I had to stop for a break around the 2hr mark because I did not think of the salt/fluids being lost and was feeling the effects significantly. After a hasty retreat to my kitchen to fill a shaker-cup with some powdered electrolytes I was back at it.
The versa-climber is an excellent torture device! I recently added a Jacobs Ladder to my home setup and enjoy the similar stimulus it provides to the Versa