Original sentence: Stride length is reduced, so to achieve competitive speeds, racewalkers must attain cadence rates comparable to those achieved by Olympic 400-meter runners—and they must do so for hours at a time since the Olympic distances are  and
Edited sentence: Stride length is reduced, so to achieve competitive speeds, racewalkers must attain cadence rates comparable to those achieved by Olympic 400-meter runners—and they must do so for hours at a time since the Olympic event are the 20 kilometres race walk and  race walk