The influence of sex, age, and socioeconomic conditions on specific grip strength of 6-18-year-old individuals was studied among 1,704 males and 1,956 females belonging to the so-called "Cape Coloured" community in the western part of South Africa. Half of the participants of both sexes came from communities in the Greater Cape Town area where living conditions are comparable to those of middle-class First World communities (high SES). The other half came from the poorest rural communities of Klein Karoo (low SES). Arm circumferences, triceps skinfold thickness, and grip strength of the right and of the left hand were greater in individuals from high SES at all ages. Females within each SES group had skinfolds thicker than males, especially at older ages, and were weaker. Specific grip strength (SS), estimated as grip strength per unit area of cross section of the fat-free arm, increased with age in each group, was greater in males, and was significantly lower in low SES groups, than in the high SES ones, especially during and after puberty. It seems that SES difference in SS will persist into adulthood. Sexual differences in SS can be attributed to hormonal differences; while the SS increase with age and the difference between SES groups find no clear explanation in current theories of muscle growth and development. Since the speed of neuromuscular reaction observed in our participants is slower among low SES individuals, it seems that the difference in neuromuscular control of strength may be responsible for our findings. Differences in muscle metabolism and hormonal regulation must also be considered.
Associations between anthropometric variation and reproductive performance have important ecological and evolutionary implications. Bivariate associations between measures of reproductive performance (live births and offspring still living at the time of interview) and 24 anthropometric variables were examined in 150 females, aged 21-44 years, from the Eastern Highlands district of Papua New Guinea. Where significant linear or curvilinear associations with age existed, the reproductive and anthropometric variables were age-corrected. Linear, quadratic and cubic regressions were computed for each bivariate regression of age-corrected reproductive variable on age-corrected anthropometric trait. Positive linear regressions were found in the cases of body weight, triceps skinfold and head breadth. Positive cubic regressions were found in the cases of upper arm circumference, calf circumference, bicondylar femur and wrist breadth. It is suggested that these associations may reflect important ecological factors which influence both anthropometric and reproductive variation. U-shaped associations were found in the cases of wrist breadth and bicondylar femur. Inverted U-shaped associations were found for stature, sitting height, bizygomatic diameter and morphological face height. These curvilinear associations may be interpreted in terms of natural selection, and suggest that stature and sitting height may be undergoing stabilizing selection in this population.
Growth in length of children during the first 10 months of life in Hong Kong and Khartoum is compared in terms of levels of between-child variability and length and increment correlations. In Khartoum, all measures of variability are strikingly greater, and correlational patterns differ strikingly from those in Hong Kong. Growth in Hong Kong can be explained largely in terms of a mixture of genetic determination and short-term homeostatic cycles. Such a model does not fit the Khartoum data where there is evidence of at least one additional and different systematic force. This appears to arise from infants who are long at birth being handicapped in their subsequent increment by early weaning, but may also involve widespread catch-up growth from birth. © 1992 Wiley-Liss, Inc.
Objective: To ascertain whether individuals whose short stature is caused by poor living conditions differ in their other biological characteristics from those individuals who grow short, supposedly due to their genetic endowment, under favourable environmental conditions. Design: From the growth survey of nearly 4000 children of the`Cape Coloured' community aged 6±18 y half of whom lived in the middle-class suburbs of Cape Town [high socio-economic status (SES)], the other half who lived in poor rural settlements (low SES), boys and girls of similarly short stature were selected. Average body height by sex and age in each selected sample was close to the 5th percentile of height distribution among all high SES individuals surveyed. Setting: Cape Town and neighbouring rural settlements in South Africa. Subjects: Four thousand children of the Cape Coloured community aged 6±18 y. Among these were 109 high SES boys, 123 high SES girls, 302 low SES boys and 344 low SES girls selected for short stature study. Interventions: Anthropometric measurements in public schools with appropriate permissions. Results: Both short stature males and females from the low SES group tended to be signi®cantly (P`0.05) different from the high SES group of comparable stature in having lower body weights, shorter limbs, longer trunks, narrower shoulders, hips and chests, thinner skinfolds, smaller arm circumferences, and were very notably weaker and had poorer neuromuscular reaction times. Biepicondylar widths and pulse rates were little different between groups. Conclusions: Genetically short children do differ in various anthropometric and functional traits from those who are small from environmental causes. Sponsorship: MRC (South Africa), Foundation for Research Development and the Universities of Cape Town and the Witwatersrand.
Correlations are examined between adjacent velocity and acceleration growth in stature, weight and skinfold thickness in a group of adolescent boys measured approximately quarterly. It is concluded that some substantial component of the variability behaves rather like measurement error, and this is likely to represent negative feedback homeostasis.
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