Effects of a novel prototype noncircular chainring on mechanical efficiency in well trained cyclists and triathletes

摘要

Introduction: Cycling performance can generally be improved in two different ways: physiological and biomechanical. The gross of research has been done about maximal oxygen uptake (VO2max) and fractional utilization of VO2max on the lactate or ventilatory thresholds. All of these physiological parameters have been shown to have positive relationships with cycling performance (1). On the other hand, more and more studies have recently been developed on biomechanical factors, such as aerodynamics (2) and mechanical efficiency. Therefore researchers have created many shapes and sizes of noncircular chainrings to ameliorate the efficiency of cycling (3). Results from investigations on this topic are rather inconclusive. This text handles about a completely new shape of chainring developed by the company somovedi SAM (Monaco). The hypothesis states that mechanical efficiency will be higher when cycling with the noncircular chainring compared with cycling with a conventional round chainring.Methods: Protocol: 15 well trained cyclists and triathletes participated in this study. They all had at least 2 years of cycling experience, rode there bike for at least 6000km a year and had an average VO2max of 65.5 ml.kg-1.min-1. An incremental maximal exercise test to exhaustion was done as a pre-test before the actual protocol, which consists of two experimental trials on the same day, separated by a 10min seated resting period. Subjects were randomly assigned to start either with the conventional or prototype chaining. They performed the exact same incremental test as mentioned before (pre-test), but had to stop the exercise at 90% of their maximal heart rate. Respiratory gas exchange values and heart rate were measured throughout the whole test. These values were required to calculate mechanical efficiency. Finally, rate of perceived exertion (RPE, Borg) was measured as well. Material: A schematic overview of the chainring is presented in fig 1. The novel chainring has a greater radius at 100° and 260° of the cyclus and a much smaller radius at both top and bottom death center. This would theoretically help the cyclist to generate more power at ±100° of the cyclus and furthermore help him to overcome top and bottom death center.Results: Throughout the test VO2, VCO2, heart rate and Borg were similar for every incremental step (100-220W), no significant differences were found, except for the Borg values at 140 W. We also used values of VO2 and VCO2 to calculate rate of energy expenditure and so mechanical efficiency. Mechanical efficiency tended to be the same for conventional or prototype chainrings at every power output.Conclusions: So overall, no positive effects where found of the noncircular chainring compared with the conventional chainring. Application to competition seems not useful to us. Further research is necessary.References 1.Coyle E.F, Feltner M.E., Kautz S.A., Hamilton M.T., Montain S.J., Baylor A.M., Abraham L.D., Petrek G.W. Physiological and biomechanical factors associated with elite endurance cycling performance. Med Sci Sports Exerc 23:93-107, 19912.Jeukendrup A.E., Martin J. Improving cycling performance: how should we spend our time and money. Sports med 31, 559-69, 20013.Ericson M.O., Nisell R. Efficiency of pedal forces during ergometer cycling 9, 118-22, 1988