Predicting MAOD Using Only a Supramaximal ...

Training & Testing 477

Predicting MAOD Using Only a Supramaximal Exhaustive Test

Authors

R. C. M. Bertuzzi1, E. Franchini1, C. Ugrinowitsch1, E. Kokubun2, A. E. Lima-Silva3, F. O. Pires1, F. Y. Nakamura4, M. A. P. D. M. Kiss2

A liations

1

Key words oxygen uptake blood lactate excess post-exercise oxygen consumption

Abstract

University of São Paulo, School of Physical Education and Sport, São Paulo, Brazil São Paulo State University, Physical Education, Rio Claro, Brazil 3 Sports, Science Research Group, Federal University of Alagoas, Alagoas, Brazil 4 Universidade Estadual de Londrina, Departamento de Educação Física, Londrina, Brazil

The objective of this study was to propose an alternative method (MAODALT) to estimate the maximal accumulated oxygen deficit (MAOD) using only one supramaximal exhaustive test. Nine participants performed the following tests: (a) a maximal incremental exercise test, (b) six submaximal constant workload tests, and (c) a supramaximal constant workload test. Traditional MAOD was determined by calculating the di erence between predicted O2 demand and

Introduction

accepted after revision September 24, 2009 Bibliography DOI http://dx.doi.org/ 10.1055/s-0030-1253375 Published online: April 29, 2010 Int J Sports Med 2010; 31: 477–481 © Georg Thieme Verlag KG Stuttgart · New York ISSN 0172-4622 Correspondence Dr. Rômulo Cassio de Moraes Bertuzzi University of São Paulo, School of Physical Education and Sport Department of Sport Avenida Professor Mello Moraes, 65 - São Paulo - SP, CEP. 05508-30 Tel.: 55 11 3735-3353 Fax: 55 11 3735-3353 [email protected]

The maximum amount of ATP that can be resynthesized by the breakdown of phosphocreatine and intramuscular glycogen, followed by muscle and blood lactate accumulation, is defined as anaerobic capacity (AC) [10]. It has been reported that AC is a determinant for exhaustive shortduration sports, such as 200 and 400 m track events [26]. Thus, a wide range of mechanical and physiological tests have been proposed to assess the AC [10]. One of these tests, the maximal accumulated oxygen deficit (MAOD), is considered to be a valid measurement of the AC [20, 21]. Consequently, the MAOD has been used to determine training status [27], the metabolic profile of high intensity exercises [26], and to validate other anaerobic tests [22, 25]. According to the classical method that was proposed by Medbo et al. [20], MAOD represents the di erence between the predicted oxygen demand and the accumulated oxygen uptake as measured during a supramaximal exhaustive test that lasts from 2 to 16 min. In order to calculate the oxygen demand, participants are required to complete 6 [27] to 20 [20] sub-maximal exercise bouts that are performed on di erent days. Unfortunately, this time-consuming procedure has discouraged

accumulated O2 uptake during the supramaximal test. MAODALT was established by summing the fast component of excess post-exercise oxygen consumption and the O2 equivalent for energy provided by blood lactate accumulation, both of which were measured during the supramaximal test. There was no significant di erence between MAOD (2.82 ± 0.45 L) and MAODALT (2.77 ± 0.37 L) (p = 0.60). The correlation between MAOD and MAODALT was also high (r = 0.78; p = 0.014). These data indicate that the MAODALT can be used to estimate the MAOD.

sport scientists and coaches from using the MAOD. Therefore, less time-consuming methods that could assess MAOD would be very appealing from an applied stand point. Data from previous studies indicate that the fast component of excess post-exercise oxygen consumption (EPOCFAST) corresponds to the total energy that is used to resynthesize high-energy phosphate stores [12, 18]. In addition, di Prampero and Ferretti [5] suggested a procedure to express the glycolytic energy cost based upon the blood lactate concentration ([La ]), which produces an O2 equivalent. Thus, it is reasonable to assume that the sum of these estimates of anaerobic energy expenditure (EPOCFAST + O2 equivalent from blood lactate accumulation), which can be obtained in one exhaustive supramaximal test, could be alternatively used to determine MAOD (MAODALT). Therefore the purpose of the present investigation was to evaluate the ability of MAODALT to estimate the classical MAOD. Our main hypothesis was that the sum of EPOCFAST and O2 equivalent to the energy supplied by [La ], as measured during a single exhaustive supramaximal exercise test, would be similar to MAOD.

