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Nov042011

Estimating the Maximal Lactate Steady State Power from an Incremental Test Using Lactate Pro LP1710

International Journal of Applied Sports Sciences 2009, Vol. 21, No. 1, 74-85.
Korea Institute of Sport Science
Received : 1 December 2008, Accepted : 10 February 2009

By: Asgeir Mamen, & Roland van den Tillaar Sogn og Fjordane
University College, Norway


The aim of the study was to explore how the Lactate Pro® LP1710 (LP1710) blood lactate analyser can be used to find the Maximal Lactate Steady State (MLSS) power from an incremental cycle test. Methods: Nine cyclists were tested.

They performed an incremental test to establish a power vs. blood lactate concentration (BLC) curve and find two threshold definitions: Lactate Breakpoint (LB) and Onset of Blood Lactate Accumulation (OBLA). Then several continuous load tests were performed to establish the power output that elicited MLSS power (WMLSS). Results: From the blood lactate curve of the incremental test a BLC of 2.7(0.6) mmol․ L-1 (or 1.7(0.6) mmo․ L-1 above resting BLC) equalled the WMLSS. The W, HR and VO2 from the LB and OBLA tests had a range of 91-93% (LB) and 103-111% (OBLA) of MLSS values. The LB produced the lowest power, 228(46) W, 18 W below WMLSS (p=0.005), OBLA the highest, 273(47) W, 27 W above WMLSS (p=0.007).

The oxygen uptake at LB was 70(5)% of VO2max, at MLSS 77(5)% and OBLA 82(3)%. Conclusion: From the results of an incremental test the WMLSS can be estimated with LP1710, if a fixed BLC of 2.7 ± 0.7 mmol․ L-1 is used.

key words: MLSS, OBLA, Lactate Breakpoint, blood lactate concentration, training 

Introduction

The definition of the lactate threshold is the highest load a subject can endure over time without a rise in blood lactate concentration (BLC), often called Maximal Lactate Steady State (MLSS) (Weltman, 1995). This load can be found by performing several constant load tests, usually of 30 minutes duration (Beneke, 2003; Harnish et al., 2001). Such a method is time-consuming. Therefore, several indirect methods have been developed, mostly using an incremental protocol with step durations of 3-8 minutes (Weltman, 1995). These tests produce a power vs.BLC curve that can be used to define the point of threshold using some criteria.

Unfortunately, no agreement on criteria for threshold determination exists (Weltman, 1995). Two common ways of defining a threshold are the Lactate breakpoint (LB), which is the first increase in BLC > 1.0 mmol․L-1 seen in an incremental protocol (Davis et al., 1983) and the Onset of Blood Lactate Accumulation (OBLA), which Sjödin defined as a fixed BLC level of 4 mmol․L-1 (Sjödin & Jacobs, 1981b).

When comparing results of threshold tests, several factors need to be taken into consideration. point to stage duration and size of load increment as factors that may affect the test result, and recommend the use of 3-minute stages Bentley (Bentley, Newell, & Bishop, 2007). Foxdal have pointed out that if BLCs from incremental and continuous tests are to be compared, the stage duration of the incremental test should be eight minutes, to assure a steady state of lactate (Foxdal et al., 1996).

The measured BLC is dependent on sampling site and type of blood (El-Sayed et al., 1993; Feliu et al., 1999; Foxdal et al., 1990). Finger sampling produces higher BLC than ear lobe sampling (Feliu et al., 1999). El-Sayed found that the OBLA load calculated from venous blood was too high for the subjects to sustain with stable BLC, whereas the OBLA load from capillary blood could be endured in a BLC steady state (El-Sayed et al., 1993). Results from tests using different sampling sites should thus be compared with caution. When using resting BLC as a baseline for threshold determination, sampling site might seriously influence the result, as the difference between ear and finger sampling is greatest at low BLCs (Feliu et al., 1999).

Foxdal concluded that direct comparisons between BLC in capillary finger blood, venous whole blood and plasma could not be made (Foxdal et al., 1990). Even more caution should be exercised when different lactate analysers have been used as the BLC result is analyser specific. Medbø et al.(Medbø et al., 2000) and Buckley and co-workers (Buckley et al., 2003) have shown that the BLC will differ between lactate analysers, so that results from one brand of analyser are not always interchangeable with another analyser. Medbø et al. (2000) compared the LP1710 with several YSI 1500 sport analysers and found that the LP1710 blood lactate results was ~40% higher than the YSI results (Y(LP1710)=-0.21+(1.50․X(YSI)). A difference between analysers is especially important to be aware of for threshold determinations that use a fixed BLC (as OBLA). A difference between two analysers of 10% might satisfy the OBLA criterion in one analyser, but gives only 3.6 mmol․L-1 in the other. Threshold determinations based on a relative change in BLC (as LB), seem not to be as prone to analyser specificity (Buckley et al., 2003), neither should it be so sensitive to variation in sampling site as the calculations are not dependent on absolute BLC values.

