CURRENT TOPICS AND CONCEPTS OF LACTATE AND GAS EXCHANGE THRESHOLDS

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1 J. Human Ergol.,16: ,1987 Center for Academic Publications Japan. Printed in Japan. CURRENT TOPICS AND CONCEPTS OF LACTATE AND GAS EXCHANGE THRESHOLDS Takayoshi YOSHIDA Exercise Physiology Laboratory, Faculty of Health and Sport Sciences, Osaka University, Toyonaka, Osaka, 560 Japan Current topics and concepts underlying lactate and gas exchange anaerobic thresholds are reviewed. The attractive applications of these parameters are: (1) to evaluate the ability of subjects to perform endurance exercise, (2) to predict the level of performance, (3) to evaluate training effect, (4) its use for training pace or exercise prescription, and (5) to evaluate exercise tolerance ability in patients with pulmonary or heart disease. To provide more useful applications of these parameters, the precise technical procedures should be standardized in laboratories throughout the world. WASSERMAN and MCILROY (1964) introduced the concept of the anaerobic threshold. They proposed that the respiratory gas exchange ratio (R) be used to detect the onset of anaerobic metabolism, during a standard exercise test, for the purpose of determining the work rate at which the cardiovascular system fails to supply the oxygen requirements of active muscles. The basis of this proposal was that the metabolic acidosis caused by lactate accumulation could be discerned, noninvasively, by gas exchange parameters which detect the C02 release from buffering during an incremental exercise test (WASSERMAN et al., 1967). Thereafter, WASSERMAN et al. (1973) have defined the anaerobic threshold as "the level of work or 02 consumption just below that at which metabolic acidosis and the associated changes in gas exchange occur." As a result, this parameter has been thought as one of the most attractive parameters because intracellular metabolic changes could be determined noninvasively, i.e, without blood sampling, by gas exchange measurements. Hypothesis proposed by Wasserman In 1984, WASSERMAN amplified the definition of the anaerobic threshold by describing it as the level of exercise oxygen uptake (VO2) above which aerobic energy production is supplemented by anaerobic metabolism. The hypothesis 103

2 104 T. YOSHIDA underlying this definition requires that (a) the O2 required by the metabolically active muscles can exceed the O2 supply to mitochondria when the work rate becomes sufficiently high; (b) the imbalance between the O2 supply and O2 requirement brings about a net increase in anaerobic oxidation in the cytosol of the cell with pyruvate conversion to lactate; (c) lactate is buffered in the cell primarily by HCO3-; (d) the CO2 generated from buffering increases CO2 output while HC03- exchanges for lactate across the muscle cell membrane according to the new electrochemical gradients; and (e) the buffering and acid-base disturbances produce predictable changes in gas exchange (Fig. 1) (WASSERMAN, 1984). Debating the hypothesis I n recent years, there has been considerable debate as to the term "anaerobic threshold," the mechanisms of the increase in lactate in blood and muscle during exercise, the relationship of metabolic-cardiovascular-ventilatory coupling, and the detection of the point at which anaerobic glycolysis is accelerated in active muscle (Section for Letter to the Editor-in-Chief; J. App!. Physiol., 53: , 1983; 55: , 1983; 57: , 1984; 60: , 1986; 61: , 1986; Med. Sci. Sports Exert., 17: , 1986; BROOKS, 1985; DAVIS 1985). Therefore, several aspects of these debates stemming from the hypothesis will be discussed in this article. Controversy of terminology WASSERMAN used the word "anaerobic" to indicate that the O2 requirement of some contracting muscle fibers was greater than that required by working muscle (assuming the adequacy of O2 delivery to exercising muscles). However, some investigators have stated that the increase of muscle lactate during incremental exercise did not necessarily indicate "anaerobic" status; it has been demonstrated that the critical mitochondrial oxygen partial pressure would be estimated at between 0.1 and 0.5 Torr (CoNNETT et al., 1986). Furthermore, it was argued by opponents of the anaerobic threshold concepts and the anaerobic significance of the increased blood lactate that the mitochondrial PO2 would not decrease to its critical value, because during maximal leg exercise femoral venous PO2 did not fall below 10 Torr. WASSERMAN et al. have countered this argument by pointing out 1) the calculated O2 supply to the exercising muscle was normally very nearly equal to the O2 requirement during moderate work and could easily be in negative balance at high work rates or in the case of uneven O2 flow to O2 requirement ratio in the contracting muscles and 2) a partial pressure gradient for O2 must be maintained between the capillary and the mitochondria in order for mitochondria to consume O2 and a venous PO2 of any value did not assume that the capillarymitochondrial difference gradient would be adequate to more O2 at the rate required to support the phosphagen requirement of complete availability. It was pointed out that mean muscle PO2 was not meaningful when attempting to determine

