Micro Intervals simulate the demands of racing. In this video Power Education Specialist Benjamin Sharp explains how to athletes preparing for an event, but haven't the opportunity to ride in a group or to do training races beforehand can get the intensity. Micro intervals are a great way to jump start the system to simulate the demands necessary during a race.
Most often Benjamin Sharp prescribes micro intervals that are 10-15 minutes sets of 15 seconds on and 15 seconds off. The ON portion is VO2 (zone 5) and the OFF portion is a little below your FTP (zone 3). Then you "simply" follow this ON/OFF pattern continuously for the entire 10-15 minutes. Note, that you are never at rest during this 10-15 minutes.
These micro intervals are to be performed on flat to rolling terrain so you can stay in the same gearing/cadence throughout the entire interval. That means you won't have to shift as you switch from the ON to OFF portions. Rather, during the ON portion you'll accelerate and increase power and cadence and during the OFF portion you'll ease up, decreasing force and reducing cadence.
The most important part of these intervals is to make sure you're hitting the zones during each portion. This means not over powering the ON portions to the point at which you're having to reduce your power below Zone 3 during the OFF portions.