Edberg's way of playing is very stressful on the body yes. But great technique can only take you so far. Lot's of Edberg's contemporaries hit technically sound BH volleys much as he did but lacked the strength and balance to stick them the same way he did. You can see why players resort to taking PED'sYes, all great players have natural talent, some just have more than others. It's well known that Mcenroe really never practised (thus played dbls. instead), where as Lendl was a work horse on and off the court. As for Edberg, IMO he looked like it was hard work, serve and volleying.