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Climbing physics and physiology
Alberto Contador wearing the yellow jersey leading Andy Schleck wearing the White jersey at the 2009 Tour de France.
Sports physiologists have attributed the advantage that small stature holds in cycling up steep ascents to the way in which body mass and body surface area scale according to height (see square-cube law). As a hypothetical cyclist’s height increases, the surface areas of his body increase according to the square of his height whereas the mass of his body increases according to the cube of his height. The surface area relation applies not only to the total surface area of the body, but also to the surface areas of the lungs and blood vessels, which are primary factors in determining aerobic power. Thus, an equally proportioned cyclist who has 50% more body mass (i.e. is 50% heavier) will generate only about 30% more aerobic power. On a steep climb most of the cyclist’s energy goes into lifting his own weight, so the heavier cyclist will be at a competitive disadvantage. There is, of course, a lower limit to the benefit of small stature because, among other factors, the cyclist must also lift the weight of his bicycle. The additional power is proportional to the grade or slope of the road and the speed of the rider along the slope (or along the level line). For a 5% grade, each meter of road requires lifting the body weight by 5 cm. The power (watts) is equal to change in gravitational potential energy (joules) per unit time (seconds). For a 60 kilograms (130 lb) rider, the additional power needed is about 30 watts per meter/second of road speed (about 8 watts per km/hour).
Scaling factors also account for the relative disadvantage of the small cyclist in descending, although this is a result of physics, not physiology. A larger rider will be subject to a greater gravitational force because of their greater body mass. Additionally, as mentioned, the frontal area that creates aerodynamic drag increases only quadratically with the rider's size, and hence the larger rider would be expected to accelerate faster or attain a greater terminal velocity.
Although these factors might seem to cancel each other out, the climber still has an advantage on a course with long ascents and long descents: adding several miles per hour on a slow, time-consuming climb is much more valuable than the same increase on a fast and brief descent. Any rider, of course, can improve his climbing speed by increasing his aerobic power and reducing his body weight and can increase his descending speed through better bike handling and the willingness to accept an increased risk of crashing. One of the few elite riders to use descending skill as a competitive advantage is Paolo Savoldelli, nicknamed "the falcon."
For a more quantitative treatment of climbing physics and physiology, see Swain, DP, Cycling: Uphill and Downhill
