The ratio between the mechanical work produced and the energy expended. Efficiency is usually expressed as a percentage where:
% efficiency = (mechanical work accomplished ÷ energy input) × 100.
The efficiency of the human walking, running, or cycling is around 20 to 30 per cent. However, determining the mechanical work accomplished during a complex movement such as walking is very difficult in practice since the various body parts are each moving in a complex manner and much of the work being done is non-propulsive. The term economy is often used when considering human movement as an alternative to the engineer's precise use of efficiency in the study of machines. Economy is defined as the energy cost of moving at a certain speed. For example, the typical energy cost of running at 3 m.s-1 is about 0.18 kilocalories per kilogram per minute.
Economy of movement is affected by skill, limb length, mass, gender, age, and equipment. Trained athletes may have a running economy that is 10 per cent better than an average runner, and in highly skilled sports such as swimming an elite swimmer may require half the energy to swim at a particular speed compared with a recreational swimmer. Two forms of external factor, both related to resistance, can considerably affect the economy of movement during sport or recreational activity. First, the energy cost of overcoming air resistance is relatively modest when moving slowly on a calm day but can impact considerably during fast motion or in a headwind, an effect vividly displayed by the echelon formations of the Tour de France peloton when a crosswind affects a stage and the riders adopt a formation that attempts to minimize additional effort. The second effect relates to the mechanical properties of equipment. A major influence in the design of sports equipment is the minimizing of resistance, as seen in the skintight suit of a swimmer or the aerodynamic helmet of a cyclist.
Subjects: Sport and Leisure.