We know that humans are well adapted to running long distances. But if that´s the case, why do runners get injured so often?
Researchers at Harvard Medical School and the National Running Center at Harvard-affiliated Spaulding Rehabilitation Hospital wanted to answer this question. They set out to determine whether runners with high impacts are at greater risk of developing injuries.
The study focused on heel-strikers, since they account for most of today´s runners, and included a group of athletes who are seldom studied: those who have never been injured.
“We can learn a lot from that group,” said Irene Davis, professor of Physical Medicine and Rehabilitation. “What are they doing right?”
Davis and colleagues recruited 249 female recreational athletes who each ran at least 20 miles a week. They investigated the participants´ strides and collected data from a monthly online questionnaire that detailed injuries over two years.
First, the researchers looked at reports from the 144 runners who experienced a mild injury and the 105 who didn´t, finding little difference between the two large groups.
Next they analysed the smaller groups at the two extremes of the spectrum: those who had been injured seriously enough to seek medical attention and those who not only went uninjured during the course of the study, but who reported never having been injured.
This revealed significant differences between the two groups in a variable called “vertical average loading rate”, which was highest in the seriously injured runners and lowest in the uninjured group.
The key difference relates to the suddenness of impact, with a softer footfall appearing to reduce the likelihood of injury. Weight of the runner was not a factor, Harvard Medical School noted, with heavy runners among the light-footed and lighter runners among the stompers.
Previous studies have shown that one potential way for runners to try to reduce the chances of injury is to adopt an impact-absorbing forefoot strike. But even the committed heel-striker can learn from the softer landers, Davis said.
For example, their soft-landing steps tend to be very quiet. Davis advised runners to take out the earbuds and pay attention to the sound of their footsteps.
“If you land louder, it´s harder,” she said. “It´s work, but you can make your foot-strikes softer.”