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.
I get the same crunching/popping sounds in by neck and back. I try to stretch everyday but the sounds seem to get worse. I also have what feels like severe muscle tension. Sometimes when it's really bad after I walk somewhere and stop it feels like I am still moving. It's like a swaying motion. Very weird sensations.