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Validation of the lactate minimum test as a specific aerobic evaluation protocol for table tennis players.

INTRODUCTION

Table tennis is a major competitive sport characterized by intermittent efforts that alternate periods of fast movement and pause. As a result, the oxygen that is required for muscle contraction at the cellular level comes from both aerobic metabolism and anaerobic metabolism. As to the percent of energy expenditure from both systems during table tennis, aerobic metabolism corresponds to ~40 to 50% of the energy expended during the game. The anaerobic lactic system corresponds to ~10 to 20%. The anaerobic alactic system is the main source of energy resynthesis during moments of dynamic effort while the contribution of the anaerobic lactic system is increased during rallies of prolonged duration (5,9,15,16,18). However, what is interesting is that the predominant system of ATP resynthesis in table tennis has not had its stress percentage reported (18,23).

During a table tennis match, the real exercise time corresponds to ~28% of the total time, showing on average a mean of 3.3 sec of exercise and 8 sec of pause (10). However, after a change in the ball diameter from 38 mm to 40 mm and a decrease in game speed so as to make the sport more attractive to spectators and television, changes in the duration of the rallies resulted in a decrease of ~1 to 2% in the initial ball speed and 5 to 20% in the effect. These changes resulted in an increase of 2 to 4% in the duration of the rallies (20).

Compared to other sports, it is rare to find studies that have evaluated table tennis athletes during the actual game situation itself. However, Zagatto et al. (24-27), having adapted the model of critical power (12), proposed a test protocol for the determination of the aerobic critical frequency (critf) in table tennis. A mechanical ball launcher is used to show that it is possible to determine the critf and the anaerobic work capacity (AWC) of the athletes. They concluded that: (a) the test protocol in table tennis must respect the specificity of the sport; and (b) critf can be used to estimate aerobic capacity. But, it was unclear whether AWC represented the actual anaerobic work capacity in table tennis.

There are several models and protocols to evaluate and determine aerobic and anaerobic capacities. Among them, the lactate minimum ([Lac.sub.min]) test proposed by Tegtbur et al. (21) demonstrates the individual's aerobic and anaerobic transition that measures the balance point between lactate production and removal (14). While this model has been adapted for treadmill (7,8) and cycling (11,18) exercises, it has not been validated for table tennis (13). Jones and Doust (7) indicate that the [Lac.sub.min] test is a way to determine the maximal lactate steady state (MLSS), which is the gold standard of anaerobic threshold verification.

If their thinking is confirmed in our findings, we will be able to suggest this method as an acceptable approach to estimating the intensity of aerobic training in table tennis. In the end, then, the protocol may be useful in supporting the training, evaluation, and development of the athletic performance of table tennis players. Thus, the purpose of this study was to validate the [Lac.sub.min] test in forehand attacks using a mechanical ball launcher (robot) to simulate the table tennis.

METHODS

Subjects

Eight male tennis players (age, 15.9 [+ or -] 2.6 yrs) with at least 1 yr of national competition experience participated in this study. The subjects and their parents signed the informed consent form to participate in the study, which was approved by the local ethics commission.

Procedures

The table tennis players were submitted to the game forehand attack simulations, hitting balls shot by a robot (THIBAR Robot RoboPro[R]) at variable shot frequencies. The ball bounce occurred at 60 cm in front of the net, in the subjects' side of the table. The speed and lateral oscillation of the balls were maintained unchanged throughout the test. The robot has several controls that regulate its functions. One is located on the upper portion of the robot. It controlled the amplitude, which remained between 70 and 80 cm, and the oscillation of the launch. The table control regulated the speed and frequency of the balls shot. A third control adjusted the simple and double combinations that varied from 1 to 5.

This study used an adjustment equivalent to 1 to 4, which resulted in balls shot at the amplitude of the two lateral extremities of the table. The table control allowed for speed adjustment for the ball, ball frequency, and lateral oscillation, with units that vary from 1 to 9. The speed that was maintained during the test corresponded to the control number 4 and lateral oscillation of the balls was also maintained constant in every specific test. The frequency control provided units that range from 1 to 9, where 1 represents 32 balls x [min.sup-1] and an increase of approximately 8 balls x [min.sup-1] for each numerical increase. Before the test, the subjects performed stretching and warming up at the table with the aid of the robot, with 4-min duration and a 40 balls x [min.sup-1] frequency. The lateral oscillation and ball speed were kept equal to those applied during all tests. The protocols began 5 min after warming up.

