BACKGROUND:Competitive athletes exercising in high-temperature,high-humidity,or low-oxygen environments experience intensified skeletal muscle deoxygenation and reduced fat oxidation,which can impair athletic performance.OBJECTIVE:To evaluate the impact of high-temperature,high-humidity,and low-oxygen environments on the fat oxidation rates of athletes during incremental load exercise,and to analyze the differences in deoxyhemoglobin kinetic parameters in skeletal muscle,thereby clarifying the relationship between fat oxidation capacity and skeletal muscle oxygenation under varying environmental conditions.METHODS:Twelve male modern pentathlon athletes were recruited for tests under three environmental conditions:normal(23 ℃,RH45％,FiO2=21.0％),high temperature and high humidity(35 ℃,RH70％,FiO2=21.0％),and low oxygen(23 ℃,RH45％,FiO2=15.6％).Resting metabolism and incremental load exercise were tested.Gas exchange data during and post-exercise were collected to calculate fat oxidation rate,carbohydrate oxidation rate,energy expenditure,and excess post-exercise oxygen consumption.Simultaneous measurements of SmO2 and total hemoglobin in the vastus lateralis muscle were used to calculate deoxyhemoglobin(HHb)levels.Deoxyhemoglobin change parameters-linear fittng slope(ΔEHHb),slope before the inflection point(ΔEHHB-1),and slope after the inflection point(ΔEHHB-2)-were determined using a bilinear function model.Fat oxidation curves were fitted using a SIN function model to identify the intensity(FATmax)that induced maximal fat oxidation(MFO),along with the curve's expansion,symmetry,and translation.RESULTS AND CONCLUSION:(1)Energy metabolism:No significant differences in maximal fat oxidation were observed across environments in each group(P>0.05).Compared with the normal environment group,both high temperature and high humidity group and low oxygen group showed significantly decreased time to maximal fat oxidation and FATmax(P<0.05).The percentage of maximal fat oxidation corresponding to peak oxygen uptake was lower in the low oxygen environment group(P<0.05).Fat oxidation was consistently low in the low oxygen environment group during exercise,while in the high temperature and high humidity environment group,it decreased only at higher exercise loads.Additionally,the expansion parameter was significantly reduced in both high temperature and high humidity and low oxygen environment groups(P<0.05).(2)Deoxyhemoglobin dynamics:The ΔEHHb was significantly higher in the high temperature and high humidity environment group,and ΔEHHB-1 was significantly increased in both high temperature and high humidity and low oxygen environment groups(P<0.05).(3)Correlation analysis:ΔEHHb was significantly negatively correlated with symmetry;ΔEHHB-1 was negatively correlated with FATmax and maximal fat oxidation;ΔEHHB-2 was positively correlated with maximal fat oxidation,and V?O2@BP was positively correlated with symmetry,expansion,and FATmax.(4)These findings indicate that incremental load exercise in high temperature,high humidity,and low oxygen environments accelerates skeletal muscle deoxygenation,thereby inhibiting fat oxidation capacity.Compared with high temperature and high humidity,low oxygen environments may more rapidly disrupt the balance between oxygen delivery and utilization in athletes'skeletal muscle,leading to a greater reliance on anaerobic glycolysis and a consequent reduction in fat oxidation capacity during exercise.

BACKGROUND:Competitive athletes exercising in high-temperature,high-humidity,or low-oxygen environments experience intensified skeletal muscle deoxygenation and reduced fat oxidation,which can impair athletic performance.OBJECTIVE:To evaluate the impact of high-temperature,high-humidity,and low-oxygen environments on the fat oxidation rates of athletes during incremental load exercise,and to analyze the differences in deoxyhemoglobin kinetic parameters in skeletal muscle,thereby clarifying the relationship between fat oxidation capacity and skeletal muscle oxygenation under varying environmental conditions.METHODS:Twelve male modern pentathlon athletes were recruited for tests under three environmental conditions:normal(23 ℃,RH45％,FiO2=21.0％),high temperature and high humidity(35 ℃,RH70％,FiO2=21.0％),and low oxygen(23 ℃,RH45％,FiO2=15.6％).Resting metabolism and incremental load exercise were tested.Gas exchange data during and post-exercise were collected to calculate fat oxidation rate,carbohydrate oxidation rate,energy expenditure,and excess post-exercise oxygen consumption.Simultaneous measurements of SmO2 and total hemoglobin in the vastus lateralis muscle were used to calculate deoxyhemoglobin(HHb)levels.Deoxyhemoglobin change parameters-linear fittng slope(ΔEHHb),slope before the inflection point(ΔEHHB-1),and slope after the inflection point(ΔEHHB-2)-were determined using a bilinear function model.Fat oxidation curves were fitted using a SIN function model to identify the intensity(FATmax)that induced maximal fat oxidation(MFO),along with the curve's expansion,symmetry,and translation.RESULTS AND CONCLUSION:(1)Energy metabolism:No significant differences in maximal fat oxidation were observed across environments in each group(P>0.05).Compared with the normal environment group,both high temperature and high humidity group and low oxygen group showed significantly decreased time to maximal fat oxidation and FATmax(P<0.05).The percentage of maximal fat oxidation corresponding to peak oxygen uptake was lower in the low oxygen environment group(P<0.05).Fat oxidation was consistently low in the low oxygen environment group during exercise,while in the high temperature and high humidity environment group,it decreased only at higher exercise loads.Additionally,the expansion parameter was significantly reduced in both high temperature and high humidity and low oxygen environment groups(P<0.05).(2)Deoxyhemoglobin dynamics:The ΔEHHb was significantly higher in the high temperature and high humidity environment group,and ΔEHHB-1 was significantly increased in both high temperature and high humidity and low oxygen environment groups(P<0.05).(3)Correlation analysis:ΔEHHb was significantly negatively correlated with symmetry;ΔEHHB-1 was negatively correlated with FATmax and maximal fat oxidation;ΔEHHB-2 was positively correlated with maximal fat oxidation,and V?O2@BP was positively correlated with symmetry,expansion,and FATmax.(4)These findings indicate that incremental load exercise in high temperature,high humidity,and low oxygen environments accelerates skeletal muscle deoxygenation,thereby inhibiting fat oxidation capacity.Compared with high temperature and high humidity,low oxygen environments may more rapidly disrupt the balance between oxygen delivery and utilization in athletes'skeletal muscle,leading to a greater reliance on anaerobic glycolysis and a consequent reduction in fat oxidation capacity during exercise.