the stretch. Hold for 30 to 60 seconds, then release.