Get tighter buns, zero running required.

This exercise from fitness instructor and TV personality Brooke Burke-Charvet involves zero running and works your butt, quads, and hamstrings.
Here's how to do it: Begin in a runner's start position, right foot crossed behind your left, knees bent and both hands on the floor. Keeping your hands on the ground, straighten your left leg as you flex your right foot and kick it straight back and up toward ceiling. Return to start. Start with 30 seconds per side and work up to a minute.

Try this move: Runner's Extension