Differences in blood pressure according to physical fitness and body mass in a sample of Mexican schoolchildren.

Background: Physical fitness is the ability to perform activities of daily living without excessive fatigue. The potential protective role of fitness against high blood pressure in childhood is relevant to diminish the risk of hypertension in adulthood. A negative association between cardiorespiratory fitness (CRF) and hypertension has been found in the pediatric population. However, the role of body mass as a confounding variable of this association has not been evaluated. This study aimed to analyze whether the association between fitness and blood pressure in Mexican schoolchildren is independent of body mass.

Methods: A cross-sectional study was conducted with a sample of 1010 children (574 females and 436 males) aged 9-12 years (mean age = 10.3 ± 0.9 years) from 13 elementary schools in Mexico City. Fitness was evaluated with tests from the FitnessGram battery. Z-scores of body mass index (BMI)-for-age and height-for-age were estimated.

Results: Low fitness showed a high prevalence (from 45.8% for trunk lift to 77.5% for push-ups). Children with poor CRF (assessed by the 20-m progressive aerobic cardiovascular endurance run test) and upper body strength (assessed by push-ups) showed a higher probability of hypertension (p < 0.05). However, these differences disappeared after adjusting for BMI.

Conclusions: After considering the body mass, cardiorespiratory and musculoskeletal fitness were not independent predictors of blood pressure.