|Chronic Energy Deficiency : Consequences and Related Issues (International Dietary Energy Consultative Group - IDECG, 1987, 201 pages)|
|Effects of chronic energy deficiency on stature, work capacity and productivity|
Studies in nutritionally normal and malnourished men have shown that the physical work capacity, as measured by the VO2 max. is dependent on nutritional status, such that relative to the degree of malnutrition, undernourished subjects have depressed work capacities due largely to decreased muscle mass. Since productivity in hard physical work is also directly related to physical work capacity, by implication the productivity of undernourished individuals would also be depressed in heavy physical work.
During the growth of school children, even marginal malnutrition results in growth retardation, slowing of sexual maturation, delay of the growth spurt and reduction in physical work capacity (VO2 max) due to the smaller body size. There are data which suggest that in adulthood these smaller boys will be unable to produce as well in heavy physical work as their nutritionally normal counterparts and will earn less.
Studies of load-carrying in men and boys indicate that only the body size (weight) and weight of the load carried influence the energy expended independently of nutritional status. While bigger men have more lean body mass and higher values for maximum physical work capacity, they also expend more energy on body movement during work but at lower relative effort (% VO2 max) than smaller, nutritionally normal or undernourished men. The limits of effort which can be sustained for an 8-hour work day are about 35-40% VO2 max. However, upper limits of daily work and, consequently, of effects on productivity may have been estimated from too few data on restricted populations.
There is little information on sustained work efforts (% VO2 max) in undernourished subjects. Furthermore, a question arises about whether energy expenditure measurements are appropriate indicators for fatigue and productivity. There is some indication that strain and fatigue of back muscles can occur in long-term work, even when metabolic rates are below so-called acceptable levels.
In any event, more detailed studies are needed of relative efforts sustainable for long periods in individuals of small stature, as well as those with poor nutritional intakes. Anecdotal information abounds of small men, perhaps poorly nourished, who seem to perform superhuman work tasks. However, data are scarce. It would be important to carry out these suggested studies precisely in populations where these individuals seem to flourish.
Small children may have higher VO2 max values per kg of body weight or LBM than adults, while their total VO2 max (L/min) is related to their body size and, therefore, is very much lower than in adults. Consequently, the proper expression of the aerobic capacity of individuals, children or adults, is in terms of total VO2 max (L/min) when discussing their ability to perform physical work.
Finally, the efficiency or economy of work in malnourished individuals needs to be studied in detail. Presently available data do not permit a definitive answer to the question of whether there is an improved efficiency of work as part of an adaptation to chronic energy deficiency.