Lactate Minimum Test

For acidosis specific induction, the robot launched the balls at the frequency of 72 balls x [min.sup-1] for 90 sec. The subjects were given directions to attack balls with forehand movements at the shot rate during this induction phase. Blood samples (25 pl) were collected at 1, 3, 5, and 7 min at the end. The incremental phase began 8 min after the specific acidosis induction, in which the progressive charges phase began with a frequency of 40 ballsmin-1 and an increment of 8 balls x [min.sup-1] every 3 min until exhaustion. The exhaustion was voluntarily established or determined when the participant performed 3 consecutive mistakes. These faults were: (a) not reaching the ball or not returning the ball correctly; (b) not executing the correct movement; and (c) not returning the ball to the other side of the table. The blood samples were performed at the end of each 3 min frequency stage. The minimum lactate was obtained from derived equal zero of the second order polynomial fit of the 'U-shaped" curve of blood lactate concentration versus time test of the incremental phase of the lactate minimum test and the curve of blood lactate concentration versus ball frequency of the incremental phase of the [Lac.sub.min] test.

Determination of the Maximal Lactate Steady State

The subjects performed 3 to 4 sessions of continuous tests in consecutive days, in which the shot frequency was maintained constant at a duration up to 30 min. The first session was performed at a speed corresponding to [Lac.sub.min] (that was determined via a specific test). The other intensity frequencies were defined according to the lactate concentration responses in each of the intensities. The MLSS intensity was considered as the higher value that did not show a rise in lactate concentration above 1 mM, from the 10th to the 30th-min of the session. The subjects were given directions to attack the balls at this shot frequency with forehand movements. Blood samples were collected every 5 min until the 30th-min.

Blood Sampling and Analysis

In every test, 25 [micro]l of blood were sampled from the earlobe in capillaries to determine the lactate concentration. The samples were transferred to 1.5 ml Eppendorf tubes that contained 50 pl of NaF (sodium fluoride - 1%). The homogenate was analyzed (25 pl) in an YSI, model 1500 SPORT (Ohio, USA). The blood lactate results were expressed in mmol x [l.sup.-1].

Statistical Analyses

Normality and homogeneity of the data were verified through the Shapiro-Wilk test and the Levene test, respectively. Comparisons of test values for minimum lactate and the maximal lactate steady state ([Lac.sub.min] vs. MLSS and [Lac.sub.peak] vs. [Lac.sub.min]) were performed using the paired Student f-test and the Pearson correlation. In addition to the calculation of the coefficient of variation (CV), an analysis was performed using Bland-Altman to determine the concordance in the results. Statistical significance was set at P<0.05.

RESULTS

The subjects' correspondent value to the [Lac.sub.min] was found via the minimum lactate, which was determined in the incremental phase through the second order polynomial adjustment in lactate concentrations obtained in relation to time (Table 1) where the mean was equal to 53.1 [+ or -] 1.5 balls x [min.sup-1] adjusted for the time test ([Lac.sub.min]_time). However, when adjusted for ball frequency, a mean for minimum lactate ([Lac.sub.min]_Freq) of 51.6 [+ or -] 1.6 balls x [min.sup-1] was obtained, which resulted in a high correlation between the forms of adjustment (r = 0.96 and P = 0.01).

The [R.sup.2] average of the polynomial adjustments at degree 2 was 0.91 [+ or -] 0.02 for [Lac.sub.min]_time. For the set obtained through the frequency 0.86 [+ or -] 0.05, no statistical differences between the [R.sup.2] (P = 0.32) were found.

At the MLSS, the one with the highest value was considered that did not show a rise in lactate concentration higher than 1 mM (of which the mean obtained was 52.6 [+ or -] 1.6 balls x [min.sup-1]).

Also, the test by Bland-Altman showed correspondence, but no significant difference between [Lac.sub.min]_time X MLSS and [Lac.sub.min]_Freq X MLSS (Figure 4).

The Pearson's correlation for [Lac.sub.min]_time vs. MLSS and [Lac.sub.min]_freq vs. MLSS were significant (P = 0.03 and r = 0.86, P = 0.03 and r = 0.85, respectively. In the correlation between lacpeak vs. [Lac.sub.min]_time and lacpeak vs. [Lac.sub.min]_freq there were no significant differences (P = 0.81 and r = -0.13, P = 0.48 and r = -0.29, respectively (n=8).

