Here's a couple of exercises. Stand with the rig in front of you, feet 2' apart, then shift your weight from one leg to the other moving side to side keeping your body erect and your knees locked. Feel how your pelvis moves, and the vest with it, then take a few steps allowing the same movement to happen naturally.
Also try taking a few steps deliberately swaying your pelvis like a catwalk model just to stretch out the muscles that are usually in tension, then continue walking normally, just allowing your pelvis to move normally. Your gluteus medius and your abdominal muscles should be relaxed.
Let us know how it goes!