Have you ever watched a toddler run? If so, you’ve seen a lesson in energy conservation. (If not, watch this. And this.) They’ll move as fast as they can for a few seconds and then slow down to a walk. Then, when they’ve recovered, they’ll start running again.
Apparently toddlers know what they’re doing. According to a study published recently in the Journal of the Royal Society Interface, a mixture of running, walking, and resting may be the most effective way to conserve energy and still reach a destination on time. Or, as the authors put it, “sometimes, steady locomotion may not be energy optimal, and not preferred, even in the absence of fatigue.”
Participants in the study repeatedly traveled a given distance (a little over 100 meters in most cases) with an exact amount of time to reach the end. They couldn’t be late, and they were not allowed to arrive early and just rest. Thus, the average speed for all participants was fixed, but they could go as fast or as slow as they liked at any given moment. Participants made the same trip from start to end point 15 times with an average speed that ranged from about a seven-minute mile pace to a leisurely walk.
When given a lot of time participants walked the whole way. When given little time, they ran the whole way. When given an intermediate amount of time, the majority of participants mixed running and walking rather than trying to run slowly or walk quickly. This was true regardless of variables such as height, weight, and leg length.
Using previous research, the authors of the study show that a mixture of running and walking was the most efficient way to cover the distance at intermediate speeds. So the participants naturally chose the most efficient way to cover the distance.
Writing about the study on RunnersWorld.com, Scott Douglas noted the possible explanation for this pattern:
This intuitive energy minimization likely had evolutionary advantages, especially if you believe the running-made-us-human perspective on the central role of persistence hunting in human development. As [authors] Long and Srinivasan point out, modern persistence hunters have been filmed traveling at an average speed of just under 4 miles per hour. This average speed involves running fast when necessitated by keeping prey close, but otherwise going only as fast as necessary, which can sometimes mean walking or even stopping. In the ancestral setting that molded us, when every calorie was precious, there was great incentive to travel in the most economical way.
For modern runners, the relevance is that a walk-run mixture results in the lowest energy expenditure for marathon times around 5:00. A 5:00 marathon involves averaging 5.24 miles per hour. This is in the range of average speeds (being engineers, they express it in terms of meters per second) that Long and Srinivasan found was intuitively covered by mixing the two basic human gaits.
In this regard, Long and Srinivasan agree with Jeff Galloway that mixing walking and running might be the best choice for some marathoners even if you don’t feel like you need to walk.
So, should you employ a run-walk-rest combo in your next race? Maybe, but this study can’t really answer that question. The study described how the participants moved, but it didn’t offer an optimal mix of running and walking to complete (or win) a race. Also, to make the study meaningful, researchers had to eliminate several factors that would obviously play into the decision to run or walk during a race—most obviously fatigue and fitness level. The distances used in the study were intentionally short and all participants were capable of running the entire distance, which obviously might not be the case in some races.
Still, what’s particularly interesting about this study is that it indicates that we’re programmed to minimize energy use. The participants naturally tended to move in a way that conserved energy: They ran like a toddler.