Validity and Reliability of an on-bike sensor system for the determination of aerodynamic drag in cycling

Abstract

Objectives: Cycling performance is strongly influenced by aerodynamics, with most resistive drag forces being attributed to the rider. Optimising aerodynamic position from accurately and reliably measuring aerodynamic resistance (CdA) is therefore in the interests of all competitive cyclists.  The Body Rocket device (BR) is an on-bike sensor system that uses the same load cell technology as a wind tunnel, directly measuring real-time CdA from the rider. This study aimed to measure the validity and reliability of CdA measures from BR in two experiments. Design: Experiment 1, validity of BR was assessed in wind tunnel with a rod and discs of known diameter attached to the end change CdA by a known amount. Experiment 2, validity and reliability of BR was assessed in an indoor velodrome. Methods: Ten cyclists performed 7 identical efforts at ~40km/h for 10 laps of the velodrome, the first 4 to assess validity with the same rod and discs used in the wind tunnel, with the remaining 3 without changes in resistance or the riders changing position to assess reliability. Results: Validity results demonstrated BR measured CdA to be strongly correlated with calculated CdA from the disc addition (r² = 0.99), with the smallest identified changes being 0.002m² across wind tunnel and velodrome. A high level of reliability was demonstrated during experiment 2 with strong intra-class correlation (0.99) and small coefficient of variation (1.67%). Conclusions: Findings of this study demonstrate BR is a valid and reliable device for measuring real-time CdA during cycling in an indoor velodrome.