What Is Normalized Power?

Normalized Power (NP) is a training tool developed by Cycling Peaks (Training Peaks).  It was developed to account for the variables associated with riding: wind, hills, sprints, steady state, etc.  Using average power does not account for these variables, however NP does.

The calculation of NP is rather complicated, however it is based on two factors:  First, the fact that physiological responses to rapid changes in exercise intensity are not instantaneous but follow a predictable time course.  Second, the fact that many critical physiological responses are curvilinearly, rather than linearly, related to exercise intensity.  Other than that, you can purchase the book if you'd like more details on the formula.

NP is the estimated wattage you would have averaged if you had pedaled smoothly for the entire effort.

"In other words, it is an estimate of the power that you could have maintained for the same physiological 'cost' if your power output had been perfectly constant (such as on a stationary cycle or ergometer), rather than variable." - Hunter Allen

Because NP accounts for all the factors associated with cycling, it is a more accurate measure of the actual intensity of a training session or a race.  Take a look at the screen shot below (it opens in a new window for a closer look).  This data is from the bike portion of a triathlon this past September.  Notice the three red arrows.  The one on the top left is pointing to the yellow graph line.  Notice the variability of my wattage.  Here's a quote from Hunter Allen's book:

"...the power line is very jagged and constantly fluctuating, indicating that this section of the race contained times of high wattage and times of low wattage....Since these changes from high power to low power occur so quickly, various physiological systems do not have enough time between them to recover.  Thus, although the muscles get shorter breaks, the overall body does not, and therefore, the body experiences the same amount of stress that it would if you did one hard constant effort" - Hunter Allen

The next two red arrows, bottom right, point to my average power and my normal power.  You will notice my average power (243 watts) is lower than my normalized power (257 watts).  Thus, the 'cost' to my body was equivalent to 257 watts.  The greater the gap, the greater the variability there is in the course.

So why is any of this important?  When using NP correctly you can better prepare the demands of your event.  In my example, the average power was 243 watts, however the normalized power was 257 watts.  Thus, when training for this event, I need to prepare my body for the true cost (257 watts) that I will experience during the race.

"Knowing the demands of your event is one of the key factors to training specifically for that event.  If you are a mountain biker and you are only training on the road, then most likely you will not be ready to handle the constant change in power, cadence, and speed that you will encounter in your next mountain bike race.  "  - Hunter Allen

That last quote is important because it helps explain why my extensive training for triathlons has really hurt my mountain bike performance.  I am no longer training strictly for mountain bike races, but instead for three events.  So when I enter a mountain bike race, I've dropped off the radar, yet in a triathlon, I can finish the bike in the top percentile.