Having undergone a secret operation and regained his belts by winning Saturday’s rematch, Joshua told the BBC: “I didn’t know what was wrong with me though I’d been having health issues.
“I couldn’t understand why I felt so tired. In the dressing room in New York I was so tired I had to put my head in an ice bucket.”
Rumours abounded over Joshua’s well-being after he was stopped by Ruiz at Madison Square Garden in one of the biggest upsets in heavyweight boxing history.
Joshua, who exacted revenge on Ruiz in Saudi Arabia on Saturday night, repeatedly refused to use any excuses for his loss six months ago.
Comparing his preparation for Saturday night’s fight to that dreaded night in June, the Briton said: “Now I have energy, I haven’t missed a session.’
“After my check-ups, it showed what the problem was and this is what you have to get sorted.
“Even in this camp I had an operation done but as I’d started training in June I had no issues.”
