TKO Abdominal Crunch / Back ExtensionDescription TKO Abdominal Crunch Back Extension Core & Lower Back Strength Training The TKO Abdominal Crunch Back Extension Machine is a high performance, dual function strength machine designed to target both the core and lower back in a single, space efficient unit. With multi position seat pad adjustment and a quick cam adjustment system, users can seamlessly switch between exercises and adjust their range of motion for a personalized workout.