I have recently started to teach Pilates, both Mat and Equipment, to young tennis players. They range in age from 10 to 17. I am very surprised at their inability to sit up straight (shoulders over ribs over hips) when their legs are extended. I realize some of this may be due to tennis but one group of players is more recreational and don't play as much as the other. Just wondering if this is typical for children? Also is it just kids these days or is it a muscular/skeletal issue due to being kids and growing? These tennis players are primarily boys but the girls seems to be just as bad.