Understanding GRF (Ground Reaction Forces)

[iacas]

When I was shadowing/observing Larry Ward before my daughter played NCAA Nationals last year in Kentucky, one of his lessons involved trying to get the golfer to push harder with his left (lead) foot; to increase his vertical forces. The kid was trying for awhile, trying to "stomp" down into the ground and "land" with his weight into the ground. It wasn't working.

I spoke up, and told him the way to push into the ground was to push against the ground, and you do that by trying to jump off of it, by shoving the ground downward by extending your hip, knee, etc. The golfer was almost trying to do it backward - he was trying to use gravity to do the pushing downward, when what he wanted to do was push himself upward.

Golfers are generally really bad, in my experience, at understanding how ground reaction forces (GRF) work. For example, to push your left hip back more or to "clear" your hips in the downswing, you have to try to push the ground toward the golf ball. The ground doesn't move, though, so what does move is your left hip… in the opposite direction.

For example, if you stand an inch from a solid wall, with your hands against the wall and your elbows fully bent, and you push against the wall by extending your elbows, YOU will move away from the wall. The wall — like the ground — isn't going anywhere. By pushing east, you move west.

Ask a golfer to add force to their right foot… and they'll often shove themselves to the right, which adds force beneath their left foot.

To be honest, it's one of the reasons that, despite having been one of the first people to own a SwingCatalyst, and owning a BodiTrak as well, we've not really used force plates in the past six years. (The other main reason is that they're a bit of a pain to set up.)

This video does a pretty good job of illustrating a few things. I encourage you to watch it, should you have a lesson on force plates in your future.

[saevel25]

I really like the video of the Chasing Scratch guys going to TPI. The TPI guy had him try to push himself using a swivel chair. You had to push and rotate the chair. I think it’s a decent representation of how the lead leg works. 

Any athletic movement usually requires moving in the opposite direction in which you want to move first. 

Yea, it’s tough when you have so many movements going in the golf swing. Lateral, vertical, rotation. 

[iacas]

10 hours ago, saevel25 said:

I really like the video of the Chasing Scratch guys going to TPI. The TPI guy had him try to push himself using a swivel chair. You had to push and rotate the chair. I think it’s a decent representation of how the lead leg works. 

Tons of people have that chair, and I also have a slide board (for skating)… and… we made the Crush-It a long time ago, too. There are ways to train it, but the point was… golfers often do it backward, and would do well to wrap their heads around some basic things. 😄 

[GolfLug]

'Stomp' down the ground to increase GRF?? Not only that makes very little sense, I have never understood the infatuation with increasing vertical GRFs in general as it is some unlimited source of clubhead speed. I think at some point in time someone took Tiger's comment about him snapping his left knee straight at impact to get extra yardage when needed and then ran with it. Ha. 

Edited October 21, 2024 by GolfLug

[saevel25]

10 hours ago, iacas said:

There are ways to train it, but the point was… golfers often do it backward, and would do well to wrap their heads around some basic things.

It was years ago, and it might be just a me thing, I always thought the golf swing requires you to do the opposite of what you think you should do. I will chalk this up to that 😉

Yea, 100% agree. 

2 hours ago, GolfLug said:

I have never understood the infatuation with increasing vertical GRFs in general as it is some unlimited source of clubhead speed.

I think people who use GRF incorrectly are conflating the concept of normal forces and external forces. Normal force being a way to balance the equation of basically weight of pressure into the earth, since we do not move the earth when we move. Versus something like, hurricane force winds which can blow us over. 

I do not think GRF should be used as some sort of external force acting upon the golf swing. Is there a correlation between GRF and swing speed, sure. Using increases rotation, which increases club head speed. GRF should just be a metric.

Edited October 21, 2024 by saevel25