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.
âAnd in the case of the neck pop, you hear a crack as the gas pops out of the fluid.â. Generally, joint cracking is not harmful, Dr. Visco said, but when extreme stretching becomes a habit (to relieve tension, for instance), it can cause irritation of soft tissue or cartilage. And because important nerves and blood vessels run through the neck, amateur neck-cracking is ill advised. A gentle stretching routine is preferable.