Over the past several years it has become apparent that lead knee movement has a significant impact on the golf swing. The interesting aspect is this movement is often overlooked when diagnosing one's own swing issues. Thus, I see a lot of folks chase non-existent swing fixes which are predicated upon faulty lead knee movement, including myself.
Upon the takeaway, the lead knee should bend down relative to the flared position of the lead foot. When that movement occurs, the chances of being stacked and tilted over the ball are far greater, and the trail hip will want to travel upwards on the backswing. Plus, it also promotes backswing extension. If the lead knee travels to the right, or towards the trail knee, then all of the above good things do not happen, and worse, one's weight will transfer onto, or over the outside of the trail foot.....into the zone of death.
Likewise, correct lead knee movement also promotes a shoulder driven takeaway with good shoulder tilt at the top from a down the line view vs. an arm swing. It's not entirely automatic, but if the lead knee is bending down towards the flared lead foot, the shoulders will want to rotate up, and the body will feel more tilted at the top, which means getting stacked over the ball is much easier.
Stance width is also important. The narrower the stance, the chance of moving weight onto the top of, or worse, to the outside of the trail foot increases. This is why many folks have problems hitting the driver because their stance is too narrow, plus their lead knee buckles inward, causing a right sided swing. This is also why many struggle with the 3W and longer irons with narrower stances. A narrow stance may feel more "controlled" but it actually invites more weight shifting to the trail side.
At the start of the downswing, the lead knee moves towards the target. Watch Tom's lead knee movement in his videos. Many folks buckle their lead knee inwards on the backswing, then push off the buckled lead knee which pushes the swing arc to the right for fat, thin, topped shots, etc. To that extent, flipping the right wrist vs. maintaining the "cheese wedge" is required to save the shot. When the lead knee moves towards the target to start the downswing, that movement keeps the low point and weight on the left side (aka "peg leg" swing). The lead knee doesn't have to travel like a "slide", maybe an inch or two, but that slight movement serves to keep the low point at and after the ball. When the lead knee does not move left, it is more "underneath" the torso and will then push off upward on the downswing, moving the low point to the right.
I highly suggest focusing on Tom's videos by watching his lead knee movement and getting that right first. The lead knee, in my opinion, drives the majority of the golf swing. If we were all in a room right now, I would bet serious money that most folks would have a very hard time executing both the backswing and downswing lead knee movement because most folk's lead knee moves inward, and then stays inward and pushes off early to start the downswing.
Most excellent and appreciated, @GolfLivesMatter. There is nothing I can add to this absolutely spot-on summary of this critical component of a truly centered swing.
Thanks for posting this newest installment from your upcoming book. 😎 I've pinned it to draw more attention to it.