I was thinking about knee injuries while I was writing, great to get a feedback that they don’t take all the fun from riding EUCs. My knees also gently hint that they were not designed for the pressure applied sideways, I do feel a minor discomfort riding on one leg and I try not to do it for unnecessarily long periods of time, just for start/stops and to reposition feet during long rides to restore blood flow :). Riding on one leg, like any other non-competitive athletic activity is not something to do through pain or major discomfort. EUC is a bit of an athletic vehicle, it does require some fitness, I definitely did not have it when I was learning to ride, my feet hurt, my calves hurt, my legs were stiff, but it was all gone within two-three weeks of practice, maybe a month.