The fitness level can also influence the result of an incremental test. Bentley found that well-trained and lesser-trained cyclists responded differently to incremental protocols with short (3 min) and long (8 min) step duration (Bentley et al., 2001). Results from a low BLC threshold (Lactate Threshold; first increment above resting BLC) differed between the two-step durations in the well-trained group, but not in the lesser-trained group. OBLA results were not affected by step duration in either fitness groups.

According to Bentley no threshold definition can be termed “best” (Bentley et al., 2007). The selection of a diagnostic test must be made according to specific needs, but coaches and athletes should be aware of how changes in the test protocol, analysers included, can influence the result.

Thus there is a need to investigate how a specific lactate analyser behaves with respect to specific lactate threshold tests and MLSS. The lactate analyser Lactate Pro® LP1710 (Arkray inc, Japan) (LP1710) has become popular due to both size and pricing. It is easy to use and requires little blood and consequently is well suited for both laboratory and field measurements. Several investigators have examined this analyser and found it accurate and reliable (Buckley et al., 2003; Mc Naughton et al., 2002; McLean et al., 2004; Medbø et al., 2000; Pyne et al., 2000; van Someren et al., 2005).

The aim of this study is therefore to investigate how the MLSS power can be estimated from the results of an incremental lactate profile test using capillary blood from the finger and the LP1710 in cycling.

 

Material and Methods

Subjects

Nine male subjects participated in this experiment (Table 1). All were physically active with cycling as their main activity. This study complied with the requirements of the Helsinki declaration and with current Norwegian law and regulations. The subjects signed an informed consent that stated that they participated of free will, and could leave the project at any time without explaining why.

 

Methodology

A resting blood lactate sample was taken from the fingertip before warming up.

The subjects performed an incremental lactate profile test with 5 min step duration and an increase in load of 30 W per step from a starting load of ~1.5 W kg-1 body mass, giving a slope of 6 W․min-1. BLC was measured at the end of each step, again by pricking a finger. There were no resting periods during the blood sampling. When BLC exceeded 4 mmol․L-1, the test was terminated and after a resting period of ~20 min, a maximal oxygen uptake test started. In this test load was increased by 30 W each min from a load of approximately 2 W kg-1 body mass until voluntary exhaustion.

The load at LB (WLB) was defined in each individual as the load preceding an increase in BLC of >1.0 mmol․L-1 (Davis et al., 1983). The load at a BLC of 4.0 mmol․L-1 was defined as the OBLA load (WOBLA) (Sjödin & Jacobs, 1981).

Within a week after the incremental test, the MLSS testing was started. The first 30 min constant load test had a load ~12% below WOBLA. This load would in most cases be below the MLSS power (WMLSS), but so close that only two or three constant load tests would be required to reach the WMLSS. Blood samples were taken at 0, 5, 10, 20 and 30 min of exercise. According to the development of the BLC, the load was either raised or lowered for the next constant load test by 10 W, continuing until a steady increase in BLC was obtained during the test or the BLC did not increase more than the MLSS definition allowed. The highest load that resulted in a BLC increase less than 1 mmol․L-1 during the last 20 min was considered the WMLSS (Harnish et al., 2001). The heart rate of the MLSS test (HRMLSS) was the mean HR from the 15th to the 20th min of exercise. Oxygen consumption (VO2MLSS) was the mean VO2 from the 15th to the 20th min. This sampling interval was chosen to avoid possible drift in HR and VO2.

BLC was measured with a Lactate Pro LP1710® (Arkray Inc, Kyoto, Japan). It is a small size analyser (84x55x14.5 mm, weight 50g) that uses lactate oxidase and K ferricyanide to measure the lactate content of whole blood. Values are displayed as haemolysed values. Only a small amount of blood, 5 μL, is necessary. The manufacturer claims a coefficient of variation (CV) of ~3%.

