Between championship rings, millions of records sold, worldwide fame and Olympic gold medals — they have practiced their entire lives to be at the top of their respective careers. 

However, there was nothing that could prepare these 16 celebrities, including Jamie Lynn Spears, FIFA Women's World Cup champion Carli Lloyd, Mel B from the Spice Girls, "The Bachelorette's" Hannah Brown, and former MLB player Mike Piazza for the physical and mental anguish of surviving grueling training from top-tier military agents in the middle of the desert for the new FOX survival show, "Special Forces: The Ultimate Test."

NBA champion Dwight Howard told Fox News Digital that nothing could have truly prepared him for this "transformative, life-changing experience" working with former special forges agents Rudy Reyes, Mark "Billy" Billingham, Jason "Foxy" Fox and Remi Adeleke. 

"I've always respected our men and women in uniform, but doing something like this really opened my eyes to show how incredible the special forces are, the true superheroes of our time, and I'm glad I had this experience," the eight-time All-Star said.

FOX GREENLIGHTS MILITARY ENDURANCE SHOW FEATURING SPICE GIRL MEL B, JAMIE LYNN SPEARS AND MORE

Dwight Howard, Jamie Lynn Spears, Gus Kenworthy and Carly Lloyd prepare for physical endurance test on FOX show

Celebrities, including Jamie Lynn Spears, Dwight Howard, Kate Gosselin, Real Housewife Kenya Moore, Olympic gold medalist Carli LLoyd and Gus Kenworthy, are challenged on new FOX series, "Special Forces: The Ultimate Test." (FOX)

Billingham, who has also served as a private bodyguard for Angelina Jolie, Brad Pitt and Michael Caine, said the "Special Forces world is 1% of the planet. It's a brutal real world, and the show replicates that, and it's based on experience. Every single one of us have been there and done it.  It's not telling some tale. It's giving you a sample of what our life is really like."

Spice Girls singer Mel B said her journey on the show was "more of a mental" experience and trusting herself to truly being able to commit the process. 

VETERAN'S DAY: TOM CRUISE IN 'TOP GUN,' BRADLEY COOPER IN 'AMERICAN SNIPER' HEADLINE ICONIC MILITARY MOVIES

"To be in a situation where you are literally getting firsthand experiences from professionals, from people that have served our country, everyone's country, the DSs, (Directing Staff) I had so much respect for them," she said. "What they taught you along the process was to just suck it up, follow my orders, and it's all about the team effort.  Nobody's left behind. That mentality and their experiences that they shared with us individually and us as a group —  you can't buy that." 

The stars, including R&B musician Montell Jordan, "Real Housewives" star Kenya Moore, Dr. Drew Pinsky, Beverly Mitchell from "7th Heaven," and Kate Gosselin of "Jon & Kate Plus 8" fame, faced obstacles on a training facility in Wadi Rum, Jordan.

Kenya Moore and Danny Amendola get sweaty during grueling challenge on FOX show

"Real Housewives" star Kenya Moore and NFL player Danny Amendola run through the desert in "Special Force: The Ultimate Test." (FOX)

The recruits of "Special Forces: The Ultimate Test"

Jamie Lynn Spears and Mel B join Dwight Howard and Mike Piazza for 10 days of extreme challenges from special forces agents. (FOX)

"I've always respected our men and women in uniform, but doing something like this really opened my eyes to show how incredible the special forces are, the true superheroes of our time, and I'm glad I had this experience." 

— Dwight Howard

NFL player Danny Amendola, Olympian Nastia Liukin and Food Network chef Tyler Florence also attempt to survive the epic challenges, which focus on "emotional resilience, and revealing deepest and truest character."

The heart-stopping trailer detailed showed the cast jumping out of helicopters and free-falling down canyon slopes. "An elite team of ex special forces soldiers will put them through a version of the highly classified special forces training program. Each task based on the real course," the trailer revealed. "The only goal is to last 10 days without quitting." 

"You can't prepare. It's nothing like we've ever experienced in our life. We thought — well, I know for myself — I thought that I could go just train like I would train for basketball or anything else," Howard said. "But once you get there in that Wadi Rum desert, you know, we found out that it was no fun in Wadi Rum."

Dr. Drew agreed wholeheartedly. "I thought I was training properly for it, running hills, running with packs on, spending weeks just focusing on that, which is one of the sort of rewarding parts. As I got into the training, I thought, ‘Hey, I can do this.’ But, no, no, the DS and the Wadi Rum will have its way with you, no matter what."

Montel Jordan carries backpack through desert

Contestants must survive 10 days of extreme training in the desert from special forces operatives. (FOX)

A helicopter hovers of water while a contestant dives into the ocean

Celebrity recruits had to jump out of helicopters and free-fall from canyon cliffs in the trailer for FOX's "Special Forces: The Ultimate Test."  (FOX)

"Mentally, emotionally, you don't know what's coming for you," Lloyd said. "It was literally surviving one minute, one hour, one day. Me being a professional athlete for so long, you know, physically you can train for it. It was incredible."

Piazza wondered in the trailer if he "still had that fire" as he carried heavy bags above his head before attempting to escape a room filled with smoke. 

"This experience pushed you past the point of exhaustion unlike anything probably all of us ever – we've never experienced that," the former National League Rookie of the Year said. 

"I mean, even the athletes here who have trained professionally. I think the biggest thing I sort of come to realize was that when you get to a point of pure exhaustion, then you go into some alternative survival mode, and from there, it's fight or flight, really. You find yourself reacting in ways that you never thought were possible, both good and bad for that matter." 

CLICK HERE TO SIGN UP FOR THE ENTERTAINMENT NEWSLETTER

Spears agreed with Mel B that the "mental preparation" was hardest as she was away from her two children. 

Carli Lloyd emerges from underwater on Special Forces show

World Cup winner and Olympian, Carli Lloyd, catches her breath during one particularly challenging water test. (FOX)

"I believe all of us, even the DS, we're fiercely patriotic. We fought hard for our country in many combat zones around the world. This becomes almost a civics exercise for each recruit. You think how blessed I am to come from a country that has these liberties, that has these freedoms, because this is the blood, the sweat, the tears it takes to protect it. And I think it makes all of us come away with a deeper sense of love for our country and country men and women." 

— DS agent Rudy Reyes said. 
The Directing Staff of "Special Forces: The Ultimate Test"

"Special Forces: The Ultimate Test" agents include Directing Staff agents Rudy Reyes, Mark "Billy" Billingham, Jason "Foxy" Fox, and Remi Adeleke. (FOX)

"I have to say that it is everything that I didn't know I needed," the former Nickelodeon star said. "I really went in there and got so much out of it. It doesn't matter one second, 10 days, 20 days, you take so much away from it. I have so much more respect just for what they go out there and do. I mean, and it's not a show, it's real life for them, and the sacrifices they make to be away from their children. It was a perspective I needed."

"I believe all of us, even the DS, we're fiercely patriotic. We fought hard for our country in many combat zones around the world," DS agent Rudy Reyes said. 

"This becomes almost a civics exercise for each recruit. You think how blessed I am to come from a country that has these liberties, that has these freedoms, because this is the blood, the sweat, the tears it takes to protect it. And I think it makes all of us come away with a deeper sense of love for our country and country men and women. 

Reyes added, "I find it really illuminating and good for my soul to remember just how blessed I am." 

"Special Forces: The Ultimate Test" premieres on FOX Jan. 4.

CLICK HERE TO GET THE FOX NEWS APP