Completing an ideal FTP test can be a very elusive challenge. Go too hard and you blow up. Go too easy and you wind up with a too-low FTP. Either way, you end up with an FTP that is lower than your true capabilities. Here are a few pointers to help you find out if your FTP is set too low.
Rest intervals are too easy
The TrainerRoad interval workouts are designed to push you to the point where you need those rest intervals. If you come to the rest intervals but you don't feel as though you need the recovery time, then your FTP may be set too low.
Over-unders are not exhausting
An over-under workout forces you to play jump-rope with your FTP line in an exercise of pain and suffering. These workouts are known for pushing you to the limit both physically and mentally. If you are completing the over-under sets with minimal emotional trauma, then your FTP may be set too low.
Long threshold intervals are too easy
If you can sustain 40 total minutes at FTP, even done over the course of several intervals, with minimal rest and minimal feelings of despair, then your FTP may be set too low.
Takeaway: Interval training should be hard, so if you are never struggling with completing your workouts, then your FTP may be too low.