workout - n. a period of physical exercise that you do in order to improve your fitness, ability, or performance
fitness - n. the condition of being physically fit and healthy. (fit - adj. physically healthy and strong)
bulk - v. to make (something) bigger or thicker
weights - n. heavy objects that are lifted during exercising
treadmill - n. an exercise machine which has a large belt that moves around while a person walks or runs on it
rowing machine - n. an exercise machine that you use by moving your body as if you are rowing a boat