Issues of work intensity, pace, and sustainability in relation to work context and nutritional status.

This article raises issues about work intensity, pace, and sustainability during physical activity, focusing attention on the nature of work in labor-intensive societies, the management of exertion in habitual tasks, and the health and broad socioeconomic correlates of alternative ways to regulate work patterns. At the heart of this review are concerns to document human adaptability (in terms of the physical and behavioral management of heavy work) and to renew debate regarding the conceptualization and measurement of work intensity (variously evaluated in absolute or relative terms, as indexed by oxygen consumption, energy expenditure, percentage maximal work capacity, heart rate elevation, time and motion indicators, or physiological cost). Three questions are examined: Is heavy work primarily a matter of time or energy intensity? How is heavy work habitually sustained? What is the bigger picture relating work performance to work context and to nutritional or health status? It is argued that many arduous activities, such as carrying loads, demand endurance over time rather than intensive effort per unit time, and that work pace management lies in regulating both the rate of work and the time in rest during physical activity. Furthermore, strategies that maximize long-term endurance (adopted by "tortoises") and those that maximize short-term productivity (adopted by "hares") are appropriate to different work contexts (e.g., a subsistence or wage-labor economy) and suit individuals with different health status and ability. Thus, work intensity is an important aspect of the links between physical activity, health, productivity, and society, as noted in literature reviewing objectives for sustainable development and public health messages for disease risk management. These areas of scholarship are underresearched, partly because consensus has been slow in agreeing on which are the best measures of work pace and work intensity for use in field situations, and which are the most meaningful thresholds for evaluating absolute or relative effort across a range of populations.