Ermm let me find the study, it was lean body mass, comparing, 4 groups.
One sat on their bum, eating normally.
One sat on their bum eating normally injected with testosterone.
One went to the gym, doing a normal strength and conditioning routine and eating normally.
One went to the gym, doing a normal strength and conditioning routine and eating normally, injected with testosterone.
Both the testosterone supplementing group's scored a higher muscle gain, than the other 2 groups,
Basically you can supplement with testosterone and sit on your arse and beat the guy working out at the gym without supplementing of course the group at the gym working out and supplementing scored highest.