My biggest fear with this type of discipline would be turning the child off exercise, which would be a shame, but if they're doing it in a controlled manner, I don't think they are harming the child. It's probably even more effective and less cruel than yelling....and let's be honest, we've all lost our tempers and yelled!
Are they of a different nationality? I used to train competitively in my sport and it sounds a little Russian....
Overall, it doesn't concern me, personally. Maybe I ought to try it with my 7 year old son