Brock Lesnar: Why His Third Title Defense at UFC 121 Will Be Hardest Yet

Brock Lesnar will defend the UFC Heavyweight Championship against Cain Velasquez at UFC 121 this Saturday night.

The mixed martial artist once known as "The Next Big Thing" will have just his second fight since returning from a life-threatening bout with diverticulitis in July.

In his first fight back, Lesnar defeated interim champion Shane Carwin by submission, handing Carwin his first loss and unifying the heavyweight titles in the process.

But at UFC 121, the 6'3", 265 pound Lesnar faces maybe his toughest test to date, the 6'1", 240 pound Cain Velasquez.

We're just one day away from one of the biggest fights in MMA history, so let's take a look at why Velasquez will be the biggest challence of Lesnar's young UFC career.

10. The Gas Tank

Obviously both Lesnar and Velasquez are going to enter this fight in tip-top shape, but Velasquez's conditioning is unparalleled in the sport.

"He's one of those guys at that weight class who has an unlimited gas tank. He's not going to get tired," said all-time MMA great Randy Couture.

ESPN's Sportscenter even ran a "Sports Science" segment that tested Velasquez's levels of conditioning. It was found to be on par with the top endurance athletes in the world.

9. Quickness and Speed

In no way is Brock Lesnar a slow or immobile athlete. In fact, the guy does things in the octagon that 265 pound men shouldn't be able to.

But even though Lesnar is quick and certainly agile, the lighter Velasquez has the edge in both categories.

It's going to be a game of cat and mouse between the powerhouse (Lesnar) and the speedster (Velasquez). 

8. Velasquez's Fights Are Usually Quick

Brock Lesnar will be facing a fighter who doesn't like to go the distance.

In eight career MMA fights, Cain Velasquez hasn't spent much time outside of the first round.

Five of his fights have been stopped in the first round, and all five of them ended with a technical knockout by Velasquez. 

7. Wrestling

Lesnar was a four-time collegiate All-American and won a Divsion I national championship at Minnesota, and we know that Lesnar is one of the best wrestlers in MMA.

But Velasquez isn't so bad himself.

He was a junior college national champion and two-time All-American at Arizona State, so he might be the one guy who stacks up with Lesnar in terms of wrestling ability.

6. Ground Game

Things might be different when facing Lesnar, but Velasquez has relied on his ground game more often than people realize. 

Velasquez has spent well over half of his fights—22:47 out of 35:06— in fact, on the ground.

Lesnar has the better ground game in the fight, but Velasquez does have the ground game experience to battle out if Lesnar takes him down early.

5. Punch Percentage

In five career UFC fights, Lesnar has landed just 30 percent of his punches in the standup game.

On the other hand, Velasquez lands a majority of his punches, 53 percent to be exact.

Lesnar may pack the bigger punch, but Velasquez lands his a lot more often.

4. All-Around Game

These are obviously two of the best fighters in the world, but an argument can be made that Velasquez is the better all-around fighter.

He has very quick hands and feet, a nearly unlimited gas tank, very good boxing skills and is an excellent wrestler/grappler.

It will be hard for Lesnar to deal with such a balanced fighter.

3. TKO

If there was one phrase you could use to describe Cain Velasquez, it would be TKO.

He's won seven of his eight career fights by technical knockout while Lesnar has just two career TKOs.

However, Velasquez has no career submissions, and Lesnar did submit Carwin in his last fight.

2. Standing Strikes

In Lesnar's five UFC fights, he has connected on just 44 percent of his standup strikes, but that number is even inflated by the fact that Lesnar connects on 66 percent of his kicks.

He lands only about 30 percent of his standup punches.

Velasquez, on the other hand, lands roughly 62 percent of his standup strikes—including an astounding 83 percent of his kicks.

Edge: Velasquez. 

1. Velasquez Is Undefeated

Brock Lesnar will enter tomorrow night's fight as the champion and the favorite.

But Lesnar has a submission loss to Frank Mir on his record. Cain Velasquez has never lost.

To be the man, you have to beat the man.

Is the man Lesnar or Velasquez? We'll find out on Saturday night.