Peter Kostis on Patrick Reed's GRF

[iacas]

GRF - Ground Reaction Forces - are a hot topic in golf. It's dying down a little bit, but @david_wedzik and I, along with the rest of the Golf Evolution group (and a scattering of tens of other professionals around the globe), were pretty early into this. We were also two of the first people to kind of get out of it, because there's not a ton to learn there.

Yes, how we use the ground is important, but using the ground a bit better is not going to take someone's swing speed from 92 to 110 MPH. It likely won't even do half of that. Something like 70%+ of the swing speed you generate comes from just your arms. Another big chunk comes from rotation (which uses lateral shear forces to keep your lower body from spinning the other direction against the ground, yes) of your body. A little bit that's left over at the end? Vertical GRF.

It's a pretty simple concept, and we've covered it multiple times. Though my pet peeve still exists - people use the words "weight" and "pressure" and "force" interchangeably, I'm going to split "weight" off to be the static weight, but will let "pressure" and "force" be essentially synonyms for this article.

Here's what we generally know about GRF and weight/pressure. The below is very generalized, but virtually every good player follows the pattern. I'll type this out from memory, and in a general form:

A1: weight and pressure are equal, and somewhere between 60/40 forward or back, often close to 50/50.
A2: weight shifts back slightly as the arms and sometimes the pelvis and torso shift back. Some players only move the arms back and stay centered, but the weight of the arms will still shift weight back. (Less likely if the player already has his weight slightly back.) Pressure starts to build as the weight not only shifts back (very slightly), but the trail knee extends.
A3: the weight shift tends to peak here at 60/40 or a bit less as the arms are as far "back" as they're going to be - any motion after A3 moves the arms closer to the center. The pressure under the trail foot is near the maximum amount, often 65-80%.
A4: things are quieter here - the weight is usually 55/45 except in the case of the guys who start their hips forward well in advance of the club stopping its backward motion. Pressure settles down a few points as the knee stops extending and the golfer begins to bump his hips forward.
A5: sometimes there's a little "hiccup" here between A4 and A5 where the pressure shifts a little back because the arms are again as far away from the target, but that depends on where and how the hips have gone. By A5, though, the pressure is usually at about 50% already as the weight reaches a similar number due to the hips pushing target-ward.
A6: pressure is already well forward, often 80% or more, by here. The weight is not as far forward, because the arms are still back and pressure != weight, but it too is forward.
A7: From A6 onward the golfer extends the lead knee to really spike the pressure. Those who do it a lot will actually get airborne just before or just after impact (which can obviously lead to some weird "flashes" back of the pressure numbers, but only because the golfer has pushed so hard under the lead foot they've overcome gravity). The weight (75%+) is still not as far forward as the pressure (85-95%) forward.
post-A7: The golfer's weight and pressure get closer together as the violent, dynamic parts of the swing are about done. Golfers finish with 90-95% of their weight and pressure forward.

Other things that we know:

• When a knee is flexing, it's actually reducing the pressure beneath it. If you're standing on a scale, and you suddenly flex your knees, your measured "weight" will drop temporarily while flexing.
• Conversely, a knee that's extending is actually pushing against the ground - it's pushing your body's mass upward, and the ground is "reacting" by pushing back.
• These vertical GRF, because they're not directly through your center of mass, apply a vertical torque to the body, which can help you rotate and help the club build up a little speed. As noted at the top, it's not a lot. If it were a lot, we'd all spin counter-clockwise (righties, face-on) and maybe land on our butts at the end of the golf swing.

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So where does Peter Kostis get it all so wrong?

Note: Peter says at the outset that this is a misunderstood fundamental "with the driver swing." The last bit is important because the general numbers above are true for irons hit off the ground, but you can get away with keeping your weight back a little (and your pressure a bit less), because the ball is effectively in the air. We don't have to hit down on it, so the bottom of our swing can be behind the ball.

But anyway, with timestamps…

0:46: 

"Has a lot of good down pressure into his right foot and right leg." Not too bad a start. But this is the backswing, so yes, pressure is building under the right foot.

0:54: 

"As he starts back down, he keeps that down pressure on the right leg." No, he doesn't. The pressure likely peaked at about A3, and is decreasing somewhat rapidly here, particularly by A5.5 as shown above.

