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Some studies have suggested that a higher impact loading rate, or how quickly the impact of foot strike is spread to the foot and lower leg, can increase risk for stress fractures, especially in the tibia, the larger of the two shin bones. In the new study, French and Canadian researchers measured the impact loading rate in a variety of scenarios in nine runners who usually run with a heel strike.
For a baseline measurement of loading rate, the runners ran at their normal pace with their normal gait while wearing conventional motion-control shoes (a French model, the Kalenji Kiprun 2000). Then the researchers measured loading rate under four other scenarios: having the runners switch to a racing shoe that's 5 ounces lighter than the training shoe (the Kalenji Insipid Comp); having the runners increase their turnover by 10%; having the runners switch to a midfoot strike; and doing all three of the preceding changes at once (what the researchers called "combi").
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When the runners switched to a midfoot strike, or when they ran in "combi" mode, they no longer produced an impact peak (a spike of impact concentrated in a fraction of a second), and they reduced their overall loading rate by about 50%. Only increasing turnover, or only switching to the racing shoes, didn't produce these changes. (It should be noted that the racing shoe used in this study has a heel-to-toe drop of 10 millimeters, which is 2 millimeters higher than that of the training shoe used. A larger heel-to-toe drop is often associated with a higher impact peak.)
The takeaway is that a midfoot strike by itself is as effective as midfoot striking with higher turnover in racing shoes in reducing impact loading rate; theoretically, this finding should be of most interest to runners who have a history of shin stress fractures.
Blaise Dubois, a Canadian physical therapist who was one of the study authors, is quick to caution that this study doesn't mean all heel strikers should suddenly start forcing themselves to become midfoot strikers.
"Every change—shoes, cadence, biomechanics—can cause injuries if the transition is done too quickly, and the 'gradual' of my patients is not always gradual enough," Dubois told Runner's World.
Dubois prefers changes that more organically encourage better running form, such as shoes with a low or no heel-to-toe drop and strengthening the feet and lower legs, over consciously making a change that one's body isn't ready for. In the study, the runners' loading rates were measured only during 5-minute bouts of running. A runner who usually heel strikes but who consciously switches to a forefoot strike for a more typical training run would likely wind up with compensatory pain or even injury elsewhere. As the study authors wrote:
"[A]dopting a [midfoot strike] style for longer periods of running and/or in the long-term training process may induce a higher load on the forefoot and midfoot joints than during the acute 5-min conditions tested here."
Dubois also cautions that runners currently dealing with acute foot or lower-leg problems should get over those injuries before making a concerted effort to change their running form.
Scott is a veteran running, fitness, and health journalist who has held senior editorial positions at Runner’s World and Running Times. Much of his writing translates sport science research and elite best practices into practical guidance for everyday athletes. He is the author or coauthor of several running books, including Running Is My Therapy, Advanced Marathoning, and Meb for Mortals. Scott has also written about running for Slate, The Atlantic, the Washington Post, and other members of the sedentary media. His lifetime running odometer is past 110,000 miles, but he’s as much in love as ever.
