Mechanical energy transformations and energy expenditure in running man
It has been suggested that the lower oxygen consumption of some running athletes may be caused by differences in "running style". In an initial study of treadmill running, segmental potential and kinetic energy changes were determined using a three-dimensional fifteen-segment rigid body model of the human body. Energy expenditure was determined by expired air analysis. The more economic running patterns were characterised by variations in total body energy of lower amplitude and greater exchange of energy within and between body segments. The analytical procedures were develooed in several ways. An automated system for the breath by breath monitoring of respiratory function and energy expenditure was developed. Since expired air analysis only enables the direct measurement of the aerobic component of energy expendi ture, the validity of a commonly used method for the detection of the "anaerobic threshold" from respiratory responses was investigated. The validity of this indirect method was not supported, A generali sed energy analysis procedure was developed, allowing constraints on passive energy exchange to be varied. A method for the determination of the elastic compliance of the knee extensor muscles was devised and used to incorporate a strain energy component into the energy analysis. In a further analysis of ten athletes, energy storage in the elastic components of the knee extensors was found to be significant during the supoort phase of the running stride. The inclusion of the elastic comoonents resulted in a significant reduction of the magnitude of changes in the whole body energy curve even though the sum of the absolute changes in the partitioned energy components increased. it was found that there is some correspondance between the magnitude of passive energy transfers and the "economy" of a running style. Also, muscle elasticity appears to act as an energy conserving mechanism during the support phase, reducing both the amount of work and the work-rate required of the extensor muscles. The additional energy transfers due to elastic energy storage may account for the unusually high efficiency values previously reported for running.