Men’s Health recently released its rankings of “The 50 Fittest Male Athletes in the World.” The rankings take into consideration speed, strength, agility, power and endurance—plus an intangible “X-factor.”

Several phenomenal athletes among the 50 have worked with STACK and revealed their intense training routines and workout secrets. Take a look below:

Colin Kaepernick

The San Francisco 49ers quarterback, who earned his starting spot in 2012 after Alex Smith sustained an injury, simply put, trains like a crazy person. He could have played professional baseball, having achieved California All-State status twice in high school. Drafted by the Chicago Cubs in 2009, he opted to pursue a different path.

The quote (borrowed from film producer Ian Smith) on Kaepernick’s Twitter profile seems pretty self-encompassing: “Do not underestimate the determination of a quiet man.”

Stay tuned to STACK later this month for exclusive new footage of Kaepernick getting all beastly in the gym.

RELATED: 6 Really Important Things You Can Learn From Kaepernick

Tim Howard

His stellar performance and outrageous display of athleticism in the World Cup confirmed Tim Howard as the biggest name in USA soccer. According to Men’s Health, Howard pays the most attention to his core work, and rowing, kayaking and sparring are among his cross-training methods.

Howard was STACK Magazine‘s cover athlete for the 2013 Holiday Issue. Among other things, he took us through his “Shutout Workout”—designed to build flexibility and explosiveness on the pitch.

J.J. Watt

At 6-foot-5 and just shy of 300 pounds, defensive machine J.J. Watt is all business.

“From a training standpoint, I need to do everything I can to make me prepared for the season,” he told STACK. Watt also said he focuses on adding mass while maintaining, if not improving, his quickness and agility. His Box Jump is almost 60 inches; his 40 time is 4.8 seconds.

In case you missed it, watch Watt destroy a bunch of 1,000-pound tire flips.

Adrian Peterson

Adrian “All Day” Peterson, 2007 NFL Offensive Rookie of the Year and 6-time Pro Bowler, is a natural talent. But that doesn’t mean he didn’t work hard to earn his spot on the Minnesota Vikings, or that he hasn’t experienced more than his share of adversity. In 2011, Peterson tore his ACL and MCL in one incident. He responded that the injury was a “blessing in disguise.” Eight months later, he suited up for Week 1. He then went on to be named Offensive Player of the Year and league MVP.

Peterson graced STACK Magazine‘s cover in 2007 as an NFL rookie, and then again last fall. Peep all that AP intel here.

Mike Trout

2012 American League Rookie of the Year Mike Trout, nicknamed the “Millville Meteor,” is just 23 years old. Still early in his career, he is already considered by many to be the MLB’s best all-around player. In his rookie year, he won a Silver Slugger Award and led the league in runs scored and stolen bases.

Check out Trout’s insane Box Jump.

Louie Vito

With four U.S. Grand Prix Championship titles under his belt, professional snowboarder Louie Vito first took the spotlight at age 17, when he pulled off a backside 1080 at the 2005 Australian Open Championships. Vito also has half a dozen X Games medals, and he is likely to bedazzle us for years to come.

Vito told STACK that his off-snow exercise regimen is what makes the difference in his ride, particularly his landings. “It’s not like I’m lifting heavy weights, getting all Jersey Shore up in the gym,” he said. “It’s mostly just making sure my body is warmed up, stretched and my muscles feel good.”

More on his training style here.

Kris Letang

Canadian ice hockey defenseman Kris Letang has got the goods. Selected by the Pittsburgh Penguins in the third round of the 2005 NHL Early Entry Draft, he is the winner of back-to-back World Junior Championships, the backward skating contest at the 2012 NHL Skills Competition, and a Stanley Cup.

Letang’s weight room regimen is intense, to say the least. He harnesses his lower-body power through heavy lifting and explosive dynamic movements. For starters, Letang practices Hurdle Hops and sports a 40-pound weighted vest when performing Bulgarian Split-Squats. Check it out here.

Usain Bolt

Need we even bother to rehearse the accomplishments of the world renowned Olympic sprinter Usain “Lightening” Bolt? Often referred to as the world’s fastest man, Bolt, who has amassed six Olympic gold medals, is harder at work than ever before. Don’t miss a sample of his speed workout and his weight room workout here.

Jordan Burroughs

Burroughs, 26, has won an Olympic Gold medal (2012) and two World Championships in freestyle wrestling. He boasts a 69-match winning streak to boot. When Burroughs broke his left ankle a month before he was to compete in the 2013 World Championships, he forced himself to continue training every other part of his body. Men’s Health reported that Burroughs’ training now includes performing over 30 Pull-Ups while saddled with two 25-pound chains.

Read our exclusive interview with Burroughs to check out more of his weight room moves.

Floyd Mayweather Jr.

Currently undefeated in his pro career (46-0), Mayweather has won 10 world titles and has dominated four different weight classes. The highest paid athlete in the world right now, he is ruthless in the gym. Watch his “Money Walk” Pull-Up here.

LeBron James

The King’s performances—and his innate athleticism—speak for themselves. Now that James is moving back Cleveland, also STACK’s home base, expect to see him on his third STACK cover in the near future.

We snagged LBJ’s high school workout and got a look at his 2014 post-season workout, but it now seems like he’s changing his methods. Don’t miss the rest of our LeBron James content.

Blake Griffin

Dunker extraordinaire Blake Griffin doesn’t get his killer moves from sitting back and eating sub sandwiches all day. Since entering the NBA, he has dealt with a slew of injuries, but they haven’t stopped him from making his exceptional athleticism known to the world. He told Men’s Health that he has learned to adjust the way he approaches dunks to avoid crashing his head into the rim or the backboard.  “Energy is something you can control,” he said.

Griffin doesn’t buy into the notion that a bigger upper body translates into better performance. Instead, he focuses his workouts on core strength and cardio capacity.

Don’t slack off. Try one of Griffin’s workouts for yourself.

Jon Jones

Jon Jones was nicknamed “Bones” by his high school football coach due to his “slight” frame (for a defensive lineman). The nickname spurred him to work hard to fight in UFC’s light-heavyweight division, to become the youngest champion ever at 23 years old, set the longest win streak and win the most consecutive titles in UFC light-heavyweight history.

Set to defend his title in late September against Daniel Cormier, Jones would not be caught dead neglecting his training, which means two-a-days at least five days a week. Recently, Jones told Jimmy Kimmel that he works out up to four times a day, adding, “I don’t work out, I out-work.” Jones also said he likes to cross-train, singling out swimming for its two-for-one cardio and recovery benefits.

Get a taste of the Bones regimen.

Calvin Johnson

With a 40-Yard Dash time of 4.35 seconds, tremendous size (6-5, 235) and superb athletic ability, Calvin “Megatron” Johnson can do whatever he wants—although, for him, that means being even more disciplined in his off-the-field training. His one tip for aspiring professional athletes? Early on in his career, STACK caught an interview with Johnson in which he advised simply to “Stay relaxed . . . just go out there and do what you do.”

See who clocked in at No. 1 and read more about all 50 athletes at Men’s Health.