Delt "sweeps" work well for high reps in metabolic stress fashion:
The execution is really important. On the lifting side, it's really a pull back – as if you were doing a face pull and lateral raise hybrid. With the supporting arm you're going to be pushing slightly as you lift with the other arm. (It's not a one-arm upright row motion.)
If you get this right you'll feel it big time in the lateral delt and even some posterior delt and traps. Start light and play around with it until you can feel the contraction.
Not too many years ago, the idea of an endurance athlete like a cyclist, triathlete, or runner hitting the weights was almost unheard of. Why, everyone knows that weight training will make you big, bulky, and slow, right? Well, believe it or not, endurance athletes are lifting weights to improve performance.
The most underutilized pieces of equipment in most gyms are the dumbbells. Oh sure, you might see people pumping out a few sets of biceps curls, bench presses, or flyes, but in most gyms the dumbbell racks are primarily used as a place to lean against between sets of barbell squats or benches.