Thank you for you message. I think we did not understand each other or I have not expressed myself clearly.
Do you really still think this would be all that bad?
No, I agree but I separate training from daily "physical activities". The kids I coach (at that age) do 2-3 TRAININGS a week but they go for a swim, footy, basketball, or martial arts staying OFF the track. I was talking about training ON the track (5-6 times a week) and I do disagree only with that part. The rest is OK.
In fact, I think the type of 400m training that I was recommending might be perfect for most young athletes because it develops physical fitness as well as some speed.
Maybe, but as you are aware there are many other ways to develop physical fitness. I particularly like "boxing" fitness training methods combined with 200m (athletics) training (and there are other things I include as well) for 8-12 y.o kids who want to run 400m. Or middle distance runners who train for 800-1500m are generally good in 400m at that age. So what am I suggesting is avoiding to take up on 400m training regime (because it is the toughest one even for an elite athlete) rather train for 200m or 800m but RUN 400m. Again I am talking about 8-12 y.o. maybe up to 14 y.o. kids (depends on physical development of a child).