↓ INTRO
↓ WHAT IS A CYCLING POWER METER?
↓ DATA ANALYSIS PLATFORMS
↓ BREAKING DOWN TYPES OF POWER AND HOW TO INTERPRET THEM
↓ IDENTIFYING TRENDS IN A POWER METER CYCLING FILE
↓ TRACKING AEROBIC FITNESS IMPROVEMENTS WITH EFFICIENCY FACTOR (EF)
↓ TRACKING DURABILITY AND ENDURANCE WITH PW:HR
↓ DETERMINING FUNCTIONAL THRESHOLD POWER (FTP) FROM A POWER FILE
↓ CONCLUSION

Intro

Cycling power meters have completely changed the way cyclists train. While cycling power meters have been around for several decades, it’s only been in the last 10 years or so that they have become commonplace for cyclists.

Now, the best power meters for cycling are affordable and user friendly, and they’re one of the best investments you can make. If you’re looking for speed, a reliable power meter is a better investment than a new set of wheels. A power meter doesn’t actually make you faster, but it will help you create a training program that will help you get to the next level.

A power meter will optimize your training, giving you tangible numbers so that you can know how much stronger you’re getting. You will be able to create training that is optimized to your strengths and weaknesses.

However, if you’re new to training with a cycling power meter, all the metrics can be a bit daunting. What does all this data mean, and how can you interpret the data to make informed decisions about your training? Read on!

WHAT IS A CYCLING POWER METER?

Power meters are devices that measure the power you put into the bike. They come in several different forms: crank-based, power pedals, or within a wheel hub.

Cycling power meter data is measured in Watts (W) and is the product of force and velocity.

W = Force x Velocity

Force (measured in Newtons) is a measure of how much pressure you are putting on the pedals. Velocity is a measure of how quickly you are turning over the pedals (also known as cadence). The harder and/or faster you pedal, the more power you produce.

This power meter data will transmit to a cycling head unit in real-time to give you feedback on how much power you are putting into the bike. You can then analyze this data with a number of different programs. Check out a suggestion on how to set up your head unit here.

In days past, cyclists would pick a segment of road to test themselves on or track their average speed to guesstimate whether or not they’d improved. The best part about a cycling power meter is that it is reliable no matter what. It gives you quantifiable data that you can use to track your progress.

DATA ANALYSIS PLATFORMS

To analyze your power meter data, you will need to upload it to an analysis software. There are many different power meter data loggers, but TrainingPeaks is the most common. Other programs, like WKO5, give you advanced metrics to delve into your data further.

For this article, we will go through the basic metrics in TrainingPeaks. However, many of these metrics or their analogs are also tracked in other platforms, so you will gain a good understanding no matter what platform you use.

BREAKING DOWN TYPES OF POWER AND HOW TO INTERPRET THEM

When you first upload your data to TrainingPeaks, you will notice a lot of different numbers! We won’t go over all of them here, but this will give you a good understanding of the most important metrics.

AVERAGE POWER

This one is pretty simple. Your power meter will track second-by-second data while you are on a ride. An average value is then calculated.

NORMALIZED POWER

Average power takes into account times where you are not pedaling, like coasting down a descent or rolling up to stop signs. (zero values). As a result, it is not always the best way to measure the strain of a ride.

For example, you could average 300 Watts for 15 minutes, and then coast at 0 Watts for the next 15 minutes to yield an average power of 150 Watts for 30 minutes… OR you could just ride steady at 150 Watts for 30 minutes. While your average power was the same for both rides, one was obviously a lot harder!!

This is why Normalized Power (NP) is sometimes a better metric for the overall strain of a ride. NP takes into account the variance between the fluctuations in a ride to give you a number that better matches your effort level.

See Also: Polarized Training for Cycling

For example, in a criterium, you will go from coasting through a corner to a full-on sprint repeatedly. Due to all the time spent not pedaling, the average power might not be anything crazy. However, the NP is probably going to be a lot higher due to the large variance between surging/coasting.

As you can see from this race, the average power was only 252 Watts, which would be low Zone 2 for this athlete, however, the NP was 336 Watts, which is 82% of FTP… for 5 hours. Ouch!

SHOULD I USE AVERAGE OR NORMALIZED POWER?

Average power works for steady efforts, such as an endurance ride or intervals requiring a steady power output. If the pace is steady enough, NP and average power will be nearly identical. For racing or group rides, NP is a better gauge of your effort.

INTENSITY FACTOR (IF)

Intensity factor is an easy way to determine the power zone and overall effort of a ride or segment. The equation for IF is:

Normalized Power (NP) / Functional Threshold Power (FTP)

Essentially what this number tells you is what percentage of FTP you were riding at. For example, if your FTP is 300 Watts and you did 290 Watts NP during a 45 minute criterium, it would come out as follows:

290 Watts / 300 Watts = 0.96

If your IF exceeds 1.0, you are riding above FTP.

