Human Power Output in Short-term (anaerobic) exercise

Professor Anthony J Sargeant carried out this seminal research while working for the Medical Research Council during 1975-76 although the data was not fully analysed, written up and finally published in the prestigious Journal of Applied Physiology until 1981. The subject of the research was human power output in short-term exercise lasting seconds rather than minutes. It was curious that while there had been an wealth of publications in the literature documenting Maximum Aerobic Power (VO2 max) in every conceivable situation and population there was scant systematic research on the power that humans could generate in exercise lasting a few seconds although AV Hill had carried out some early experiments as had Rodolfo Margaria. More recently Griffiths Pugh in the UK had initiated some attempts at measuring sprint performance on cycle ergometers although this had not been published. Pursuing Pugh’s approach Tony Sargeant used the cycle ergometer that he had developed to measure the forces generated on the cranks during sustained exercise but this time during brief sprint efforts lasting for seconds rather than minutes. It soon became clear that one of the problems with quantifying maximum short term power was simply that muscle force and muscle power were velocity dependent – as indeed AV Hill and others had shown in experiments many years previously. The consequence and paradoxical confounding effect of this inter-relationship was that in an all-out sprint lasting 20 seconds the subject would within a few revolutions reach maximum power when a load was applied to the ergometer and then as fatigue set in power would decrease in each revolution and the pedalling rate would start to slow. Paradoxically because the leg muscles were contracting at a slower rate muscle force actually increased during the maximum fatiguing sprint exercise because of the shift back down the force velocity relationship of muscle. At the same time it was obvious that the measurement of maximum power during each revolution was also dependent on the speed of muscle contraction as determined by the power velocity relationship such that loss of power was a product of both fatigue and the shift back down the power velocity relationship of human muscle.
To eliminate the confounding effect of velocity Tony Sargeant added a powerful electric motor which drove the cranks at a range of constant speeds despite the maximum efforts of subjects who were asked to attempt to speed up the rate of crank rotation. In this way it was possible for the first time in the scientific literature to measure the power velocity and force velocity relationship of the whole leg musculature of humans during brief exercise.
This approach allowed a whole series of studies to be undertaken in later years which looked at energy turnover in human muscle. The study was designed and all of the data collected by Tony Sargeant working alone. In pre-digital and pre desk-top computer days the forces generated and measured with the strain gauges were measured using high speed ultra-violet paper recorders. These paper recordings were then laboriously transcribed by hand by Tony before the computer programme designed by the MRC statistician, Elizabeth Hoinville, generated power and force data. In part of the study Professor Archie Young contributed his expertise by obtaining muscle biopsies from the subjects to determine the effect of muscle fibre type on the power output.
Journal of Applied Physiology
J Appl Physiol Respir Environ Exerc Physiol. 1981 Nov;51(5):1175-82

Force exerted and power generated were measured during short-term exercise performed on a bicycle ergometer that had been modified by the addition of an electric motor driving the cranks at a chosen constant velocity. Five subjects made a series of 20-s maximum efforts at different crank velocities (range 23–171 rev/min). The forces exerted were continuously monitored with strain gauges bonded to the cranks.

Peak force was exerted at approximately 90 degrees past top dead center in each revolution. During the 20-s effort peak force declined from the maximum level (PFmax) attained near the start of exercise, the rate of decline being velocity dependent. PFmax was found to be inversely and linearly related to crank velocity and when standardized for upper leg muscle (plus bone) volume (ULV) was given by PFmax (kgf/l ULV) = 27.51–0.125 crank velocity (rev/min). Integration of the force records with pedal velocity enabled power output to be calculated. Maximum power output was a parabolic function of crank velocity, the apex of the relationship indicating that the velocity for greatest power output was 110 rev/min. At this velocity our subjects achieved a maximum mean power output, averaged over a complete revolution, of 840 +/- 153 W (85 +/- 5 W/l ULV). This was compared with the calculated value for maximum mechanical power output from aerobic sources, which was 272 +/- 49 W (30 +/- 1 W/l ULV)


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