You can practice by running for more than eleven minutes every day, and then use fat to lose deltoid muscle. You can run for more than 20 minutes. Run 10 km if necessary. People who like marathons are all thin. It's not just the deltoid, because the muscles of the whole body will be balanced, and the thin body is also the whole body. Genetic factors will also affect deltoid muscle, mainly the long-distance running I mentioned above to reduce fat and gain muscle. Trapezius training also has an effect on shoulder width. After all, it will want to extend outward, so it will get bigger.