Monitoring screen time is seen as a method of improving Joshua’s reaction time to deal with the fast combination punches of Ruiz Jr.
Joshua told Behind The Ropes: “If you watch some of his fights a lot of his knockouts have come from combination punches.
“And I feel like it’s the punch you don’t see that hurts. And Ruiz Jr has got speed in both hands.
“So I have got to make sure I work on my reactions – staying off my phone to make sure that my eyes aren’t too tired because I’ve got to stay sharp with my eyes and how I react to these type of punches.”
Joshua is defending his IBF, WBA and WBO heavyweight titles against Ruiz Jr in his US debut in New York on June 1.
Ruiz Jr’s only defeat in 33 fights was against Joseph Parker in 2016, a result which he still disputes.
Joshua described his upcoming challenger: “His strengths are his ability to come forward and absorb punishment and avoid punishment, as well.
“Because a come-forward fighter seems to walk into punishment – he doesn’t take too much stick.
“He can knock guys out so that means he’s heavy handed.
“He has the ability to throw combination punches whereas I feel like the European style that I have been taught is ‘jab, one, two, jab, one, two, hook’.
“But he can throw left hook, right hook, left hook, right hook, uppercut, hook, right hook to the body.