I don't think that the definition of injury is at all obvious. Most people probably feel a little sore when they're first learning ukemi, if only because they're using their muscles in a new way. Technically, when a muscle is sore, that's because the tissue is damaged, but does that count as an injury in aikido terms?
I didn't have any injuries that kept me off the mat in my first year or so of training, but I had a few dings and bruises which might have healed better if I'd taken a rest. Anyway, I didn't answer the poll, because I couldn't figure out what counted as an injury.