DISCUSSION

The purpose of this study was to validate the lactate minimum test ([Lac.sub.min], an aerobic evaluation protocol) using a mechanical ball launcher to simulate forehand attacks on table tennis players. Validation of a new physical test is required to determine the consistency of results that the test provides relative to a validated test (i.e., the gold standard). This is necessary to be sure that the test is reliable (6). To confirm the validity of the test, the present study examined the error or standard deviation between tests, comparative analysis of average attempts, and calculating the coefficient of variation (CV) (6).

The main objective was achieved, since [Lac.sub.min] showed no statistical differences in relation to MLSS, still having a great homogeneity, with CV below 10%. Therefore, the [Lac.sub.min] test is a reliable test when evaluating the aerobic athletes' skill in table tennis. Still, the Bland-Altman analysis confirmed the correspondence/equivalence of the data (given the random distribution of the data). Also, among the different evaluation protocols, the [Lac.sub.min] test is a good measure of anaerobic threshold since it determines the balance point between lactate production and removal per individual (8).

Zagatto et al. (26,28) investigated whether the test protocol to verify the critical frequencies (critf) in table tennis using a mechanical ball launcher would be reproducible. The critical frequencies were determined with four progressive frequency charges. The authors concluded that the model proposed for determination of the critical frequency of mechanical launcher ball shots is reproducible and that the cardiac frequency does not show intensity sensitivity in the work range of the test protocol.

In another study, Zagatto and colleagues (27) with the objective of testing the validity of the critical frequency model determined by using a specific protocol on table tennis, the researchers analyzed the aerobic (critf) and anaerobic (anaerobic work capacity--AWC) parameters of the model, the realization of two specific tests on table tennis and two on conventional ergometers were proposed. Specific tests used a mechanical ball launcher (robot). In test 1, the critical frequency (critf) was determined and tested. In test 2, the anaerobic threshold in specific protocol ([AT.sub.esp]) was determined incrementally. The tests with conventional ergometers used the minimum lactate protocol to determine the anaerobic threshold when using a cycle ergometer or an arm ergometer. The anaerobic working capacity (AWC) did not show important correlations with other anaerobic parameters in the conventional ergometers, not even with peak lactate ([Lac.sub.peak]). The authors concluded that the table tennis evaluation protocols should respect the specificity of the sport. Hence, even though the [Lac.sub.min] test is an excellent parameter to obtain the anaerobic threshold (AT), it is not sensitive enough to evaluate table tennis (27).

The abovementioned results represent why it is necessary to use a specific protocol to table tennis, as proposed by Morel and Zagatto (13). They adapted the model and applied it to the game table taking into account the frequency of ball hits. It was found that the [Lac.sub.min] test for table tennis is reproducible, and can be applied to evaluate the metabolic transition in table tennis respecting its specificity. However, the specific incremental test using fixed lactate concentration, and also by means of the bi-segmented linear regression model proved to be unsuitable (13).

Although the proposed adaptation is very similar to tests performed in our study, the induction was performed with the hyperlactatemia Running Anaerobic Sprint Test (RAST) (13), thus it did not take into consideration the specificity of this kind of sport. Our protocol proved more reliable, since the induction of hyperlactatemia was performed in the game area consistent with the specificity of table tennis. We succeeded in confirming that it is a good parameter to determine AT. After all, the study achieved an excellent correlation with the MLSS (i.e., the gold standard for lactate concentration evaluations of aerobic protocols) (2).

A limitation of the study is the increase of firing balls (8 balls x [min.sup-1]) imposed by the ergometer in order to perform the MLSS, although this is not the best methodology to reach the MLSS. Since the increase was slightly higher than the 5% expected (22), our aim in achieving the MLSS was simply to check the stability of lactate in the lactate minimum intensity. Still, it is worth remembering that this is a commercial ergometer, the ergometer mainly used by coaches; thus the use of such an ergometer makes our research even closer to practice.

