Capelli, C., Pendergast, D.R., & Termin, B. (1998). Energetics of swimming at maximal speeds in humans. European Journal of Applied Physiology, 78(5), 385-393.

The energy costs per unit of distance of the front-crawl, back, breast and butterfly strokes were assessed in 20 elite swimmers.

At sub-maximal speeds energy cost was measured dividing steady-state oxygen consumption (VO2) by velocity (m/s). At supra-maximal velocity, energy cost was calculated by dividing the total metabolic energy spent in covering 45.7, 91.4 and 182.9 m by the distance. E was calculated as: E = Ean + alphaVO2maxtp - alphaVO2maxtau(1 - e(-(tp/tau))), where Ean was the amount of energy (kilojoules) derived from anaerobic sources, VO2max l/s was the maximal oxygen uptake, alpha ( = 20.9 kJ per liter of O2) was the energy equivalent of O2, tau (24 s) was the time constant assumed for the attaining VO2max at the muscular level at the onset of exercise, and tp (seconds) was performance time. The lactic acid component was assumed to increase exponentially with tp to an asymptotic value of 0.418 kJ per kg of body mass for tp> or =120 s. The lactic acid component of Ean was obtained from the net increase of lactate concentration after exercise (delta[La]b) assuming that, when delta[La]b = 1 mM/l. The net amount of metabolic energy released by lactate formation was 0.069 kJ per kg.

Over the entire range of swimming velocities, front crawl was the least costly stroke in terms of energy expenditure. For example at 1 m/s energy cost amounted, on average, to 0.70, 0.84, 0.82 and 1.24 kJ/m in front crawl, backstroke, butterfly and breaststroke, respectively. At 1.5 m/s energy cost was 1.23, 1.47, 1.55 and 1.87 kJ/m in the four strokes, respectively. Energy cost was a continuous function of velocity in all of the four strokes. It increased exponentially in crawl and backstroke, whereas in butterfly it only increased exponentially at higher velocities. Energy cost in breaststroke was a linear function of velocity probably because of the considerable amount of energy spent accelerating the body during the pushing phase to compensate for loss of velocity in the non-propulsive phase.

Implications. Crawl stroke uses less energy to cover a set distance than any other stroke. In terms of effort, it is the easiest stroke to swim, which probably accounts for why so much crawl is practiced and preferred by most swimmers. Crawl and backstroke increase energy costs exponentially with increases in velocity. Butterfly increases energy costs exponentially but only at higher velocities. For these three strokes it can be concluded that attempting to go faster by exerting more energy (effort) when already performing near maximum velocity will not produce a worthwhile performance change. At high effort levels, performance improvements are more likely to occur through more precise technique changes than extra effort.

Breaststroke energy costs increase linearly with speed. Both technique and extra effort can contribute to performance improvements at near maximal velocities in this stroke.

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