Midfielders don’t improve by only playing soccer. Neither do wide receivers by only playing football or swimmers by only swimming. So why is it that many long-distance runners think the key to becoming a better runner is, well, only running? According to University of Montreal researchers, progress may come from an unlikely source —plyometrics. They had 35 male runners engage in an eight-week endurance-training regimen, with one group also doing plyometric training and another group adding in dynamic weight training. The results, published in the July 2010 issue of Journal of Strength and Conditioning Research, show that the plyo guys experienced the biggest benefit with regard to the energy cost of running. (In other words, they could run without sapping as much juice.) So if you’re prepping for a 5K, 10K or marathon, don’t just run — mix in some explosive training and leave your Kenyan rivals in the dust. Theoretically.