| The highest blood lactate concentration representing an equilibrium between lactate production and elimination is termed maximal lactate steady state(MLSS).The MLSS test usually requires subject participated 2～6 constant load tests lasting 30 min.The interval between two tests is usually not less than 48 h,and a blood sample is collected every 5 min in a constant load test.Although the MLSS test is considered to be the gold standard methods for the anaerobic threshold,the program of MLSS is cumbersome,time-consuming,and is highly invasive,which greatly reduces the subject’s compliance.Therefore,many studies have tried alternative program or indicators of MLSS testing.Maximal metabolic steady state(MMSS)only requires one test,and the metabolic steady state is estimated from the correlation between oxygen uptake(VO2)and power output.Nearinfrared spectroscopy(NIRs)reflects changes in metabolic intensity by measuring changes in oxygenation/deoxygenation during exercise.These two methods provide the possibility to replace MLSS testing.In the early,the studies on running adult men found that the MLSS was about 4 mmol/L,which makes 4 mmol/L the lactate threshold used in many subsequent studies and training practices.However,subsequent studies found that MLSS is affected by multiple factors such as exercise modes,test subjects,and program.Although studies have shown that the age,gender and exercise level of subjects do not seem to affect the blood lactic acid of MLSS,a unified test program can also avoid the impact on the blood lactic acid of MLSS to the greatest extent.However,the effect of exercise modes on the blood lactic acid of MLSS has not yet been supported by direct evidence.Recent studies hypothesis that differences in metabolic stress and muscle recruitment may affect MLSS in different exercise modes.KAATSU training has emerged in recent years,KAATSU training provides the possibility to explore the influence of metabolic pressure on MLSS by applying pressure to the proximal limbs.The standing or sitting double-poling support movements corresponding to the SkiErg provide the possibility to explore the influence of different muscle participation on MLSS.Purposes(1)to explore the feasibility of MMSS test and NIRs oxygenation/deoxygenation index to replace ML SS test;(2)to explore the effect of metabolic stress on MLSS by external pneumatic compression to the limbs during exercise;(3)to explore the effect of different muscle participation on MLSS by comparing standing and sitting double-poling on SkiErg and cycling ergometer.MethodsStudy 1:Seventeen collegiate male from Shanghai University of Sport volunteered to participate this study(age 23±3 yrs,height 175±6 cm,weight 73.0±6.3 kg,body fat 12.6±3.8%).All subjects were required to perform once MMSS test and 2 to 6 constant load MLSS tests on a cycling ergometer to explore the difference between MMSSw and MLSSw.The MMSS test includes an incremental ramp exhaustion and a passive rest for 30 min,followed by 12 min of constant load cycling with intensity of 60%Pmax.Ventilatory threshold 1(VT1),ventilation threshold 2(VT2)and the corresponding relationship between VO2 and power output of the subject’s incremental load test were calculated to obtain MMSSw.The MLSS test requires the subject to performed 2～6 cycling at constant power for 30 min test.In the constant load test,blood samples taken from the subject’s earlobe every 30 s interval of 5 min and asked for Ratings of perceived exertion(RPE).In the MLSS test,the highest power at which the blood lactate increases less than 1 mmol/L at 10～30 min was MLSSw,and the average blood lactate at 10～30 min in the MLSSw test was MLSSc.NIRs collected the changes in oxygenation/deoxygenation indexes of the lateral femoral muscle of the dominant leg in all tests.One-way repeated measures ANOVA was used to statistics the differences of VT2,MMSSw and MLSSw,and Bland-Altman plots were used to identify potential systematic bias via mean bias(Bisa± SD)and 95%limit of agreement(LoA)between MLSS,MMSS and VT2.Paired samples t-tests were used to identify the difference between MLSS and MLSS+(workload of MLSSw+5%Pmax)blood lactate and NIRs results at the same time and 10 and 30 min in the same test(the results corresponding to the end of the test selected for the uncompleted test).The level of significance was set at P ≤0.05.Study 2:The subjects were the same as Study 1,except for the initiative quit and did not complete,a total of 11(age 23± 2 yrs,height 176± 5 