As the product expert for Health Mark,Inc. I can tell you that this product will definitely lock out in the complete vertical position as long as the unit has been properly balanced for your particular height and center of gravity, and the Pivot Arm Bracket is set at the top hole (as in accordance with the owner's manual). From the complete vertical position, it is both safe and effective to perform exercises in a slow and controlled manner such as torso or trunk twists. However, although inverted crunches or sit-ups are a popular exercise for inversion tables, we do not recommend this movement as it can be extremely harmful if performed incorrectly; additionally we do not advise performing any movement from a completely vertical position unless you have someone to spot or monitor you.