An analysis of variability in power output during indoor and outdoor cycling time-trials

Purpose: Regulation of power output during cycling encompasses the integration of internal and external demands to maximise performance. However, relatively little is known about variation in power output in response to the external demands of outdoor cycling. We compared mean power output and the magnitude of power output variability and structure during a 20-min time-trial performed indoors and outdoors. Methods: Twenty male competitive cyclists (V ̇O2peak 60.4 ± 7.1 mL·kg-1·min-1) performed two randomised maximal 20-min time-trial tests i) outdoors at a cycle-specific racing circuit or ii) indoors on a laboratory-based electromagnetically braked training ergometer, 7 days apart. Power output was sampled at 1 Hz and collected on the same bike equipped with a portable power meter in both tests. Results: Twenty-min time-trial performance indoor (280 ± 44 W) was not different from outdoor (284 ± 41 W) (P = 0.256), showing a strong correlation (r = 0.94; P < 0.001). Within-person SD was greater outdoors (69 ± 21 W) compared to indoors (33 ± 10 W) (P < 0.001). Increased variability was observed across all frequencies in data from outdoor cycling compared to indoors (P < 0.001) except for the very slowest frequency bin (<0.0033 Hz, P = 0.930). Conclusions: Our findings indicate a greater magnitude of variability in power output during cycling outdoors. This suggests that constraints imposed by the external environment lead to moderate and high frequency fluctuations in power output. Therefore, indoor testing protocols should be designed to reflect the external demands of cycling outdoors.