Application Of Near-infrared Spectroscopy In Determining Anaerobic Threshold

Purpose:Anaerobic threshold is an important reference index of aerobic capacity.How to obtain anaerobic threshold by simple test has always been a difficult point in research.In the graded exercise testing,Near-infrared spectroscopy（NIRs）monitoring HHb_bp and TSI_bp has the advantages of simplicity,non-invasiveness and high data sampling rate.It is an index to determine the anaerobic threshold strength in the graded exercise testing.However,the validity of HHb_bp and TSI_bp in the determination of anaerobic threshold needs to be further verified.The purpose of this study is to monitor HHb and TSI in the graded exercise testing by NIRs,obtain HHb_bp and TSI_bp power by linear fitting,and examine the differences and consistency between HHb_bp,TSI_bp,VT2 and MLSSw.Methods:14 college students(age 22.2±2.4yrs,height 176±6cm,weight 73.8±6.9kg,body fat 14.0±4.9,VO_2max51.9±5.5ml/min/kg)were recruited to participate in this study.All subjects perform an graded exercise testing and 3～5 MLSS tests on bicycle ergometer.The ramp testing used a linear incremental protocol,with a 4-min at 50W,followed by a30W/min increase in load until exhaustion.Changes in lung ventilation were monitored by the Cortex,and changes in oxygenation/deoxygenation of the dominant lateral vastus lateralis muscle were monitored using NIRs.In the MLSS test,60%of the maximum aerobic power was used as the starting intensity,and the subjects performed 6 groups motion,resting for 30s every 5 minutes,and collecting blood samples from the subjects’earlobes during the rest period.In the test,the highest power of the subject’s blood lactate increase of less than 1m M in 10～30min is MLSS,the average blood lactate of 10～30min in this test is MLSSc,and the corresponding output power is MLSSw.The HHb and TSI of the graded exercise testing were calculated using a double-linear regression model,and the intersection of the regression lines was HHb_bp and TSI_bp.One-way repeated measures ANOVA was performed for HHb_bp,TSI_bp,VT2,and MLSSw,and Cohen’s d was used to calculate the effect size.Then,Pearson correlation was calculated for HHb_bp,TSI_bp,VT2 and MLSSw,and the consistency of the test results was checked by Bland-Altman.P<0.05 was selected as the significant level.Results:The P_max of the graded exercise testing was 286.2±26.3W,the VO_2max was51.9±5.5ml/min/kg,the VT2 was 220.1±30.9W.The HHb_bp in the incremental loading test was 216.6±19.7W,the mean squared weighted deviation and coefficient of determination of the fitted line were both greater than 0.97.The TSI_bp was 211.0±28.8W,and the mean squared weighted deviation and coefficient of determination were greater than 0.95.The MLSSw of the MLSS test was 161.5±27.2 W and the MLSSc was 6.06±1.16 m M.MLSSw was significantly lower than VT2（P<0.001,95%CI 44.9～72.3,ES=2.01）,HHb_bp（P<0.001,95%CI-73.3～-36.5,ES=2.32）and TSI_bp（P<0.001,95%CI-67.3～-31.6,ES=1.77）,the differences among VT2,HHb_bp and TSI_bp were not significant.There was no correlation between MLSSw and HHb_bp and TSI_bp.Except for the high correlation between HHb_bp and TSI_bp（R²=0.937,P<0.001）,VT2 vs.MLSSw（R²=0.699,P=0.001）,VT2 vs.HHb_bp（R²=0.725,P=0.003）,VT2 vs.TSI_bp（R²=0.637,P=0.014）were strong correlation.The average difference between HHb_bp and TSI_bp was 5.4±10.7W,the limits of agreement was-15.5～26.4W,and the concordance results were better than other groups.The respectively average difference of VT2 and HHb_bp and TSI_bp were 3.7±23.1W and 9.1±26.5W,and the limits of agreement were-41.6～49.0W and-42.7～61.0W.The concordance results were inferior to HHb_bp and TSI_bp.The mean differences between MLSSw and VT2,HHb_bp,TSI_bp were higher.Conclusions:In the graded exercise testing,there was a high consistency between TSI_bpand HHb_bp measured by NIRs,and the break points were also consistent.The differences between HHb_bp,TSI_bp and VT2 are little and the consistency is high,but all three are higher than MLSSw.TSI_bp and HHb_bp can be used as a method to monitor the anaerobic threshold in the graded exercise testing.