Most of us who lift use heavy weights to focus on strength, moderate ones to emphasize building muscle size, and light weights to focus on muscle endurance. Hence, the weights we use are a reflection of our training goals.
While these modes of training are oftentimes very distinct, they can actually be combined into a single workout. That is, you can train for strength, muscle size, and endurance in the same workout, which allows you to generate some of—but not necessarily maximize—the benefits of each type of training.
This kind of program is called the Four-Rep Method, and it’s very easy to implement. Quite simply, you do 3-5 exercises for a given body part, choosing moves that work the target muscle group from a slightly different angle.