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.