Which movement produces the greatest hydrodynamic resistance in water-based exercise?

• A. Moving slowly toward the surface
• B. Moving quickly toward the surface
• C. Moving slowly away from the surface
• D. Moving quickly away from the surface

Answer: (D)

Hydrodynamic resistance, or drag, in water rises sharply with speed because drag force increases with the square of velocity. In vertical movements, moving quickly away from the surface drives a strong downward and outward displacement of water, forcing a large mass of water to accelerate around and past the body. That greater water movement and turbulent flow around you produces the highest drag. Moving toward the surface, even at high speed, tends to involve interactions with the boundary at the surface and less vertical water displacement, so the resultant drag is less than when moving rapidly away from the surface.