These seven key power meter terms will get you up to speed fast and start unlocking the potential of training with power.

Triathlon training with a power meter can seem daunting at first but don’t be put off by all the seemingly complicated spreadsheets, figures and acronyms. By concentrating on a few key metrics, you’ll start to understand just what a valuable tool your power meter is beyond showing your watts.

These seven power meter terms will help you get a better sense of your current fitness as well as your progression, race pacing and even when to top-up on nutrition. To access this data post-ride, you’ll need an online service or other computer software. Free training logs like Garmin Connect feature some of these power meter terms, while more advanced options like Training Peaks – our go-to choice – have them all. You can also use offline software such as RaceDay Apollo or the totally free Golden Cheetah.

FTP – Functional Threshold Power

Your FTP (Functional Threshold Power) is one of – if not the – most important figures in your power training toolbox. It’s the maximum power you can sustain for an hour and is used to set your training zones, plan pacing strategies and show fitness increases – basically, it’s the number that anchors all your power training.

Completing a 20-minute FTP test will give you your FTP figure so you can set your zones and improve the specificity and quality of your bike training.

Focus on: regular FTP tests every four to six weeks to judge improvement.

NP – Normalised Power

NP (Normalised Power) is a method of calculating a ride’s average power while taking into account the variance in power over different terrain – meaning zero power when freewheeling or the additional wattage needed to get over hills are accounted for.

This makes it the best figure to judge your performance ride-to-ride as well as staying in your zones when hills would skew your regular average power figure. It also means you’re not chained to repeating exactly the same ride to judge improvement over time, allowing you more freedom to keep training interesting by riding different courses while still gathering useful data.

Focus on: gradually increasing NP overtime when riding over similar durations and using NP to ensure you are sticking within power ranges for your session type.

IF – Intensity Factor

Your average power divided by your FTP equals your IF (Intensity Factor) – effectively the percentage of your max hour power expressed as a decimal. It’s a quick view of how hard you’ve ridden and great for pacing.

For example, in his superb book The Power Meter Handbook, triathlon coaching guru Joe Friel suggests the following intensities for triathlon bike legs in order to conserve enough energy for the run.

DistanceIntensity Factor
Olympic and Sprint0.90-1.04
Ironman 70.30.70-0.79
Ironman0.60-0.70

Focus on: finding the IF you can sustain for the duration of your goal event while being able to run afterwards.

VI – Variability Index

NP divided by average power equals your VI (Variability Index), which gives a figure of how well you’ve paced a ride. Unless you’re at the pointy end of the race, where surging and other tactics come into play, a triathlon bike leg should be a solo time trial and judging an even effort is crucial to avoid going out too hard or not reaching your potential.

When it comes to VI, the lower the figure the better – attack hills or put in big surges and it’ll rise. Below 1.05 indicates perfect pacing and should mean you get to the run with fewer matches having been burnt.

Focus on: riding steadily without surging to keep VI low.

Understanding power meter terms can take your training sessions to the next level.
Understanding power meter terms can take your training sessions to the next level. (Photo: Beau Runsten, Unsplash)

EF – Efficiency Factor

By dividing NP by your average heart rate, you get your EF (Efficiency Factor). This figure indicates how efficient your aerobic system is – the higher the number, the better your aerobic fitness. Therefore, after regular Zone 2 heart rate rides over the same course and duration you should see your EF figure grow. If you’re following a traditional periodisation plan, once these numbers plateau, it’s time to move onto harder efforts.

Focus on: consistent aerobic training over a race-applicable duration to steadily increase EF.

Aerobic decoupling

Decoupling – shown as Pw:Hr in Training Peaks – is the relationship between power and heart rate. After you’ve been riding for a while at a steady intensity either your heart rate will rise in relation to power, or your power will drop off in relation to heart rate. By dividing the differences in EF from the first to the second half of an aerobic ride with a VI of 1.05 or less, you’ll get a percentage figure of decoupling, which indicates your aerobic fitness.

Looking at a ride graph, the point at which decoupling begins can also show you the limits of your current aerobic fitness in terms of duration – or signal that your energy needs aren’t being met, providing a cue for your nutrition strategy.

Focus on: regular steady aerobic rides (VI of 1.05 or less) with until decoupling is consistently less than 5%.

TSS – Training Stress Score

A combination of duration, NP and IF give TSS (Training Stress Score) for each ride. The more stress your body is put under – either by higher intensity or longer duration – the higher your TSS score will be. TSS can be used to plan and monitor your workouts and recovery to help improve your fitness while also avoiding becoming too fatigued.

Focus on: coping with higher scores week to week without overdoing it.

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