cm,weight 74.6± 5.5 kg,body fat 14.5± 4.7%)collegiate male students from Shanghai University of Sport completed this studies.Subjects were required to take an incremental ramp test on a cycling ergometer(Lode Excalibur Sport,Lode,The Netherlands).Subsequently,perform 2 to 5 MLSS tests with(AOP40-MLSS)and without pressure,and finally perform a pressure MLSS test(MLSS-AOP40).Compression pressure was 40%of the estimated arterial occlusion pressure(AOP40)of the subject’s thigh circumference to explore the influence of AOP40 on MLSS.The incremental load test adopts a ramp incremental program,and the load increase was 30 W/min.The average maximum value of VO2 for 20 s before the end of the exercise was VO2max,and the average power 1 min before the end of the test was Pmax.The MLSS test requires the subject to performed 2～6 cycling at constant power for 30 min test.In the constant load test,blood samples taken from the subject’s earlobe every 30 s interval of 5 min and asked for RPE.In the MLSS test,the highest power at which the blood lactate increases less than 1 mmol/L at 10～30 min was MLSSw,and the average blood lactate at 10～30 min in the MLSSw test was MLSSc.The external compression equipment used in the AOP40 test can be inflated to adjust the pressure of the cuff(Kaatsu-smart,Kaatsu,China).The position of the compression part was from the patella to 2/3 of the inguinal fold.The pressure was applied immediately at the beginning of each 5 min,and the pressure was released intermittently within 30 s during the test.All tests need to wear a heart rate belt(Polar T31,Polar Electro Oy,Finland)to record heart rate changes throughout the test.NIRs collected the changes in oxygenation/deoxygenation indexes of the lateral femoral muscle of the dominant leg in all tests.One-way repeated measures ANOVA was used to statistics the differences of MLSS,AOP40-MLSS and MLSS-AOP40 test results.The level of significance was set at P ≤0.05.Study 3:The subjects were the same as Study 1,except for the initiative quit and did not complete,a total of 11(age 23±2 yrs,height 175±5 cm,weight 73.9±5.4 kg,body fat 12.7±4.7%)collegiate male students from Shanghai University of Sport completed this studies.Subjects were required to perform double-poling on SkiErg(SkiErg,Concept 2,America),mainly simulates the whole body and upper limb muscle participation through standing and sitting positions,while the cycling MLSS test of Comparative Study 1 mainly simulates the lower limb muscle participation,to explore the influence of different muscle participation on MLSSc.MLSS test requires subjects to complete 2～6 times 30 min constant power output tests of double-poling of the dynamometer.In the constant load test,30 s interval of every 5 min.Blood sample of the subject’s earlobe is collected and asked about the RPE,and analyzed the blood lactate(Biosen S_Line,EKF,Germany).The starting power of constant load test was free chosen by the subjects with RPE of 15.The output power of constant load test increased or decreased 5～10 W every two tests.The highest output power of constant load test was MLSSw when the blood lactate increased less than 1 mmol/L for 10～30 min.The average blood lactate corresponding to 10～30 min was MLSSc.The heart rate band(Polar H7,Polar Electro Oy,Finland)was worn throughout the MLSS test to recorded throughout the test.Two NIRs monitors(Portalite,Artinis Medical Systems,Netherlands)were used to measure the changes in oxygenation/deoxygenation indices of dominant vastus lateralis and latissimus dorsi muscle.One-way repeated measures ANOVA was used to statistical the MLSS difference between standing and sitting posture of SkiErg,and Cohen’s d was used to calculate the effect size of MLSS test results.The level of significance was set at P ≤0.05.ResultsStudy 1:The VO2max,Pmax and MLSSw of test results were 51.5 ± 5.4 ml/min/kg,286.7 ± 29.1 W and 167.4±28.2 W respectively.The difference test results showed that VT1(159.3± 26.4W,P=0.229,95%CI=-21.7-5.6,ES=-0.41),60%Pmax(172.0 ± 15.8,P=0.445,95%CI=-7.8～17.0,ES=0.20),MMSSw(174.9± 30.5W,P=0.080,95%CI=-1.0～16.1,ES=0.25)and MLSSw were not significantly different.However,VT2(228.6±32.4W,P<0.001,95%CI=49.4～73.0,ES=2.01)and(VT1+VT2)/2(193.9±27.3W,P<0.001,95%CI=15.6～38.2,ES=0.95)was significantly higher than MLSSw.The Bland-Altman results show that VT2(Bisa±SD=61.2±23.0 W,LoA=16.2～106.2 W),(VT1+VT2)/2(Bisa±SD=26.9±22.0 W,LoA=-16.1～70.0 W)and the average deviation and Limited of Agreement between MLSSw was relatively