The cyclists used their own bikes mounted on a Computrainer PC1 electromagnetic roller (RacerMate Inc, Seattle, USA). As load is independent of cadence, they were free to choose pedalling frequency. For one person, a Monark mechanical ergometer cycle (Monark Exercise AB, Varberg, Sweden) was used for all testing, as his own bike was not available. In his case, a cadence of 75 RPM was used throughout. Oxygen consumption was measured with a MetaMax CBS metabolic cart (Cortex Biophysik, Leipzig, Germany) at 10 s intervals throughout the test. Heart rate was assessed with a Polar heart rate monitor (Polar Electro OY, Kempele, Finland) every 5th second 

Statistical analysis

Results are presented as mean (SD) unless otherwise stated. An ANOVA for repeated measurements was used to compare power, heart rate, oxygen uptake and percent of HRmax and VO2max between the three definitions. When a significant difference was found, a Holm-Sidak post hoc test was performed. Data normality was investigated both with Kolmogorov-Smirnov (Lilliefors modification) and Shapiro-Wilk's tests due to the low number of subjects. If any of the normality tests failed, a Kruskal-Walis ANOVA on ranks was performed with Tukey post hoc test.

Pearson's r was used for correlations. Level of statistical significance was set to p<0.05. Statistical software: SigmaPlot 10/SigmaStat 3.5 (Systat Software Inc, San Jose, CA, USA), Winks 4.80 (TexaSoft, Cedar Hill, TX, USA) and Mystat 12 (Systat software, Inc, Chicago, IL, USA). 

Results

The power that equalled the WMLSS at the incremental test corresponded to a BLC of 2.7(0.6) mmol․L-1. When exercising at WMLSS at the constant load test, the BLC was 3.4(0.7) mmol․L-1. The mean resting BLC was 1.0(0.2) mmol․L-1. A low BLC on the first load of the incremental test (1.1(0.3) mmol․L-1) indicated that the starting load was suitable for the subjects.

An ANOVA on repeated measurements showed significant differences for BLC (F2,8=58.8, p=0.001), W (F2,8=51.1, p=0.001), HR (F2,8=30.1, p=0.001) and VO2 (F2,8=28.3, p= 0.001) between the three definitions. The LB definition gave the lowest results; the MLSS results were intermediate and the OBLA results highest (Table 2).

 

The LB threshold occurred after the second to fourth load, and had an average BLC of 1.8(0.5) mmol․L-1. The 4.0 mmol․L-1 BLCOBLA was reached after the third to sixth load. LB results were 91-93% of the MLSS values, whereas OBLA values were 103-111% of them (see Figure 1). The different conditions correlated significantly for absolute values, but not for relative values, as expected. The three conditions did correlate highly with VO2max, but not with %VO2max. See Table 3a and b.

Figure 1. Box-plot of threshold results. Boxes represents 25 to 75 percentile, whiskers are 5th and 95th percentile. Horizontal line is median. LB=lactate breakpoint, OBLA=onset of blood lactate accumulation, W=watt, HR=heart rate, VO2 =oxygen uptake.

 

 

Discussion

Our main finding is that the load corresponding to WMLSS can be estimated from the results of an incremental test with the LP1710 by using a fixed BLC of 2.7(0.6) mmol․L-1 or alternatively, using a delta value of 1.7(0.6) to the resting BLC.

When using the threshold definitions of LB and OBLA, the load has to be heightened by 8% (WLB) or lowered by 11% (WOBLA) to equal WMLSS. Equally, HRLB and HROBLA, were 8% and 3% to low/high respectively compared with the MLSS results.

From incremental tests the MLSS results can be found by adding or subtracting from LB or OBLA data. The workload, heart rate and oxygen uptake from the LB definition had values of 91% to 93% of the MLSS values. As LB is a threshold definition that uses a relative BLC change, the results are probably less dependent of the analyser used (Buckley et al., 2003). Such a threshold definition is on the other hand sensitive to sampling site (Feliu et al., 1999), so finger sampling must be used for comparison with our data. The OBLA W, HR and VO2 were from 3% to 11% higher than MLSS values. OBLA is thought to equal MLSS (Heck et al., 1985), but the finding that OBLA exceeds MLSS is not unique. In an investigation by Laursen et al. (Laursen et al., 2002) on ultra-endurance athletes, the power output during a 5 h triathlon was 69% of the secondary ventilatory threshold (VT2). This threshold is regarded as being close to the OBLA threshold (Lucia et al., 1999), indicating that OBLA would over-estimate ultra-marathon performance.

