Abstract
Comparisons of physical fitness measures between children or within group measures over time are potentially confounded by differences in body size. We compared measures of strength (handgrip) and aerobic fitness (running-speed [20m shuttle-run]) of 10.0–15.9 year-olds from Dar es Salaam, Tanzania (n = 977) with schoolchildren from England (n = 1014) matched for age and sex. Differences in fitness were analyzed using general linear models, with allometric scaling for body size (mass and stature) and further adjustments for physical activity. Mean handgrip of Tanzanians was lower than English youth (F = 165.0, P<0.001, ηp2 = .079). The difference became trivial when run-speed was scaled for body size (ηp2 = .008). Running-speed of the English children was higher than in Tanzanians (F = 16.0, P<0.001, ηp2 = .014). Allometric scaling for accentuated this between-county difference in running-speed (ηp2 = .019) but when adjusted for physical activity between-country differences in running-speed were trivial (ηp2 = .008). These data contradict those studies showing poor muscular fitness in African youth and highlight the need for appropriate scaling techniques to avoid confounding by differences in body size. In contrast to those from rural areas, our sample of contemporary urban Tanzanians were less aerobically fit than European youth. Differences were independent of body size. Lower aerobic fitness of urban Tanzanian youth may be due to reported physical activity levels lower than those of English youth and lower still than previously reported in rural Tanzania.
Highlights
Economic growth and urbanization means the historical risks from under-nutrition[1] have been replaced by those from changes in lifestyle indicative of nutritional and physical activity transition[2,3,4]
Concurrent with findings of studies from across sub-Saharan Africa[10, 12, 15, 17] we found Tanzanian youth children had lower body mass and shorter stature than Europeans of the same age
It is likely that Tanzanian children may have spent more time engaged in these activities than English or North American youth. These data present a challenge to the consensus that handgrip strength of African children is inferior to that of Europeans and highlight the need for appropriate scaling when comparing fitness between groups of different body size [15, 20, 22, 25]
Summary
Economic growth and urbanization means the historical risks from under-nutrition[1] have been replaced by those from changes in lifestyle indicative of nutritional and physical activity transition[2,3,4]. Between 1990 and 2010 Dar es Salaam was the third fastest growing urban area in Africa[5] with an annual growth rate of 4.7%[6]. Population growth and migration have driven rapid urbanization in Dar es Salaam which increased in size from 9 km in 1945 to become an urban conurbation covering 1000 km today.[7]. The growing populations of adult Tanzanians who live in urban areas are less physically active and have less-favorable blood-lipid profiles than rural their rural counterparts Tanzanians.[8] Rural to urban migration is associated with reduced physical activity levels and weight gain data in Tanzanian adults.[9]
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