Of the ongoing research, the most economical runners in the world have one consistent trait in common: they all maintain a forward lean. Leaning forward is the safest and more economical way to use your upper body when running. Why?
Strong evidence has confirmed that forward learning during running enables your foot to land closer to the center of mass (upper body) which permits the center of mass to move farther ahead more quickly vs maintaining an upright upper body posture. The problem with running too upright with your upper body produces a longer brake force duration period, which was found to be incredibly straining on the knees. Also, research found that forward leaning during running not only shaved down time spent braking, it also reduced propulsion forces which resulted in less mechanical work and muscle power to move the body forward. This also expended less metabolic energy! Read more here!
