Remember any and almost all exercises designed on the Pilates equipment whether it be the Reformer, Cadillac or Stability Chair is resistance training. It’s also full body. So, in the time that you spend in your private session, you will be building long, lean muscle by using the resistance from the equipment. It’s impossible to “bulk up” in Pilates because of this reason. Muscles get to fully lengthen and flex with or against resistance while maintaining stability throughout the rest of the body and this creates the long, lean muscle, versus traditional equipment at the gym or spin bikes that create a more bulky looking physique.