How To Measure Aerobic Fitness Improvement

How To Measure Aerobic Fitness Improvement

In this post, how to measure improvements in your aerobic fitness, to gauge whether your training is improving your fitness.


Improving aerobic efficiency during the pre-season is paramount for a steady ramp of fitness throughout the season and regular field testing plays an important role in measuring how these improvements are progressing. Along with a 20 minute Functional Threshold Power test, cyclists should also look to introduce another key test into their training plan. This is a ‘rate of decoupling’ test. This is a test almost everyone can do, provided they have an input and an output measurement, like heart rate and power, and doesn't require a lab or another person to assist you. Let's get into it...


Decoupling refers to measuring a variable relative to a constant, such as HR relative to wattage and looking at the change over time.

By standardising the length of the test based on a length of time of the athlete’s competition, it’s quite simple to measure if the athlete is aerobically fit enough for their chosen cycling discipline.

For instance, a road cyclist whose race is typically around 3 hours in length would need to show aerobic fitness for that duration before moving on to focus on anaerobic capacity workouts or other high levels of fitness.


So, what does aerobic fitness look like and how can the athlete or coach work this out? The answer is to start by using a power meter to accurately quantify the intensity of the test. Then, using a HR monitor to record the input measurement, ride at a steady wattage or HR for the goal duration (e.g. 3 hours).


After completing the workout, take the file and start by dividing the HR number by the wattage number. Then apply the same calculation to the second half of the workout. Subtract the first half figure from the second half figure and then divide the remainder by the first half number. Finally, multiply this result by 100 to get your decoupling rate as a percentage. An example could be:

220/135 = 1.62

215/134 = 1.60

1.62-1.60 = 0.02

0.02*100 = 2 (This example athlete would have decoupled 2% during this test)



For an aerobically fit athlete, we should be looking for a figure of around 5% or less for the goal duration. If the figure is more than 5%, then it is likely that more time needs to be spend on building aerobic efficiency by riding long duration workouts at around 60-75% of Functional Threshold Power. Handily, if you're using an app like TrainingPeaks, this measurement is calculated for you every ride as long as you have HR and power data to analyse and it's labelled Efficiency Factor. 

This is why it’s so important to do regular FTP testing, to ensure that the training zones anchored around it are accurate.

Depending on time until the first major goal, an athlete or coach should assess whether to continue aerobic efficiency building by raising the wattage number they are exercising at or move on to the higher level abilities as discussed above.


It is worth bearing in mind that this test may not always be 100% accurate if conducted under different conditions, as heart rate can fluctuate quite considerably for a number of reasons, including stress levels, sleep quality and temperature. Even so, this is an effective and relatively non-stressful test and cycling tip that can really help athletes and coaches determine how their fitness is progressing and where they are in relation to where they want to be.

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