In 2011 I did an Instructable
on how I added removable wheels so our NordicTrack ski machine could be moved up and down steps by one person without difficulty. Since I have added springs with hooks I can grasp for attachment or release. These serve two purposes. They keep the axle for the wheels in place, and they block the skis from sliding when the ski machine is stored vertically or being moved.
I experimented with using the ski machine while the wheels are in place and after the springs had been released so the skis can move normally. But, the ski machine can move forward and backward a little on the wheels. That creates havoc with the protective floor pads at the rear of the machine. Earlier I found a broken weld on the rear support, but it was probably unrelated to putting wheels under the front of the machine.