Welde and co-workers (Welde et al., 2003) used a LP1710 for OBLA determination in running and skiing, and found that well-trained female skiers had an average of 95% of VO2OBLA during a six km simulated ski competition lasting less than 25 min, indicating that the OBLA values found by the LP1710 would over-estimate the athlete. Higher OBLA results compared with MLSS results were also found by Stegmann (Stegmann & Kindermann, 1982) in rowers, and Aunola, using cycling as the form of exercise (Aunola & Rusko, 1992). HROBLA was 89% of HRmax. That value is significantly lower than what Impellizzeri (Impellizzeri & Marcora, 2007) found (p=0.009) using highly trained MTB cyclists. They reported a HROBLA of 93% of HRmax. It is known that highly trained endurance athletes can utilise a larger proportion of their aerobic power over time than less trained individuals (Wilmore & Costill, 2004), so training status may explain the difference we see in our data. This is further highlighted by the findings of Chicharro et al. who compared professional and amateur cyclists on HR, VO2 and W at OBLA and at a heart rate of 175 (HR175), (Chicharro et al., 1999). For professional cyclists OBLA results were significantly higher than at HR175, p>0.01, but no difference was found for the lesser trained amateur cyclists, documenting the effect of training status on threshold performance as HRmax did not differ significantly between the groups.

Foxdal, compared the BLC of 50 min continuous runs at the OBLA speed (4 mmol․L-1) determined by steps protocols of different durations (4 to 8 min step duration) (Foxdal et al., 1996). They found that the continuous runs gave higher BLC than the incremental tests if step duration was shorter than eight minutes and warned that OBLA results from incremental tests with step durations shorter than 8 min would over-estimate MLSS performance. This is compatible with our finding; the BLC during the MLSS test was 26% higher than the BLC from the incremental test that we found could reproduce the WMLSS. This difference may be due to how the lactate is distributed in blood during exercise (Medbø & Toska, 2001).

Our subjects must be classified as fit with a mean VO2max of nearly 60 ml․kg-1․min-1 and Bentley found that well-trained cyclists had different “low BLC threshold” (Lactate Threshold; first increment above resting BLC) in incremental tests of 3 and 8 min step duration (Bentley et al., 2001). Recreational cyclists, on the other hand, performed equally on both tests. Dividing our group into “high level” (VO2max >64 ml․kg-1․min-1) and ”low level” fitness (VO2max <65 ml․kg-1․min-1), no difference was found in LB or OBLA results. This discrepancy with the results of (Bentley et al., 2001) may be caused by a higher fitness level of their trained subjects, or may be due to the fact that the duration of our incremental test, five minutes, was long enough to eradicate any differences in response. It’s also important to note that the two threshold definitions are not equal; the BLC from the LT definition is probably lower than our LB definition, thereby making exact comparison difficult.

Given the large variability of resting BLC in the small sample of the current study (range 0.8 mmol․L-1), and the fact that a threshold definition based on relative changes in BLC are less analyser sensitive, an approach that uses a fixed level of BLC does not seem to be preferable. By adding 1.7 ± 0.6 mmol․L-1 to resting BLC, the power corresponded to WMLSS. It is important to note that the spread of this delta value was large in our group, from 0.8 to 3.0 mmol․L-1, so the use of a fixed delta value will therefore lead to underestimation of some, and overestimation of others.

All conditions correlated highly with aerobic power, (table 3b, p<0.02). The highest correlation was seen in the WOBLA, r=0.89, which has the highest BLC. WLB had r=0.78 and the lowest BLC. Relating power with %VO2max did change the situation, and none of the relations were statistically significant (r<0.35). Our results are in line with Tokmakidis and co-workers (Tokmakidis et al., 1998) who were unable to find a unique BLC that had a superior correlation with performance compared to other levels of BLC, indicating that it is the profile of the whole curve that matters (Bentley et al., 2007).

Despite several attempts to develop a simple method to estimate the MLSS power (Billat et al., 1994; Harnish et al., 2001; Van et al., 2004), if the coach and athlete need high accuracy in their testing, the time consuming MLSS test protocol has to be applied.

Conclusion

It is possible to estimate the WMLSS from an incremental test with the LP1710 analyser. A fixed BLC of 2.7(0.6) mmol․L-1 or a delta value of 1.7(0.6) mmol․L-1 added to the resting BLC gives the WMLSS. These results are valid for incremental tests with step durations of five minutes, and finger sampling. MLSS power can also be derived from LB and OBLA test results. The values here found are analyser specific and may induce errors in the diagnostics of athletes if applied to other brands of analysers.

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