2. Energy costs of exercise

In the simple locomotor sports that involve walking, running, or cycling, the energy cost of activity is readily determined and can be shown to be a function of speed. Whether body mass is supported by the muscles as in running, or the athlete is seated as in rowing or cycling, or where it must be moved against gravity as in cycling uphill, then this too is an important factor in determining the energy cost. For walking, running, and cycling at low speeds, there is a linear relationship between velocity and energy cost, if the energy cost is expressed relative to body weight. At higher speeds, the relationship becomes curvilinear and the energy cost increases disproportionately. In cycling a large part of this is due to the need to overcome air resistance, which increases as the square of velocity. The effect of air resistance becomes significant at the speeds involved in cycling, and explains the attention paid by elite cyclists to methods of reducing it. Bicycle design, cycling position, and clothing all affect the aerodynamics and hence the energy cost.