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.
1. Bicycle Crunches: Lie on your back. Clasp your hands behind your head and make your abs tight. Raise your right leg a bit and make it parallel to the ground. Bring your left knee towards your chest, then stretch it straight in the air.Do the same with the right knee, while raising your left leg.. Bicycle Crunches: Lie on your back. Clasp your hands behind your head and make your abs tight. Raise your right leg a bit and make it parallel to the ground. Bring your left knee towards your chest, then stretch it straight in the air.