This 20 min interval train will provides you normal warm-up, and subsequent cycle between equal intervals (30 sec.) of biking at max depth and biking at a restoration depth.
Quick depth is biking at 90-100% of your maximal exertion, with heavy respiratory. Be happy to extend resistance /stress in your gadget.
Sluggish depth is biking at 50-60% of you maximal exertion.