The experiment was designed to test a theory in motor learning that distinguishes between directing your focus internally or externally. A large body of research suggests that focusing externally, on the consequences of your actions rather than on the actions themselves, produces better results. For example, you’ll do better shooting a basketball free throw if you’re told to focus on seeing the ball go through the rim than if you’re told to focus on the angle of your elbow or the motion of your wrist. Focusing internally on the details of your movements disrupts the “automaticity” of these familiar actions.
I’ve been thinking about this since I mildly injured my knee a couple months ago, trying to diagnose what may or may not be wrong with my stride or cadence that could’ve contributed. This research makes sense to me intuitively that overthinking form in a running stride, golf swing, or basketball shot could force you to overemphasize a particular phase of the motion. The caveat the article points out is that this holds true for experienced runners tweaking their form. If you’re a novice or have never really learned proper form to begin with, the risks of changes negatively impacting performance are lower.