Carter et al. (26) showed that the initial charge used in the incremental test in the lactate minimum protocol seems to influence both the minimum lactate concentration and the speed corresponding to the minimum lactate. However, our findings showed that the values of [Lac.sub.min] were not dependent on the value of Lacpeak. In other words, the results of the proposed test do not seem to be dependent on the manner of causing the hyperlactatemia, as well as on its own dimension. Corroborating our findings, Smith et al. (17) performed an evaluation of the effect of different ways of causing a hyperlactatemia that precedes the lactate minimum test. It was concluded that the different methods of inducing the rise of lactate concentration for testing did not reflect alterations in the determination of the intensity of exercise that corresponds to the minimum lactate (1).

Therefore, we conclude that it is possible to evaluate table tennis players in the game area itself, since the specific protocol for the [Lac.sub.min] test in the game area showed itself to be a way of determining the MLSS (i.e., the gold standard of the verification of anaerobic threshold). Furthermore, the second order polynomial adjustment coefficients showed excellent results ([R.sup.2] = 0.91 [+ or -] 0.02), denoting that the expected kinetic for this type of protocol has adequately adjusted itself to the developed ergometer (ball launcher robot). Thus, this suggests that the [Lac.sub.min] test can be used by table tennis athletes who need to be aerobically evaluated. Besides, it is expected to get [R.sup.2] above 0.8 in order to consider the performed test successful, as was disclosed in our findings.

CONCLUSIONS

According to the results obtained in this study, it can be concluded that the [Lac.sub.min] values may foretell the MLSS (the gold standard of anaerobic threshold verification). Hence, it is an excellent instrument to obtain the anaerobic threshold of athletes since it is a protocol that can be performed in a single day respecting the game characteristics. Moreover, it can be performed in the game area itself. Lastly, it may also be concluded that the [Lac.sub.min] value is not dependent on the [Lac.sub.peak] value.

ACKNOWLEDGMENTS

The authors are grateful to the athletes and the financial support of CNPq.

Address for correspondence: Barbieri RA, Department of Physical Education, Sao Paulo State University, Rio Claro, Sao Paulo, Brazil 13506-739. Email: Barbieri_ef@hotmail.com

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Ricardo A. Barbieri [1], Claudio A. Gobatto [2]

[1] UNESP, Sao Paulo State University at Rio Claro, Sao Paulo, Brazil, [2] Laboratory of Sports Applied Physiology, Campinas State University (UNICAMP), Sao Paulo, Brazil

Table 1. Mean [+ or -] Standard Deviation of the Variables.

                            Absolute Values      CV         CI
                                                 (%)       (95%)

[Lac.sub.min_time]         53.1 [+ or -] 3.92   7.37    47.40-56.60
  (balls x [min.sup.-1])
[Lac.sub.min_Freq]         51.6 [+ or -] 4.73   9.34    49.71-57.86
  (balls x [min.sup.-1])
MLSS (balls x              52.6 [+ or -] 4.27   8.13    47.40-56.59
  [min.sup.-1])
CD. [R.sup.2]              0.91 [+ or -] 0.05   5.52     0.88-0.97
  [Lac.sub.min_time] (%)
CD. [R.sup.2]              0.86 [+ or -] 0.13   15.2     0.69-0.96
  [Lac.sub.min_Freq] (%)
[lac.sub.peak]             7.44 [+ or -] 1.50   21.15    6.79-7.31
  (mM x [L.sup.-1])

                             t          P
                                    (P < 0.05)

[Lac.sub.min_time]          1.93       0.11
  (balls x [min.sup.-1])
[Lac.sub.min_Freq]         -0.87       0.42
  (balls x [min.sup.-1])
MLSS (balls x
  [min.sup.-1])
CD. [R.sup.2]              -1.067      0.32
  [Lac.sub.min_time] (%)
CD. [R.sup.2]
  [Lac.sub.min_Freq] (%)
[lac.sub.peak]
  (mM x [L.sup.-1])

CV: coefficient of variation; CI: Confidence interval; CD.
[R.sup.2]: Coefficient of Determination. Paired f-test
= [Lac.sub.mintime] X MLSS; [Lac.sub.minFreq] x MLSS;
CD. [R.sup.2] [Lac.sub.mintime] x CD. [R.sup.2] [Lac.sub.minreq]
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Author:Barbieri, Ricardo A.; Gobatto, Claudio A.
Publication:Journal of Exercise Physiology Online
Article Type:Report
Geographic Code:3BRAZ
Date:Oct 1, 2013
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