Feel vs real: the golf swing on your screen

The stranger in the frame is you

You press play expecting the swing you just made, and a stranger appears: lead arm bent, club pointing somewhere you would have sworn it never went. The camera is fine. What has gone wrong is the comparison, because the swing you remember and the swing on the screen were never built out of the same material.

Position sense starts in the muscles. Reviewing proprioceptive integration in the Journal of Physiology, Mortensen and Christensen describe the type Ia afferent as chiefly signalling the rate of change in muscle length, a velocity signal, and the type II afferent as chiefly signalling muscle length itself. Muscle length, and how fast it is changing. Shaft plane and hand path are not on that feed.

What position sense reports, in degrees

1.05° to 7.0°Published limb-position acuity in healthy adults, by method

Elangovan, Herrmann and Konczak measured forearm position sense in healthy young adults against a 10-degree reference. The psychophysical threshold came out at 1.05 degrees. Reproducing the position with the same arm gave a mean error of 1.51 degrees, and with the opposite arm, 1.84 degrees. Whatever is wrong with your swing, it is not that you cannot tell one forearm angle from another.

Ask differently and the answer changes size. Deblock-Bellamy and colleagues sat 30 healthy adults in an exoskeleton, showed them a virtual arm offset from the real one by 1 to 27 degrees, and asked which was more flexed. Mean discrimination thresholds were 7.0 degrees, then 5.9 on a second visit.

One degree or seven, according to the method. Both came from a seated adult moving one joint slowly under good light, and no published study measures a golfer's position sense during a downswing. Read them as a ceiling, not as your error at the top.

Repeat a movement and your zero moves with it

3.88°Shift in felt hand position after six reaches with rotated feedback

Resolution is not the real trouble; the reference drifts. Ruttle, Cressman, 't Hart and Henriques had people reach to targets while a cursor showed their hand rotated 30 degrees from where it actually was. After six such trials their reaches had shifted 7.57 degrees and their felt hand position 3.88 degrees. Six trials, and straight had moved.

Now count the repetitions behind your own pattern. What your body has done for years is the position it treats as neutral, which is why the position a coach puts you in feels like a mistake rather than a correction. The zero it is measured against is your habit.

The limits matter. That was a reaching task with a cursor, and the shift had gone a week later. It shows the felt reference is movable and quick to move. It does not show that a golf swing recalibrates by 3.88 degrees, and nobody has measured that.

Your own effort is reported quietly

A second distortion runs in one direction. Kilteni, Engeler and Ehrsson summarise the force-matching result: asked to reproduce a force applied to their own finger, people press harder than the task required, because self-generated force is perceptually attenuated. What is done to you registers louder than what you do.

How far that travels matters. Those experiments measured force at a fingertip, not limb position across a whole body. They are a reason a coach's hands moving your trail shoulder feel like a bigger event than moving it there yourself. They are not a measured law about swing changes.

Why the instruction is deliberately too much

Put those together and an instruction that sounds like bad coaching makes sense. If the felt zero has drifted, and effort you produce yourself reads quietly, then asking for the position you want returns a fraction of it. Asking for far more than you want returns the position.

Justin Thomas, asked about this by GOLF.com, said he fights a club that drifts across the line at the top by feeling extremely laid off, and summed the gap up himself: "The rehearsals never look the same as the real thing." Justin Rose described the same trade in the same magazine: a feel of the club sitting far behind him, which becomes the delivery he wants once rotation joins in.

An exaggeration is a dose, not a doctrine. It is sized to one player's drift on one pattern, and borrowed whole it carries you past the position rather than to it. Read the frame afterwards, never the size of the sensation.

What the camera adds, and what it cannot hand you

Video supplies the one thing the body has no receptor for, an outside view, and on the question of where the club was it ends the argument. Worth having, since the felt version was never a recording in the first place.

It runs the other way too. What moved felt hand position in those reaching studies was seeing the hand somewhere it was not. Vision does not sit politely alongside position sense; it pulls it. Watching yourself is an input, not a neutral observation, and it changes what the next swing will feel like.

What a frame cannot hand you is the sensation that produced it. That translation is private, and it has to be rebuilt whenever the position changes. Note the cue you used beside the clip, so the next session compares a feel to a frame rather than a memory to a memory. Pebble Swing reads joint angles out of the frames and the backswing-to-downswing tempo ratio out of the motion; it can tell you the angle moved, not which sensation moved it.