Economy, Efficiency & Effectiveness of Human Movement PDF

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Economy, Efficiency & Effectiveness of Human Movement • In sport and exercise activities it is useful to examine the energy cost associated with the work done. • Generally accepted that lowering the energy cost associated with a sporting activity is beneficial (may be converse in exercise). Many ways of examining the relationship between an activity and the energy cost. Terminologies are often confused.

Economy: Economy is defined as: the amount of oxygen required to perform a sub-maximal task. Economy is related to running endurance performance among athletes of comparable VO2 max values (Morgan & Craib, 1991). Athlete A may be more economical than Athlete B, but may be less efficient. Efficiency Efficiency is defined simply as: Work Done / Energy Expended or Power Output / Rate of Energy Expenditure

Energy expended (at least for sub-maximal exercise) can be calculated on the basis of the Oxygen consumption (VO2) and RER/RQ (conversion tables available to estimate energy consumption per litre of O2 based on RER/RQ). Metabolic energy cost • Problem - not all the energy expended is associated with the mechanical work being performed. • There is a metabolic cost associated with the maintenance of normal body systems – resting metabolic rate. • This cost increases when we perform movement against a zero resistance – e.g. unloaded cycling. • Energy cost increases further with the addition of external resistance.

• Efficiency values will differ depending upon the metabolic value used. – Gross Efficiency uses the total metabolic energy cost – Net Efficiency uses the energy cost above baseline – Work Efficiency uses the energy cost above zero load – Delta efficiency uses the difference in energy cost between two work loads Work done • As with quantifying metabolic cost, there are different approaches to evaluating the mechanical work done. • Relatively simple to determine the mechanical work performed on an ergometer (cycling, rowing, wheelchair). • Far less simple when movement is less constrained e.g. locomotion over ground or swimming.Need to consider work to overcome vertical displacement of the body and horizontal motion against resistance, e.g. air resistance, hydrodynamic drag.

External work • Even where work can be measured on an ergometer this does not give a complete picture of external work. • Rather we record ‘useful’ work and don’t consider work done on other bodies or not directly contributing to the task. • e.g in wheelchair propulsion a portion of the contact force will act to distort the wheelchair wheel vertically and laterally (only the tangential component contributes to propulsion). Force effectiveness

The term force effectiveness is commonly used to represent the ratio between the so called ‘useful’ force and total force applied. FE = useful force / total force In activities such as cycling and swimming, much of the applied force is ‘wasted’ as it does not contribute directly to the task....