Elbows key for walkers' efficiency

Wandering through the Harvard campus one day in 2015, graduate student Andrew Yegian recalls how something unusual caught his eye. "I noticed a person running with straight arms," he explains. This really stood out for Yegian, as runners usually bend the elbow, while walkers keep their arms straight, which made him wonder: "If straight arms are better for walking, why aren't they better for running, and vice versa?" he puzzled. Was there a trade-off between the cost of keeping the elbow bent and swinging the arm at the shoulder that could benefit runners? Could walkers conserve energy by keeping their swinging arms straight? Intrigued, Yegian and this thesis advisor, Dan Lieberman, decided to film athletes walking and running with straight and bent arms to find out why runners keep their arms bent while walkers let them swing loose. They publish their discovery that walking with a straight arm is much more efficient than walking with a bent arm in Journal of Experimental Biology.

source https://www.lifetechnology.com/blogs/life-technology-news-blog/elbows-key-for-walkers-efficiency