When you run, your stride rate is never perfectly, metronomically consistent, even when you try to run at a very steady pace. There are subtle fluctuations.
A team of researchers from Tokyo University led by Yushi Nakayama investigated whether stride rate at a steady running pace was more consistent in trained runners than in non-runners. What they found was that the stride rate of trained runners is more variable—and less variable—depending on how you measure it.
The study (published in Gait and Posture) was a bit too technical for me to fully understand, so I asked my friend Stephen McGregor, a running biomechanics expert and coauthor (with me) of The Runner’s Edge, to explain it for us. Here’s what he said:
The Nakayama et al. study used seven trained and seven untrained runners to examine the ‘variability’ of stride frequency between these two groups. The investigators had the subjects run on a treadmill at their preferred speed, as well as 20 percent above and below. As expected, the preferred speed was faster for the trained runners, and the stride interval at preferred speed was smaller [that is, they had a higher stride rate], but when expressed relative to absolute speed, there was no difference in stride interval between groups. [In other words, the faster runners had a higher stride rate simply because they were running faster.] When the authors compared a measure of variability, the coefficient of variation, of stride rate they found that the trained runners exhibited a lower variability of stride rate by this measure.
What this finding means is that, in trained runners, there is less variation in stride rate from one stride to the next. McGregor says this finding indicates that trained runners have a more practiced stride. They have figured out how to do it right, and they do it right every time. Reduced stride-to-stride variation in stride rate is a manifestation of the principle of “practice makes perfect” in running.
The story does not end there, however. “Using a more esoteric measure,” McGregor says, “Detrended Fluctuation Analysis, which determines if there are long-range correlations in stride frequency, they found that long-range correlations tended to be greater in the untrained than in the trained runners.”
What this finding means, according to McGregor, is that, while there is less stride-to-stride variation of stride rate in trained runners, these same runners actually exhibit more stride-rate variation over the course of an entire run. Why?
McGregor’s own past research provides an answer. His studies have revealed that the running stride becomes less varied at very fast speeds and at the onset of fatigue. Put another way, as a runner approaches his performance limits, his stride becomes constrained, hence less varied.
By contrast, when a runner is running at a comfortable pace and is not fatigued, his stride is unconstrained, hence more “playful” and varied. Since trained runners typically have higher performance limits than non-runners, they exhibit more variability in their strides at equivalent effort and fatigue levels.
Nakayama and his colleagues came up with a slightly different explanation for the greater variability in stride rate at the preferred running pace that was seen in trained runners over the course of an entire run. They postulated that “it is possible that the decrease in the runners’ α (long range correlations) reflects their ability to perceive movement-related information such as visual, tactile, or proprioceptive feedback.”
In other words, as a runner gathers experience in practicing the stride, he may learn to be more perceptive of feedback from his body and his environment and thus better able to use this information to make quick, small adjustments in his stride rate to maximize efficiency.
To summarize, this study found that trained runners show less stride-to-stride variability in stride rate when running at a steady pace but more variability over the course of an entire run compared to non-runners. The greater short-term stride rate consistency probably indicates a stride that has been honed to optimization through repetition. The greater long-term stride-rate variability in trained runners probably indicates a greater freedom from biomechanical and physiological limits, or constraints, which allows the stride to exhibit great “play.”
Originally published on June 9, 2014. Updated on September 21, 2018.