Efficiency of movement in health and chronic disease.

Mechanical efficiency of movement expresses the efficacy of skeletal muscles to transform biochemical energy into "external work" or movement. In young healthy humans, the mechanical efficiency and/or the work economy of various locomotor activities such as cycling, up-hill walking or running, stair climbing or swimming varies from 5 - 9% for swimming to 20-25% for cycling ergometry or stair climbing. There are five potential steps at which an extra demand or "wasting" of energy may occur in supplying energy to the contracting muscle: a) the resting metabolism b) the cost of ventilation b) the percentage of moles of ATP produced per mole of atomic oxygen processed through the mitochondria c) the percentage of molecular ATP used by myofibrils for tension production and d) the cost of multi-segment movement coordination towards a locomotor displacement. This article presents the little evidence available on the efficiency of movement in patients with chronic diseases such as COPD and discusses the mechanisms through which chronic disease may contribute to a potential "exaggerated energy demand" or "energy wastage".