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Subjects Nine healthy male subjects (23 ± 4 years, 71.7 ± 8.4 kg, 175.0 ± 5.5 cm, 12.1 ± 4.8 % of body fat), who were familiar with exhaustive exercise, volunteered to participate in this study. At the time of the study, none of the participants were engaged in any competitive training program but had been active in recreational sports (jogging, soccer, and tennis) for at least one year. Participants were informed of the experimental risks and signed an informed consent form prior to the investigation. This study was approved by an Institutional Review Board for the use of human subjects.

Experimental design The participants performed four experimental sessions that were separated by at least a 72 h interval. During the first session, anthropometric parameters were obtained, followed by a maximal incremental exercise test in order to measure the maximal oxygen uptake (V˙ O2max) and the power output that corresponded to V˙ O2max (Wmax). Six constant workload tests (three tests per session) at sub-maximal intensities (40–90 % Wmax) were conducted during sessions two and three in order to estimate oxygen demand during the supramaximal test. A supramaximal test was performed until voluntary exhaustion at 110 % Wmax during the fourth session. The order of test sessions two, three, and four was randomly assigned. All tests were performed at the same time of the day, in the temperature range (i. e. 20–24 ° C), and at least two hours after the last meal. The participants were asked to refrain from exhaustive exercise, alcohol and ca eine ingestion 48 h prior to data collection. Participants were instructed to maintain the same diet throughout the study.

Anthropometry Subjects were weighed using an electronic scale to the nearest 0.1 kg. Height was measured with a stadiometer to the nearest 0.1 cm. Skinfold thickness was measured with a Harpenden caliper (West Sussex, UK) to the nearest 0.2 mm. Body density was predicted using the generalized equation of Jackson and Pollock [16] and body fat was estimated using the equation of Brozek et al. [4].

[La ] determination. Lactate concentrations were assessed using an automatic blood lactate analyzer (1 500 Sport, Yellow Springs Instruments, Yellow Springs, OH, USA), and the highest value was retained as the peak blood lactate concentration ([La ]peak). After a 3-min warm-up using only the inertial resistance of the equipment, the participants exercised at a pedal frequency of 60 rpm with power output increments of 30 Wmin 1 until voluntary exhaustion, which was defined as the incapacity to maintain a minimum pedal cadence of 50 rpm. The participants received strong verbal encouragement to continue as long as possible. V˙ O2max was determined when two or more of the following criteria were met: an increase in V˙ O2 of less than 2.1 ml · kg 1 · min 1 on two consecutive stages, a respiratory exchange ratio greater than 1.1, blood lactate concentration higher than 8.0 mmoll 1, and ± 10 bpm of the maximal age-predicted heart rate [14]. Wmax was established as the power output that elicited V˙ O2max. The maximal heart rate (HRmax) was defined as the highest value obtained at the end of the test.

Constant workload tests The same cycle ergometer and conditions used for the maximal incremental test were used for the constant workload tests. The participants exercised for 10 min at six constant workloads, which were 40, 50, 60, 70, 80 and 90 % Wmax, presented in a random order. The recovery time between the constant workload tests was ~10 min or until the V˙ O2 returned to V˙ O2 baseline. The V˙ O2 for each workload was defined as the average over the last 30 s of the test. A supra-maximal test was performed using a workload that corresponded to 110 % Wmax. Supra-maximal test intensity was determined based upon the findings of Weber and Schneider [28] for estimating the MAOD of non-athlete subjects who were measured on a cycle ergometer. Participants were asked to rest quietly on the cycle ergometer for 5 min in order to determineV˙ O2 baseline. Peak oxygen uptake (V˙ O2peak) was defined as the average of the last 30 s of the supramaximal test. Blood samples were collected from the ear lobe at rest at time points immediately, three minutes, and five minutes after exercise was stopped for the determination of [La ]peak. The peak heart rate (HRpeak) was defined as the highest value that was obtained at the end of the test.

