Abstract
Aim: It is well known that capacity for exercise performance is progressively limited with increasing altitude. Furthermore, the maximal exercise capacity is an indicator of the capacity of humans to adapt and acclimatize to high altitude. Chronic Mountain Sickness (CMS) is associated with inadequate adaptation or acclimatization abilities to high altitude. CMS is more common among immigrants who have immigrated from areas of low altitude to high altitude areas than among native highlanders. Any differences in factors related to the acclimatization ability between populations living in high altitude may indicate differences in risk of CMS. In Tibet, the prevalence of CMS among natives Tibetans older than 15 years is estimated to 1.2% and among immigrants from low altitude inland areas of China the prevalence is 5.6%. The aim of the present study is to investigate possible differences between native Tibetan children and immigrant children with respect to selected factors which may be potential risk factors for later development of CMS, such as peak workload (Wpeak), hemoglobin concentration ([Hb]), arterial oxygen saturation (SpO2), and physical activity levels.
Methods: The present cross-sectional study was carried out among 9-10 year old Tibetan (n=406) and Chinese (n=406) children in Lhasa, Tibet. Nine primary schools were randomly chosen and the subjects were considered representative for children living at the altitude of 3,700m above sea level. Peak workload, arterial oxygen saturation and heart rate were measured at rest and during Maximal Watt Cycle Eegometer (MWCE) test. Furthermore, hemoglobin concentration was measured and anthropometric measurements were recorded. Finally, a questionnaire about physical activity, food habits (PEACH-questionnaire and WHO questions) and socio-demographic factors was included.
Results: Both Tibetan boys and girls reached significant higher Wpeak compared with Chinese (boys: 107.3 ±1.0 vs. 96.7 ±1.0 W, p<0.001; girls: 93.8 ±1.2 vs. 87.9 ±1.1 W, p<0.001). Only Tibetan boys had higher weight related relative Wpeak than Chinese (3.7 ±0.03 vs. 3.5 ±0.03 W, p=0.002). Both Tibetan boys (197.6 ±0.7 vs. 194.4 ±0.6 beat/min, p<0.001) and girls (197.5 ±0.6 vs. 194.8 ±0.7 beat/min, p=0.005) had higher heart rate at maximal exercise than Chinese but there was no difference in heart rate at rest. SpO2 at rest was higher in Tibetan than Chinese and the difference was significant for girls only (91.1 ±0.2 vs. 90.2 ±0.3%, p=0.004). SpO2 at maximal exercise was significant higher in Tibetan boys and girls than Chinese (boys: 87.3 ±0.3 vs. 84.7 ±0.3%, p<0.001; girls: 87.9 ±0.3 vs. 85.1 ±0.4%, p<0.001), while [Hb] was lower in Tibetan than Chinese children (boys: 14.6 ±0.1 vs. 15.3 ±0.1g/dL; girls: 14.6 ±0.1 vs. 15.4 ±0.1g/dL, p<0.001). Moreover, Both Chinese boys and girls as compared with Tibetans look less physical activities in the school areas after the school day was finished (boys: p=0.002; girls: p=0.018) and the Chinese boys were less physically active with respect to outdoor activities outside school (p=0.030).
Conclusion: Higher Wpeak and SpO2 at maximal exercise indicate that Tibetan children have higher exercise capacity than Chinese. The lower exercise capacity together with higher [Hb] among Chinese children may indicate that Chinese children are at greater risk for developing CMS later in life. However, the hypothesis should be verified in a prospective study.