Validity And Reliability Of A Pedal-based Power Meter During Maximal Ergometer Testing

Abstract

The development of mobile power meters (eg: SRM, Garmin Vector Power Meter (VPM), PowerTap (PT) has allowed cyclists to track their power output (PO) while both training, competing, and as an assessment tool to establish training zones. The VPM is a newer power meter that measures PO at the pedal as opposed to other methods such as crank or hub-based meters. However, being a more recent device, the VPM has not been independently tested in any research studies to our knowledge. PURPOSE: Thus this study was done to determine the validity and reproducibility of the VPM by comparing it to the PT during a maximal ergometer test. METHODS: Two active college students (age: 21.5 +/− 0.7 years, height: 172.4 +/− 0.5 cm, body mass: 70.2 +/− 10.6 kg) volunteered to participate in the study. After being fitted for the bike, the subjects performed a 5 min warm-up at 40 W. After the warm-up, the subjects completed a maximal step-wise test to exhaustion beginning at 60 W. The subjects were instructed to ride at greater than 70 RPM, and the resistance increased 20 W every 3 minutes until their cadence dropped below 60 RPM. RESULTS: The power data from the tests were combined and statistically analyzed via a Bland-Altman plots (Figure 1) and a simple linear regression. Bias was random based on heteroscedasticity of the Bland-Altman plots (r(25)=0.418, p<0.05), and a significant regression equation was found (F(1, 25) =5460.330, p<0.001), with an R of 0.998. The standard error of estimate was 2.795 watts based on 95% confidence intervals. CONCLUSIONS: Based on these results, the VPM appears to be a valid power measurement tool during sub-maximal and maximal intensities between 60 and 220 W when compared to the PT. This study showed that the VPM may be an acceptable device for both sub-maximal and maximal step-wise ergometer testing; however, further testing needs to be done to explore a wider range of parameters such as sprint testing and field tests for a range of subject populations.