Undergraduate Honors Theses

Thesis Defended

Spring 2016

Document Type

Thesis

Type of Thesis

Departmental Honors

Department

Integrative Physiology

First Advisor

Rodger Kram

Second Advisor

David Sherwood

Third Advisor

Kevin Krizek

Abstract

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.

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