Story by Sarah Portella, TWCP team member and coach at Bolton Endurance Sports Training
You look at your workout for the day and stare blankly at it. Described below it says something about your percent of FTP and then something about NP and TSS. What?! Whether you have been training with power for a while, or new to it, having a basic understanding of some of the terms can make your training much more beneficial. Four basic terms to know are FTP, NP, VI, and TSS.
- The most common term to know is FTP, or Functional Threshold Power. Basically this is the maximum power you can hold for one hour without fatiguing. Your coach most likely had you take a 20-minute effort on the bike to come up with this number. A few calculations later your training is now broken down into training zones based on this, your FTP.
- NP, or Normalized Power represents the effect of a lot of different variables during a specific block or segment of a ride. For example, if you had a ride segment with many surges, that is going to feel harder than a steady, constant effort. Therefore, normalized power takes that (the surging) into account and can give you a better representation of your effort over that segment. This is used more frequently for segments lasting longer than 20 min. because potential differences are more easily appreciated.
- VI, or Variability Index, indicates how smooth or how variable your ride was. If you are Ironman distance training (or triathlon in general) the closer the VI number is to 1.00 (you should not go higher than 1.05 during this type of training) the better. 1.00 indicates that you maintained even, steady power for the duration of your ride. Now, if you were racing a criterium, your VI would be much higher because of the surges throughout the race. A criterium VI may look higher, such as 1.10-1.2.
- The final term we’ll discuss is TSS, or Training Stress Score. Training Stress is the physiological cost of training on the body. For example, a workout with a TSS of 150 is going to be much harder than a workout with a TSS 70.
All of these terms can really help you maximize your training with power and help you to better understand why your coach puts specific workouts for you on specific days. By staying within the training zones created from your FTP you can now train more precisely and see the gains that can be made. Happy Training!
A good resource, if you want to know even more about training with power, is Hunter Allen and Andrew Coggan’s book, “Training and Racing with a Power Meter.”