3 TOPICS AND CONCEPTS OF ANAEROBIC THRESHOLD 105 adequacy of the O2 requirement. To avoid dealing with these conflicting reviews the term "lactate threshold" is often preferable to describe the point at which the arterial or mixed venous blood lactate concentration increases above the resting value. If gas exchange variables are used to determine this threshold parameter, gas exchange threshold of metabolic acidosis would be appropriately descriptive. We do not like to use the term of "ventilatory threshold," because this term seems to be measured ventilation (J) alone, or the slope of VE vs. VO2. Lactate production and removal during exercise Since the study of FLETCHER and HOPKINS (1907), it had been thought that lactate production in muscle would reflect muscle hypoxia or an oxygen deficit condition. BANG (1936), and SAIKI et al. (1967) estimated that blood lactate accumulation would depend on the O2 deficit. On the other hand, KEUL et al. (1967) pointed out that even during maximal exercise femoral venous PO2 did not fall below 21.3 }3.18 Torr, values which they assumed would be adequate to support the muscle mitochondrial oxygen requirement. This result questioned the possibility that the supply of O2 could be the limiting factor for sustained muscular work. KEUL et al. (1967) and DOLL et al. (1968) also suggested that lactate accumulated when glycolysis proceeded aerobically. By using a fluorometric method, JOBSIS and STAINSBY (1968) measured the steady-state oxidation-reduction level of intracellular NAD in dog gastrocnemius and gracilis muscles (basically red muscles) during muscle contraction. During exercise NADH was consistently oxidized on the surface site studied; thus they concluded that the lactate which accumulated during exercise was not caused by anaerobic glycolysis and change in cell redox state but rather was the result of a temporary imbalance between the rates of pyruvate production and pyruvate utilization in the TCA cycle. In other words, lactate can accumulate even when muscle energetics are completely aerobic. WASSERMAN et al. (1985a) describe two mechanisms to explain the lactate increase in the muscle tissue and blood during exercise as follows : (a) glycolysis increases so rapidly that the mitochondria cannot utilize pyruvate rapidly enough to prevent its elevation in the cytosol (low mitochondrial/glycolytic capacity), resulting in lactate increase by mass action, i.e., without a change in L/P ratio; or (b) the mitochondrial membrane proton shuttle, which normally oxidizes cytosolic NADH+H+ as it transfers protons and electrons to mitochondrial O2, is too slow to reoxidize the reduced cytosol NAD. This results in the conversion of pyruvate to lactate with a resultant increase in L/P ratio as dictated by the altered redox state (Fig. 2). They have demonstrated that the first mechanism is very small and that the second mechanism accounts for the lactate threshold. Additionally, the fate of lactate during exercise is also currently being debated (GOLLNICK et al., 1986). One hypothesis is that almost all lactate can be con-

4 106 T. YOSHIDA Fig. 1. Effect of lactate production on blood HCO3- and CO2 output (Reproduced from WASSERMAN et al., 1987a). verted to H2O and CO2. Another is that some of the lactate could undergo gluconeogenesis in active and inactive muscles and in the liver. In this context, the apportionment between gluconeogenic and oxidative fates of lactate is not precisely known. Several investigators have emphasized that blood lactate concentration results from an imbalance between lactate production and removal (Fig. 3). By using an isotope tracing method, BROOKS and his colleagues suggested that blood lactate increase during exercise is not necessarily due to lactate production but might be increased consequent to inadequate removal. However, it is well documented that endurance training can substantially decrease blood lactate levels at specific high work rates, while BROOKS and his colleagues (BROOKS, 1985, 1986; DoNOVAN and BROOKS, 1983; STANLEY et al., 1985) have concluded from radiolabelled lactate turnover studies that the effect of endurance training is not on role of lactate production but on its clearance rate. Contradicting that conclusion, HoLLOSZY and his colleagues (HURLEY et al., 1984; FAVIER et al., 1986) have demonstrated that endurance training induces adaptations in the muscle cells which result in a reduced production of lactate during heavy exercise. Because of the use of labeled lactate to measure lactate production, fate and turnover has many theoretical differences (NORWICH and WASSERMAN, 1986). Further studies will be needed to clarify this issue.

