S6 Swimming

Topic

The swimmer's action in the water establishes a specific fluid-dynamic model within the broader system; the swimmer must generate propulsion while minimizing hydrodynamic resistance.

Propulsion is generated primarily through the arm stroke: the hand and forearm act as a paddle, applying force to the water and receiving a propulsive reaction force—an application of Newton's third law.

The resulting propulsive force on the hand comprises both lift and drag components, making the quasi-static model the most widely used in swimming biomechanics. Increasing the lift component relative to the drag component enhances the efficiency of the swimmer's propulsion.

The swimmer's active drag—generated by the body's frontal orientation against the water—is significantly higher than the passive drag experienced by a static swimmer, particularly in strokes that cause greater water turbulence. Greater water turbulence during the stroke results in even higher active drag. This specific propulsive efficiency of the swimmer actually represents the lowest overall efficiency in the sport—considerably lower than the efficiency found in cycling, which establishes a different model within this group—thereby explaining the swimmer's enormous metabolic cost per meter swum.

Consequently, this model—characterized by propulsion through water that minimizes hydrodynamic drag—results in wave-making hydrodynamics at the water's surface that limit the swimmer's maximum speed; this speed limit is determined by the model based on applied power, regardless of how much additional power the swimmer exerts. If the swimmer applies power beyond this hydrodynamic wave limit, their speed no longer increases in proportion to that additional power.

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