One of the major reasons behind the recent peak of interest in single leg training (i.e. lunges, single leg RDLs, etc.) is these movements’ activation of your glute muscles (i.e. your butt). This glute strengthening isn’t to impress your significant other, or pass the Functional Movement Screen (see Sparta Point 11/6/09), but this ability allows athletes to set up the initial portion of an explosive movement.
Baseball pitchers start by balancing on one leg, the squat begins by slowing pushing knees out, the volleyball approach jump is initiated by loading the heel, and the examples of initial glute activation goes on and on. Our athletes are always amazed by how much more explosive movements are (i.e. faster sprints, higher jumps, etc.) when they start slower, due to increased stability from their butts.