5 TOPICS AND CONCEPTS OF ANAEROBIC THRESHOLD 107 Fig. 2. Mechanisms of lactate increase during exercise (Reproduced from WASSERMAN et al.,1987). Metabolic-cardiovascular-ventilatory coupling According to WASSERMAN's hypothesis, since the increase in blood lactate is accompanied by an almost equal molar decrease in bicarbonate, causing CO2 production to accelerate, it is possible to detect cellular acidosis by measuring the rate of increase in VCO2 relative to that of VO2 during an incremental exercise test (BEAVER et al., 1986). Several studies have reported that there is no significant difference between lactate threshold and anaerobic threshold by gas exchange (DAVIS et al., 1976; CAlozzo et al., 1982; IVY et al., 1980; REINHARD et al., 1979; YOSHIDA et al ). Correlation coefficients between lactate threshold and gas exchange threshold were of the order of On the otherh and, more recent studies have shown a dissociation between the lactate threshold and gas exchange or ventilatory threshold (DAVIS and LASS, 1981; FARRELL and IVY, 1987; GAESSER et al., 1984; GAESSER and POOLE, 1986; GLADDEN et al., 1985; HAGBERG et al., 1982; HUGHES et al., 1982; HUGHSON and GREEN, 1982; NEARY et al., 1985; POOLE and GAESSER, 1985; POWERS et al., 1984; SIMoN et al., 1983, 1986; YEH et al., 1983). The disagreement of these thresholds might be depend on procedural or analytical differences such as attempting to determine the threshold from the change in slope of the plot of VE vs. VO2, a plot which is basically curvilinear, objective identification of the threshold, and different sites of blood

6 108 T. YOSHIDA Fig. 3. A scheme of dynamic nature of the major tissues that influence blood lactate (Reproduced from GRAHAM, 1984). sampling etc. s or even if lactate increase does cause a change in gas exchange. 1. Cause and effect relationship. HAGEERG et al. (1982) compared the lactate threshold with ventilatory threshold in patients lacking muscle phosphorylase (i.e., McArdle's syndrome), who are incapable of increasing blood lactate and (H+) during exercise. The result showed that the patients indicated a distinct increase in ventilation without increase in blood lactate and this led to suggest that changes in ventilation occur independent of blood lactate. This, of course, proved nothing in relation to the threshold because the argument is not that the increase in blood lactate is the only cause of increase in VE but rather that an increase in blood lactate must be accompanied by a decrease in HC 3 and the associated changes in gas exchange described in Fig. 1 (WASSERMAN, 1987a). In patients with chronic obstructive lung disease, VE might not increase despite an increase in lactate, because of C 2 retention. Thus threshold methods which depend on chemoreceptor sensitivity lead to inherent error in subjects with poor perceived chemoreceptor sensitivity or impaired ventilatory mechanisms. These results suggest that an appropriate method be used for evaluation of exercise tolerance in a particular patient. SIMON et al. (1983) indicated that using normal subjects the ventilatory threshold occurred at a significantly lower work rate than the lactate threshold. In contrast, GREEN et al. (1983) reported that the ventilatory threshold occurred at a significantly higher work rate than the lactate threshold. There is no clear basis

