The purpose of this study was to determine the intra-individual differences of energy expenditure between front crawl and back crawl at the same speed below the anaerobic threshold. Seven male swimmers performed 300m front crawl and back crawl at 95 percent of back crawl anaerobic threshold speed. During the trial each swimmer's respiratory gas was analysed using a portable gas analysis system. The speed of each swimmer was controlled by a visual light pacer, and each trial was recorded by a digital video camera. Energy expenditure during the trial was assumed to be equal to the swimmer's oxygen consumption. Stroke frequency and stroke length of the swimmer were calculated from the video image. Energy expenditure in back crawl was significantly higher than front crawl (mlO2/kg/min, front crawl: 38.91±3.13, back crawl: 48.20±5.31). However, there was no difference in stroke frequency (cycle/sec, front crawl: 0.43±0.04, back crawl: 0.43±0.04) and stroke length (m/cycle, front crawl: 2.53±0.17, back crawl: 2.53±0.22) between the two. The results suggested that the superiority of front crawl over back crawl at aerobic intensity is due to the difference of the economy between them, rather than the differences between stroke parameters.
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