BACKGROUND: A high level of activity is commonplace in traditional subsistence societies. Physiological characteristics of individuals, including body composition and physical fitness, could be limiting factors when performing daily tasks. OBJECTIVES: The study investigated the relationships between cardiorespiratory fitness, nutritional status and physical activity patterns, so as to test the hypothesis that these relationships are less straightforward in children than in adults. STUDY DESIGN: Four different groups of individuals from rural Senegal were investigated: 99 10-13-year-old children of both sexes (11.1 +/- 1.5 years old) from two settings in Senegal (Lambaye and Podor), 43 adolescent girls (15.5 +/- 0.5 years), and 30 adult women (17-40 years). METHODS: Subjects undertook a step test, and anthropometric measurements were collected. Continuous heart rate (HR) monitoring was performed for 8-12 h. The flex-HR method was used to estimate levels of activity (per cent of time spent under or over the flex-HR). RESULTS: Ten to 13-year-old children and adolescent girls presented slight degrees of malnutrition. Adult women were apparently not nutritionally deprived. Differences in cardiorespiratory fitness were found among 10-13-year-old children, while adult women performed better than adolescent girls. Children from Lambaye had a higher level of activity than children from Podor. Similarly, adult women were more active than adolescent girls. No relationships were found between cardiorespiratory or anthropometric measurements and per cent of time spent above the flex-HR (> flex-HR) in 10-13-year-old children. In contrast, in adult women and adolescent girls, body composition and cardiorespiratory indices were significant predictors of activity levels. CONCLUSION: Our data support the hypothesis that activity levels are less dependent upon physiological characteristics in children than in adults in traditional subsistence societies.