Instinctive reaction?

I noticed the other day when I was out riding my bike through rugged terrain that when I rode in the standing up position, my legs and arms absorbed all the bumps that occured while I was riding. This allowed my head to remain steady. What I was wondering is, how do I do this? How are my legs and arms absorbing these bumps without thinking about it?

I've noticed something similar. If I'm holding a drink of some sort while I'm driving, I try not to let my arm or hand rest on anything in the car when I'm going over a bumpy road. If I hold it with my arm away from my body, my arm absorbs the shocks of the road and the drink doesn't slosh or spill.

I think inertia causes the the object being supported (your torso, my Mountain Dew) to continue in a smooth motion. The limbs then reflexively catch up to the motion and catch the weight before it can follow the bouncing of the vehicle.

How's your neck? I would assume your head and body stay pretty much the same distance apart while biking, and most of your weight, and hence momentum ((weight/G)*velocity), is in your body. . .most likely? Inertia (weight/G) has long antedated brains, and once a body gets kicked into motion, the resultant momentum will keep it in a certain trajectory (read, 'rut' -- as bikers are often wont ;-) ) -- until it/you hit(s) a brick wall).

Ray (a hiker)

Well, MrKnowItAll seems to have gotten in there while I was putting frills on my answer.

I think the drink case requires more than the biker's head case. It seems to me it *must* additionally involve reflexes or part of the cerebellum, in sensing the momentum of the cup, which is definitely much less than that of the holder's body, which is definitely taking a path of irregular mostion in the inertial field that the cup is not. I might reluctantly allow a little of such bodily control also to the biker out there tearing up the trail. ;-)

Ray

I would assume your head and body stay pretty much the same distance apart while biking I think that's probably a fair assumption considering the fact most bikers are equipped with a neck.