Ab / Back Machines for Abdominal Workouts and Low Back Extension Exercises help develop True Functional Core Body Strength building Abdominals and Low Back Muscles. Dual Functioning Abdominal Machines deliver a great Total Ab Workout allowing users' to Perform Crunches and Knee Raises Independently or in Tandem in an ergonomically correct position. Semi Recumbent Synchronized Dual Ab Machine allowing users to Increase or Decrease Resistance with Weight Plates The days of dreading Ab Exercises such as Sit ups and Crunches on a cold, hard, unforgiving floor are over. Make Ab Workouts more comfortable with an Ab Machine. FREE Shipping in the Contiguous United States.