Yeah....that's for guys like me who got their knees crushed by a drunk driver and have (had) to endure months of physical therapy. They use those to get you to move at all and work your way up to actually walking and/or exercising again.
Three months on your back is not fun and it's worse once you are "allowed" to start walking again.
On the positive side, if I could really pedal a bike very far, I wouldn't have bought an engine kit.
