knee extensions

[stefanos]

NSCA discusses shearing forces in the knee during knee extensions. I know that the upper 30% puts heavy stress on the ACL and that the lower 30-45% is taxing. Does anyone know specifically what they might be talking about. Where is this dangerous sounding stress (shearing force) the greatest during a knee extension?

 

[TJohn]

Are you talking about leg extensions ?? If so, I know they are tough on the knees for people with problems though I'm not sure about where that stress comes into play.

TJohn

 

[Preacher]

Get out the ol' physics books ...

Danger One
Danger Two

For a (very) simple diagram: