If you can't practice deltoid muscle, the possible reasons are as follows:

1. The tendon bundle of deltoid muscle is not fully stimulated in every exercise.

(Exercise should be based on the principle of large weight, multiple groups and full frequency)

2. I didn't stretch the ligaments and joints of deltoid muscle after exercise.

(Stretch your muscles properly after exercise)

3. protein was not added after the exercise.

Supplement high-protein food after exercise, preferably after 25 minutes.

These are basically the reasons.

I hope it helps you. Come on!