Michael Jordan and Kobe Bryant are two of the greatest shooting guards in NBA history.

On Saturday, Jordan introduced Bryant's widow, Vanessa Bryant, at Kobe Bryant's posthumous Hall of Fame induction. "Thank you for being here. Kobe admired you," Vanessa said to Jordan.

Jordan and Bryant were constantly compared by commentators and they were great friends. They even had the same trainer.

In 2007, Jordan introduced Bryant to Tim Grover. Grover trained Jordan for 15 years after he had retired from the NBA for the second time, and he trained Bryant from 2007 to 2012.

But the routine Grover used with Jordan was completely different than the one he used with Bryant. "Different body types, different stages in [their] career, different areas that needed to be addressed," Grover tells CNBC Make It.

In his new book, "Winning: The Unforgiving Race to Greatness," Grover discusses some of the differences between Jordan and Bryant.

"I don't like to compare, because to me they were so different and unique that it's an injustice to both," Grover writes.

But one thing he will say: "Kobe worked harder. MJ worked smarter."

Kobe 'never stopped'

Grover says Bryant "never stopped"; he was always working to improve himself. For instance, Bryant constantly questioned Grover about every aspect of his training — he needed to know why and how everything worked, Grover writes.

Bryant also carried a DVD player to watch game film over and over wherever he was. Breaking down film on every game and on every opponent helped him strategize for every possible scenario before a game, Grover says.

"From 2:00 a.m. to 4:00 a.m., that was Kobe's focus…unless he was in the gym putting up shots," Grover writes.

"If there was an open gym at 3:00 a.m. and he wanted to work on something, he'd be in that gym," writes Grover.

Grover says he would sometimes have to make him leave so Bryant could get some rest. But Bryant would find a way to sneak back (which meant Grover didn't get much sleep either, just naps).

"Of all the things we worked on, the most challenging was simply getting him to stop," Grover writes.

Jordan processed things very quickly

Unlike Bryant, Jordan knew when to stop, says Grover.

Jordan also processed things very quickly and would only look at game film to confirm what he had already replayed in his mind, Grover says.

"His head was like an infinite library of images and moments and plays; he recalled every action and reaction, and knew how to prepare for whatever was ahead," Grover writes.

Jordan also liked to get enough sleep because he knew sleep was part of his training.

"You'd never find him on a court at 4:00 a.m.," Grover writes.

Instead Jordan trained almost every day at either 5, 6 or 7 a.m., depending on his schedule and time zone, with the occasional night training session, Grover says.

Jordan also never questioned anything. Instead, he relied on "his ability to feel what was working for him," Grover says.

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