7 TOPICS AND CONCEPTS OF ANAEROBIC THRESHOLD 109 for this discrepancy. Furthermore, SIMoN et al. (1986) used trained cyclists and untrained subjects in an attempt to examine whether lactate threshold and ventilatory threshold occur at the same work rate because of specificity of muscle fiber type. Although the lactate threshold and ventilatory threshold for the trained group occurred together, the ventilatory threshold occurred at a lower work rate than the lactate threshold in the untrained subjects, suggesting the variances in lactate diffusion and/or removal processes between the trained and untrained subjects. Furthermore, GAESSER and his colleagues (1984, 1986) investigated a sequence of training adaptations on lactate threshold and ventilatory threshold responses. They found that training-induced increases in lactate threshold and ventilatory threshold were not correlated, and that lactate threshold and ventilatory threshold responded differently to continuous and interval training. Clearly, different investigators are using different methods for determining the threshold and are therefore measuring different thresholds related to the development of metabolic acidosis. WASSERMAN (1984) has pointed out that there are 3 stages of change in gas exchange that occur in response to metabolic acidosis. The measurements to be made should depend on the exercise protocol. But the stage 1 change, i.e. lactic acid buffering causing CO2 output to increase relative to O2 uptake is the obligatory change which might be measured to determine the lactate threshold by gas exchange. 2. Objective procedure for identification. a) Lactate threshold: For invasive studies, blood samples can be taken from many sites; artery, femoral vein, antecubital vein, dosal hand vein, or capillary. It is well documented that lactate (lactic acid) is formed from pyruvate and is catabolized through pyruvate and that its concentration depends on the dynamic imbalance between glycolysis and the utilization of pyruvate in the TCA cycle (JOBSIS and STAINSBY, 1968). Therefore, the lactate threshold indicates the point at which increased glycolysis during exercise can cause small increases in lactate (<1 mm), but it is aerobic. NADH was oxidized by mitochondria and not via pyruvate to lactate. In other words, the lactate threshold is the point at which the lactate to pyruvate ratio increases. The produced lactate has been found to be utilized in inactive muscle, heart muscle, liver, as well in active muscle (GRAHAM, 1984). Lactate uptake in the forearm has been indicated during bicycling exercise, so this would affect the values for lactate concentration obtained at different blood sampling sites, resulting in different values of lactate threshold. YOSHIDA et al. (1982b), YEH et al. (1983), and YOSHIDA (1984a) indicated that differences between arterial and deep venous lactate concentrations exist during incremental exercise (Fig. 4). In other words, when venous blood lactate in the forearm is used instead of the arterial blood, the lactate threshold is systematically higher when a fast increase in work rate, such as 1-min incremental exercise test, is used. If lactate steady state is applied, venous blood lactate is suitable for lactate threshold determination (YOSHIDA, 1984a).

8 110 T. YOSHIDA Fig. 4. Arterial and venous blood lactate concentrations in forearm during 1-min incremental bicycle exercise (Reproduced from YOSHIDA et al., 1982b). The lactate threshold has been detected in different ways as follows; (a) the point at which blood lactate concentration begins to increase above the resting level, (b) the point at which blood lactate increases 1 mm above the resting level, (c) the point at which blood lactate concentration reaches a fixed value of 2 mm, (d) the point at which blood lactate concentration reaches a concentration of 4 mm, which is named as the onset of blood lactate accumulation (OBLA) (YosHIDA et al., 1987). Even in the onset of blood lactate increase indicated in method (a), there are several methods for detecting the point such as an abrupt increase, a nonlinear increase, a slight increase, and/or an exponential increase in blood lactate concentration. Therefore, the objective detecting method for the lactate threshold should be required. YEH et al. (1983) failed to detect the threshold phenomenon of blood

9 TOPICS AND CONCEPTS OF ANAEROBIC THRESHOLD 111 lactate accumulation by using computerized semi-log plotting method. This was not confirmed by BEAVER et al. (1986) when fitting these data to a semi-log model. WASSERMAN et al. (1985a) and BEAVER et al. (1986) proposed mathematical models to more precisely fit the experimental data and from which the lactate threshold could be determined with high resolution. A model, using a transformation defined by plotting log lactate-log VO2, shows that during incremental exercise test, arterial lactate exhibits a threshold-like change, i.e., an abrupt transition from a phase of slow increase to a phase of rapidly accelerating increase. In place of the lactate threshold, some investigators suggested that the anaerobic threshold might be detected from the lactate concentration when it reaches a specific level. Thus, blood lactate concentrations of 2 or 4 mm have been recommended. In particular, the concept of OBLA which the blood lactate concentration reached a value of 4 mm has been well developed for evaluation of aerobic capacity and endurance performance (KARLSSON et al., 1984; HOLLMANN et al., 1985; HECK et al., 1985). To avoid subjective determination, this method has the advantage, because a fixed value of blood lactate is selected for the measurement procedure. However, since the absolute blood lactate concentration at rest and during exercise appears to be affected by the free fatty acids in the blood (Ivy et al., 1981; POWERS et al.,1983), glycogen content in muscles (HEIGENHAUSER et al., 1983; HUGHES et al., 1982), the acid-base status in the blood (KOWALCHUK et al., 1984), the intake of carbohydrate-rich diet (YOSHIDA, 1984b), the hypoxic condition (HERMANSEN and SALTIN, 1967; YOSHIDA, 1986a), and the luteal or follicular phase of the menstrual cycle (GAMBERALE et al., 1975; JURKOWSKI et al., 1981), parameters of aerobic functions which rely on a rigid value of lactate (e.g., OBLA), are most certainly affected by these factors (Fig. 5). b) Gas exchange threshold : The problems concerned with detecting the lactate threshold by gas exchange methods rest on the objective determination of the gas exchange alterations induced by lactate. The first criterion for determi- Fig. 5. Lactate concentration during incremental exercise as a function of VO2 following the three kinds of dietary modifications (Reproduced from YOSHIDA, 1984b).

10 112 T. YOSHIDA nation of gas exchange anaerobic threshold was the measurement of the respiratory gas exchange ratio (R) during a standard exercise test (WASSERMAN and MCILROY, 1964). Thereafter, WASSERMAN et al. (1973) introduced four criteria for gas exchange anaerobic threshold: 1) nonlinear increase in VE, 2) nonlinear increase in VCO2, 3) an increase in end-tidal O2 without a corresponding decrease in end-tidal CO2, and 4) an increase in R, during an incremental exercise test. WASSERMAN et al. suggested that of these criteria, R was least sensitive. In addition to these criteria, DAVIS et al. (1979) employed the abrupt increase of FEO2 as another index of the onset of lactic acidosis. Furthermore, DAVIS et al. (1979) suggested two criteria for discernment of the gas exchange threshold from the 1- min incremental exercise tests; l) a systematic increase in the ventilatory equivalent for O2 (i.e., VE/VO2) without an increase in the ventilatory equivalent for CO2 (i.e., VE/VCO2), and 2) a systematic increase in end-tidal PO2 (PETO2) without a decrease in end-tidal PCO2 (PETCO2). During incremental exercise test, VE/VO2 changed from a downward to an upward direction, so that the threshold detection could be readily discerned by the inflection in this measurement as work rate was increased. This has obvious advantages compared with methods which rely on a nonlinear increase of VE or VCO2. CAlozzo et al. (1982) compared gas exchange criteria to detect the ventilatory threshold. They found that the criteria of VE/ VO2 proved to be the most sensitive and reliable; because it has the highest correlation with the lactate threshold, and it has the highest test-retest correlation. However, the detection of the gas exchange threshold required a criteria for visual display of graphics from which criteria can be ratified. Traditional methods available for the determination of ventilatory threshold in many laboratories involve blind review from plots of graphic display produced by independent evaluators. ORR et al. (1982) have recently developed a computer model for detecting the ventilatory threshold using a multisegment linear regression method of VE vs. VO2. DAVIS (1985) and BEAVER et al. (1986) have pointed out that this method more likely gives a measurement which approximates the requiring compensation point and not the anaerobic threshold. SMITH and O'DONNELL (1984) have also introduced a computer algorithm for detecting the anaerobic threshold by gas exchange. More recently, BEAVER et al. (1986) developed a computerized method for selecting the anaerobic threshold by gas exchange which is based on detecting CO2 from bicarbonate buffering of lactate. They referred to this as the V-slope method and demonstrated its closeness to lactate and bicarbonate thresholds. Advantage for lactate and/or gas exchange thresholds measurement Although several debates exist concerning the concept of lactate and gas exchange thresholds, these thresholds have been well accepted and used in the fields of exercise physiology and clinical medicine, because they have several advantages for practical usage. DAVIS (1985), and JACOBS (1986) have reviewed the characteristics of these

