Accuracy of Cycling Power Meters Against a Mathematical Model of Treadmill Cycling
Billed as the biggest study of cycling power meters of its kind, scientists affiliated with the Swiss Federal Institute of Sport in Switzerland compared the accuracy of 53 power meters from nine manufacturers. The results of which were recently published in the International Journal of Sports Medicine.
This study is the first to evaluate multiple power meters from multiple manufacturers against a first principle-based mathematical model of treadmill cycling. Previous studies had compared power meters being used simultaneously on the same bike and comparing measurements. However, this method has typically not accounted for drivetrain loss in a mathematical model.
To address this concern, Maier and his team opted for an alternative way to more accurately power output in a lab setting. A motorized treadmill was selected for this purpose, as it has shown to be highly reliable.
During the study all data was collected in a controlled lab setting away from the variant conditions of road or track. Each power meter was calibrated three times with four different masses, yielding 12 measurements per power meter.
Once the data was collected, the researchers set out to measure and compare accuracy. For the purposes of this study, accuracy was defined as the combination of trueness and precision, as per the International Organization for Standardization.
Regarding trueness, the scientists noted six units of concern: 1 power2max, 1 Quarq and 4 Stages power meters. As for precision, five individual power meters were found outside of the expected parameters (1 Quarq, 1 Polar, 3 Stages). Additionally, the data showed that that accuracy was overall high within – but not between – manufacturers.
The researchers found a high general precision among the power meters, with power meters from SRM and PowerTap being more precise compared to Stages. These results are in line with a previous study exploring the precision between SRM and PowerTap units.
What do These Results Mean for You?
1. Try Not to Compare Red Apples to Green Ones
Whether we're ticking off Strava segments or comparing data on group rides, to ride is to compete. With so many bike power meters on the market, chances are you aren't riding the same meter as the Cat 1 in your Wednesday night crew or the last winner of Kona. And while we're all riding and training with power, this study shows that there can be notable differences between manufacturers. So unless you're comparing PowerTap to SRM or within a portfolio of products from the same power meter brand, take those data differences with a grain of salt.
2. Calibrate Your Power Meter
If you're reading this, chances are you use a cycling power meter as a coach, an athlete or perhaps both. As a training tool, a power meter is just that – a piece of gear to help you improve on an effort-to-effort basis. To ensure you're seeing accurate numbers with every ride, calibrate your power meter before you hit the road. And if you have questions about your power meter's calibration value, reach out to the manufacturer.
Accuracy of Cycling Power Meters Against A Mathematical Model of Treadmill Cycling by Thomas Maier, Lucas Schmid, Beat Müller, Thomas Steiner and Jon Peter Wehrlin, published in the International Journal of Sports Medicine, 2017.