They respond to just about any type of training, as long as it's hard and as long as it's not the same damn thing you've always done. That's the beauty of density training: It's a whole lot of stuff you haven't tried yet. And best of all, it'll hit your major muscles in a fraction of the time. Instead of counting reps and sets, you'll focus on the total amount of work you can accomplish in a fixed amount of time. As you progress, you'll naturally increase your sets and reps, be able to use more weight, and perform exercises that are more challenging.