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.
Protect Your Neck Protect Your Neck Gentle neck stretches can help you avoid or relieve neck pain. Bring your ear to your shoulder and gently hold for 5-10 seconds. Then, slowly bring your chin to your chest and hold this for 5-10 seconds.