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 you crack your neck and back, it often feels good afterwards, especially if there was a great deal of tension or pain prior. The reason it feels good is because pressure is being relieved.Just as when any of your joints crack, gases are being released from within the synovial membranes. also crack my wrists, ankles, knees, shin, toes, the bones at the top of my food near the. ankle, and especially my neck and back. In the morning I'll twist both ways and my neck and back will crack like 10+ times, no lie. I do it because it feels good, and it does relieve pain.