SWIMMING EFFICIENCY IS VELOCITY DEPENDENT
Toussaint, H. M., Knops, W., De Groot, G., & Hollander, A. P. (1990). The mechanical efficiency of front crawl swimming. Medicine and Science in Sports and Exercise, 22, 402-408.
Swimmers lack a fixed point in the water from which to push. In moving the body forward, the swimmer also moves water backwards. The water acquires a kinetic energy change. Thus, propulsion in swimming involves two forms of power output: 1) to move the body forward by overcoming drag, and 2) that imparted to the "compression" of the water that is moved backwards. If gravitational and hydrostatic forces are ignored (the velocities occurring in the vertical direction are rather small), two forces remain: the propulsive force acting on the hands and feet and the drag force acting on the body.
This study used the MAD system developed in Holland to measure forces associated with horizontal movement. Special facial valves were developed to minimize increased drag so that gas analyses could be measured.
The gross efficiencies ranged from 5.1% to 9.5%, measures that are slightly below those obtained for arm cranking and wheelchair riding. The reduction is probably due to the extra energy required to overcome the hydrostatic pressure on the thoracic cavity and to compensate for heat loss of the body to the water. The amount of power consumed to push the water ranged from 30-50%.
Implication. Efficiency increases as the speed of swimming increases. Therefore, when considering efficiency it must be relevant to a particular speed. There is no difference between males and females in movement efficiency at the same speed of swimming.
When looking at other studies concerning efficiency, it is necessary to determine if those studies have or have not accounted for the movement of water backward in their assessments.
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