The concept of the Pilates Powerhouse has been given multiple meanings.
Some use it to refer to this term in purely anatomical terms - as the abdominal part of the body, from the diaphragm to the top of the pelvis - both posterior and anterior.
This is the center of your body, and in Pilates, the main focal point of your practice. Therefore, many use an imaginative interpretation to engage cueing (providing clear and concise movement instructions) in explaining how to connect to a particular muscle group typically within the muscles of the body's torso (e.g. transverse abdominis, diaphragm, multifidus, quadratus lumborum, lateral rotators and the pelvic floor).
We think Romana Kryzanowska, Joseph Pilates' legendary student, meant for the "Powerhouse" to be a dynamic approach to movement and a way to move with strength, stability and energy.
In this context, the Powerhouse is a set of actions that produce an optimal practice to achieve correct posture, and progression in one's practice. Instructors use this concept of cueing to assist their clients on various pieces of Pilates equipment/machines in achieving greater spinal health which is dependent on spinal flexibility and mobility.
The Powerhouse isn't just the area that you work on to strengthen and stretch in a Pilates session, but also the actions that build on each other in all planes of movement, and include opposition and concentration. These actions are specific for working the area that each progressive Pilates level of practice is ready to engage.