Like others have said....he's no bigger than Wlad..so if Wlad can do 12 rounds as we know he can and has why can't Joshua ? And fellow keyboard warriors...do you think his trainers/promoters are totally naïve and need your advice ? Does Joshua already realise that he's gassed out after a few rounds of sparring ? I'm sure he will know how much stamina he has. In camp I'm sure they'll leave no stone unturned. He's fighting safety pin next so we might see him go more rounds or even the distance. What is that going to be 10 rounds ? I dunno but Johnson will have durability to take Joshua into deeper waters and we might see how he fairs there. Then again Joshua might be the first man to blow safety pin out and do it early. I'm not concerned about his level of muscularity. He and his handlers will know about stamina and if there are any such issues to be concerned about. What I see in Joshua is skills and fundimentals that are way above Wilders this early in his career. I see a strong fit young man with a ton of power to go with his skills. Yes he is still untested and questions will eventually be answered. But that is always the case for any upcoming prospect in any division.
Joshua would have no problems going 12 either if he spent half of every round resting on his opponents back. Wlad would blow his tank after 5 rounds if he was forced into a fight.
Wlad controls the fight and the workrate to enable himself to go 12 rounds. If Joshua fails to control his opponent he is going to have a hard time.
Boxing not work that way if Wlad can go 12 rounds, Joshua is same size, same weight, blq, blq, blq he can go to .... Its not working like that, if he have cardio and can pace himself he can go 12,15, and so on. And only in Wlad camp know how good trainer Banks is. Also he is not his only trainer. I also think that James Bashir would be fit better, but Klitschko probably know better then us. Still Bashir is his second coach ...
I think Vitali is a little busy right now running one of the biggest cities in Europe during a civil war.