1:06: 

A lot here. "Now watch as he starts to come forward. As he gets the club coming through impact, watch the left foot. He's keeping down pressure on the right foot and as the club goes on through, the entire left foot is off the ground, much like Bubba Watson." The only reason it's off the ground, Peter, is because the pressure was so great under his left foot that he overcame gravity and literally pushed himself off the ground in a mini "jump" move. At the same time, you said he's "keeping down pressure on [the right foot]" but the heel of the right foot is in the air as well, and only the tippy toes are touching, and trust me, they're not pushing down very hard at all.

1:11: 

The end result of all that "pushing down with the right foot so that you can unweight the left foot." (Paraphrased, obviously.) It's backward. The right foot is the unweighted one, and the left foot was pushed down so hard it actually popped into the air.

Peter continues: "The key is don't get off your right leg too soon with the driver. You're far better off to keep pressure in your right leg through impact than it is to get to your left side too soon." Patrick Reed does a good job of that.

For those who know what they're looking at here… it sure looks like Jamie Sadlowski got off his right side pretty quickly.

[1badbadger]

I am certainly not an expert on the golf swing, but two things don't seem to make sense about Peter's analysis...

"The key is don't get off your right leg too soon with the driver. You're far better off to keep pressure in your right leg through impact than it is to get to your left side too soon."

Isn't one of the biggest faults amateurs make is not getting their weight to the left side through impact?

"Now watch as he starts to come forward. As he gets the club coming through impact, watch the left foot. He's keeping down pressure on the right foot and as the club goes on through, the entire left foot is off the ground, much like Bubba Watson."

I can't imagine that a player's front foot coming off the ground through impact is a good thing.  Where he planted it during his follow-through was in a much different spot than where it started!  @iacas, if he was one of your students, is that something you would change?

[Vinsk]

26 minutes ago, 1badbadger said:

if he was one of your students, is that something you would change

I would imagine if that student just won The Masters nothing needs to be changed unless there’s an injury concern. Sorry I know my opinion is quite meaningless but if Reed or anyone is hitting their drives that well I’m not sure a change is due. But I can’t imagine anyone deliberately teaching that.

[iacas]

@1badbadger, in order for your left foot to come off the ground it would have needed tremendous pressure before to push off.

I wouldn’t change it if it didn’t need changing. A lot of better women players do the same thing.

[saevel25]

46 minutes ago, iacas said:

I wouldn’t change it if it didn’t need changing. A lot of better women players do the same thing.

I can't remember her name, but I believe there was a LPGA golfer back in the 90's and early 2000's that would be on her toes at impact? I could be mistaken though.

That was a good read.

[iacas]

17 minutes ago, saevel25 said:

I can't remember her name, but I believe there was a LPGA golfer back in the 90's and early 2000's that would be on her toes at impact? I could be mistaken though.

Laura Davies, Lexi Thompson, etc.

[saevel25]

1 minute ago, iacas said:

Laura Davies, Lexi Thompson, etc.

That is who I was trying to think of!

[billchao]

Justin Thomas is barely on his feet at impact with the driver as well.

 

[mvmac]

12 hours ago, 1badbadger said:

"The key is don't get off your right leg too soon with the driver. You're far better off to keep pressure in your right leg through impact than it is to get to your left side too soon."

Isn't one of the biggest faults amateurs make is not getting their weight to the left side through impact?

Correct. The players that do this are landing on that left side early and like @iacas said, exerting a lot of force to "fly" the foot.

What I think Kostis is getting into is the idea that a "push-off" can create RPT early (right pelvic tilt, right hip lower than the left), which would then lead to a slide and stall/flip. Not really the case IMO, how your body moves creates the pressure/weight shift, the right foot doesn't really "push" in transition.

12 hours ago, 1badbadger said:

I can't imagine that a player's front foot coming off the ground through impact is a good thing. 

There are actually some instructors teaching it now.

I don't think it's wrong or right. If the sequencing is good and the foot flies, then so be it...especially if it's with a driver. It's kind of like lag, it's a result of good mechanics/sequencing/speed, not something that should be consciously done.

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Posted this last night. Player on the Web who will be on tour next year, he is good friends with a longtime buddy of mine so we've played some golf together. He has a similar move to Reed, Bubba, Sadlowski, Holmes. He bombs it.

This is more on the extreme end 😛

 

[nevets88]

Holy jeez, I don't think bottom guy is swinging hard enough.

[billchao]

2 hours ago, mvmac said:

This is more on the extreme end 😛

 

I like how he's pushing off the ground so much that he's damaging the turf.

1 hour ago, nevets88 said:

Holy jeez, I don't think bottom guy is swinging hard enough.

Nope, not quite. Shoes are still on.