Maximal incremental exercise test The maximal incremental exercise test was carried out on an electromagnetically braked cycle ergometer (Standart Lannoy Ergometer, Godart-Statham, Bilthoven, Holland). The seat height was adjusted for each participant, allowing near full leg extension during each pedal revolution, and these conditions were reproduced for all experimental sessions. Oxygen uptake (V˙ O2) was measured breath-by-breath throughout the test using a portable gas analyzer (K4b2, Cosmed, Rome, Italy) and averaged over 30-s intervals. The calibration of the device was performed according to manufacturer specifications using ambient air, a gas of composition containing 20.9 % O2 and 5 % CO2, and a 3 L syringe (K4b2 instruction manual). Heart rate was measured during the test with a heart rate transmitter (Polar Electro Oy, Kempele, Finland) that was coupled to the gas analyzer. Blood samples (25 l) were collected from the ear lobe immediately, at the third minute, and at the fifth minute after the exercise for

Calculations MAOD was calculated according to Medbo et al. [20]. Briefly, the V˙ O2 of the six submaximal cycling bouts and their relative intensities were used to develop linear regression equations. These equations were used for estimating individual oxygen demand during the supramaximal test. The V˙ O2 was measured breath-by-breath and integrated over time to obtain the accumulated V˙ O2 during the supramaximal test. Thus, the MAOD was calculated as the di erence between the estimated oxygen demand and the accumulated V˙ O2 at 110 % Wmax. Absolute MAOD values were reduced by 10 % to correct for the contribution of body oxygen stores to the energy supply [20]. EPOCFAST was used as an estimate of the alactic anaerobic metabolism contribution to MAODALT [18]. The breath-to-breath V˙ O2 o -transient response of the supramaximal exercise test was fitted using a biexponential model (Eq. 1) (Origin 6.0, Microcal,

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Methods

Training & Testing 479

Massachusetts, USA) [24]. Eq. 2 was then applied in order to obtain the EPOCFAST (Eq. 2) [2, 11]. VO2(t) = VO2baseline + A1 e −(t −!) / "1  + A 2 e −(t −!) / "2 

EPOCFAST and the lactic metabolism contribution. In addition, these estimates of the anaerobic components are also expressed as a percentage relative to MAODALT.

Statistical analysis

where V˙ O2(t) is the oxygen uptake at time t, V˙ O2baseline is the oxygen uptake at baseline, A is the amplitude, is the time delay, ! is the time constant, and 1 and 2 denote the fast and slow components, respectively. To calculate the lactic metabolism contribution, the di erence between [La ]peak and [La ]rest, which was measured during supramaximal test, was expressed as a delta value ([La ]net). A value of 1 mmoll 1 [La ]net was considered to be equivalent to 3 ml O2kg 1 body mass [5]. MAODALT was obtained by the sum of

Table 1 Physiological parameters measured during incremental maximal exercise test (n = 9). VO2max (l · min 1) VO2max (ml · kg 1min 1) Wmax (W) RER HRmax (beats · min 1) [La ]peak (mmol · l 1)

2.9 ± 0.4 41.3 ± 6.0 247 ± 39 1.30 ± 0.08 179 ± 9 10.5 ± 1.3

Data are reported as mean ± SD. VO2max: maximal oxygen uptake; Wmax: power output corresponding to maximal oxygen uptake; RER: respiratory exchange ratio; HRmax: maximal heart rate; [La ]peak: peak blood lactate concentration

