A Physiological Basis for the ‘Optimum’ Level of Energy Expenditure

Abstract

THE level of oxygen consumption, compared with the maximum intake, at which an individual can work safely for 6–8 h, from month to month, has been variously defined. The Max Planck Arbeitsphysiologie Institute group in Dortmund support the idea that the rate of oxygen intake equivalent to the “Pulsdauerleistungsgrenze” (a heart-rate of about 120 beats/min) is the safe limit. The sole basis of this criterion is that, in their experience, the heart-rate continues to rise and does not remain in a steady state when the level of oxygen consumption has caused the heart-rate to exceed 120 beats/min. The “Pulsdauerleistungsgrenze” is said to occur at about 30 per cent of the individual's maximum level of oxygen intake¹. Christensen et al.² have a sounder, even if empirical, basis for their safe limit. They found that men engaged on hard manual work, such as lumber-jacking, on high financial incentives, do not, in general, work at a level which exceeds 50 per cent of the maximum level of oxygen intake.