Colosseum -4 is 60 minutes of aerobic Endurance ranging from 50-60% FTP. Improvements in aerobic endurance & efficiency are the aim when working at a moderate intensities well below lactate threshold. By sustaining this effort level for fairly long and sometimes quite long, minimally interrupted periods of time, your body will improve its aerobic capabilities thereby improving your level of power output at low-to-moderate levels of exertion. Greater aerobic efficiency (your ability to better utilize oxygen to turn over ATP) means you can work harder before dipping into your far less sustainable sugar stores and preserve those stores for the higher-intensity efforts. This also means you'll require less food to fuel your effort during your events. Try to maintain a cadence between 85-95rpm. https://www.trainerroad.com/cycling/workouts/1035877