Exercise prescription and monitoring of the effectiveness

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1 Effect of Test Interruptions on Blood Lactate during Constant Workload Testing RALPH BENEKE 1,3, MATTHIAS HÜTLER 2,3, SERGE P. VON DUVILLARD 4, MARTIN SELLENS 1, and RENATE M. LEITHÄUSER 1,3 1 Centre for Sports and Exercise Science, Department of Biological Sciences, University of Essex, UNITED KINGDOM; 2 Department of Physical Medicine and Rehabilitation, Haukeland Hospital, University of Bergen, NORWAY; 3 Institute of Sports Medicine, Free University Berlin, GERMANY; and 4 Human Performance Laboratory, Department of Kinesiology and Health Promotion, California State Polytechnic University, Pomona, CA ABSTRACT BENEKE, R., M. HÜTLER, S. P. VON DUVILLARD, M. SELLENS, and R. M. LEITHÄUSER. Effect of Test Interruptions on Blood Lactate during Constant Workload Testing. Med. Sci. Sports Exerc., Vol. 35, No. 9, pp , Objective: To determine whether repetitive test interruptions (TI) during constant load testing influence blood lactate concentration (BLC), maximal lactate steady state (MLSS), MLSS workload (P-MLSS), and relative MLSS intensity (Int-MLSS). Methods: Nineteen males participated in this study. In experiment A, 10 subjects ( yr; cm; kg) performed 30-min constant load tests: one without TI, one with TI of 30 s, and one with TI of 90 s after every 5 min of cycling at a given workload. In experiment B, nine subjects ( yr; cm; kg) performed 30-min constant load tests at different workloads until MLSS had been determined for all three TI protocols. Results: In experiment A, the BLC after 30 min net working time (BLC 30 ) was higher (P 0.001) without TI ( mmol L 1 ) than with TI of 30 s ( mmol L 1 ) or 90 s ( mmol L 1 ). The change in BLC during the final 20 min ( BLC ) was greater (P 0.01) without TI ( mmol L 1 ) than with TI of 30 s ( mmol L 1 ) or 90 s ( mmol L 1 ). In experiment B, the MLSS was not affected, but P-MLSS and Int-MLSS were lower (P 0.01) without TI ( W and %) than with TI of 30 s ( W and %) or 90 s ( W and %). Approximately 35% of the variance of BLC 30 and BLC 10 30, and 70% of the variance of P-MLSS and Int-MLSS were explained by TI duration (P 0.001). Conclusions: TI decreased BLC 30 and BLC but has no effect on MLSS. Consequently, with TI, the MLSS is achieved at higher P-MLSS and Int-MLSS. Key Words: MAXIMAL LACTATE STEADY STATE, EXERCISE PROTOCOL, INTENSITY, CYCLE ERGOMETRY Exercise prescription and monitoring of the effectiveness of training is often based on the measurement of changes in blood lactate concentration (BLC). Moderate exercise intensity does not elevate BLC significantly above resting values (Fig. 1). BLC measurement is more relevant to intensive endurance training and heavy and severe exercise intensities. The maximal lactate steady state (MLSS) is presumably the highest BLC at which equilibrium can be achieved between lactate appearance and disappearance during prolonged exercise at constant workload (3,4,7 10). The MLSS defines the boundary between heavy and severe exercise intensities (Fig. 1). Successful athletes perform more than 80% of their training below MLSS intensity (11). The rationale for this may be that a significant increase of the Address for correspondence: Ralph Beneke, B.Sc., M.D., Ph.D., FACSM, Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, England; rbeneke@essex.ac.uk. Submitted for publication December Accepted for publication May /03/ MEDICINE & SCIENCE IN SPORTS & EXERCISE Copyright 2003 by the American College of Sports Medicine DOI: /01.MSS D training volume above the exercise intensity corresponding to the MLSS is found to result in unfavorable changes in performance and an increase in fatigue markers within short periods of time (13). Therefore, the MLSS seems to indicate a borderline intensity with relevance for the prescription of endurance training because above this limit inadequate training load may result quickly with negative consequence leading to symptoms of over-reaching and over-training. The MLSS has also been found to depend on the motor pattern of exercise (3,7,9). The latter results based on measurements of MLSS using a variety of exercise modalities may have been affected by the testing procedure. Capillary blood samples can easily be collected from subjects during cycle ergometry; however, running, rowing ergometry, and field testing require test interruptions for blood sample collection. Repetitive test interruptions (TI) may lower BLC even when the test is prolonged to compensate for the TI. Furthermore, MLSS is defined by determining the BLC during exercise of defined net duration (1 4,7 10,14 16,19,21). TI may modulate not only the value of the MLSS but also the absolute workload and relative intensity at which MLSS is achieved. The possible impact of TI on MLSS parameters has not previously been investigated. Therefore, two experiments (experiment A and B) were conducted. In experiment A, we investigated the effect of TI of two different durations,

