Originally Posted by The Historian
The bridge: Everybody does this one, and it regularly appears in articles on exercises for cyclists. Lay on an exercise mat, face up, feet on the exercise ball. Raise your torso so you form a bridge between your shoulders and your feet on the ball. Keep the motion steady. Hold for five seconds, release, and repeat for a set of 12 reps.
This exercise can also be done without an exercise ball. Lay on an exercise mat, face up, knees bent, feet flat on the mat. Raise your torso so you form a bridge between your shoulders and your feet. Keep the motion steady and don't sway side to side. Hold for five seconds, release, and repeat for a set of 12 reps.
And another:
Marching in place. This helps stretch the hip flexors. Lay on your back, knees bent at a comfortable angle, feet flat on the floor. Raise one leg as if you were marching, raising it as far as you can without bringing your butt off the mat. Return leg to starting position. Alternate legs.