Type of Thesis
The rapid evolution of bicycles in the 1800s increased the speed of human powered transportation ten-fold compared to walking and decreased the metabolic power required by 300%. However, the metabolic gross efficiency has hardly changed. I tested the null hypothesis that the metabolic costs of cycling at different relative crank angles would not differ. I tested ten healthy, male, recreational bicycle riders (27.8 ± 8.2 yr, mean ± SD, mass 69.8 ± 3.2 kg) on a custom, pan-loaded cycle ergometer equipped with a standard Monark flywheel. The ergometer had a Shimano Octalink® bottom bracket, which allowed us to set the relative crank arm angles at 45° increments. Each subject completed six, 5-minute trials. The first and last trials were at a relative crank angle of 180°. We randomized the order of the middle trials (135°, 90°, 45°, and 0°). We averaged V̇O2, V̇CO2, and respiratory exchange ratio (RER) for the last 2 minutes of each 5-minute trial. From the V̇O2 and V̇CO2 measurements, we calculated metabolic power. I reject my null hypothesis; crank angles other than 180° required greater metabolic power. As relative crank angle decreased from 180°, metabolic power monotonically increased by 1.6% at 135° (p<0.002) to only 8.2% greater when the relative crank angle was 0° (p<0.001). Despite radically changing the relative crank angle, metabolic efficiency decreased by only ~8%. Thus, I conclude that attempts to enhance efficiency via pedaling technique or technology are likely futile.
Straw, Asher H., "Could a kangaroo win the Tour de France? The effect of relative crank angle on metabolic efficiency in cycling." (2016). Undergraduate Honors Theses. 1141.