high.VT1(Bisa ± SD=-8.6 ± 26.5 W,LoA=-60.1～44.0 W),60%Pmax(Bisa ± SD=4.6 ± 24.2 W,LoA=-42.8～52.0 W)and MMSSw(Bisa±SD=7.5±16.6 W,LoA=-20.1～40.1 W).The average deviation between MLSSw and MLSSw is less than 10 W,but the consistency boundary between MMSSw and MLSSw is less than VT1 and 60%Pmax.In addition,7 of 17 subjects in this study had a difference of more than 20 W between MMSSw and MLSSw,and one subject with the most difference reached 38 W.In the 60%Pmax and MLSSw,12 subjects had a difference of more than 20 W,and VT1 and MLSSw had a difference of more than 50 W in 5 subjects.The MLSSc in the MLSS test was 6.00±1.12 mmol/L,which was significantly lower than the average blood lactate of 7.41 ± 1.35 mmol/L in the MLSS+test for 10 to 30 min(P<0.001).There was no significant difference in blood lactate between 10 min and 30 min in the MLSS test(P=0.059),but the blood lactate at 30 min in MLSS+ was significantly higher than the blood lactate measured at 10 min(P<0.001).In the MLSS and MLSS+ tests of the subjects,both HHb and StO2 reached a stable after the start 5 min of the test,and there was no significant difference between MLSS and MLSS+.O2Hb and tHb first decreased after the start of the test,and gradually increased after 5 min.Among them,O2Hb and tHb at 30 min were significantly higher than 10 min(P<0.001).However,were no significant difference between O2Hb and tHb at the same time point in the MLSS and MLSS+tests.Study 2:The VO2max and Pmax of cycling ergometer were 51.3±6.1 ml/min/kg and 282.2±27.7W,respectively.MLSSw and%MLSSw were 161.3 ± 28.1 W and 56.7 ± 5.5%,which were significantly higher than 152.5 ± 28.8W and 53.4 ± 5.7 of AOP40-MLSS(P<0.05).However,MLSS and AOP40-MLSS tested MLSSc(5.61±0.81 vs 5.69±1.16 mmol/L,P>0.05),heart rate(150.7±10.7 vs 152.6 ± 14.8 bpm,P>0.05)and RPE(14.9 ± 2.9 vs 14.8 ± 3.3,P>0.05)the difference was not significant.In addition,the MLSS and MLSS-AOP40 test results showed that the blood lactate(5.61 ± 0.81 vs 6.58 ± 1.37 mmol/L,P>0.05),heart rate(150.7±10.7 vs 156.5±13.1 bpm,P>0.05)of the MLSS test)and RPE(14.9 ± 2.9 vs 16.5 ± 3.1,P>0.05)were significantly lower than AOP40-MLSS.There were no significant differences in HHb,O2Hb,tHb and StO2 in MLSS,AOP40MLSS and MLSS-AOP40 tests(P>0.05).Study 3:The MLSSc of the SkiErg double-poling standing position was 4.32±0.75 mmol/L,which was lower than the cycling(5.78±0.61 mmol/L,P<0.001,ES=2.14)and sitting position on SkiErg(6.03 ± 0.69 vs 5.83 ± 0.91 mmol/L,P<0.001,ES=2.37),but there was no significant difference between SkiErg sitting posture and cycling(P=0.310,ES=0.38).In addition,the heart rate(131.8± 13.9 bpm)and RPE(13.8± 1.7)of the SkiErg sitting were significantly lower than the standing(heart rate:153.7±8.5 bpm,P<0.001,ES=1.90;RPE:15.0±2.6,P<0.001,ES=0.55)and cycling(heart rate:149.1 ± 9.6 bpm,P=0.045,ES=1.45;RPE:15.6 ± 2.1,P=0.023,ES=0.94).However,there was no significant difference in heart rate and RPE between the SkiErg standing and cycling(P>0.05).In the SkiErg double-poling of standing and sitting,HHb of the latissimus dorsi and lateral femoris muscle increases after the start,and reaches a stable after 5 min(except for the lateral femoris muscle).O2Hb and tHb tend to increase with time,and StO2 decreases after the beginning.It remained relatively stable after 5 min(the sitting lateral femoris muscle remained relatively stable throughout the test).Whether standing or sitting,the change rates of HHb,O2Hb,tHb and StO2 of the latissimus dorsi was higher than the lateral femoris muscle.The change rate of HHb,O2Hb,tHb of the sitting posture of latissimus dorsi was higher than that of the standing posture,and the StO2 of the sitting lateral femoris muscle is higher than that of the standing posture.ConclusionsStudy 1:The MMSSw and MLSSw obtained from the cycling MMSS test was a high agreement,MMSS tests can be used as an alternative to MLSS,but the individual differences between MMSSw and MLSSw should be emphasized.The HHb,O2Hb,tHb and StO2 measured by NIRs in the MLSS and MLSS+tests are not significantly different,and the NIRs results failured to replace the blood lactate test.Study 2:BFR increases metabolic pressure could not affect MLSSc,but decreases in MLSSw.Study 3:The amount of muscle invovement corresponding to different exercise modes could affect MLSSc.The higher the muscle mass involved in exercise,the smaller the MLSSc.However,MLSSw was not relate to the muscle invovement of exercise modes. |
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