Originally Posted by DieselWeasel
Tried it just now for the first time. Seems pretty easy, but I didn't test to see how long I can hold it.
Yep, for some with good back strength, it's easy enough; the time held is when the shakes start to set in and it suddenly becomes a whole new ball game.
Personally, I don't see the need to do this kind of "exercise", more a test IMO, very often because once a base of back strength has been built, it becomes obvious that the time a person can hold it for will either become static or increase and only decrease if back strength decreases, in general.