YES we know there have been Olympians who run with arms straight. Sprinters are pained to watch them. 😀
They’d have been even better vaulters with superior sprint technique.
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Running Arms | Product Video
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Gymnastics Coaching.com 
There is a fundamental problem with all these products and gymnastics coaches in general. They don’t understand that there is a difference between velocity and acceleration.
F = m • a
Force = mass x acceleration
Acceleration has nothing to do with how fast you run. It is about how fast you change speeds. Turnover is the key not arm swing.
The other major flaw in comparing vault with a sprint is that a gymnast runs approximately 70 feet. A sprinter 100 meters. A good 100 meter sprinter keeps their head down for the first 20 meters. Would you tell a vaulter to look down for the first 60 feet?
Sprinters also run side to side for the first 10 steps. Would we want vaulters to do the same?
Finally watch worlds and the Olympics finals for the last 20 years and you will see nearly all female and male vaulters run with straight arms. Why? Because they are running at a stationary object with acceleration and introduction of any lateral movement would be another vector introduced and then ultimately to be corrected before the contact with the board.
This trope about sprinters is as erroneous as telling a young gymnast to put their toes to the bar on a Kip. Watch any college bars line up and you see the bar contact the leg right above the patella.
These repeated physical and physics errors are constantly repeated and without a single person asking is it true with the laws of physics.
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