"I saw in Serena Williams this ability to rise above her weaknesses, her fatigue" - Fitness trainer Mackie Shilstone

In the latest episode of 'The GOAT: Serena' podcast, fitness trainer Mackie Shilstone spoke about working with Serena Williams and his role in helping her navigate past the health scares in her career.

Shilstone joined Williams' camp 11 years ago, and he told podcast hosts Chanda Rubin and Zina Garrison that the 23-time Slam champion had the ability to rise above her weaknesses. He also described how he urged Serena Williams to push her opponents to the "fatigue threshold", which in turn gave her the energy to survive the grind.

"I saw in her this ability to rise above her weaknesses, her fatigue," Shilstone said. "Fatigue makes cowards of us all. And I told Serena, 'Serena, we've got to bring your opponent to the fatigue threshold we've got, and you've got to survive to do that'."

"At that point there's only a 10% margin and that’s where you win because your mind is stronger, but both of you have to be at a broken point," he added. "And then there will be one person to survive. And I said, and that's what we’re going to work towards."

The 71-year-old fitness guru went on to recall an incident from Wimbledon 2016 to reiterate his take-no-prisoners approach to Serena Williams' tennis. Initially skeptical of Serena playing doubles over concerns of physical exertion, Shilstone came to terms with her decision but advised her to "slam" her opponents if they come towards the net.

Serena had paired up with sister Venus and was accidentally hit by the opponent during one of the matches. Shilstone, who was looking on from the stands, vociferously yelled "payback!" So the next time one of the opponents came to the net, Williams thundered down the shot past her.

"I asked her, 'You're going to play this doubles?' She said, 'Yeah, with Venus.' I said, 'You're going to tire yourself out. I know you're doing it for hand-eye coordination.' Then I told her, "Okay here's what we going to do. If this woman comes up to the net, I want you to slam her. You are going to hit 'em'," Shilstone recalled.

"So I was sitting at her doubles (match) and Serena goes up to the net. The girl hits her and I stand and yell 'payback!' So when the girl comes to the net, she (Serena) smacks her. They win (Venus and Serena) and when it's all over, Serena comes up to me and says, 'Are you happy now?' I said, 'Well, it was about time you got slapped'. And then she says, 'I know. But I paid it back'."

"If it happens to you on the court, you know you can survive" - Mackie Shilstone on how he helped Serena Williams recover from her pulmonary embolism

Serena Williams has experienced pulmonary embolism twice

Mackie Shilstone also spoke about Serena Williams' experience with pulmonary embolism, which led her to miss parts of the 2010 and 2011 seasons. Pulmonary embolism is the clotting of the blood in the lungs, something which Williams also suffered after childbirth.

Shilstone recalled an incident from 2011 when, while training to get back on tour, the 23-time Major winner felt breathless and stopped midway through their session. Determined to bring Williams' stamina back, Shilstone forced her to enter the deep end of a pool.

"We were in Palm Beach Gardens and I see Serena pulling for air," Shilstone said. "I'm thinking, 'Wait a minute, her fitness is better than this.' I said, 'We’re going to your pool in the back of your house… tell the lady that's cleaning the house, I want a big bleach bottle, you're going to become a Navy seal. Cause I'm going to do what I said, we're going to survive'."

Shilstone then gave Serena a bleach bottle to hold over her head and asked her to somehow survive in the water until the bleach completely drained out.

"I got the bleach bottle, cleaned it out," he continued. "And I said, 'Serena, I'm going to put a heart rate monitor on you and electricity conducts in the water so I'll see it over on the sidelines. Go out there in the deep end and fill that thing with water, and then raise it above your head and you can't stop until all the water's gone and you're going to bob up and down. I look at it this way - you're either going to survive or you'll be down at the bottom of the pool and I'll have to do CPR on you'."

When Serena came out of the pool, Shilstone told her that he wanted to make her believe in her ability to persevere if she were to feel breathless during a match.

"She said, 'Why did you make me do that? I was gasping for air.' And I said, 'That's exactly what I saw you do. So if it happens to you on the court, you know you can survive'."