Two sets of 4 6 second sprints. Only this time first come to a complete stop and then start sprinting for only 6 seconds. Try to choose a gear that brings you to more then 100 rpm after 5 seconds when you go all out and without shifting gears.
Explore this cycling workout
Try the JOIN cycling app to export the workout to Zwift, Garmin, TrainingPeaks and Wahoo.