Correlation Study On Cardiorespiratory Fitness And Body Mass Index In Native Tibetan Residents At High Altitude

ObjectiveTo compare the cardiorespiratory fitness(CRF)and BMI of native Tibetans living at 2516 m,3660 m,4500 m and 5018 m above sea level,as well as to further analyze the correlation between CRF and BMI and its influencing factors;At the same time,to analyze the correlation between the detection rate of overweight,obesity and the blood lipid with CRF or BMI.MethodsA total of 872 native Tibetan residents aged 18 years or older were randomly selected from four different altitudes:Naxi town and Guizika town of Mangkang County,Chamdo City(2516 m),Lhasa(3660 m),Guoqing town of Baxoi County,Chamdo City(4500 m)and Pumaqiangtang town of Nagarze County,Shannan City(5018 m)in order to analyze BMI distribution,of whom 131 male subjects underwent cardiorespiratory fitness testing.A cardiopulmonary ergometer(Mata Max3B)coupled with an incremental load bicycle(Custo.med)was used to test the maximal oxygen uptake(VO_2max)while relevant anthropometric(height,weight,etc.)and physiological indicators(hemoglobin concentration,oxygen saturation,etc.)were also examined.Quantifications according to the normal distribution were expressed by?X±s.Comparisons of means between different altitude and between different ages were performed by one-way ANOVA;comparisons of body mass indexes between different genders were performed by independent samples T-test,and the correlation analysis was performed by multiple linear regression.P<0.05 was considered statistically significant.Results(1)Comparison of BMI at different altitudes:using 4500 m above sea level as reference,BMI was significantly different(P<0.001)with populations exposed to 5018 m above sea level,but no difference with those exposed to 2516 m and 3660 m above sea level(P>0.05).BMI decreased with increasing altitude and was significantly lower when the altitude exceeded 4500 m.The detection rates of overweight and obesity were the lowest at an altitude of 5018 m(21.3%),while those at the other three altitudes were 50.4%,56.2%,and 46.9%,respectively.(2)Comparison of cardiorespiratory fitness indexes at different altitudes:the mean values of HR_peak,S_pO_2peak,RER,absolute VO_2max and relative VO_2max of the subjects were 167.8 beats/min,81.45%,1.11,4.5 L/min,and 37.4 m L/min/kg,respectively.Taking the altitude of 4500 m above sea level as a reference,S_pO_2peak was significantly different with all other three groups(P<0.01);RER was significantly different with elevations of 2516 m and 5018 m(P<0.001),whereas VO_2max was only significantly different with elevations of 3660 m(P<0.001).HR_peak,absolute VO_2max and relative VO_2maxvalues at different ages were significantly different(P<0.05),of which absolute VO_2max and relative values showed a decreasing trend with age,while the difference with S_pO_2peakand RER were not significant(P>0.05).(3)Correlation between CRF and BMI:results of regression analysis revealed that negative correlation between CRF and BMI without any confounder correction,with the correction of age and occupational type,no association was found between CRF and BMI.(4)Regression analysis results indicated that TG and LDL-C were positively correlated with BMI,while HDL-C was negatively correlated with BMI;and one-way ANOVA showed that TC,TG and LDL-C differed among the high,medium and low endurance groups.Conclusion(1)The CRF showed a decreasing trend with increasing altitude,but those at 3660 m had lower cardiorespiratory endurance than the other three group,and it decreased gradually with age at the same time.(2)CRF and BMI were inversely correlated.But there was no correlation after adjustment for age and occupation.(3)The BMI of Tibetans varied between different altitudes,which showed a downward trend with the increase of altitude,and it decreased significantly when the altitude exceeds 4500 m.In addition,BMI increased with age.(4)The detection rate of overweight and obesity was not optimistic.(5)TG and LDL-C increased with BMI,whereas HDL-C decreased with BMI;the dyslipidemia was more pronounced in those with low endurance levels.