The test: To understand if the ACTN3 protein affects running ability, researchers conducted a test. They recruited a group of competitive runners and measured the level of ACTN3 protein molecules each runner had in their bodies. Then, they had the runners participate in a sprint (a short-distance run). During the test, the runners sprinted as fast as they could for 100 meters. Scientists found that the runners who sprinted the fastest had the highest amount of ACTN3 protein molecules in their bodies.