Marathon runners, for example, are usually smaller than middle distance or sprint runners. Running at high altitudes can increase speeds by 1.5 to 2.0 percent because wind resistance is less due to the lower air density, although this does not explain all of the benefit. Some other factor is involved, perhaps drag. Wind resistance can be reduced significantly by clever design of clothing, which can improve sprint times by as much as 1.5 percent. Energy is lost also from the heat that is generated because of the metabolic reactions associated with muscle control.
Air moving around an object creates drag.
To counteract drag, turbulence must be created. For this reason, for example, golf balls are dimpled to increase turbulence at the ball surface and reduce drag that slows down the ball's speed. Clothing has a similar effect. A runner can reduce drag by wearing very smooth, well-fitting clothing with small ribs running down each side of the chest and thighs, to reduce drag. This enables a sprinter to run about 1.5 percent faster.