The research is clear: You can stimulate growth without the use of heavy loads by increasing the release of local growth factors during exercise.
This is the foundation of occlusion training as well as the constant-tension rep style. But the latter is the one that is of interest to us today. When a muscle is contracting, blood flow into the muscle is restricted. Blood will rush in when the muscle relaxes – between reps if the muscle stops contracting and at the end of the set.
As long as the muscle is working and blood flow is restricted via muscular contraction, metabolites will build up in the muscle and this will lead to the release of local growth factors. That's the basis of this training approach to the shoulders. When you use it after focusing only on the big basic lifts, your physical appearance changes, almost like muscle is migrating toward the delts!
To maximize growth factor stimulation, the main thing to focus on is stimulating as much lactate build-up in the target muscle as possible. You need to have a high pain tolerance for this to work optimally. Lactate accumulation through muscular work is maximized when the muscle is under tension for 45-70 seconds. Here's an example of how to use constant time under tension to build your delts.
Dumbbell Press Multi-ROM
This is similar to the good old 21 technique, which is also based on constant tension and lactate build-up, but we'll do sets of 5-5-10 instead of 7-7-7. That means:
A. Do 5 partial reps – only the bottom half of the movement
B. Do 5 partial reps – only the top half of the movement
C. Do 10 full reps
On the full reps you want to do the reps smoothly, not stopping at the top or bottom between the phases of the lift. Stop about half an inch before locking out to keep the deltoids under tension. The partial reps will cause a rapid hypoxic state (lack of oxygen) and a rapid build-up of lactate, whereupon you do your full reps in that state. Do 3 sets with about 90 seconds of rest in-between sets.