VARIABILITY INDEX (VI)

Variability index is an easy way to see how variable your effort was throughout the ride. It is calculated as follows:

Normalized Power (NP) / Average Power

A larger discrepancy between the NP and average power means that the ride had a lot of surges and coasting. For example, a criterium could have a NP of 300 Watts, but due to all of the zero values from coasting, the average power was only 240 Watts. This equates to a VI of 1.25.

For endurance rides, we want VI to be as low as possible. A VI between 1.0 and 1.02 is a properly executed endurance ride. The effort for these rides should be steady, and anything above 1.02 indicates too much surging and coasting. Unfortunately, many riders never seem to get this right and miss out on the huge benefits of endurance rides

KILOJOULES (KJ)

Kilojoules measure the amount of energy expended for the ride. A higher average power means more energy expended. While KJs do not equate exactly to Calories (due to variability in efficiency), the number is a good estimate of Caloric expenditure of a ride.

IDENTIFYING TRENDS IN A POWER METER CYCLING FILE

Now that you know all about the basic metrics within a power file, we can go over some ways you can identify trends in your power data to make informed decisions about your training.

If you want one of our expert coaches to take a look over your power meter data and give you feedback on your training, take advantage of our Free Power File Analysis!

TRACKING AEROBIC FITNESS IMPROVEMENTS WITH EFFICIENCY FACTOR (EF)

Heart rate in conjunction with power can be a very useful tool to track fitness improvements. If your heart rate is lower at a given power output than previously, this indicates you have made fitness gains. Your body is not working as hard to maintain the same power.

Efficiency factor (EF) is the metric used to track this and it is calculated as follows:

Normalized Power (NP) / Heart Rate

A higher EF value over time indicates improved aerobic fitness. For example, you may do a 3 hour ride at 200 Watts with a 140bpm heart rate (EF = 1.42). A few weeks later, your heart rate at 200 Watts is only 133 bpm (EF = 1.50).

There will be some day to day variation in this due to fatigue, life stress, temperature and what type of workout you did. But EF is quite useful to track long term changes and trends.

TRACKING DURABILITY AND ENDURANCE WITH PW:HR

On a long ride as you get more tired, you will usually see a rise in heart rate relative to power, even if the power stays steady. For example, you might ride at 200 Watts for the whole ride. In the first hour your heart rate (HR) might be 130bpm, after four hours, it could be higher, perhaps 140bpm. This phenomenon is called “HR drift.”

This is completely normal and can be due to a variety of factors. As you progress through a long ride, your muscles will become fatigued and you will draw on additional muscle fibers to maintain power output. Neural fatigue can also cause a loss in efficiency. This decline in efficiency causes extra energy to be expended, and your heart rate will naturally increase.

Hot weather can be a very large contributor to HR drift. As your core body temperature rises, your body will have to work harder to dissipate that heat. Dehydration can further exacerbate this.

As your endurance improves, you can track improvements with the Pw:Hr metric in TrainingPeaks that finds the percent difference between your EF in the first half of the ride vs. the second half of the ride.

A large increase in heart rate and/or decrease in power in the second half of the ride due to fatigue will yield a higher Pw:Hr value. Over time, as your endurance improves your Pw:Hr should decrease and the difference between EF in the first and second halves will be smaller. If you can complete a 4+ hour endurance ride with <5% Pw:Hr, then you’re in great shape!

DETERMINING FUNCTIONAL THRESHOLD POWER (FTP) FROM A POWER FILE

By looking at heart rate and power meter data within a data file, you can get a pretty close estimate of a rider’s FTP without formal testing. This can be useful for athletes who are making rapid progress or those who do not wish to take time out of their training for frequent testing.

For a tempo or FTP workout, you should expect your heart rate to plateau after a few minutes. Your body has reached a state of equilibrium and can sustain this pace for quite some time.

You can see from the above chart that there is not much difference in heart rate between the beginning or end of the interval, or between the intervals. This indicates that the rider is below their FTP. This rider did these intervals at 345 Watts, so we know this might be close to where his FTP is.

The same rider did this over/under workout with an average power of 355 Watts. Notice the disproportionate increase in heart rate between the beginning and end of the intervals. This indicates that the rider was above his FTP. As his body began to flood with lactate, his heart and lungs were having to work harder to maintain pH balance within his system.

From this we can conclude that this rider's FTP is very close to 350 Watts. If, over time this rider does the same over/under workout with a more stable heart rate, this could indicate a further FTP increase.

Related Post: FTP Workouts For Cyclists

CONCLUSION

While there is A LOT more data you can glean with your power meter, this should give you the basic framework to get started training with power.

A power meter is a great tool to train with. However, it is only a small piece of the puzzle and there is lots more to cycling than power numbers. What are your strengths and weaknesses? How can you get from where you are now to achieving your full potential?

One-on-One coaching from EVOQ.BIKE is the ultimate cycling training program. Each of our coaches has over a decade of training and racing experience; we’re here to share our experiences with YOU. All of our training programs include a dynamic, customized training program and one-on-one communication with your cycling coach.

View our training programs or contact us for more information!

Understanding Power Meter Data for Cycling