The 34-year-old former professional was quoted in a newspaper in Belgium as saying that it is "inconceivable" that players can play for five hours in hot temperatures and "still run like a rabbit" the next day.
"I would say that is far from the truth," Murray told reporters. "Anyone can see the amount of hours of training and practice that go into what we do and there are other sports that are endurance-wise far more challenging than tennis.
"The guys can't play five or six hours and then come back the next day and run around like a rabbit. When guys play five or six hours in the slams, like we often do, we have a day's rest.
"I was told that after our match last year here. I was told that Novak, on the day off, didn't practice, didn't hit a ball, didn't get out of bed till three o'clock. Providing you put the work in, it doesn't mean it hurts any less when you have to play a couple of days later after a five-hour match, but I would not say it is impossible."
Murray takes on world 110 Ricardas Bernakis in the next round of the Australian Open.