The Brit reclaimed his world titles that he lost to the Mexican-American in June with a unanimous point decision in the Saudi Arabian capital Riyadh at the weekend.
At the end of another gruelling year and with Christmas just around the corner, the 2012 Olympic champion would have been forgiven for taking a break from the sport after his latest win.
Instead, the 30-year-old returned to the gym to keep himself in shape ahead of his expected next bout in 2020 against either Kubrat Pulev or Oleksandr Usyk.
Joshua is currently the holder of both the WBO and IBF titles, with both governing bodies requesting the Brit faces their mandatory challenger or relinquish the belt.
Bulgarian Pulev is the IBF’s selected boxer, while former unified cruiserweight champ Usyk is in line for a crack at the WBO strap.
There is a chance Joshua could fight both next year, before chasing a super fight with the winner of the rematch between Deontay Wilder and Tyson Fury in 2021.
While Joshua has shown great professionalism in getting back into the gym quickly, defeated foe Ruiz Jr has been criticised by promoter Frank Warren over his preparation for the rematch.
The Mexican-American weighed in more than three stone heavier than AJ for the clash and admitted he wasn’t as focused as he could have been in training, prompting Warren to speak out.
“This was ridiculous. When eyebrows were being raised at the weigh-in he literally was the elephant in the room,” said the legendary promoter.
“Just because you’re a heavyweight it shouldn’t mean you don’t have an obligation to display a degree of athletic intention.
“Ruiz Jr brought disgrace to himself and the sport by failing to prepare to any sort of level. Joshua must’ve wondered which chin he was supposed to aim for.”