Table 2 Physiological responses during the supramaximal test (n = 9). VO2peak (L) VO2peak (ml · kg 1min 1) HRpeak (beats · min 1) [La ]peak (mmol · L 1) [La ]rest (mmol · L 1)

2.6 ± 0.3 36.6 ± 5.3 173 ± 14 10.9 ± 1.2 0.7 ± 0.2

The distribution of the data was analyzed by the Shapiro-Wilk test, and the results showed a normal Gaussian distribution. Data are reported as mean and standard deviation (SD). Paired t-test was used to examine the di erences between MAOD and MAODALT. In addition, Bland and Altman [3] plotting was used to assess the level of agreement between MAOD and MAODALT. The significance level was set at p < 0.05.

Results Physiological parameters that were measured during the maxiTable 1. The mean mal incremental exercise test are shown in absolute workload of the supramaximal test and the time to exhaustion were 272 ± 44 W and 154 ± 38 s, respectively ( Table 2). Regression analysis of the six bouts of submaximal cycling showed a linear correlation between V˙ O2 and power output that was always higher than r = 0.97 (p = 0.001). The oxygen demand in the supramaximal test was 8.8 ± 1.8 L, while the accumulated V˙ O2 was 5.6 ± 1.7 L. The comparison between MAOD and MAODALT using Bland-AltFig. 1. The bias when comparing the man plotting is shown in MAOD estimates by the Bland-Altman analysis was very close to zero. There was no significant di erence between MAOD and MAODALT (p = 0.60). The correlation between MAOD and MAODALT was also high (r = 0.78; p = 0.014). Mean EPOCFAST and O2 equivalent from blood lactate accumulation were 0.61 ± 0.12 L and 2.16 ± 0.32 L, respectively. The values of the alactic and lactic metabolism contribution corresponded to 22 ± 7 % and 78 ± 6 % of MAODALT, respectively.

Data are reported as mean ± SD. VO2peak: peak oxygen uptake; HRpeak; peak heart rate; [La ]peak: peak blood lactate; [La ]rest: blood lactate at rest

Difference between MAOD and MAODALT (I)

3.5 3.0

Oxygen (I)

2.5 2.0 1.5 1.0 0.5 0.0 MAOD

MAODALT

1.0 0.8

Mean + 1.96 SD

0.6 0.4 0.2

Mean

0.0 –0.2 –0.4 –0.6

Mean - 1.96 SD

–0.8 –1.0 2.2

2.4

2.6

2.8

3.0

3.2

3.4

3.6

Mean of the MAOD calculated by two methods (I) Fig. 1 Comparison between maximal accumulated oxygen deficit calculated by a method similar to that described by Medbø et al. [20] (MAOD) and by the alternative method proposed here (MAODALT) (left panel). Bland-Altman plot for visual comparison of the mean di erence between

MAOD and MAODALT (right panel). The central horizontal line represents the mean di erence detected between methods, with the top and bottom lines indicating the 95 % limits of agreement ( ± SD). No significant di erence was observed between the two methods (p > 0.05).

