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Comparing Two Methods to Assess Power Output Associated With Peak Oxygen Uptake in Cyclists

Rønnestad, Bent R.

Journal of Strength and Conditioning Research: January 2014 - Volume 28 - Issue 1 - p 134–139
doi: 10.1519/JSC.0b013e3182987327
Original Research
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Rønnestad, BR. Comparing two methods to assess power output associated with peak oxygen uptake in cyclists. J Strength Cond Res 28(1): 134–139, 2014—The aim of this study was to compare 2 methods that are frequently used to calculate the power output (MAP) that is associated with peak oxygen uptake (V[Combining Dot Above]O2peak) in the exercise mode of cycling. One method calculates the MAP by extrapolation of the individual V[Combining Dot Above]O2 to submaximal power output relationships to the measured V[Combining Dot Above]O2peak (MAPDaniels), whereas the other method uses the minimal power output that elicits V[Combining Dot Above]O2peak during a graded V[Combining Dot Above]O2peak test (MAPBillat). Thirteen male competitive cyclists (V[Combining Dot Above]O2peak = 66 ± 5 ml·kg−1·min−1) performed 3 test sessions; first to determine MAPDaniels and MAPBillat; second and third sessions were used to measure the time to exhaustion during continuous cycling exercise to exhaustion (Tmax), time to 95% of V[Combining Dot Above]O2peak, and time ≥ 95% of V[Combining Dot Above]O2peak with MAPDaniels and MAPBillat. Whether it was MAPDaniels or MAPBillat that was used on the second or third test session was randomized. There was no difference between mean MAPDaniels and mean MAPBillat (380 ± 38 vs. 383 ± 34 W, respectively) and their associated Tmax, time to 95% of V[Combining Dot Above]O2peak, and time ≥ 95% of V[Combining Dot Above]O2peak during a Tmax test. In conclusion, this study did not find any difference between MAPDaniels and MAPBillat. The practical application of this study is that the choice of a method to calculate the MAP can be determined by practicality and that findings from studies using these 2 methods are comparable.

Section for Sports Science, Lillehammer University College, Lillehammer, Norway

Address correspondence to Bent R. Rønnestad, bent.ronnestad@hil.no.

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Introduction

For trained endurance athletes who are targeting their maximal genetic potential in both maximal oxygen uptake (V[Combining Dot Above]O2max) and endurance performance, it seems crucial to perform a certain amount of high-intensity training (25,33). A large amount of work has been performed to reveal the exercise protocols that allow a large time at V[Combining Dot Above]O2max or close to it (16,22,23). It has been concluded that, to spend a long time at or close to V[Combining Dot Above]O2max, the exercise intensity that is associated with V[Combining Dot Above]O2max is an essential training intensity (6,16,25).

There are several different methods to assess the exercise intensity associated with V[Combining Dot Above]O2max (7). These methods have been compared and investigated in the exercise mode of running and found to calculate different exercise intensities (1,7,15). Surprisingly, the literature seems to lack comparisons of these methods to calculate the power output associated with V[Combining Dot Above]O2max (MAP) in the exercise mode of cycling. There seems to be 2 methods to calculate the MAP in the exercise mode of cycling that are frequently used. One was first introduced by Daniels et al. (12) in middle distance runners. This method calculates the MAP by extrapolation of the individual V[Combining Dot Above]O2 to submaximal power output relationships to the measured V[Combining Dot Above]O2max (MAPDaniels). This method has later been used to assess the MAP during cycling (30–32). Billat and coworkers were inspired by Lacour et al. (21) when they introduced a slightly different and maybe more direct approach to determine the MAP (5). This method uses the minimal power output that elicits V[Combining Dot Above]O2peak during a graded V[Combining Dot Above]O2peak test to exhaustion (MAPBillat). Also this approach was originally used in the exercise mode of running but has later been used in the exercise mode of cycling (3,4,22–24). These 2 methods to calculate MAP have been compared in the exercise mode of running, and a nonsignificant difference in the MAP of approximately 4% was found (15). Based on previous observations of differences in V[Combining Dot Above]O2 kinetics between the exercise mode of running and cycling (10,11) and a greater degree of metabolic acidosis during cycling than during running (20), it may be suggested that findings from running cannot directly be transferred to cycling. It may be argued that the method developed by Billat et al. (5) is less time consuming, is based on a “real” power output, and is easier to use than the method introduced by Daniels et al. (12), which on the other side gives the opportunity of tracking exercise economy over a range of intensities. It is therefore important to get more knowledge of the application of these 2 methods. Because the MAP is one of the many parameters that has been suggested for use in monitoring the training status of athletes and for use in prescribing exercise intensity, it is important to know whether these 2 methods of calculating the MAP are comparable and actually describe the same parameters.

The purpose of this study was thus to compare MAPDaniels with MAPBillat and their associated time to 95% of V[Combining Dot Above]O2peak, time ≥ 95% of V[Combining Dot Above]O2peak, and time to exhaustion during continuous cycling exercise to exhaustion (Tmax). Based on findings from running, it was hypothesized that there was no differences between the 2 methods to calculate MAP.

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Methods

Experimental Approach to the Problem

The participants visited the test laboratory on 3 separate occasions. The first test session included submaximal cycling to obtain data for use in defining the power output—V[Combining Dot Above]O2 relationship followed by a graded protocol to exhaustion to determine V[Combining Dot Above]O2peak. The first visit was therefore used to establish MAPDaniels, MAPBillat, and V[Combining Dot Above]O2peak. On the second and third visits, Tmax, time to 95% of V[Combining Dot Above]O2peak, and time ≥ 95% of V[Combining Dot Above]O2peak were measured with MAPDaniels and MAPBillat. Whether it was MAPDaniels or MAPBillat that was used on the second or third test session was randomized. Ninety-five percent of V[Combining Dot Above]O2peak was chosen because previous studies have considered V[Combining Dot Above]O2 to have reached a “plateau” during the Tmax test when it reaches 95% of V[Combining Dot Above]O2peak (16) and this method of calculating time at, or near to, V[Combining Dot Above]O2peak has been used in previous studies (13,16,17,22).

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Subjects

Thirteen male competitive cyclists (age: 29 ± 6 years, height: 181 ± 5 cm, body mass: 76 ± 5 kg) volunteered for the study. All the participants trained for ≥6 h wk−1 during the 3 months before the intervention. All the participants provided written informed consent to participate in the study that was approved by the institution's ethics committee, in accordance with the Declaration of Helsinki (14).

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Procedures

The cyclists were instructed to refrain from all types of intense exercise the day preceding each of the 3 test days, to consume the same type of meal before each test, and were not allowed to eat during the hour preceding a test or to consume coffee or other products containing caffeine during the 3 hours preceding the tests. All the tests were performed under similar environmental conditions (18–20° C) and at the same time of day (±1 hour) to avoid the influence of circadian rhythm. The cycle ergometer (Lode Excalibur Sport, Lode B. V., Groningen, The Netherlands) was adjusted according to each cyclist's preference for seat height, horizontal distance between tip of seat and bottom bracket, and handlebar position. Identical seating positions were used in all tests.

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Submaximal Cycling

The test started without warm-up, with 5 minutes of cycling at 125 W. Cycling continued, and power output was increased by 50 W every 5 minutes. Blood samples were taken from the fingertip at the end of each 5-minute bout and were analyzed for whole blood [la] using a portable lactate analyzer (Lactate Pro LT-1710, Arcray Inc., Kyoto, Japan). The V[Combining Dot Above]O2, respiratory exchange ratio (RER), and heart rate (HR; Polar S610i, Polar, Kempele, Finland) were measured during the last 1.5 minutes of each bout, and the mean values for this period were used for the statistical analysis. The V[Combining Dot Above]O2 was measured (30-second sampling time) using a computerized metabolic system with mixing chamber (Oxycon Pro; Erich Jaeger, Hoechberg, Germany). The gas analyzers were calibrated with certified calibration gases of known concentrations before every test. The flow turbine (Triple V; Erich Jaeger) was calibrated before every test with a 3-L calibration syringe (5530 series; Hans Rudolph, Kansas City, KS, USA). The same metabolic system with identical calibration routines was used on all subsequent tests. Submaximal values were recorded from power outputs below a [la] of 2.5 mmol·L−1. After the termination of the submaximal cycling, the participants had 15 minutes of recovery cycling before completing a graded protocol to exhaustion for the determination of the V[Combining Dot Above]Opeak. This test has been described elsewhere (28). Briefly, the test was initiated with 1 minute of cycling at a power output corresponding to 3 W·kg−1 (rounded down to the nearest 50 W). Power output was subsequently increased by 25 W every minute until exhaustion. The V[Combining Dot Above]O2peak was calculated as the average of the 2 highest V[Combining Dot Above]O2 measurements. The HR ≥ 95% of known maximal HR, RER ≥ 1.05, and [la] ≥ 8.0 mmol·L−1 were used as criteria to evaluate if V[Combining Dot Above]O2peak was obtained.

