You walk over to the dumbbell rack and there are approximately 700 choices. Now what? If you're like most people, you probably do one of three things: Grab the same dumbbells you always use because they haven't killed you yet. Look around and see what everyone else is lifting. Pick a weight that just feels appropriately fitness-y and hope for the best. And listen, I get it. Nobody really teaches you this stuff. You find a workout online and it says, “3 sets of 10 dumbbell squ