If you're looking for an idea for a pro feature, have users calculate their stride length (they'd need to run say a mile and count their footsteps)
then convert that to a tempo in BPM for a desired speed (that's like a five minute math problem there, to quote my math profs, it's an exercise for the reader)
then convert that to a tempo in BPM for a desired speed (that's like a five minute math problem there, to quote my math profs, it's an exercise for the reader)
then play songs within 5% of that BPM.
Boom. Pace yo self.