Elbows key for walkers' efficiency

July 09, 2019

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 at http://jeb.biologists.org.

Selecting eight undergraduate and graduate students - ranging from runners who dabbled twice a week to serious marathon competitors - to walk and run on a treadmill, Yegian says, 'We wanted to study that kind of variation because bent arm running seems to be an almost universal behaviour, regardless of how much a person runs'. Together with undergraduates Yanish Tucker and Stephen Gillinov, Yegian placed reflective markers on the athletes' shoulders, elbows and wrists before asking the runners to walk at ~1.4 m s?1 and run at ~3 m s?1 with straight and bent arms while they filmed the volunteers' movements in 3D. 'The hardest thing was running with straight arms', recalls Yegian, adding that all of the athletes found the movement strange. Then, Yegian and his undergraduate colleagues invited the volunteers to return 2 weeks later, so they could repeat the running and walking trials, but this time the athletes breathed through a mask to measure their oxygen consumption, allowing the scientists to calculate their energy consumption as they moved with their arms in different positions.

Comparing the energy costs, the team was impressed that holding the arms bent while walking increases the walkers' cost by 11%. And when they calculated the amount of effort required to keep the arm crooked, it was clear that bending the elbow came at a cost, although this was slightly offset by the lower cost of swinging the relatively short arm. So, walking with straight arms is by far the most efficient option.

However, when the team compared the runners' energy costs, the outcome was less clear. 'We didn't find any evidence that the energy cost was different between arm postures when running', says Yegian, who had suspected that running with bent arms would be more efficient, 'since that's what almost everyone does', he says.

So the jury is still out as to why runners bend their arms, although Yegian suspects that there must be some benefit that bears no relation to energetic costs, which keeps runners' arms pumping when pounding the streets.

REFERENCE: Yegian, A. K., Tucker, Y., Gillinov, S. and Lieberman, D. E. (2019). Straight arm walking, bent arm running: gait-specific elbow angles. J. Exp. Biol. 222, jeb197228.

DOI: 10.1242/jeb.197228

This article is posted on this site to give advance access to other authorised media who may wish to report on this story. Full attribution is required, and if reporting online a link to jeb.biologists.com is also required. The story posted here is COPYRIGHTED. Therefore advance permission is required before any and every reproduction of each article in full. PLEASE CONTACT permissions@biologists.com

The Company of Biologists

Related Walking Articles from Brightsurf:

Why walking to work may be better for you than a casual stroll
Walking with a purpose -- especially walking to get to work -- makes people walk faster and consider themselves to be healthier, a new study has found.

Spinal cord gives bio-bots walking rhythm
Miniature biological robots are making greater strides than ever, thanks to the spinal cord directing their steps.

These feet were made for walking
Many of us take our feet for granted, but they have a challenging job in the biomechanics department.

Walking sharks discovered in the tropics
Four new species of tropical sharks that use their fins to walk are causing a stir in waters off northern Australia and New Guinea.

Micro implants could restore standing and walking
Researchers at the University of Alberta are focused on restoring lower-body function after severe spinal injuries using a tiny spinal implant.

Walking changes vision
When people walk around, they process visual information differently than at rest: the peripheral visual field shows enhanced processing.

Virtual walking system for re-experiencing the journey of another person
Virtual-reality researchers have developed a virtual-walking system that records a person's walking and re-plays it with vision and foot vibrations.

A large study indicates how cities can promote walking for travel
Coinciding with the European Mobility Week, a study performed in seven European cities focuses on walking for travel, a strategy to increase physical activity in cities.

Robotic cane shown to improve stability in walking
By adding electronics and computation technology to a simple cane that has been around since ancient times, Columbia Engineering researchers have transformed it into a 21st century robotic device that can provide light-touch assistance in walking to the aged and others with impaired mobility.

Water walking -- The new mode of rock skipping
Utah State University's Splash Lab not only reveals the physics of how elastic spheres interact with water, but it also lays the foundation for the future design of water-walking drones.

Read More: Walking News and Walking Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.