Zion Williamson gained eight pounds of muscle during a one-week heavy weightlifting routine during the offseason. The amount of weight gain from Williamson shocked staffers.

"He's not normal," David Griffin said. "So finding stasis with Zion is the challenge, because he's 19 years old. He's still growing. It's not going to be about a number. It's going to be about metrics of flexibility and strength and control and all of the different things that we can measure that really are outside of weight."

One NBA athletic trainer who is familiar with Williamson agrees.

"If you're not moving well, I don't care if you're 300 pounds or if you're 175 pounds, there's going to be a problem," the trainer said. "It's got to be quality movement. The mechanics have to be done right."

"Zion has the highest peak force of any athlete we've ever assessed -- and he was still in high school," said Dr. Marcus Elliott, founder of P3.