Tiger @ 50: State-of-the-art tech reveals an important metric in Tiger's golf swing

Conversations about Tiger Woods' golf swing—and, indeed, his career—and inextricably linked to the health of his knee.

The hope of staving off a knee injury was a motivating factor in why he decided to leave the legendary instructor Butch Harmon and re-tool his dominant 2000 era golf swing.

His 2008 U.S. Open victory with a broken leg marked one of the most iconic moments of his career, and the start of a more than 10-year major drought.

And because all the muscles in the human body work together as a system, things often work like an avalanche when something starts to go wrong. When one part fails another steps in compensate for it, before itself failing under the excess load. Could Tiger's ongoing back injuries in later years have stemmed from his knee issues in his younger ones?

Regardless, Tiger's golf swing changed a lot through the years, but it's how his lower body moved that in some ways tells the best story—and offers the rest of us a lesson

We can measure this with an app called SportsBox AI. SportsBox uses AI technology to measure different parts of our body during our golf swing. We plugged in a bunch of old swings of Tiger's, and using SportsBox's pelvis sway metric, we can see exactly how the engine of Tiger's swing evolved.

Tiger's early dominance, winning three-consecutive U.S. Junior Amateurs followed by three-consecutive U.S. Amateur Championships, soon followed by his 1997 Masters win, was the product of what is perhaps the most powerful pound-for-pound swing of all time.

Tiger's young swing was characterized by significant side-to-side movement:

• Sportsbox measuring his pelvis shifting more than an inch and a half away from the target halfway through his backswing.

• By the top of his backswing, his pelvis had moved back towards the target forward but was still almost an inch further away from the target than where it started, a subtle movement known as recentering.

• By impact, Tiger's pelvis had shifted more than six inches towards the target.

• By his follow-through, his pelvis had slid almost nine inches towards the target. You can notice a hint of his reverse C finish because of this huge amount of pelvis slide.

This side-to-side movement was a product of the time—many players in the persimmon era had big hip slides towards the target to generate power. For Tiger, it was also a necessity, as his strong grip and closed clubface required an aggressive slide to prevent the clubface from closing even further.

The swing that propelled Tiger to the career grand slam and one of the most dominant stretches in golf history was a more refined version of his younger move, which makes sense, because it was Butch Harmon who was the man overseeing both swings.

Tiger's goal following his 1997 Masters win was to trade a little power for a lot more consistency. He did this by bringing the club and clubface into a more neutral position at the top of his backswing, less across the line, and while toning down his huge hip slide towards the target.

• Interestingly, in this iteration of Tiger's swing, Tiger's pelvis had slid further away from the target on the backswing than in earlier years: More than 2 inches, according to SportsBox's measurements.

Dom Furore

• But by impact, Tiger's pelvis had moved less than five inches towards the target, which is pretty standard amoung tour players and almost an inch and a half less than before.

Most amateurs would struggle to return to their lead leg sliding that far away from the target on the backswing. Butch and Tiger's genius was recognizing that Tiger could handle it: The big shift away on the backswing gave him power, and his explosive, athletic lower body ability allowed him to return to the ideal spot by impact, without fear of over-sliding.

You can see Tiger working on preventing over-sliding in this Golf Digest swing sequence taken at the time. Notice how his right foot is staying more on the ground—that's to prevent his lower body from sliding too far ahead.

Dom Furore

Despite the dominant success of his newly-refined swing, Tiger began to fear that the side-to-side thrusting would take a toll on his knees in the long run. As he began retooling his swing under Hank Haney, the pair made significant changes to his arm, wrist, and grip positions, but one of the most notable changes was his lower body movement, particularly during the backswing.

• Under Haney's guidance, Tiger's pelvis sway on the backswing was nearly eliminated, with his lower body never shifting more than one inch away from the target on the backswing.

• By the top of his backswing, SportsBox measures Tiger's pelvis was within 0.2 inches of where it started at setup.

• This resulted in a less dramatic thrust towards the target at impact, with his hips moving four inches from their starting position by impact and five and a half inches by the end of his release.

Whether this had the intended effect of protecting his knees in the long run is impossible to say. What's undeniable is that Tiger created a golf swing with less side-to-side movement than before, and was hugely successful with it.

After parting ways with Haney, Tiger once again reinvented his swing, this time focusing on new metrics brought about by the rise of nre technology, particularly better compression with his iron shots.

This change was reflected in his pelvis sway numbers, once again.

• SportsBox measured his pelvis moving no more than 0.2 inches away from the target at any point during the backswing, and a one-inch shift towards the target by the top of his backswing.

• By impact, Tiger's pelvis had shifted a massive eight inches towards the target, well above tour standard more than in his younger years.

This swing also featured a lowering of Tiger's head, creating a significant amount of shaft lean. While this swing generated some controversy and was often criticized, Tiger achieved impressive results with it after an initial adjustment period, winning five times in 2013 and narrowly missing out on another Masters victory.

In recent years, Tiger seems to have adopted a hybrid approach to his swing, combining elements from his work with Butch Harmon and Hank Haney. His grip, arms, and club positions resemble those from his Harmon years, while his body movement and structure are more reminiscent of his Haney-era swing.

Currently, Tiger's pelvis moves about two inches away from the ball at mid-backswing, then recenters to about half an inch away by the top of his backswing.

His head moves slightly further back to accommodate his limited back mobility, and by impact, he achieves a pelvis shift of around six and a half inches towards the target, which is considered the high end of the optimal range for pros.

The evolution of Tiger's swing highlights the importance of pelvis movement for golfers of all skill levels. For amateur golfers, side-to-side movement is crucial for generating power, but failing to move sufficiently towards the target can lead to a variety of issues. While professionals typically shift their hips six inches towards the target, amateurs often struggle to move more than two inches, resulting in inconsistent strikes and reduced distance.

Tiger's career-long focus on optimizing his pelvis movement underscores its significance in achieving a powerful, consistent, and efficient golf swing. By studying the changes in Tiger's technique over the years, amateur golfers can gain valuable insights into the role of lower body movement in the golf swing and work to incorporate these lessons into their own game.