(@RoryMcIlroy)

As he attempts to become just the sixth player to ever complete the career Grand Slam, Rory McIlroy has turned himself into one of the fittest golfers in the world.

He recently graced the cover of "Men's Health" and discussed his workout routines, and did a promotional video for Nike documenting his workouts.

According to Brian Wacker of PGATour.com, McIlroy has dropped his body fat percentage to 10% from 24% in 2010, when he couldn't do a plank longer than 30 seconds. Charles Siebert of the New York Times reports that he has added 20 pounds of muscle during that period.

Siebert reports, "Since 2010, McIlroy has been working out five times a week, 90 minutes a day, under the close supervision of his British trainer, Dr. Stephen McGregor, a fitness consultant for the Manchester City soccer club and formerly for the New York Knicks."

In an interview with PGATour.com, McGregor described the way McIlroy's physical conditioning has affected his golf swing:

“Over time the arm speed has quieted down but his clubhead speed has increased and his body efficiency has improved. He can practice more, hit balls more and he has been more consistent.”

“His misses were wide. We needed to tighten that up. As he was going into impact he was going to spray it. As he has gotten more stable so has his swing, and he has been able to add more power and more distance.”

Here's a picture of McIlroy in 2010, when he won his first PGA tournament:

(Jae C. Hong/AP)

Look at him now:

(Getty Images)

(Phelan M. Ebenhack/AP)

He's a fitness buff:

(Via YouTube)

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It's a far cry from this guy:

(Getty Images)

Not everyone sees this as a good thing. Legendary coach Butch Harmon is worried that McIlroy's training may be going too far. Harmon told Irish radio show Off The Ball earlier in March:

"The only caution I would give Rory is, I see a lot of pictures of him lifting a lot of very heavy weights and I think, in a way, you can almost hurt yourself in the gym if you get too bulky. Hopefully, he will keep his body tone down, more like a Dustin Johnson, who’s in absolutely perfect physical shape to play golf."

Harmon compared McIlroy to Tiger Woods, who many people think became too ripped for his own good.

Getting in shape hasn't hurt McIlroy yet. As McGregor argues, McIlroy's swing is more consistent, he's tighter in his core, and less reliant on arm and hand strength, which can produce variables in a swing.

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