2 FIGURE 1 BLC during prolonged constant workload at moderate, heavy, and severe exercise intensity. Peak workload at termination of a prior incremental load test was 400 W. similar to those for blood sampling during prolonged constant load testing protocols on BLC at a given workload intensity. In experiment B, we analyzed the effect of TI on MLSS, MLSS workload, and MLSS intensity. Three hypotheses were studied: 1) repetitive TI decrease the level of the BLC at given workload intensity (experiment A), 2) repetitive TI increase the level of the MLSS (experiment B), and 3) repetitive TI increase the workload and relative exercise intensity at the MLSS (experiment B). METHODS Nineteen male endurance athletes volunteered and signed informed consents conforming to internationally accepted policy statements on the use of human subjects as approved by the local ethics committee. All tests were conducted at similar times in the afternoon on separate days at least 2 h after a light meal. The time interval between each testing session was h. The subjects were instructed not to engage in strenuous activity during the day before an exercise test. All subjects performed a maximal incremental test followed by several 30-min constant load tests on separate days (with or without TI; see below) on an electronically braked cycle ergometer (Elema Schönander 380, Siemens, Germany). According to previously published procedures, the incremental load test started with 100 W and was increased by 50 W every 3 min (7,9,10). The test was terminated at individual maximal power output indicated by volitional fatigue. The maximal incremental load test was conducted to determine subject s peak oxygen uptake and to enable estimation of the starting workload for each subsequent series of constant load tests. After the incremental load test, the subjects were assigned in random order to either experiment A or experiment B. Ten subjects (mean SD age: yr; height: cm; body mass: kg; peak oxygen uptake: L min 1 ) participated in experiment A. To test the effect of TI on the BLC at a given workload, the subjects performed three constant load tests lasting 30 min with identical workload. Workload was set according to previously published procedures with reference to the BLC value of 4.0 mmol L 1 obtained during the incremental test (7). In randomized order, one test was conducted without TI, one with TI of 30 s and one with TI of 90 s. The TI was conducted after every 5th minute. The pedaling rate was maintained constant throughout cycle ergometry tests for each subject. After completion of this test series, all subjects were asked to perform additional series at a different workload. Five of the 10 subjects in experiment A agreed and performed tests at an exercise intensity, which was approximately 5% higher than the first series of tests. Nine subjects (age: yr; height: cm; body mass: kg; peak oxygen uptake: L min 1 ) participated in experiment B. To test the effect of TI on MLSS and the workload at MLSS, three series of constant load tests were conducted. One series was conducted without TI, one with TI of 30 s and one with TI of 90 s after every 5th minute. The first workload of the series without TI was set according to the BLC value of 4.0 mmol L 1 obtained during the incremental test (7). To minimize the number of tests per subject, the initial workloads of the series with 30 s and 90 s TI were approximately 5% and 10% higher than the latter. Subsequently, the workload was increased from test to test by 5 10% until no steady state of the BLC was observed to establish MLSS for all three constant load protocols. Therefore, the net work time was 30 min except in those experiments that were terminated earlier due to volitional fatigue. Tests with different TI were conducted in randomized order. The pedaling rates were constant for each subject. MLSS was defined as the highest BLC that increased by no more than 1.0 mmol L 1 during the final 20 min of net working time and was calculated as the average value of the BLC measured at min 15, 20, 25, and 30 of the MLSS workload (3,4,7 10). Capillary blood samples (20 L) were taken from the hyperemic (Finalgon forte, Thomae, Biberach, Germany) earlobe using the same puncture hole before and during the final 15 s of every stage of the incremental load tests. In each constant load test, blood samples were collected during the 15 s before and during the final 15 s of every 5-min fraction of exercise. The BLC was measured by an enzymatic photometric method (Spectrophotometer 1101 M, Eppendorf, Germany; Test-Combination Lactat, Boehringer, Mannheim, Germany). The coefficients of variation for replicate samples were 5% (5). Oxygen uptake was determined with a portable spirometry system (K2, Cosmed, Rome, Italy) at 15-s intervals. Before each test session, the device was calibrated according to the manufacturer s instructions. The coefficient of reliability for oxygen uptake measurements with this system has been reported to be about 0.99 (17). Compared with other methods of oxygen uptake measurement, the K2 showed similar (17,18) or slightly lower values of oxygen uptake at levels above 2.7 L min 1 (6). TEST INTERRUPTIONS AND BLOOD LACTATE Medicine & Science in Sports & Exercise 1627

