A human participant walking on a treadmill while wearing a mask. Photo credit: Molly Bartels/Auburn University Photographic Services.
Unlike many animals, humans don't start walking immediately after they're born; in fact, it can take children up to 18 months before they start walking. This could be because being bipedal, or walking on two legs instead of four, requires more balance when you only have two points of contact with the ground. Once we've finally learned to walk normally, we perfect it so that it costs us as little energy as possible to be stable. But there are still other challenges for us to master when it comes to moving. Walking on uneven surfaces such as cobblestones or attempting to walk on a rocking boat require us to learn new ways to manoeuvre. How long it takes us to learn these new skills is still unknown. This led Sarah Brinkerhoff, Meral Culver, William Murrah, Danielle McCullough, Matthew Miller and Jaimie Roper of Auburn University, USA, to team up with Natalia Sánchez of Chapman University, USA, and Austin Robinson of Indiana University, USA, to find out how long it takes people to learn to walk in a new way and whether their strides, stability and metabolic rate all respond at the same time.
Seventeen human participants visited the lab and walked on a special treadmill which has two belts, one for each leg. At first, the researchers had the participants walk normally for 4 min while wearing a mask to measure how much oxygen and carbon dioxide they were breathing out. Then they adjusted the speed of each leg so that one leg was moving faster than the other (1.5 versus 0.5 m s–1) and videoed how the participants were coping with their new walking pattern. After 20 min of this unusual walking style, the team returned the treadmill to its normal walking speed.
After reviewing the videos, the researchers noticed that the participants modified their stride so that the leg on the faster side of the treadmill took longer steps. They also saw that the participants were able to modify their stride rather quickly (∼30 s) and that they could maintain their stability in this new walking style. But did the participants’ metabolic rate go down at the same time as they got used to walking with each leg going a different speed? Surprisingly, no. ‘People are really good at making sure that they are stable when they walk, even if they start out very unstable and can achieve stability in under 1 min. Making walking more energy efficient, on the other hand, occurs gradually, and even after 10 min of steady walking with their legs walking at two different speeds, they are still tweaking how they walk to use less and less energy,’ explains Brinkerhoff.
Generally, scientists use metabolic rate during walking to determine whether someone is used to walking in a certain way. As the participants’ metabolic rate didn't change at the same time that their stability did, the scientists suggest that the length of our strides is not the only thing humans need to change to improve how efficiently we walk. Whatever that something is remains unknown. Regardless, it's still impressive how fast humans can get used to walking in an ungainly way and quickly gain some stability on the most uneven terrain, even if it takes their metabolic rate a little while to catch up.
