Mbalilaki and associates have reported very high daily energy expenditures for a sample of Masai pastoralists and farmers (56% of whom were women)(1). The stated average of 10.7 MJ/day (2565 kcal/day) appears to be a gross value for that part of the day when the subjects were physically active, although this is not specifically indicated in their paper. The expenditure is suggested as equivalent to 19 km of walking, which would occupy a total of some 4 hours. The remaining 20 hours would contribute at least a further 6 MJ of resting energy expenditure, for a daily total of some 16.7 MJ or 4010 kcal. One earlier Kofranyi-Michaelis respirometer study of traditional male Inuit did observe daily expenditures ranging from 10.5 to 18.5 MJ/day for different categories of hunting in a harsh arctic environment (2). However, the figure of 16.7 MJ/day proposed for the Masai sample is somewhat surprising on several counts, including the low average body mass of the subjects (56.8 kg), the relatively low physical working capacity seen in a previous Masai sample (3) and the conclusions from at least one energy input-output analysis that food requirements in this environment could be satisfied by working only two days per week (4).
One potential issue is the method adopted when determining energy expenditures. Mbalilaki and associates (1) apparently based their estimate on an interviewer-administered North American questionnaire (5), translated into Swahili and slightly adjusted for Tanzanian conditions. The nature of these slight adjustments and their possible impact on test validity are not discussed, but there are clearly important limitations to the absolute accuracy of information obtained from most physical activity questionnaires (including the instrument of Paffenbarger and associates, 5) even in an urban North American environment (6),and many of the items listed in the published version of the instrument of Paffenbarger et al.(5) would have little relevance to the Masai sample.
Given the importance of understanding physical activity patterns in populations that have a low prevalence of cardiovascular risk factors, I hope that Mbalilaki and associates will soon find opportunity to replicate their interesting observations, using currently available and relatively inexpensive objective physical activity monitors.
Roy J. Shepard
University of Toronto
1. Mbalilaki JA, Msesa Z, Stromme SB et al. Daily energy expenditure and cardiovascular risk in Masai, rural and urban Bantu Tanzanians. Br J Sports Med 2010; 44: 121-126.
2. Godin G, Shephard RJ. Activity patterns in the Canadian Eskimo. In: Edholm O, Gunderson EK, eds. Polar Human Biology, London, UK: Heinemann, 1973.
3. Wyndham CH, Strydom NB, Morrison JF et al. Differences between ethnic groups in physical working capacity. J Appl Physiol 1963; 18: 361- 366.
4. Lee RB. Kung bushmen subsistence: An input-output analysis. In: Vayda AP. Environment and cultural behavior. New York, NY: Natural History Press.
5. Paffenbarger RS, Blair SN, Lee IM et al. Measuring physical activity to assess health effects in free-living populations. Med Sci Sports Exerc 1993; 25: 60-70.
6. Shephard RJ. Limits to the measurement of habitual physical activity by questionnaires. Br J Sports Med 2003; 37: 197-206.