Although the effect of labour and physical stress on the height and weight of growing children is relatively well known, rather limited information concerning the influences of the work environment on the physique of working children and adolescents is available. The purpose of this study was to increase our knowledge of the effects of mechanical stress on the human physique via somatotype during the adolescent growth period. Anthropometric measurements of 509 male apprentices aged 13.50-18.49 years and measurements of 451 nonworking youth (control group) of the same age group were taken. The members of both groups were from the lower socioeconomic strata and had similar living conditions. The apprentices were working an average of I I h per day in vocations requiring intense physical effort. The subjects were somatotyped using the Heath-Carter anthropometric protocol. The overall mean somatotypes were 2.3-4.4-3.3 for working adolescents, and 2.5-3.9-3.6 for the nonworking controls. A one-way multivariate analysis of variance (MANOVA) indicated significant differences between the groups. Working adolescents were more mesomorphic and less ectomorphic than their nonworking peers. In both groups, endomorphy decreased with age up to age 15; then remained stable for the labourers but increased for the nonworking peers. In both groups, mesomorphy was stable, but decreased with ectomorphy. These results indicate that physical stress not only causes retardation in linear growth, but also produces changes in human physique during the growth period. (C) 2008 Elsevier GmbH. All rights reserved.