I am a big fan and user of the Precor ellipticals at the YMCA here in the Bay Area. I know why my hip flexors are stronger, but why are my lower abs getting a workout?

The moving platform requires that the abdominals stabilize the torso. Some stability can also come from the hip flexors as they compensate for any remaining instability. Therefore, both muscle groups get worked. This is especially true at the lower ramp and resistance settings when you can really mimic a running motion.

- Emily Cooper, M.D.