What's a timetrial in indoor cycling?

A time trial is basically a fast flat, but more intense, and has more shape to it:

• It imitates the training effect of a timetrial on the road.
• A timetrial is where you’re maintaining your highest power for the duration of the interval.
• Whereas a road timetrial has a fixed distance over a fixed route (eg 45km), the studio timetrial is a fixed time (eg 4minutes).
  
• Why you might want to use it: it’s great for muscular endurance and also good for building aerobic capacity, burning fat (although I wouldn’t use it in a class where you tend to get new people, because it’s intense and quite intimidating).
• How to instruct it:
  • Let riders know how long it is and the cadence
    
  • Tell them that they should be riding with (depending on the capability of your bikes) maintaining the highest level of resistance they can for the duration or the highest power output (FTP) or get them to reach a particular heartrate target, eg 84-86% and then keeping the resistance level where it is (due to cardiac drift, their heartrates will increase a little from this point as their muscles tire, but the challenge is to keep the same level of resistance right the way through).
• Where to put it in your session: usually you’ll want it in your second half or towards the end of the session as it’s a hard challenge and you wouldn’t normally want to tire them out early. You might want to tire them out if you’re wanting to build anaerobic capacity, but most riders don’t really need this.