It's not necessarily the speed of the falling off that cause the injuries. About 2 months ago, on a recreational group ride, a woman coming to a hill did not change to a low enough gear and effectively stalled. Fell with bike on top of her. Broke her ankle. Friday of last week another woman starting off, had not gone more than 23metres on gravel and the wheels slid from under her. Broke her leg. In both cases the women were not young so there may have been a bone density problem, the bike landed on top of them, they were reasonably experienced Ebike riders.