Relationships among estimated body composition, habitual physical activity, and physical fitness were considered in Senegalese children 8.5-13.5 years of age. Anthropometric dimensions (arm and calf circumferences, trunk, and extremity skinfolds, body mass index), four motor performances (dash, standing long jump, throw, grip strength), a step-test (cardiorespiratory fitness), and heart rate (HR) monitoring (physical activity) were collected in 140 children (66 boys and 74 girls). Age and sex had a major effect on indicators of body composition and physical fitness. Height stunting used as an indicator of chronic undernutrition had a remarkable effect on body composition but only a limited influence on physical fitness. Physical activity, represented by percentage of time above the flex-HR (%fHR), did not vary with sex, age, and nutritional status. However, there was a low-to-moderate correlation between %fHR and several body composition indices, grip strength, and cardiorespiratory fitness. Comparisons of children in the upper and lower quartiles of %fHR indicated that better indices of body composition in boys, and better strength and cardiorespiratory fitness in girls were positively associated with a higher level of physical activity. Am. J. Hum. Biol. 10:385-396, 1998. © 1998 Wiley-Liss, Inc.