One of the ways cheerleaders get the crowd excited is by doing elaborate stunts that often involve lifting a girl to an elevated position. This takes coordination as well as strength, since often the "flier" is elevated above the heads of the "bases" who hold her. Since the arms are typically a lot weaker than the legs, the bases need to recruit leg strength using the "pop" maneuver. The extension is a common stunt that requires the leg pop and at least four cheerleaders.
Stand the two bases facing each other, roughly 2 feet apart. The flier stands perpendicular to the two bases, placing one hand on each base's shoulder. The spotter then stands behind the flier. Throughout the maneuver, the spotter should have her hands nearly touching the flier's waist and should count the numbers loudly in case the other members of the squad stop counting.
Start counting by having the entire squad say "one" as the bases bend into a half-squat, tuck their elbows into their sides and extend their hands out, palms up, with the hands about 2 inches apart.
Say "two" as the flier places some of her weight on the bases' shoulders and steps onto the hands of one of the bases. Count "three" as the flier puts her weight onto that hand and presses upward against the bases' shoulders.
Count "four" as the flier steps her other foot onto the hand of the other base. The flier should crouch into a partial squat at this point.
Count "five" as the bases stand up in unison -- a basic pop -- make eye contact and brace themselves for the next step, which will involve the more significant "pop."
Count "six" as the bases simultaneously dip into a lower squat, and then count "seven" as the bases pop their legs upward so that they're standing with both legs straight, while at the same time straightening their arms overhead, thus raising the flier to an elevated position. When you're holding the weight of that flier, the pop helps recruit the strong muscles of the quadriceps and gluteals to get the flier up.
Count "eight" as the flier puts her hands into a high V a T, or another position designated by the coach. At the same time, the spotter should extend her arms overhead and grasp one wrist of each base to provide extra stability.