We just talked about changing the timing of the armswing in relation to the leg cycle. But what about changing the arm length, or even the muscles used to initiate the arm cycle?
When a cheetah runs (granted, it's front legs touch the ground and ours do not), their front legs are straighter when they are moving backwards, and they are tucked under the body when they are moving forwards. So I tried this with my arms.
As one arm straightens out and moves backwards, the center of mass of that arm moves farther from my shoulder joint. At the same time, the opposite arm is shortening and moving forward which causes its center of mass to moce closer to my shoulder joint. What does this do?
First of all, I notice that my body is forced to bend laterally at the thoracic spine like a side crunch. It leans towards the side of my body with the shorter arm, and away from the side of my body with the longer arm. What does this side-crunch of my body do?
This side-crunch of my body has an impact on my legs. Basically, when I'm airborne, moving my upper body left and down causes my lower body (including my legs) to move left and up. Since it is the left leg that will be touching the ground next, this actually improves my air-time and slows down my stride rate. When would I want this to happen?
As mentioned in the last entry, improved air-time and a slowed stried rate is associated with downhill running.
Conclusion:
So, if changing the length of each arm causes my torso to bend side to side and is good for downhill running, might I conclude that the best strategy for uphill running is to do the opposite? To have both arms with a very similar bend in the elbows? And what about flat running? Perhaps an intermediate amount of lengthening and shortening with the back and front swing.
Try this and experiment. See how it works.
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