Effect of crank arm length on oxygen consumption and mechanical efficiency during forward grinding

In America’s Cup yacht racing grinding is a major factor for boat handling. Resent changes in race regulations concerning number and anthropometry of crew members as well as the need for maintaining hydraulic pressure for boat maneuvering may emphasize the importance of optimizing grinding equipment for optimal aerobic efficiency during grinding. PURPOSE: To investigate the effect of crank arm length on oxygen consumption, mechanical efficiency and perceived exertion during forward grinding. METHODS: Eight trained male subjects participated (Age: 31.3 ± 11.5 yrs; Body weight: 85.7 ± 9.5 kg; Height: 185.4 ± 3.1 cm; Arm span: 187.9 ± 7.4 cm; Grinding VO2peak: 49.0 ± 1.4 ml O2 kg−1 min−1). Whole body oxygen uptake, mechanical efficiency (net and gross), rate of perceived exertion (local and overall) and time to exhaustion (TTE) were compared during grinding with two different crank arm lengths (Standard: 228,6 mm vs. Long: 298,6 mm). Testing was performed as an incremental discontinuous test, consisting of 3-minute bouts of forward grinding at 70 revolutions per minute separated by a 1-minute pause. Testing started at 90 W and was increased by 30 W until exhaustion. Oxygen uptake was measured using the Jaeger Oxycon Pro metabolic cart and grinding was performed at a Harken® prototype grinding ergometer (Olesen et al. Eur. J. Sport Science, 2015). Prior to the two test sessions resting metabolic rate was measured in supine position. Data were analyzed using a two-factor ANOVA repeated measures and paired t-test. RESULTS: The standard crank arm length elicited lower oxygen consumption (p<0.05) and was more efficient (p<0.05) than the long crank arm length at workloads < 180 W. Interestingly, rating of perceived exertion for local muscular fatigue (local RPE) was significantly higher (p<0.05) for the standard crank arm length at workloads > 90 W and TTE for the standard crank arm length was significantly shorter (1078 ± 44 sec vs 1144 ± 53 sec; p<0.05). CONCLUSION: The long crank arm is less efficient than the standard crank arm at lower workloads. Conversely, lower local RPE at high exercise intensities and superior TTE were found with the long crank arm. The authors wish to thank Harken® for building the prototype of the grinder ergometer. No other conflicts of interest, financial or otherwise.