Long - 6 x 4000m cadence increase 75-90 / 2 min easy
Ride six 4000 meter pieces. In each piece, ride the first 2000m @ 75 rpm. Then 1000m @ 80 rpm, 500m @ 85 and 500m @ 90. Ride for two minutes easily during the rest period.
Check this Concept2 workout on the ErgZone app: