Blood lactate concentration (BLC) is a reasonable parameter for the estimation of workload intensity in training exercise(27). The workload intensity, which depicts the transition from low- to high-intensity endurance-training exercise, presumably represents the highest constant workload that can be performed by oxidative energy metabolism (24,27).
During constant workload, the turn from oxidative to partly anaerobic energy metabolism is assumed to correspond to the highest BLC, representing the equilibrium between lactate production and lactate elimination(28). This level of BLC is termed maximal lactate steady state (MLSS). In running and cycling, with a pedal rate of 60 rpm, MLSS has been found to be approximately 4.0 mmol·l-1 (19,20). Contrary to the aforementioned results, higher levels of MLSS have been determined in speed skating(4), whereas in rowing MLSS was lower than 4.0 mmol·l-1 (2). Additional investigations about BLC dynamics during constant workload show higher steady states of BLC in arm cranking than in cycling (21).
Whether changes in MLSS correspond to different levels of workload intensity, to sport-specific types of exercise, or to the specific metabolic demand of the sport is speculative. The aim of the present study was to investigate whether different levels of MLSS may explain different BLC levels at submaximal workload intensities in nationally and internationally ranked athletes of different sports events.
The subjects were 11 male rowers (mean ± SD, age 20.1 ± 1.5 yr, height 188.7 ± 6.2 cm, weight 82.7 ± 8.0 kg), 16 male cyclists and triathletes (age 23.6 ± 3.0 yr, height 181.4 ± 5.6 cm, weight 72.5 ± 6.2 kg), and six speed skaters, two females and four males (age 23.3 ± 6.6 yr, height 179.5 ± 7.5 cm, weight 73.2± 5.6 kg). All subjects were national or international class ranked athletes and reported between 2 and 10 yr of high performance training. The rowers were taller (P < 0.05) and heavier (P < 0.05) than cyclists and speed skaters. The subjects were informed about the nature and risks involved in participation in the experiments. The experimental protocol was approved by the Human Subjects Committee of the Free University of Berlin, and all subjects acknowledged voluntary participation through written informed consent.
The subjects performed an exhausting incremental load test and three to six submaximal constant load tests on a rowing ergometer (Gjessing, Empacher, Eberbach, Germany), a cycle ergometer (Elema Schönander 380, Siemens, Berlin, Germany), or on a speed-skating track. During rowing ergometry the brake load was 29.4 N. Verbal feedback regarding the average mechanical power based on revolutions of the flywheel of the ergometer was given every 30 s during the incremental test and every 1.0 min during the submaximal constant load tests. According to Mader et al. (28) the measured mechanical power was corrected for the acceleration and deceleration of the body mass on the rowing ergometer. Dependent on the level of workload the stroke frequency was between 25 and 30 strokes·min-1. Cycle ergometry was performed with individually specific pedalling rates between 90 and 105 RPM. Speed-skating velocity was controlled by an acoustic timer every 45.63 m. The mechanical power corresponding to the speed-skating velocity was calculated according to a total energy cost above resting(C[J·m-1]) for speed skating on ice in dropped posture: C = WT + 0.79 v2 (10). The subjects were instructed to adhere to their usual diet and not to engage in strenuous activity during the day before an exercise test. The tests were performed at similar times in the afternoon on separate days. Time intervals between separated testing sessions were approximately 48-72 h. All tests were conducted during late preparatory and early competition periods of the season.
Incremental Load Tests
In rowing ergometry, the initial workload was 215 W and increased by 35 W every 3.0 min. After every work stage, the test was interrupted by a 30-s break for blood sampling. The cycle ergometry test started with 150 W and was increased by 50 W every third minute. Blood sampling was conducted without test interruption. The speed-skating incremental test began with a velocity of 8.1 m·s-1 and was increased by 0.4 m·s-1 after every eighth lap on a 365-m track. After each work stage, the speed-skating test was interrupted for 45 s to allow for deceleration of the velocity to zero, for blood sampling, and for the acceleration to the new skating velocity. All incremental load tests were finished at individual maximal power outputs indicated by volitional fatigue.
Constant Load Test
The constant load tests lasted 30 min in rowing and cycle ergometry. In rowing ergometry, workload intensity for the first constant load test was approximately 60% of the maximal workload; every test was interrupted for 30 s after every fifth minute for blood sampling. Workload and velocity for the first constant load tests in cycle ergometry and speed skating corresponded to the BLC of 4.0 mmol·l-1 measured during the incremental load tests. The 30-min constant load tests in cycle ergometry were performed without interruption. Every constant load test in speed skating consisted of 40 laps on the speed-skating track. After every eighth lap, tests were interrupted for 45 s for blood sampling and as previously described. After each constant load test on separate days the workload was increased until no steady state of BLC could be achieved.
There is a nonlinear relationship between workload and velocity of locomotion on land. Therefore, the comparison of the corresponding procedures in rowing, cycle ergometry, and speed skating was determined by increasing the ergometer workload by 3%-10% and increasing the skating velocity by 1%-5% after every constant workload.
Blood Lactate Concentration
Capillary blood samples (20 μl) were taken from the hyperemic ear lobe(Finalgon forte®, Thomae, Biberach, Germany) before the incremental load test and at the end of each stage of workload. At constant workloads, the BLC was measured at the beginning and after every fifth minute (rowing and cycling) or after every eighth lap (speed skating). The BLC was analyzed by the enzymatic photometric method in rowing and cycling (Boehringer, Mannheim, Germany) and by the enzymatic amperometric method in speed skating (Eppendorf, Hamburg, Germany). Previously, due to technical reasons, different types of instruments used in BLC determination have been compared. The BLC values were slightly lower if the enzymatic amperometric method was adopted(5). The coefficients of variation for repetitive analysis of the identical samples were < 5% for the enzymatic photometric and < 2% for the enzymatic amperometric method (5).
Maximal Lactate Steady State
According to the procedure published by Heck et al.(19,20), MLSS was defined as the highest BLC that increases by no more than 1.0 mmol·l-1 during the final 20 min of constant workload of rowing and cycling, or the final 24 laps of speed skating of constant velocity.
Data are reported as mean values and standard deviations (SD). Intraindividual mean differences were determined by Wilcoxon test and interindividual differences by Kruskal-Wallis test and Mann-Whitney test. The relationship between variables was examined by linear regression analysis. For all statistics, the significance level was set at P < 0.05.
In rowing, cycling, and speed skating, the MLSS (Fig. 1) differed (P ≤ 0.001). MLSS workload and maximal workload was higher (P ≤ 0.001) in rowing than in cycling(Tables 1 and 2). The difference between MLSS workload and the lowest workload with a clearly identifiable BLC increase was 8.1% ± 4.4% in rowing (P ≤ 0.01), 6.0% ± 2.8% in cycling (P ≤ 0.001) and 7.1% ± 4.4% in speed skating(P ≤ 0.05). No differences (P ≥ 0.05) were found in MLSS workload and maximal workload between speed skating and rowing(Tables 1 and 2).
MLSS workload was dependent on maximal workload in rowing (r = 0.71,P ≤ 0.02), in cycling (r = 0.82, P ≤ 0.001), and in speed skating (r = 0.95, P ≤ 0.01). The relationship between MLSS workload and maximal workload for all subjects is shown in Figure 2. MLSS workload intensity as related to maximal workload was independent of the sports events(Tables 1 and 2).
The presented results demonstrate that in rowing, cycling, and speed skating MLSS differ. However, the corresponding levels of workload intensity are similar. These results suggest that reliance on a single BLC, for example, 4.0 mmol·l-1, to a concept of the individual anaerobic threshold as recently reported in rowing (2) seem to be an unrealistic strategy in exercise testing. Nevertheless, the observed differences in MLSS between rowing, cycling, and speed skating may reflect differences in the test procedures, in the metabolic profiles of middle-distance and long-distance endurance disciplines and training programs, or in the motor pattern of rowing, cycling, and speed skating.
Different test procedures were caused by the adopted methods of lactate analysis, by laboratory versus field conditions, and by the performed incremental and constant load test protocols.
Direct comparison of the instruments for lactate analysis used in this study pointed out that the enzymatic amperometric method resulted in approximately 0.4 mmol·l-1 (P ≤ 0.001) lower values for BLC than the enzymatic photometric method (5). This finding was supported by similar results of Kamber (22). Employment of only the enzymatic amperometric or only the enzymatic photometric method in rowing, cycling, and speed skating would have resulted in higher MLSS differences between speed skating and cycling, or speed skating and rowing.
Field tests in speed skating include variations in ice quality. The MLSS determination demands four to seven test sessions on separate days. Due to the test schedule, and in response to individual training, only one subject was tested on the same day. Therefore, differences in tests results caused by the quality of ice might have influenced the results of the present study. However, they may be considered randomized.
The ambient temperature in speed skating is lower compared with laboratory conditions. During incremental load tests exposure to cold caused a lower BLC(14,39). The effect of cold on BLC during prolonged workload is still unknown.
A possible temperature dependent reduction of BLC during incremental speed skating may be compensated by the longer duration of the incremental load test steps which increases BLC at a given level of workload and possibly reduces maximal workload at the end of the test (19). During constant load testing, repetitive brakes increased MLSS workload (Beneke, unpublished data, 1995). The same effect can be observed in incremental load tests at given levels of BLC (19). Contrary to MLSS workload, no significant effect on MLSS was found (Beneke, unpublished data, 1995). Thus, test interruptions in rowing and speed skating may cause higher levels of workload in both incremental and constant workload. In speed skating, MLSS workload intensity in relationship to maximal workload may be increased due to the longer lasting incremental load test steps. However, the relative MLSS skating velocity of 88.4% ± 2.5% in relationship to maximal skating velocity in the present study seems to extend recent findings regarding blood lactate levels in prolonged submaximal speed skating(16). No significant effect on MLSS workload intensity could be supported in the present data. Differences in testing procedure do not explain the observed differences in MLSS.
It is generally accepted that the workload intensity regulates both lactate production and elimination (29,30). The level of MLSS depends on lactate production, lactate clearance, and the distribution of lactate (29,30). Lactate production and clearance had been described to be a function of training(11,13). Endurance training was also found to enhance the capacity of the muscle membrane to transport lactate(31).
The finishing results of top athletes can be characterized as the systematic attempt to reach maximum energy output at optimum average velocity within different periods of time. Rowing is a classic middle distance event lasting approximately 5.5-8.0 min. Speed-skating longtrack events include distances between long sprint and long distance event lasting approximately 0.6 min up to 14.2 min. National and international events demand top performance in single distance and also in all-around competitions. Cycling and triathlon are long-endurance sports events. The corresponding finish times range between 50 min and 9 h.
Training in elite performance sports depends on the metabolic profile of the sporting event (7,27). Approximately 70% of rowing training is specific or semispecific training on a boat or a rowing ergometer; 70%-90% of this training is performed at a BLC lower than 2.0 mmol·l-1, depending in the training period(18). In speed skating, the training away from the ice can be primarily categorized into 40% aerobic activities including distance running and cycling, 20% anaerobic activities such as high-intensity interval running, 15% weight training, and 25% training specific to skating movements(34). Specific training on the slideboard resulted in BLC levels of 4.8 mmol·l-1 (38). During skating on ice with low preextension angles of the knee and hip, the BLC was between 5.0 and 7.0 mmol·l-1 no matter how slow the skating velocity was (15,35,38). The latter is supported by training observations in junior athletes showing BLC levels up to approximately 4.0 mmol·l-1 during extensive endurance training exercise (25). Compared with rowing and speed skating, the long-distance events of cycling and triathlon demand a higher volume of low-intensive aerobic endurance training. Long-duration, low-intensity endurance training in cycling is performed at BLC levels at approximately 2.0 mmol·l-1 (32); a similar range of BLC was measured during rowing training of shorter duration and higher intensity.
These training observations of similar BLC levels during different training intensities indicate that the transition form aerobic to partly anaerobic metabolism corresponds to a higher BLC in cycling compared to rowing. Training observations and their levels of MLSS point out that MLSS does not correspond to different metabolic profiles of endurance sports events or to corresponding training adaptations.
During physical exercise the major site of glycolysis and lactate oxidation is the working skeletal muscle (42). Compared with the skeletal muscle, other sites of lactate metabolism such as in the heart(23), liver (43), and kidneys(45) have a small mass and/or the perfusion is limited during exercise training. Muscular lactate clearance by oxidation is limited by reperfusion and the ratio between slow- and fast-twitch muscle fibers(8).
The limb movement frequency seems to be a factor that effects the recruitment of muscle fibers (6,26). During incremental and constant workloads in cycling performed with pedal rates between 35 and 105 rpm, BLC was found to increase with pedal rate(3,6,26). But recent studies supported the assumption that compared with alterations in the pedal rate, the leg driving force per cycle revolution appears to have a greater effect on lactate metabolism (1,12,17).
The latter theory seems to be supported by the present investigation. In spite of the significant difference in the levels of MLSS, the stroke frequency of approximately 30·min-1 in rowing(28) is only slightly lower than the corresponding value of approximately 40·min-1 measured on the straight in long distance speed skating (10,40). Compared with the slight difference in stroke frequency between rowing and speed skating(<10·min-1) the differences in cycling pedal rates, which have been described to result in significant changes of BLC during given levels of workload, were found to be at least 4 times higher(3,6). Even at differences in pedal rate of 40 rpm no significant changes in muscular reperfusion could be observed(26,36).
No results concerning the influence of stroke characteristics in rowing and speed skating on lactate metabolism have been published. However, biomechanical analyses comparing rowing on a boat and rowing on an ergometer(33) and kinematic data of cycling at different pedal rates (44) or investigating ankle velocity and force time curves in speed skating (9,40) may indicate divergences in force and dynamics per stroke in rowing, cycling, and speed skating.
The possible divergences in the driving force per stroke are also associated with differences in the mass of working muscles. Rowing is a combination of leg, trunk, and arm work, which represents at least 80% of the total muscle mass (28). Cycling and speed skating are dominated by leg work (40). In cycling, driving force per stroke and its rating decreases with the increase in pedal rate(41). The mass of working muscles in rowing is significantly bigger than that in cycling and speed skating. Low pedal rates cause intensive upper body work. Cycling MLSS was found to be lower at 35 rpm than at 105 rpm (3). The level of MLSS may therefore be inversely related to the mass of dominantly working muscle.
Differences in the ratio between dominantly active muscle and assisting muscle may affect the rates of glycolysis and muscular lactate oxidation. One reason for the latter may be lower or higher forces per stroke per given mass of muscle. In addition, the ratio between dominantly working and assisting muscle may affect the maximum rate of muscular perfusion because the vascular capacity for muscle blood flow is so high that perfusion of 10 kg or more working muscle mass may be constrained by the maximal cardiac output(37).
The reduced availability of oxygen for a large mass of intensive working muscle possibly increases the rate of glycolysis and/or limits the capacity of oxidizing lactate. This could be combined with a reduced ability to oxydate lactate due to the constrained oxygen availability in the assisting muscle. This hypothesis may be supported by the fact that at maximal workload, a leveling off of the oxygen uptake can be observed if the mass of dominantly working muscle is high.
It can be concluded that differences in the level of MLSS between rowing, cycling, and speed skating do not seem to correspond to the testing procedure, different levels of workload intensity, or to the specific metabolic profile of a sports event. The level of MLSS may be related to the sport specific mass and the level of sport specific strain of the dominantly working muscles. Both factors may cause a sport-specific pattern of muscular perfusion. MLSS seems to be inversely related to the mass of dominantly working muscle. Differences in MLSS seem to suggest that unreasonable reliance on traditional concepts of exercise testing is unrealistic and may explain some controversial results concerning BLC measurements obtained during submaximal training exercises.
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Keywords:©1996The American College of Sports Medicine
LACTIC ACID; ROWING; CYCLING; SPEED SKATING