11 TOPICS AND CONCEPTS OF ANAEROBIC THRESHOLD 113 Table 1. Comparison of the correlations between endurance running performance and VO2 max with correlations between performance and lactate variables (Reproduced from JacoBS,1986). thresholds. In brief, the thresholds correlate well with endurance performance, oxidative enzyme activities in muscle and maximal oxygen uptake (PO2 max) and other indices for aerobic capacity. 1. Correlation with endurance performance. It is well documented that endurance training results in decreased muscle lactate and reduced blood lactate levels during submaximal exercise, but above lactate threshold. Because the lactate threshold has been defined as the onset of blood acidemia, i.e., the point at which the highest VO2 was attained during incremental exercise without any accumulation of blood lactate, it is thought that there is a higher correlation between lactate threshold and endurance performance. Furthermore, endurance performance is more highly correlated with lactate threshold than VO2 max. The results obtained in the literature and summarized by JACOBS (1986) are listed in Table 1. The summarized paper is also reviewed in this issue by KUMAGAI et al. (1987). 2. Correlation with muscle fiber characteristics. FARRLLL et al. (1979) demonstrated that the lactate threshold is correlated with the %ST fiber (r =0.51; p<0.05). Thereafter, Ivy et al. (1980) pointed out the strong relationships between lactate threshold and %ST fiber (r=0.74; p<0.01) and between lactate threshold and muscle respiratory capacity (r=0.94, p<0.01). These correlations are stronger than that of VO2 max (Ivy et al.,1980), suggesting that lactate threshold might be related to oxidative capacity in muscle tissue and that the lactate threshold might be one of the best indices for adaptation in muscle tissue. 3. Endurance training. GOLLNICK et al. (1973) pointed out that SDH activity

12 114 T. YOSHIDA Of the vastus lateralis increased by 95 % after endurance training, but that VO2 max increased only by 13 %. Similarly, HENRIKSSON and REITMAN (1977) indicated that endurance training resulted in an approximate 40 % increase in SDH and cytochrome oxidase activities in vastus lateralis, while VO2 max showed only a 16 increment. These findings suggested that there appeared to be more improvement Fig. 6. A comparison of the lactate threshold in pre-and post-endurance training (Reproduced from YOSHIDA et al., 1982a). Table 2. Comparison of the changes in VO2 max with the change in lactate threshold by endurance training (Reproduced from JACOSS,1986). * All the percentage changes are statistically significant unless indicated as NS.

13 TOPICS AND CONCEPTS OF ANAEROBIC THRESHOLD 115 in muscle oxidative activity than in V02 max by endurance training. The endurance training might improve mitochondrial oxidative capacity, reduce lactate production in muscle tissue during submaximal, and thus reduce blood lactate concentration above the lactate threshold, which in turn, shifts lactate threshold to a higher value after endurance training. Many investigators show an approximate 40 increment in lactate threshold resulting from endurance training, with an increment of VO2 max of about % (Fig.6). The summarized data of endurance training effect on lactate threshold have been reviewed by JACOBS (1986) and are listed in Table Correlation with indices for aerobic capacity. Maximal oxygen uptake (J"02 max) is the most objective index of aerobic capacity (AsTRAND and RODAHL, 1970). It is documented that the lactate threshold or the gas exchange (anaerobic) threshold has a higher correlation with P02 max (DAVIS et al., 1976; Ivy et al., 1980; WELTMAN and KATCH, 1979; YOSHIDA et al., 1981; YOSHIDA, 1986a, c). Consequently, the lactate threshold or the gas exchange (anaerobic) threshold has been developed as a field test not only for distance runners, but for several sports activities (CONCONI et al., 1982; DROGHETTI et al., 1985; HAGBERG and COYLE, 1983; MICKELSON and HAGERMAN, 1982; VEICSTEINAS et al., 1985; WITH- ERS et al., 1981). However, direct measurement of Y02 max requires maximal exercise tolerance, so that subjects must exercise to physical exhaustion. It follows, therefore, that in studies dealing with cardio-pulmonary patients, elderly persons, or children etc., it is not always possible to push the subject to exhaustion and thus V02 max may not be obtained accurately. Of course, this method has attendant health risks. On the other hand, lactate threshold and gas exchange threshold have the advantage of avoiding these risk possibilities, because the thresholds can be obtained during submaximal exercise and rapid, progressively increasing work rate tests. Consequently, it is thought that lactate threshold and gas exchange threshold reflecting lactic acidosis of exercise are useful measures for the evaluation of aerobic capacity of children (GAISL and BUCHBERGER, 1980; REYBROUCK et al., 1982, 1985; IZUMI and ISHIKO, 1984; ISHIKO et al., 1984) and the aged (ALLEN et al., 1985; AUNOLA and RUSKO, 1984; REINHARD et al., 1979; THOMAS et a!.,1985; YOSHIDA et al.,1983), and the evaluation of exercise tolerance capacity in patients with heart disease or pulmonary disease (CHIDA et al., 1987; MATSUMURA et al., 1983; WEBER et al., 1980, 1982; WASSERMAN and WHIPP, 1975; WASSERMAN et al., 1987a). The thresholds also have higher correlations with other indices for aerobic capacity; i.e., PWC170, step test score, 12-min run test (REYBROUCK et al., 1982; YOSHIDA, 1986c). 5. Aids for warm up and cooling down. Theoretically, the level of work rate at lactate threshold would be most effective for warm up or cooling down. Several studies have attempted to evaluate the effect of warm up or cooling down of exercise level above, at, or below the lactate threshold on blood lactate clearance rate or exercise performance (GoTO and IKEGAMI,1987; MCLELLAN and SKINNER,

