Human dynamics - hand speed when running.

[Coldamus]

My knowledge of human dynamics is zero but hopefully someone here will know this. I've googled it but can't find the answer.

What is the relationship between a running person's speed over the ground and the velocity of their hands relative to the ground? My guess is the speed of the hands on the forward stroke would peak at about twice the person's ground speed and on the back stroke would be virtually zero relative to the ground. Is that correct or am I way off?

The reason for the question is that I recently sold a radar speed gun to someone on eBay and they are using it to monitor sprinting speeds during athletic training. They claim tne speeds displayed are inconsistent and too high.

The speed gun records and displays the highest relative velocity that it measures while the trigger is held down. It occurred to me that it might be picking up hand movement and showing that as the highest velocity. The guns are quite sensitive and can measure speeds of baseball, tennis and cricket balls etc. but those are single discrete objects that don't have arms and legs fllailing about. From googling, I've noticed that the guns are sometimes used to measure punching speed in boxing.

It may be that the operator just needs to be more precise about aiming the gun to ensure it records the speed of the torso.

PS. I'm travelling today so won't be able to respond immediately.

[jok11n]

perhaps have them try and take a reading from someone running with their hands behind their back (as a test) to rule out if the arms are mucking with the readings

[lsemmens]

Try measuring the speed with them running away from you rather than towards you. That should take care of the hands.

[gordon_s1942]

One thought would be to have a radar reflective 'patch' on the torso of the runner and aim at it if possible.
This may be why they dont use radar to measure official events but use the measured distance and passing the photo cells instead.

[Coldamus]

Thanks everyone. Some very good suggestions there!

[trash]

Can they hear he audio on the gun ?
That will give an indication of what is going on.
It's unusual that the gun would lock to arm movement but it's not impossible. I have heard this on my own gun.

[gordon_s1942]

Another part of the body moving along with the arms is the legs of course and that coupled with the irregular reflective surfaces of the Human body covered in a sheen of sweat which I think would also be reflective, must drive the receiver nuts trying to obtain a solid signal return.
Then you have the inclination of the body of the runner at speed as we dont run bolt upright, do we?
The human body is looking more like the irregular shapes of a Stealth Fighter, covered in Gortex or whatever is used now isnt it.............

[Coldamus]

I've only briefly used one of the guns and as far as I could tell, it was completely silent.

The manufacturers only promote the guns for measuring the speed of baseballs, tennis balls, cars etc. They don't mention animals or people. Perhaps that is deliberate.

I think Isemmens idea of measuring speed from behind might solve the problem. From that position, the arms (or legs) should only be "visible" to the device on the back stroke when their velocity is less than that of the torso. Since the gun records the greatest velocity measured, hopefully that would be the speed of the torso. Aiming at the head might help if the beam is narrow and directional enough, although athletes might find it confronting.