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* Working group members: SPURR, (U.S.A., Chair) FERRO-LUZZI (Italy, Co-Chair), DE GUZMAN (Philippines), HUSAINI (Indonesia), NORGAN (U.K.), REINA (Colombia), SHETTY (India), SOLOMONS (Guatemala), TORÚN (Guatemala).
1. Definitions
2. Summary of existing knowledge
3. Priority studies
4. Relationship of the proposed research activities to developing countries
5. Recommendations for continuing obligations
References
1.1. Physical work capacity
1.2. Work performance
1.3. Chronic energy deficiency (CED)
Physical work capacity is
the ability to perform maximal physical work. As it is a function
of the intensity and duration of work, each individual has many
different capacities such as anaerobic, aerobic and endurance
capacity, each with its own limiting factors. In practice,
aerobic work capacity (VO2 max) is the capacity most
often considered.
Work performance has
different meanings in standardized and non-standardized
conditions of work. In the former it can be defined as either the
response to work, as indicated by physiological indices, such as
changes in heart rate, oxygen consumption and blood lactate, or
the work accomplished for a given physiological response. In
non-standardized tasks it is the work accomplished, which depends
on factors such as the rate of work, motivation, skill, etc.
Since the definition of CED
and indeed of malnutrition cuts across all the areas of
discussion of this workshop, it is left for collective
consideration. In what follows, the term malnutrition is reserved
for subjects in whom extensive biochemical measurements were used
to quantitate the degree of nutritional compromise.
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 undernutrition results in growth retardation, slowing of sexual maturation, delay of the growth spurt and reduction in physical work capacity (VO2 max) due to the small body size. There are data which suggest that, in adulthood, smaller boys may be unable to produce as well in heavy physical work as their nutritionally normal counterparts and hence 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 fat-free mass (FFM) 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). More studies are needed of small, perhaps CED individuals working at heavy tasks in developing countries.
Small children may have higher VO2 max values per kg of body weight or FFM 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 physical work capacity of individuals, children or adults, is in terms of total VO2 max (L/min). The expression of VO2 max in terms of body weight (mL/min/kg) is related to the physical condition of the subject which may influence performance.
The few
data which exist do not support the existence of an increased
efficiency of CED individuals in physical work, but neither do
they rule it out. More studies are needed.
At the present state of
knowledge in the field, more descriptive information is required
before any thought can be given to the study of mechanisms. There
are several areas in which additional studies should be
undertaker
1. Endurance
Endurance can be defined as the maximum time an individual can carry on a particular workload, usually defined at some high percentage of his/her maximum oxygen consumption (% VO2 max). It is a measure of the individual's capacity for work at a particular level of effort.
The only measurements of endurance in nutritionally normal individuals and subjects classified as mild, intermediate or severe in the degree of their nutritional compromise are those reported by BARAC-NIETO et al., (1978; 1980). Because no significant difference was found between the three nutritionally-deprived groups, and the maximum endurance times of the severely malnourished subjects decreased during nutritional supplementation and rehabilitation, these observations need to be repeated under different conditions and degrees of CED.
The ability to endure work in CED is crucial to an understanding of the work capabilities of these subjects.
2. Efficiency (ergonometric and metabolic)
Efficiency is the ratio of external work done (kg/m/min, Watts) to the energy cost of the work. By definition it requires an ergonometer to measure the external work. Since many human endeavors (e.g., walking on the level) do not lend themselves easily to the measurement of work, the term "economy" has come into use to describe the energy cost of tasks per kg of body weight (metabolic). In either case, since we do not know if CED changes the efficiency (economy) of affected people to do physical work, the first step is to establish whether there are significant differences. If the evidence shows greater efficiency in CED, the second step will be to establish the importance of this to the individual, and by extension to the community, in the performance of daily work.
3. Muscular composition
It has been shown that the acute malnutrition associated with disease is accompanied by changes in the ratio of slow to fast muscle fibers due largely to a decline in the number of the latter (LOPES et al., 1982). There appears to be no information available of the relative numbers of slow and fast muscle fibers in individuals exposed to CED for long periods, particularly during the period of growth from earliest ages to adulthood.
Existing data show that slow muscle fibers are more efficient than fast fibers (WENDT and GIBBS, 1973).
4. Speed and work (time as a mechanism of conserving energy)
This is related to (2) and (3) above and refers to measurements of work tasks at different rates to determine if energy can be conserved at slow compared to fast rates and if so, if this has any real meaning in the overall energy spent in work.
5. The reversibility and plasticity of the above
Once the above are established, it will be important to investigate the changes which are possible with nutritional intervention.
6. Patterns of energy expenditure in relation to BMR
CED may result in reduced energy expenditure both in absolute terms, and in relation to the BMR. This has to be investigated because of the lack of current information.
7. Patterns of time allocation
In addition to the pattern of energy levels followed during CED, the way in which time is allocated and the kinds of activities selected for change will be important, particularly with reference to the energy cost of the activity.
8. Autoselection of task execution
The way in which subjects decide to perform necessary physical tasks may be important in energy conservation.
The methodology and terminology of these suggested areas of investigation should be freely selected and standardized among the investigators involved to make individual studies comparable.
The
subjects of these investigations should initially be adult males
and females and those with present or past CED as compared to
normal subjects. Because of the lack of data on women in work,
studies of this group are imperative. With the results obtained,
it may be found desirable to undertake the study of additional
groups. Wherever possible, groups with severe CED should be
included for study, with appropriate and acceptable techniques.
It is considered important
to identify specific populations and investigative groups in
countries with a high incidence of CED for future research on
work capacity and physical performance.
A Committee on Nutrition
and Performance is already in existence in IUNS. Its principal
charge is directed towards physical fitness and activity
performance in relation to sports. It is recommended that a
Working Group of 5-6 individuals be formed by IDECG, perhaps with
members from IUNS and IDECG, and charged with the responsibility
of stimulating research on CED.
BARAC-NIETO, M., SPURR,
G.B., MAKSUD, M.G., LOTERO, H.: Aerobic work capacity in
chronically undernourished adult males. J. Appl. Physiol., 44,
209-215 (1978).
BARAC-NIETO, M., SPURR, G.B., DAHNERS, H.W., MAKSUD, M.G.: Aerobic work capacity and endurance during nutritional repletion of severely undernourished men. Am. J. Clin. Nutr., 33, 2268-2275 (1980).
LOPES, J., RUSSELL, D.M., WHITWELL, J., JEEJEEBHOY, K.N.: Skeletal muscle function in malnutrition. Am. J. Clin. Nutr., 36, 602-610 (1982).
WENDT,
I.R., GIBBS, C.L.: Energy production of exterior digitorum longus
muscle. Am. J. Physiol., 224, 1087-1096 (1973).