3 TABLE 1. The effect of 30-s and 90-s test interruptions on BLC an BLC TID (s) BLC 30 (mmol L 1 ) * * P BLC (mmol L 1 ) * * P 0.01 TID, duration of test interruption; BLC 30, BLC after 30-min net working time; BLC 10 30, change in BLC between 10th and 30th minutes of net working time. * Significantly different from 0-s condition. All data are presented as mean SD. Due to lack of normal distribution of selected descriptive results, multiple intra-individual mean differences were determined using Friedmann test. Paired differences were analyzed with Wilcoxon test. The relationship between variables was analyzed by linear and nonlinear regression. The significance level was set at alpha P RESULTS Experiment A. Fifteen constant load test series were analyzed. Average power of these tests was W corresponding to an exercise intensity of % of the peak oxygen uptake measured at W. After 30-min net working time the BLC (BLC 30 )was higher (P 0.05) for continuous cycling (BLC 30_0 ) than with TI of either 30 s or 90 s (Table 1 and Fig. 2). There was no significant difference between 30-s and 90-s TI for the BLC measured during the final 15 s of each exercise interval. However, after the 10th minute of net working time, the BLC at the end of the TI of 90 s was lower (P 0.01) than that measured at the end of the previous 5-min exercise. The increase in BLC during the final 20 min of net working time ( BLC ) was also significantly affected by TI (P 0.05). The BLC was higher with continuous cycling ( BLC 10 30_0 ) than with TI, and there was no significant difference between the effects of the two TI durations (Table 1). The effects of TI on the BLC during prolonged constant workload exercise can be described by nonlinear functions of the duration of TI (TID): FIGURE 2 BLC during prolonged constant workload at a given exercise intensity without and significantly (P < 0.01) modulated with repetitive test interruptions. TABLE 2. The effect of 30-s and 90-s test interruptions on MLSS, P-MLSS, and Int-MLSS. TID (s) MLSS (mmol L 1 ) NS P-MLSS (W) * # P 0.01 Int-MLSS (%) * # P 0.01 TID, duration of test interruption; MLSS, maximal lactate steady state; P-MLSS, MLSS workload; Int-MLSS, MLSS intensity related to V O 2 peak. * Significantly different from 0-s condition. # Significantly different from 0-s and 30-s conditions. BLC 30_0 BLC 30_TID 0.12 TID BLC 10 30_0 BLC 10 30_TID 0.13 TID [Equation 1;r 0.65,p 0.001] (1) [Equation 2;r 0.61,p 0.001]. (2) Equations 1 and 2 account for approximately 35% of the variance of BLC 30 and BLC 10 30, respectively. Experiment B. The MLSS values determined in tests without TI (MLSS 0 ), with 30-s TI, and with 90-s TI were not significantly different (Table 2; Fig. 3). The corresponding values of workload and relative exercise intensity increased (P 0.01) with the duration in TI (TID) (Table 2). The interrelationship between TID, P-MLSS, and Int- MLSS is depicted in Equation 3 and 4: P-MLSS 0 P-MLSS TID 3.56 TID Int-MLSS 0 Int-MLSS TID 0.87 TID [Equation 3;r 0.84,p 0.001] (3) [Equation 4;r 0.86,p 0.001]. (4) Equations 3 and 4 account for approximately 70% of the variance in P-MLSS and Int-MLSS, respectively. DISCUSSION These results demonstrate that at heavy and severe exercise intensities, laboratory and field-testing procedures that require TI for blood sampling significantly underestimate the level of physiological exertion. This may lead to an overestimation of the exercise capacity of an athlete and an inappropriate prescription of training exercise intensity if such test results are directly applied to training conditions without TI. The observed decrease in the BLC and the changes in BLC with time are caused by the combination of subsequent relative short bouts of heavy or severe exercise interrupted by passive rests. During each resting phase, the glycolytic rate of the previously working muscle is reduced while the oxygen uptake of the whole organism is still elevated as a result of increased postexercise oxygen uptake. Under the conditions of substrate saturation, the rate of lactate elimination is directly related to oxygen uptake. Substrate saturation is likely to occur at exercise intensities and levels of BLC as investigated in the present experiments (3). The observation that only after TI of 90 s the BLC was significantly lower compared with that at the end of the previous 5-min working phase appears to be caused by the interrelationship between the duration of each phase of exercise, the corresponding net lactate production, and the veloci Official Journal of the American College of Sports Medicine

