Does know a general guideline that you can take with short approach jumps to determine full approach distance? For example, how much should an 8.20m jumper, jump from half approach (10 strides), and from 12,14 etc etc…?
does anyone know?
It's really highly athlete-dependent. For practically every athlete there comes a point of diminishing returns on jump distance when speed is increased. That is, they can't properly setup a nice takeoff as speed increases. This is why you see younger athletes frequently jump further from very short approaches. For more advanced athletes the dropoff seems to not be too much between 10-7 strides because by that point you're basically operating at 92-95% max velocity. It's the very short run jumps (2-5 strides) where you see dramatic drop-offs because the takeoff velocities are so much less.