Triathlon Cycling with Shorter Crank Lengths at Same VO2 Leads to Increased Power Output

Abstract

Triathlon cycling utilizes alternate bicycle geometry and rider position compared with traditional road cycling in order to improve performance. Cycling with shorter crank lengths (CL) may benefit triathletes by allowing for improved mechanical advantage at the hip and knee, slower muscle contractions and prevent the thigh from interfering with breathing. To date, no CL research has been performed in a triathlon/time trial body position or by matching relative VO2 between CLs. PURPOSE: To examine the effect of utilizing shorter rather than traditional CLs on triathlon cycling performance metrics and ventilation. METHODS: A total of nine trained amateur triathletes completed the study. The subjects were fitted to the cycle ergometer utilizing a 78° seat tube angle. The participants completed randomized cycling bouts with CLs of 145, 155, 165 and 175 mm. For all CL trials, the subjects’ seat height and aerobar location were adjusted to maintain a 30° knee angle at bottom dead center, 30° degree torso angle and 90° of shoulder flexion. The intensity (power output) of the four cycling bouts was adjusted to maintain a relative VO2 (ml•kg-1•min-1) equivalent to 95% of the participants’ previously measured ventilatory threshold. An ANOVA followed by a Bonferroni post hoc analysis were used to determine differences in power output, cycling economy, cadence, breathing frequency, tidal volume, ventilatory equivalent for oxygen, ventilatory equivalent for carbon dioxide, respiratory exchange ratio and RPE between CL conditions. RESULTS: Participants were able to generate significantly greater power output in the 145 mm trial versus the 175 mm trial (189.4 vs 178.3 W respectively; p = .008) when relative VO2 and the triathlon cycling position were maintained. Due to greater power output but maintained VO2, cycling economy was significantly greater in the 145 mm trial vs the 175 mm trial (67.4 & 63.4 W•liter-1•min-1 respectively; p = .008). Cadence and all ventilatory parameters were not significantly different between CL trials (p > .05). CONCLUSIONS: The shorter than traditional 145 mm crank length may change mechanical advantage at the hip and knee allowing the muscle to contract slower through the pedal stroke thereby improving cycling power and triathlon performance at a long course race intensity.