I would like to think that neither are juicing.
These are both very young guys still, that have really just hit their physical peak in terms of strength and muscle development.
The modern game is clearly very physical now and I think Nadal set the bar with being heavily muscled and perhaps at a new level of fitness. They have both had to get to a similar shape to compete. I think as well with Murray, to me he just looks as if he has developed from boy to man. Its actually quite common when men hit 24/25 that their muscle development changes.
Tight clothing does play a part too.
"Tennis is just chess with balls....zugzwang"
Prince, Dunlop, Prince....who knows...who cares.