The last post I mentioned the Variability Index (VI) found in your power file summary. That led to a few questions about some of the other data points in the file and what numbers are important for most athletes to look at. To start, let's dive into Average Power (AP) vs. Normalized Power (NP).
Below are two typical 1 hour workouts that most athletes perform: a Threshold (2 x 20 min) and a Vo2max (8 x 2 min). By using these two very different types of workouts it will help us see how the structure of a ride affects both the Average and Normalized power numbers.
Let’s start with Average Power (AP) which is simply the average power for the duration of the ride; how many watts you produced over the given time. It is 100% mathematical and it does not take into consideration how the watts were distributed throughout the workout. If you look at the workouts above you can see that Workout #1 produced a higher AP than Workout #2. If you solely used the Average Power as your guide it would lead you to believe that Workout #1 was more demanding on your body.
Normalized Power is a bit more complicated to understand because it is showing the physiological cost of the workout. It is projected using a formula that takes into consideration how the watts were produced, it is basically taking into consideration how hard the interval was and how much rest followed it. If you look at the files above you can see that both workouts produce a very similar NP of 228 watts and 230 watts. This means the physiological cost of both workouts were equal to having your trainer set on ERG at 228/230 watts for an hour. So by using the NP we can see that both of the workouts were equally demanding on your body.
In a nutshell the AP is the actual mathematical average power you performed for the workout and the NP is the average power your body “feels” like it held for the workout.
Now this part is very important; DO NOT confuse physiological cost with physiological benefit. The two workouts above have the same physiological cost but they do not lead to the same physiological benefits (adaptations). Both of the workouts do provide a benefit but they each are targeted towards different energy systems and will provide different physiological benefits. Same physiological cost, different physiological benefit. Similar recovery needs, different results.
Bottom line is that the Normalized Power is the number to look at to have a better understanding of how hard/taxing the ride was. It will give you a better understanding of the physiological toll it took on your body and help you better understand the recovery that is needed. The Average Power is not as helpful as a stand alone number but can be useful in conjunction with other data points to give us additional information.
Keep pedaling,
Brian Hammond