Why do we use Normal Power (NP), Intensity Factor (IF) and Training Stress Score as measurements in Cycling?

Posted Wed, 14th May 2014

Normalised Power
Most people will probably look at Average Power as the metric to see what they were roughly putting out during the course of a ride. However, a measurement that isn’t usually calculated on Strava or other fitness apps is Normal Power. This algorithm was created to take into account the average power but adjusted for the range of variability during a ride. This measurement is therefore a better reading of the effort and metabolic cost of a ride than average power.

Over two rides, average power might come out the same despite being very different workouts. If one is a short hill climbing session and another is a long endurance ride, the average power might come out roughly the same. The Normalised Power measurement will take into account the differences in power, weight, gradient, intensity and combine that to create a measurement that is a more realistic insight into the training sessions. This is why Normalised Power is a far more effective way to measure your average power.

Intensity Factor
One of the most important aspects to training is how hard you ride, or the 'intensity' of the session. It most certainly isn’t about how long you ride, which is what most athletes believe to be the marker for greater fitness. The distance you do each week has much less of an impact on your fitness than the intensity of your individual workouts.

If I told you that I rode for an hour at 150 Watts, would you know what that meant? Most likely not as you need to be able to compare that to something. With an FTP test we have a measurable number and it allows us to compare the intensity of our workout. If my FTP is 300 then an hour at 150W is 50% and a zone 1 workout. This is therefore a low intensity workout. To get our Intensity score I would divide my average power by my FTP. This ride would have a score of 0.50 which is a 50% ride but if I rode at an average of 288W then my score would be 0.96 or 96% which is a very intense workout. Anything heading above 1.2 -1.5 is a very intense workout and should only be repeated a couple times a week.

Training Stress Score
When Training we want to make sure that we are training in an efficient manor, meaning that we aren’t ‘over fatiguing’ ourselves. The amount of work you do, it’s intensity and duration will have an impact on your body. This impact comes as ‘fatigue’. We need to make sure that our training is done at the correct levels so that we maximise our fitness but also compensate with rest, to increase our gains, with minimal fatigue.

This is where all the other factors that I have discussed come in to play. FTP, IF and NP are all part of the TSS formula to give you your Training Stress Score (TSS). The TSS is a way of mathematically calculating the duration and intensity of a single workout to produce a number or ‘score’. Every time you workout this score is added to the previous one to give you a cumulative score.

By monitoring this number you can gauge how hard you are training and can really periodise week by week, however that is another blog altogether!

By utilising our indoor facilities we can monitor all of these numbers and actually help to make sense of all this science!

Ride the Bright Way!

Graham Dawson


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