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Tmax at MAPDaniels and MAPBillat

The MAPDaniels was calculated according to the description of Daniels et al. (12): This method calculates the MAP by extrapolation of the individual V[Combining Dot Above]O2 to submaximal power output relationships to the measured V[Combining Dot Above]O2max. The MAPBillat was calculated according to the description of Billat and Koralsztein (7): The lowest power output that elicited V[Combining Dot Above]O2< 2.1 ml·kg−1·min−1 of V[Combining Dot Above]O2peak during the graded V[Combining Dot Above]O2peak protocol.

The Tmax at MAPDaniels and MAPBillat was tested in a randomized order on 2 separate test days with 3 days in between. Each test day started with a 15-minute individual warm-up that was concluded by 2–3 submaximal sprints. Just before the start of the Tmax test, the participants were pedaling with a freely chosen cadence (80–105 rpm) with zero power output. When the test started, the participants received their MAP watts instantly (1,000 W·s−1). Ventilation, RER, V[Combining Dot Above]O2, and HR were recorded at 15-second intervals throughout exercise. The athletes were blinded to the time elapsed and power output on all testing occasions. The test was stopped when cadence fell below 60 rpm. Time to achieve a V[Combining Dot Above]O2 of ≥95% of V[Combining Dot Above]O2peak and total time spent ≥95% of V[Combining Dot Above]O2peak was measured with both MAPDaniels and MAPBillat. Time to 95% of V[Combining Dot Above]O2peak was regarded as the time from the start of the test until the first V[Combining Dot Above]O2 measurement that was ≥95% of the V[Combining Dot Above]O2peak obtained from the graded exercise test to exhaustion. The sum of the V[Combining Dot Above]O2 values that were ≥95% of the V[Combining Dot Above]O2peak obtained from the graded exercise test to exhaustion was regarded as time ≥ 95% of V[Combining Dot Above]O2peak.

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Statistical Analyses

All values presented in the text, figures, and tables are mean ± SD. Pearson product-moment correlation coefficient was used to examine the relationships between the variables. Effect size of correlation coefficients was defined as r < 0.1 = trivial, 0.1–0.3 = small, 0.3–0.5 = moderate, 0.5–0.7 = large, 0.7–0.9 = very large, 0.9 = nearly perfect, and 1.0 = perfect (18). To analyze whether there were differences in peak values achieved in the Tmax test at MAPDaniels, Tmax test at MAPBillat, and in the graded test for V[Combining Dot Above]O2peak determination, a 1-way analysis of variance analysis was used. If there was a significant difference, a Tukey's honestly significant difference test was preselected for post hoc analysis (GraphPad, GraphPad Software Inc., La Jolla, CA, USA). To test for significant differences in MAPDaniels and MAPBillat and the acute physiological response during exercising at MAPDaniels and MAPBillat to exhaustion, a paired t-test was used (Excel 2010, Microsoft Corporation, Redmond, WA, USA). Test–retest reliabilities (intraclass correlations) for the Tmax test were 0.92 (p < 0.01). There was a statistical power of 80% to detect the differences between MAPDaniels and MAPBillat of 15 W, using a significance level (alpha) of 0.05 (2-tailed). Statistical significance was set at the 0.05 level.

