[bootload]

"... running an hour at a 10 minute mile (6 mph) is unlikely to lead to injury. ..."

Over short distances maybe, but longer distances? Your modern western person isn't even setting enough time to do 20 minutes of exercise per day let alone moving a 10 minute mile. To move this speed for periods of time requires serious effort. As for injury well it depends how far, how long. I know, I've been doing 10Km on a regular basis for 770Km this year across a cross-country course and I'll tell you now, moving at the speed you suggest will cause damage unless you're conditioned, fit and motivated.