First, it just won’t feel good if the body is not in optimal alignment. What you can’t see here in this picture is that the carriage (that thing she’s kneeling on) is moving! The key is that its movement creates a subtle instability, which gives instant feedback if Priscilla were to come out of good alignment. For example, if she were to lean forward a little too much (kind of like if she were leaning forward over her desk to squint at her computer monitor) she might feel as if she were going to fall forward off of the Reformer!
Second, Priscilla is using the muscles of her shoulder stabilizers (Triceps, Deltoids, Latissimus Dorsi aka “lats”, Serratus, middle/lower Trapezius, just to name a few) WHILE ALSO holding her spine in a neutral position, encouraging abdominal activation.
And finally, she is holding gentle awareness on her Dan Tien, or center. Why? Because Chest Expansion is challenging! Her body wants to come out of good alignment, and it wants to tense in places that shouldn’t be tense. So the internal focus she achieves by placing awareness on her center/Dan Tien actually helps her activate the deeper postural muscles she needs for this exercise, while also eliminating any unwanted superficial muscle tension. Plus it’s way more fun!
The result….? An awesome exercise for the physical body combined with improved energetic flow. Oh, and the amazing feeling of having meditated during the course of her session!