WU: 15' - nice smooth spinning.
MS: Then shift into a the big chain ring and into a gear that allows you to spin at about 65-70 RPMs. You will spin 3x15 minutes in this gear - HR should be mid-high Z2 - recovery will be 5' easy between sets - you will probably see HR drift into Z3 - keep the cadence up - this is where you build strength.
10x50 Z4 on 20" rest
10x50 Z5 on 30" rest
10x50 = sprint 25, easy 25 on 15" rest.