Objective: To test the relationship between physical activity and physical fitness, and the relationship between these variables and the primordial risk factor blood pressure (BP).
Design: A cross-sectional study of all Danish pupils in the same grade at 'gymnasium' (the Danish upper secondary school).
Setting: Tests and questionnaires were administered by physical education and biology teachers according to a prescribed scheme.
Subjects: Study subjects were 13810 adolescents with a mean age of 17.1 years. Physical activity, smoking habits, and physical performance were measured in 4862 boys and 6573 girls. Blood pressure was measured in 2474 boys and 3535 girls. No difference was found in BP, physical activity and fitness variables between this group and a representative group of Danish school children at the same age.
Main outcome: Blood pressure and health-related physical performance such as strength, muscle endurance, flexibility and maximal oxygen uptake (VO2max) estimated from heart rate at submaximal workload were measured. Sports activity, other physical activity and smoking habits were assessed by questionnaires.
Results: There was a negative relationship between BP and VO2max up to the 50% percentile (50 ml min-1 kg-1) in boys and up to the upper 80-90% percentile (45 ml min-1 kg-1) in girls. In a multiple regression model with BP as dependent variable, VO2max related highly significant, also after adjustment for body weight and physical activity (P < 0.001). Other performance variables only explained a small part of the variance in BP. No relationship was found between BP and total physical activity or sports activity.
Conclusion: In the adolescent population VO2max related negatively to BP after adjustment for body weight, physical activity, other fitness measures and sex, but physical activity or other fitness measures did not relate. Lower blood pressure was found with higher VO2max until levels of 50 and 45 ml min-1 kg-1 in boys and girls, respectively.