Normalised / Average Power
I’ve been riding for several months now with the Garmin Edge 820 and the brilliant 4iiii Power Meter crank. A metric I have found very useful is Normalised Power. With the recent release of the excellent new Polar M460 (reviewed here) I thought I should write a few lines to explain this useful power measurement metric often referred to as NP
What is Normalised Power?
It is a power measurement metric developed by Dr Andrew Coggan and Hunter Allen (*1). The TrainingPeaks website gives us the clearest definition of Normalised Power as
Normalized Power (NP) An estimate of the power that you could have maintained for the same physiological “cost” if your power had been perfectly constant, such as on an ergometer, instead of variable power output. NP is used to calculate TSS (Training Stress Score)
Some examples highlighting the difference
Take a look at the following 3 different cycle training rides.
All rides are 1.5 hours. All rides have a recorded AVG Power of 150 Watts
- Aim to keep the avg 10s power @ 150W. Use your gears, cadence and effort to maintain 150 Watts throughout
- Cycle for 30 mins easy @ 125 Watts – then 30 mins harder @ 200W and finish with 30 mins easy @ 125W
- Cycle for 15 mins easy @ 75 Watts – then 15 mins hard @ 225W … repeat x 3 (easy 75W + hard 225W)
Ride 1) for many riders this would be quite easy. Pushing 150 watts throughout. This ride has the Lowest NP e.g 160W
Ride 2) is more challenging, but at least there is only 1 x harder effort in the middle. Moderate NP e.g 195W
Ride 3) is harder again. Yes, the 75 Watt recoveries are easy, but the 225W for 15 mins is far harder. Greatest NP e.g 224W
All rides are of the same duration and the same average power. However, the Normalised Power attributed to each would be quite different with Ride 1 being lowest NP, Ride 2 moderate NP and ride 3 the highest NP. They all have a very different physiological effect on the body and Normalised Power highlights this.
Normalised Power compared to Average Power
The figures below have been taken from my Garmin (not yet built up enough data on the Polar M460…) It is clear from the data below that some rides yield a normalised power in excess of 50% of the average power. These rides are generally interval sessions or, in my case, short power assaults on Strava segments. The normalised power figure is useful when comparing different rides e.g. weather, terrain, solo or group etc.
Power Graph of a High NP Ride
The graph below is the power graph of the session above with normalised power @ 212 Watts and average power @ 143 Watts. There are 5 x clear intervals of power pushing in excess of 400 Watts. The first and last efforts peaking around 750W and 640W respectively.
The training objective of this type of ride is to improve my short sprint power endurance (1 minute v hard). The day after this session my quads, buttocks and calves muscles all have that familiar post training ache. Suppose I’d ridden at a constant average power of 143 Watts without any sprints/interval efforts. Would I have aching muscles the next day? No. Would there be any training benefit to a 45 minute session at constant average power of 143 Watts? No. (0ther than a recovery ride)
How does it help training?
The Normalised Power figure is a great way of comparing dissimilar training rides. Helping a rider understand that different physiological systems have been trained is a great way of training smarter. If you’ve not taken any notice of NP before, now is a good time to start taking notice.
From my own training, the rides with Average Power close to Average Normalised Power tend to be cardiovascular / aerobic improvement rides. Those with an Avg NP in excess of 50% of the Avg Power are generally Speed Endurance sessions (intervals). Those in between tend to be my Tempo paced rides. That’s not necessarily going to be the case for everyone …. but it generally works that way for me.
Normalised Power is a useful metric for those looking to improve their cycling performance. Like all training metrics it should be used in conjunction with other training data such as heart rate, cadence, duration etc. The overall aim is to ensure a balanced training programme with a sensible split between work, progression, recovery and rest.
GPS Bike Computers with NP
Two of the best GPS bike computers on the market featuring Normalised Power are the Garmin Edge 820 and the new Polar M460. Pair these up with the power meter of your choice, I recommend the 4iiii Precision Power Meter crank.