Impact forces decrease 14% with 10% increase in turnover.
See Scott’s post on Runners World regarding this new study in Medicine & Science in Sports & Exercise.
By Scott Douglas;
Published August 06, 2013
There’s increasing agreement among experts that people with chronic issues in a given body part might be able to get relief by altering their running form. New research out of the University of Wisconsin suggests that a quicker turnover could help reduce knee pain in chronic sufferers.
Thirty healthy runners ran on a treadmill at whatever speed they preferred. In the last five minutes of one run, the researchers measured the runners’ self-selected stride rate. Then, with a metronome to cue them, the runners decreased and increased their turnover by 10%; that is, they ran the same pace but while taking 90% and 110% as many steps per minute as they took at their self-selected stride rate.
For example, if Runner A’s self-selected stride rate at a certain pace was 165 steps per minute, she then ran the same pace while taking approximately 148 steps per minute (90% of self-selected rate) and just more than 180 steps per minute (110% of self-selected rate).
During the three runs at the different stride rates, the researchers measured joint forces, knee angles and other biomechanical data.
When running at 110% of their normal turnover, the runners experienced 14% less peak knee joint forces. This coincided with less knee flexion during the runners’ stance phase (when their foot was most fully on the ground). The researchers speculated that this change in form as a result of increased turnover was the primary reason that loading forces on the knee decreased.
“Hence, step rate manipulation could be an effective way of addressing [knee] pain that arises from excessive joint loading,” the researchers wrote.
There are at least two important things to keep in mind about this study.
Perhaps most significantly, the runners who were tested didn’t report having frequent running-related knee pain. So this study didn’t show that increasing turnover lessened knee pain in those suffering from it. Rather, it suggests that increasing turnover can reduce loading forces on the knee; that change, in turn, could provide relief for knee problems caused by the joint absorbing too much force. There are other ways to achieve the same goal, including losing weight and, according to some studies, running with more of a midfoot landing.
Second, less loading on the knee meant more impact forces elsewhere. Specifically, the runners’ hamstrings and rectus femoris (one of the four quadriceps muscles) experienced increased load when the runners adopted the 10%-faster-than-usual turnover. As we’ve noted with other form research, reducing impact forces in one site means increasing them at other sites. This isn’t necessarily a bad thing, especially when the other sites are better able to handle impact forces.
The research will be published in Medicine & Science in Sports & Exercise.
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