Reliabilty and Validity of the Computrainer and Powertap Power Meter

RELIABILITY AND VALIDITY OF THE COMPUTRAINER AND POWERTAP POWER METER

G.G Haff1, B. Ossenbrink2, W.A. Sands3, and M.H. Stone4

1West Virginia University School of Medicine, Morgantown, WV. 2Midwestern State University, Wichita Falls, TX. 3U.S Olympic Committee, Colorado Springs, CO. 4East Tennessee State University, Johnson City, TN.

Assessment of power during cycling with devices such as the PowerTap (PT) and the Computrainer (CT) has become a common tool for determining cycling training load. Little data exists examining the transferability of power values between different power measuring devices. PURPOSE: To compare the performance measures as determined on a CT to those recorded by a PT power meter during two different 20 km time trials. METHODS: Ten trained cyclists (age 24.7 ± 7.2 y, max power 368.9 ± 41.4 W at VO2max, VO2max = 62.4 ± 8.5 ml/kg/min) were evaluated over 4 testing sessions. The first session was used to determine maximal aerobic power, while the second, third (TT1) and forth (TT2) sessions consisted of a 20 km time trial performed on the subjects own bike on a CT and with a PT power meter. Session 2 served as a familiarization trial, while sessions 3 and 4 served as the test conditions. All testing days were separated by 6 days. Average power (AP), velocity (AV), distance (AD) and cadence (AC) were analyzed with an ANOVA. RESULTS: There were no significant inter-day variations on the CT or PT for AP (p=0.39, 2=0.09, 1-=0.13), AV (p=0.08, 2=0.30, 1-=0.42), AD (p=0.11, 2=0.26, 1-=0.35), and AC (p=0.17, 2=0.20, 1-=0.27). The PT exhibited a high reliability with for AP (ICC=0.87, CV=5.6%), AV (ICC=0.67, CV=4.4%), AD (ICC= 0.90, CV=2.0%) and AC (ICC=0.83, CV=2.1%). The CT also exhibited high reliability with AP (ICC=0.78, CV=7.0%), AV (ICC=0.76, CV=3.6%), AD (ICC=0.95, CV=1.6%), and AC (ICC=0.76, CV=2.4%). Significant differences were determined between the devices for AP (p=0.003, 2=0.68, 1-=0.95), AV (p<0.001, 2=0.90, 1-=0.10), and AD (p<0.001, 2=0.82, 1-=1.00).


CONCLUSION: The CT and PT provide reliable but different measurements of power, velocity, and distance. PRACTICAL APPLICATION: Cycling coaches who use the CT to determine power training zones should be cautious when prescribing training intensities which are monitored with the PT.

Acknowledgment: This research was partially supported by the Saris Cycling Group, Madison, WI.