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EPCOFAST = A1 ⋅ "1

Discussion

Limitations

Previous work suggested that the MAOD is a physiological, noninvasive method that can be used to assess the AC during high intensity exercise [20, 21]. However, participants are required to complete several tests in order to estimate MAOD, which makes its application cumbersome. Thus, the present study analyzed the capacity of an alternative method to estimate MAOD using only one supramaximal test. Our data revealed that MAOD can be estimated by MAODALT. In fact, MAODALT estimates are similar to MAOD values that have been reported in the literature for untrained subjects (3.01 ± 0.11 L) [23]. Additionally, the MAODALT produced substantially lower MAOD values than those that have been reported for professional sprint (4.82 ± 0.22 L) and endurance (3.82 ± 0.30 L) cyclists [9]. Thus, the MAODALT appears to produce appropriate MAOD values for untrained individuals, and it has the potential to discriminate between the training statuses of di erent groups. Although the method that was established by Medbø et al. [20] has been widely used, it is not the only one used to determine MAOD [13, 25]. Hill and colleagues [13, 25] also proposed an alternative procedure to estimate MAOD using a nonlinear regression analysis from only four all-out tests. However, Du ield et al. [7] showed that the method proposed by Hill et al. [13] overestimates the oxygen deficit during short-duration exercises. In the present study, we did not find significant di erences between the MAODALT and the MAOD values. In addition, the bias when MAOD estimates were compared was very close to zero. Even so, the shared variance between estimates was high (r2 = 0.61), which indicated that MAOD and MAODALT change similarly. Interestingly, the percentage values of the anaerobic components of MAODALT are similar to those reported in the literature for MAOD [20, 21]. In the present study, the EPOCFAST and O2 equivalent to the energy supplied by [La ] represented 22 % and 78 % of MAODALT, respectively. Bangsbo et al. [1] reported a 20 % and 80 % contribution of phosphocreatine breakdown and lactate production, respectively, to the total accumulated oxygen deficit during a knee-extensor exercise to exhaustion, using muscle biopsies. Similarly, Medbø and Tabata [21] determined the anaerobic contribution from changes in muscle metabolites and showed that, during 2–3 min of cycling to exhaustion, lactate production provided three times more ATP than phosphocreatine breakdown. Taken together, these data suggest that the anaerobic components of MAODALT may be used to estimate the alactic and lactic metabolism contributions during high intensity exercise. In this respect, it is important to note that our observations may have relevant practical applications for determining the components of anaerobic metabolism during high intensity exercises. For instance, creatine monohydrate [17] and ca eine [6] supplementation seem to enhance, respectively, the intramuscular stores of creatine [17] and the activity of glycolytic enzymes, such as PFK [6], which seems to increase MAOD by ~10 %. From this perspective, MAOLDALT may be useful to detect changes in alactic and lactic metabolisms after supplementation strategies aimed at improving the AC.

Obviously, our results are derived from the logical validity of methods that have been used to calculate anaerobic metabolism components, since there is no gold standard test for the measurement of AC [8]. In fact, it is important to point out that previous studies have reported limitations regarding the use of EPOCFAST [10] and [La ] [8]. These authors agree that the metabolic demand of active muscles may not be estimated by analyzing whole-body physiological responses. Furthermore, as the O2 equivalent from [La ] used in present study does not represent the exact stoichiometric relationship between lactate formation and ATP resynthesis [5], other O2 equivalents from [La ] (e. g. 5.3 ml O2kg 1mmol 1 lactateL 1) have also been used in previous works [15, 19]. Thus, our estimate of the lactic metabolism contribution to the MOADALT could be underestimated based on 5.3 ml O2kg 1mmol 1 lactateL 1 equivalent. On other hand, the 3 ml O2kg 1mmol 1 lactateL 1 equivalent has been considered an empirical method that allows us to estimate the energy release in the body whenever the blood lactate concentration increases by a given amount above baselines values [5]. Additionally, the low number, physical characteristics, and gender of our participants decrease the external validity of our findings. Future works should try to overcome these limitations before starting to apply the MAODALT to distinct samples. Alternatively, intramuscular metabolites may be quantified to express the AC. However, muscle tissue for these measurements is usually obtained from small muscle masses (50–100 mg), which, because of the di culty of determining the muscle mass that is involved in a specific exercise, may not accurately represent the activation of anaerobic metabolism during an exercise [9]. The time delay between obtaining and processing the muscle specimen may allow some phosphatases to remain active after tissue extraction, which would produce biases in the anaerobic metabolism estimates. Finally, muscle biopsies require specialized personnel, and athletes usually do not feel inclined to volunteer for studies that use this procedure. In conclusion, our data indicate that MAODALT provides a satisfactory estimate of MAOD with a reduced number of testing sessions. Moreover, it may give indications of the alactic and lactic metabolism contributions to the test.

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