Normalised power (NP)
NP is an important metric for all cyclists, but especially cyclocross riders, when trying to analyse race and training data. While it is a fairly complex algorithm, I will try and explain it in simple terms and debunk the many common myths surrounding this number everyone sees after training.
Basic average power is a very simple way of calculating and understanding the highs and lows of an effort over a given time. However, it is very limited in telling the athlete about the real stress they have put their body through with different types of sessions.
Here's two examples to try and explain the differences in real terms: First, let's look a steady 1 hour ride on the turbo trainer with little to no variation in power output at an average of 200 watts. This may well be a fairly easy ride for most athletes.
The second session is again an hour in length and an average power of 200 watts. However, this ride is completed as 15-60second bursts around 400w with recovery sections way below 200 watts. On paper, the initial analysis might show the rides had the same training effect on the athlete... but we all know this wouldn’t be the case. The variable power ride will carry a much higher physiological cost.
As you can see, this example illustrates the limitations of average power and why NP is used to capture a more sophisticated picture of some training sessions.
Normalised power is a great way of understanding the stress of a workout. Stress scores of sessions can be used as the building blocks for building a training plan and understanding the load on an athlete.
Training stress score (TSS)
This is a single number calculated for any individual training session. Taking into account duration and intensity, it is modelled off of the heart-rate-based training impulse system which pre-dated TSS. One hour spent at FTP is equal to 100points.
TSS scored from a power meter is the most accurate form of calculating the figure however there is also hrTSS based off of your threshold heart rate or rTSS which is based off of your threshold running pace. Normalised power and intensity factor are both used to calculate TSS. Now that you know about NP, let me explain intensity factor.
Intensity factor (IF)
For any workout (or part of workout) you can see the intensity factor score. This is the ratio of the normalised power to the athlete’s functional threshold power, which gives the athlete a relative intensity to their own threshold power. A score of 1.0 would mean the rider was riding at their FTP for the given period of time.
Watts per kilo (W/KG)
This is also known as your power-to-weight ratio. It’s a great way of comparing riders of different weights and comparing efforts over different lengths of time. Quite simply, it is your power in watts divided by your body mass in kilograms. For example, an 80kg rider with a FTP of 280watts has a power to weight ratio of 3.5 watts per kilo.
Training Peaks performance management chart (PMC)
Finally, a lot of the information calculated above is put into the PMC. This is the main graph on Training Peaks and tracks fitness and form over time. Using daily TSS scores, it calculates your acute training load (ATL) and chronic training load (CTL). There is a much more complicated algorithm to it, but in everyday terms, the ATL is a 7 day rolling average and the CTL is a 42 day rolling average.
These two figures lead to a final plotted line called ‘Form’- which is CTL minus ATL. So, if you have done more ‘work’ in the last 7 days than the previous 42, you will have a negative 'Form' number to indicate that you are tired. In the algorithm, the ATL holds more weight into the calculation, so your day-to-day form is obviously affected slightly more by what you have done recently compared to long term.
There are goal numbers for different types of athlete in terms of CTL and each individual rider performs differently at different ‘Form’ numbers. Working out your best combination is important if you are going to use the graph to monitor and predict form on a given day.
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