well, trainers who give people too much to lift are just stupid.
on the other hand, i have been looking at teenage girls at the gym (no, not in that way, get your mind of the gutter!) and i have the impression that most of them are placing themselves in circumstances that will get them easily hurt. they work out with 1kg weights, and that's all well and good - if that's what they can handle, so be it. but it's completely obvious to me that they do not eat, and still they spend 30-40 mins on the treadmill or indoor bike. if people do not eat and they spend energy on aerobic activities they will get hurt, even if they only lift their schoolbag. if i were a trainer, i'd just refuse to have such people in my care - they're a walking manifesto for easily avoidable injury.