In a 2005 study, researchers at the University of Cape Town switched 16 experienced triathletes from a heel strike to a forefoot strike and gave them 12 full weeks to practice their new running style under expert supervision. At the end of those 12 weeks, the subjects were still less economical than they had been with their natural footstrike.
So what happens when runners are left alone and allowed to train with their natural stride? An answer to this question comes from a 2012 study led by Sharon Dixon of the University of Exeter, England. Dixon and colleagues measured changes in a number of stride features as well as changes in running economy in a group of 10 beginner female runners. These women trained for 10 weeks without any technique instruction. They just ran. During that period their running economy improved by a massive 8.4 percent. This improvement was associated with no fewer than seven subtle changes in the women's stride characteristics that they couldn't possibly have been conscious of.
Taken together, the evidence that 1) all forced changes to running form worsen economy and that 2) just running without thinking about form improves economy indicates that the human running stride is self-optimizing. In other words, just as the running coaches of the old days suspected, each runner automatically develops the stride that is most efficient for him or her, just by running.
More: 7 Lower-Body Exercises to Improve Running Economy
Exception to the Rule: Injury Prevention
Does this mean that you should never consciously alter your stride under any circumstances? Not quite. While departing from your natural form for the sake of better performance will get you the opposite of what you seek, if you're injured, making a targeted adjustment to your stride mechanics may help you avoid a recurrence of the same injury.
More: The 4 Best Form Drills to Improve Your Running Technique
Research by Irene Davis of the Harvard Medical School and other biomechanists has shown that certain common overuse injuries, such as patellofemoral pain syndrome, or runner's knee, are associated with particular idiosyncrasies in a runner's stride. In the case of runner's knee, the biomechanical cause is often a knock-kneed running style caused by internal rotation of the thigh. Davis has succeeded in helping chronic sufferers of runner's knee overcome the problem by teaching them to run with their knees slightly wider apart and their kneecaps pointing straight ahead.
If you are injured, it might be a good idea to work with a physical therapist with expertise in gait retraining for injured runners. Otherwise, leave your stride alone and let it evolve naturally.
More: How to Treat and Prevent Running Injuries: Runner's Knee
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