4 ties of the invasion into and evasion out of the blood compartment (4,12). A more recent investigation clearly demonstrated that a working period of 5 min is insufficient to reach a level of BLC, which represents a steady state at exercise intensities comparable to the present investigation (4). According to the nature of dynamic steady states, the time which is required to reach a steady state depends mainly on the level of the steady state but not on the preexercise BLC (12). Therefore, under the assumption that a given exercise intensity requires a rate of glycolysis, which is more or less constant, repetitive TI prevent BLC of reaching the steady state, which corresponds to the same workload under the condition of continuous exercise (4,12). The latter also explains why under the condition of repetitive TI the workload corresponding to the MLSS is overestimated, whereas no effect on the level of the MLSS can be ascertained. This mechanism is the physiological basis of any interval like exercise-training program. The BLC lowering effect of repetitive breaks typical for heavy and severe constant workload testing in various modes of exercise can be estimated using Equation 1. The effect of TI on the BLC changes over time is possibly more important than its effect on the absolute BLC because the transition from a steady state to a nonsteady state BLC is thought to discriminate between qualitatively different limitations to performance. Heavy exercise intensities that produce BLC less than the MLSS are also associated with a respiratory steady state. Under such steady state conditions, performance time is assumed to be mainly limited by the availability of stored glycogen (3,10). However, severe exercise intensities above the Int-MLSS do not result in steady state conditions for BLC or for any respiratory measure (22,23), and performance time is thought to be limited by the disruption of cellular homeostasis. Figure 2 shows that, after an initial steep increase in BLC, a more or less linear increase in BLC may be diminished or even change to a slight decrease if the test is interrupted for blood sampling. TI may therefore produce apparently steady state conditions at exercise intensities that are unsustainable. The effect of TI on BLC can be predicted quantitatively using Equation 2. FIGURE 3 MLSS without and with repetitive 30- and 90-s test interruptions. Under laboratory conditions, 15- to 30-s breaks are sufficient for capillary blood sampling for BLC measurements. Certain field conditions and/or a requirement for an increased sample volume, for example, if blood gases are to be analyzed as well as BLC, may prolong the blood sampling process significantly. Equations 1 and 2 also illustrate that the effect of TI on BLC and BLC is dominated by the initial phase of the break and include a period of time which is sufficient for more complicated and time consuming conditions for blood sampling. The relative low explanation of the variance of Equation 1 and 2 can be contributed to the fact that the variability in BLC at prolonged constant work under such conditions is approximately 13% (R. Beneke, unpublished results). This accounts for almost half the magnitude of the observed effect of TI. The latter may also explain why TI changed workload and exercise intensity corresponding to the MLSS but not the level of the MLSS. The effect of TI on BLC means that both absolute workload and relative work intensity at MLSS were significantly overestimated (Table 2). However, this effect is unlikely to have influenced previous conclusions about MLSS intensity related to peak workloads and peak oxygen consumptions (2,3,7,10). In these studies, where TI were required for blood sampling during constant load testing, they were also used in the incremental load tests to determine peak performance. When TI during incremental load tests on the treadmill are increased from 30 to 90 s, the running speed corresponding to a BLC of 4.0 mmol L 1 increases from m s 1 to m s 1 (15). According to Pugh (20), this increase is equivalent to a change in mechanical work of approximately 10 W, a value more or less identical to the difference in MLSS workload between 30-s and 90-s TI conditions in the present study (Table 2). Despite the sensitivity of BLC and BLC to TI, the level of the MLSS appeared to be rather robust with respect to TI. Repetitive breaks did not change the level of the MLSS significantly. This result suggests that previously published data showing a dependence of the MLSS on the motor pattern of exercise (2,3,7,10) were not influenced by the fact that blood sampling during constant load testing in rowing or speed skating required TI, whereas sampling was achieved without TI in cycling. In conclusion, at heavy and severe exercise intensities, laboratory and field-testing procedures that require TI for blood sampling, significantly underestimate the level of physiological exertion but not the level of the MLSS compared with the condition of continuous work without TI. The existence of an effect on BLC at given exercise intensity, MLSS workload, and MLSS intensity but not on the MLSS can be explained by the interrelationship between the duration of each phase of exercise and TI, the corresponding net lactate production, and the velocities of the invasion into and evasion out of the blood compartment. The effects of TI on BLC, the change in the BLC during a given constant prolonged workload with and without TI, MLSS workload, and MLSS intensity can be predicted quantitatively based on a nonlinear interrelationship between the latter and the duration of TI. TEST INTERRUPTIONS AND BLOOD LACTATE Medicine & Science in Sports & Exercise 1629

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