14 116 T. YOSHIDA 1982; GENOVELY and STAMFORD, 1982). 6. Applications for usage. The applications of the lactate threshold or its gas exchange counterpart are useful as an index of training pace and training evaluation (KATCH et al., 1978; KINDERMANN et al., 1979; MAGLISCHO et al., 1982; MCLELLAN and SKINNER, 1981), the evaluation of endurance exercise ability, the estimation of marathon or long distance performance, and the evaluation of exercise tolerance in normal subjects and in patients with pulmonary or heart disease. CONCLUSION Lactate threshold and gas exchange (anaerobic) threshold reflecting lactic acidosis is one of the most attractive measures in exercise physiology and clinical physiology, because they have several advantages as described in the last section. To provide more useful applications of these thresholds, the precise technical procedures should be standardized throughout the world (including exercise testing protocol, measured parameters and criteria for invasive or noninvasive methods, and determination of the thresholds). REFERENCES ALLEN, W. K., SEALS, D. R., HURLEY, B. F., EHSANI, A. A., and HAGBERG, J. M. (1985) Lactate threshold and distance-running performance in young and old endurance athletes. J. Appl. Physiol., 58: ANDERSON, S. J., HUGHSON, R. J., SHERRILL, D. L., SWANSON, G. D., and HOMER, L. D. (1986) Determination of the "anaerobic threshold" (Letters to the Editor). J. Appl. Physiol., 60: ASTRAND, P.-O. and RODAHL, K. (1970) Textbook of Work Physiology, McGraw-Hill, New York. AUNOLA, A. and RUSKO, H. (1984) Reproducibility of aerobic and anaerobic thresholds in year old men. Eur. J. Appl. Physiol., 53: BANG, O. (1936). The lactate content of blood during and after muscular exercise in man. Skand. Arch. Physiol., 74, Suppl. 10: BEAVER, W. L., WASSERMAN, K., and WHIPP, B. J. (1985) Improved detection of lactate threshold during exercise using a log-log transformation. J. Appl. Physiol., 59: BEAVER, W. L., WASSERMAN, K., and WHIPP, B. J. (1986) A new method for detecting anaerobic threshold by gas exchange. J. Appl. Physiol., 60: BROOKS, G. A. (1985) Anaerobic threshold: review of the concept and directions for future re search. Med. Sci. Sports Exerc.,17: BROOKS, G. A. (1986) The lactate shuttle during exercise and recovery. Med. Sci. Sports Exerc., 18: CAIOZZO, V. J., DAVIS, J. A., ELLIS, J. F., AZUS, J. L., VANDAGRIFF, R., PRIETTO, C. A., and Mc MASTER, W. C. (1982) A comparison of gas exchange indices used to detect the anaerobic threshold. J. Appl. Physiol.: Respir. Environ. Exerc. Physiol., 53: C0NC0NI, F., FERRARI, M., ZIGLIO, P. G.; DROGHETTI, P., and CODECA, L. (1982) Determination of the anaerobic threshold by a noninvasive field test in runners. J. Appl. Physiol.: Respir.

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