While you don't want to go so heavy that your form suffers, you should be lifting enough weight that you feel challenged. "Of course you can lift light weights for more reps and a longer duration of time, but this isn't a very efficient way to train, and you won't see the same results over time as you will with heavy or medium dumbbells," Kalnes said.
Follow these guidelines for choosing the right weight, depending on your goals — and remember, you may need to add more weight as you grow stronger. If you don't have a lot of space for equipment, consider investing in an adjustable kettlebell or set of weights.