For athletes with a coach/training plan/race targets, it doesn't, they ride hard with gears or without. For people riding for fun or fitness it means they have no granny gear with to winch themselves up the next climb.Chopper1192":34axgk2d said:By what mechanism does singlespeed riding improve either cardiovascularor anaerobic fitness?
So it makes them fitter.
Or you get better at walking.
(and most SS bikes have three "gears" - Sit, Stand, Walk)