Here are a group of athletes performing Russian Kicks. We use this exercise often because it demands attention to so many qualities: coordination, strength, quickness, and endurance.
-the athlete's attention to leading each series with a new leg (otherwise you would always lead each new series with the same leg)
-the athlete's fight to maintain good alignment of their spine
-the athlete's fight to be light with every landing
-the athlete's fight to keep the pelvis stabilized and under the shoulders throughout the exercise
-a new leg position is added to challenge the coordination