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Results

There was no difference in the peak physiological values achieved in the graded V[Combining Dot Above]O2peak protocol, Tmax at MAPDaniels, and Tmax at MAPBillat (Table 1). There was no difference in the power output calculated by MAPDaniels and MAPBillat (Table 2). There was no difference in Tmax, time to 95% of V[Combining Dot Above]O2peak, or in time ≥ 95% of V[Combining Dot Above]O2peak between MAPDaniels and MAPBillat (Table 2). When time to reach 95% of V[Combining Dot Above]O2peak was expressed as a percentage of Tmax, there was no difference between MAPDaniels and MAPBillat (after 47 ± 11% and 51 ± 17% of Tmax, respectively; Figure 1).

Table 1

Table 1

Table 2

Table 2

Figure 1

Figure 1

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Discussion

The primary finding of this study supported the hypothesis of no difference between the mean MAPDaniels and mean MAPBillat. Furthermore, when the participants were cycling to exhaustion at MAPDaniels or MAPBillat, there were no differences between them in Tmax, in time to 95% of V[Combining Dot Above]O2peak, or in time ≥ 95% of the V[Combining Dot Above]O2peak.

The difference between the methods for the primary variable of interest, MAP, was 3 W, and is probably physiologically insignificant. This observation is in agreement with that of a previous study using the exercise mode of running (15). In the latter study, MAPBillat was nonsignificant approximately 4% higher than MAPDaniels, while in this study, it was nonsignificant, approximately 1% higher. Accordingly, in both this study and in the study of Hill and Rowell (15), there was a very large correlation between MAPDaniels and MAPBillat with a slightly larger correlation coefficient in the present study (r = 0.85 vs. r= 0.79). The precision in calculating MAPBillat is related to the size and duration of the steps in the graded V[Combining Dot Above]O2peak test (7). Based on the findings of quite similar values in MAPDaniels and MAPBillat, it seems like the protocol used in the present graded V[Combining Dot Above]O2peak test is sensitive enough when calculating MAPBillat. Furthermore, it is also likely that truly maximal V[Combining Dot Above]O2peak in the exercise mode of cycling was obtained during the graded V[Combining Dot Above]O2peak test because there were no differences between the results of the graded test and the 2 Tmax tests.

Ninety-five percent of the V[Combining Dot Above]O2peak was achieved at approximately 50% of Tmax at both MAPDaniels and MAPBillat. This is in accordance with the previous findings from distance runners which reach 95% of V[Combining Dot Above]O2peak at approximately 50% of Tmax (16,17) and slightly different from previous data from cyclists, reporting that 95% of V[Combining Dot Above]O2peak was achieved after approximately 60% of Tmax (22). This small difference may be related to the shorter V[Combining Dot Above]O2 sampling time during the Tmax test in this study (15 vs. 20 seconds, respectively). Accordingly, it has been suggested that the differences in sampling time affects both time to achieve 95% of the V[Combining Dot Above]O2peak and total time ≥ 95% of V[Combining Dot Above]O2peak during Tmax tests (25). Regardless of using MAPDaniels or MAPBillat, this study supports the frequent recommendation of using exercise duration of 60% of Tmax in repeated high-intensity interval training sessions when the aim is to train at or close to V[Combining Dot Above]O2peak (22,24,29). This means that individual interval recommendations can be given by using either MAPDaniels or MAPBillat. The present finding of mean Tmax of approximately 380 seconds in both MAPDaniels and MAPBillat is within the range of previous reported mean values of 222–390 seconds in cyclists (3,4,22) and also within the range of mean values of 269–483 seconds reported in distance runners (3,8,16,27). This relatively large variation in Tmax in both running and cycling is likely to be caused by the differences in anaerobic capacity (2,9) and the difference between workload at lactate threshold and workload at V[Combining Dot Above]O2peak (5,6), but not V[Combining Dot Above]O2peak and MAP (5,6,27). The present findings are in accordance with the findings from the exercise mode of running and thus suggests that the previous observations of differences in V[Combining Dot Above]O2 kinetics between the running and cycling (10,11) and a greater degree of metabolic acidosis during cycling than during running (20) does not acutely affect the calculation of MAPDaniels and MAPBillat or their respective acute physiological responses to a Tmax test.

