HABITUAL PHYSICAL-ACTIVITY IN 10-YEAR-OLD TO 12-YEAR-OLD BOLIVIAN BOYS - THE RELATION BETWEEN ALTITUDE AND SOCIOECONOMIC-STATUS

This study describes habitual physical activity (HPA) of Bolivian boys living at different altitudes and from different socioeconomic status. The boys were living at high altitude (HA) in La Paz (4000 m) and at low altitude (LA) in Santa Cruz (400 m). At both altitudes samples of 10- to 12-year-old boys were chosen from a relatively low socioeconomic status (LSES) and a relatively high socioeconomic status (HSES). At HA 19 boys from LSES and 10 boys from HSES were measured and at LA 14 boys from LSES and 13 boys from HSES. HPA was measured by 24-h heart rate (HR) monitoring. Also an interview was completed to recall the HPA. By comparing the registered HR data with the time they were asleep the mean HR during sleep was calculated (HRsleep). The maximal HR (HRmax) was measured from a maximal exercise test on a bicycle ergometer. Heart rate reserve (HRR = HRmax-HRsleep) was used to measure the mean level of physical activity of the subjects. The results show that HRsleep (= HRrest) in HA boys with 70 (+/- 6) beats /min was significantly lower (p < 0.05) than in LA boys with (+/- 10) beats/min. HRmax was also significantly lower (p < 0.05) in HA boys (187 +/- 12 beats/min) compared to LA boys (195 +/- 8 beats/min). Because HA influences HRsleep and HRmax in the same way, HRR is not significantly different between boys of HA and LA. The mean heart rate over 24 h (HRmean) in HA boys (87 +/- 7 beats/min) was significantly lower than in LA boys (93 +/- 8 beats/min). There was no SES effect and also no interaction between SES and altitude. If the mean 24-h HR is expressed as a percentage of HRR (HRR%) there were no significant differences between the four groups, neither between altitudes nor between SES. However, LSES boys spent significantly (p < 0.05) more time at 50 %, 60 %, 70 % and 80 % HRR than HSES boys. The same holds for LA boys compared to HA boys at 50 % and 60 % HRR. It can be concluded that when 24-h HR is expressed in the time they spent above the aerobic training threshold of 50 % HRR, LSES and LA boys were physically more active than HSES and HA boys.