Triathlete on a turbo trainer
Triathlete on a turbo trainer
Training > Bike

What's the difference between average power and normalised power on the bike?

Rob Banino explains how average and normalised power differ and why it's normalised power you want to monitor

Average power is exactly what it sounds like: the average wattage produced over the course of a ride. The trouble is, average power isn’t necessarily a real indication of the work-rate you’re able to maintain. Yes, average power is affected by changes in terrain and wind resistance, but it doesn’t take into account the effects they have on your ability to produce watts. 

That is, producing an average power of 250W for an hour’s ride on a flat road is a different proposition to producing a 250W average for 60mins in the hills. The figure may be the same, but the effort required is vastly different.

The harder you have to work to keep your wattage up, the greater the toll it’s going to take – and the quicker you’ll run out of steam. And since average power doesn’t take those physiological effects into consideration, it’s not the best reference to use when planning a pacing strategy.

And that’s where normalised power comes in. It’s like average power but a little more complicated. It calculates your average wattage, but incorporates adjustments for how your body responds to the different intensities of work. In other words, normalised power accounts for the cost of your exertions. As such, it gives you a figure that more accurately reflects the wattage you can realistically maintain for a particular ride, which makes it very important for pacing. 

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David Waring

I'm not sure I really understand this explanation. I thought normalised power was basically an average power calculation which excludes any periods where the power output was zero, i.e. coasting downhill. Am I wrong?

HarryD

David, sadly yes. NP takes the average power then adjusts it for the peaks and troughs of say, going up or down hill. But it does this taking into account the physiological cost to your body.
So if you average 150W for the ride, but go uphill at 200W there is a physiological cost, if you were to go up at 250W the increase in cost is greater than twice the increase to 200W. Increasing power has a disproportionate physiological cost. NP takes this into account. As you go downhill and the power drops below average the physiological cost reduction isn't as great as the same increase by going above average. NP also takes this into account. By its nature physiological cost is more of an estimate than a precise calculation.
Thats my understanding anyway.

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