RE: The tall people fight back!
This will sound a little complicated here, but hang with me and it will make sense.
A long limbed person is at a disadvantage from two perspectives--first, for every degree of range of motion through which the joint goes, the distance traveled at the end of the limb will be greater than for the person with a shorter limb. This means that for a given number of degrees of range of motion at a joint, the longer limbed person will do more work raising the same resistance than a shorter limbed person, due to the greater distance through which the resistance is being moved--work = force x distance.
At the same time, a longer limbed person is at a mechanical disadvantage since almost all of the joints of the body are part of a third class lever system. In third class levers, the effort arm (distance from the joint to where the tendon attaches to the bone) is shorter than the resistance arm (distance from the joint to where the resistance is applied), which means that the longer the limb, the poorer the mechanical advantage. The amount of force a muscle has to exert is the resistance x the resistance arm length--the longer the resistance arm length, the more force that has to be exerted, even if the resistance itself is the same amount.
With step height, the reason a taller person can use a higher step is a function of staying within a safe range of motion for the knee. Since for a given number of degrees of range of motion at the knee joint, a longer limb will cover a greater distance than a shorter limb will, the step can be higher for a longer limbed person and still keep the joint in what's considered a safe range of motion. It isn't a matter of being easier--matter of fact, from a work perspective, it is harder for a longer limbed person than a shorter limbed person of the same weight, regardless of the step height. But from the point of staying within a specified range of motion, the longer limbed person will be able to use a greater variety of step heights and still be within an acceptable number of degrees of range of motion at the knee.
Tell me if this isn't clear--it is a little tricky, but it all comes back to lever arms, torque, work and angles--good ol' physics.
Maribeth