The present similarity in time ≥ 95% of V[Combining Dot Above]O2peak during the 2 Tmax tests is expected when we see the similarity in MAP. The present Tmax durations are in accordance with the values reported from distance runners; where the mean time ≥ 95% of V[Combining Dot Above]O2peak during Tmax tests ranges between 140 and 180 seconds (13,16,17,26). However, previous studies on cyclists reported a slightly lower mean time of 95 and 136 seconds ≥95% of V[Combining Dot Above]O2peak during Tmax tests (4,22). This small difference is likely to be present because of the day-to-day biological variation, or methodological issues such as small differences in sampling time during Tmax, small differences in the graded protocol to determine V[Combining Dot Above]O2peak, and inclusion of triathletes.

To the best of our knowledge, this study is the first to compare the 2 frequently used methods to calculate MAP in cyclists; MAPDaniels (30–32) and MAPBillat (3,4,22–24). Hill and Rowell (15) compared these 2 methods in the exercise mode of running and argued that the strength of the MAPBillat method is that this exercise intensity is “real” and actually associated with the measurement of the V[Combining Dot Above]O2peak and that the method is easy to use. They claim that a potential drawback to use this method is the precision, because it depends on the length and number of stages in the graded V[Combining Dot Above]O2peak test. The same authors suggest that the advantage of the MAPDaniels method is the opportunity of tracking exercise economy over a range of intensities and that the disadvantage may be the difficulty in precisely extrapolating oxygen cost from submaximal exercise intensities (15). The present findings suggest that the choice of method can be determined by practicality and that finding from studies using one of these 2 methods are comparable. That being said, and despite a very large correlation between MAPDaniels and MAPBillat, there was some individual variation in the V[Combining Dot Above]O2 response to the 2 Tmax tests. This is shown by the moderate to large correlation in time to achieve 95% of V[Combining Dot Above]O2peak and time ≥ 95% of V[Combining Dot Above]O2peak, respectively, between the Tmax test using MAPDaniels and MAPBillat. This individual variation may be because of a repeated effect, as indicated by Laursen et al. (22) showing a intraparticipant coefficient of variation of 15 and 38%, respectively, in these measurements during 2 repeated Tmax tests. These findings may, at least partly, be explained by the observed day-to-day biological variation in V[Combining Dot Above]O2peak of ±5.6% (19).

In conclusion, this study did not find any difference between MAPDaniels and MAPBillat and when the participants were cycling to exhaustion at MAPDaniels or MAPBillat there were no differences between them in Tmax, in time to 95% of V[Combining Dot Above]O2peak, or in time ≥ 95% of V[Combining Dot Above]O2peak.

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Practical Applications

This study revealed that there is no difference between MAPDaniels and MAPBillat and their respective acute physiological responses during a Tmax test in the exercise mode of cycling. Therefore, the choice of a method to calculate a cyclist's MAP can be determined by practicality and findings from studies using these 2 methods seems to be comparable. Importantly, the precision in calculating MAPBillat is related to the size and duration of the steps in the graded V[Combining Dot Above]O2peak test and it seems like the protocol used in the present graded V[Combining Dot Above]O2peak test is sensitive enough when calculating MAPBillat (the first minute was 3 W·kg−1 followed by 25-W increase every minute until exhaustion). Moreover, when the aim is to exercise at or close to V[Combining Dot Above]O2peak the present results suggest that when using MAP as exercise intensity, the interval duration should be at least 50% of Tmax.

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Acknowledgments

Thanks are expressed to Gunnhild Hustad Vaa, Silje Øyre Slind, and Joar Hansen for their help in data collection and to the cyclists for devoting their time and effort. No funding was obtained for this study. The authors have no professional relationships with companies or manufacturers who will benefit from the results of this study, and the results of this study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association.

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Keywords:

exercise test protocol; intense cycling exercise; interval training prescription

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