The following is the abstract of the article discussed in the subsequent letter: BASSETT, DAVID R., JR., PETER W. MERRILL, FRANCIS J. NAGLE, JAMES C. AGRE, AND RENAN SAMPEDRO. Rate of decline in blood lactate after cycling exercise in endurance-trained and -untrained subjects.J. Appl. Physiol. 70(4): 1816-1820,

1991.-The purpose of this study was to compare the rate of decline in blood lactate (La) levels in nine trained men [maximal 0, consumption (.vo2 -) 65.5 t 3.3 ml kg-l . min-‘1 and eight untrained men (VO, max42.2 t 2.8 ml kg-’ . min-I) during passiverecovery from a 3-min exercisebout. Trained and untrained subjectscycled at 85 and 80% i’o, max,respectively, to produce similar peak blood La concentrations. Twenty samples of arterialized venous blood were drawn from a heated hand vein during 60 min of recovery and analyzed in an automated La analyzer. The data were then fitted to a biexponential function, which closely describedthe observeddata (r = 0.97-0.98). There wasno difference in the coefficient expressingthe rate of decline in blood La for trained and untrained groups(0.0587t 0.0111vs. 0.0579t 0.0100,respectively). However, trained subjects demonstrateda faster time-to-peak La (P = O.Ol), indicative of a faster efflux of La from muscleto blood. Thus the rate of decline in blood La after exercise doesnot appear to be affected by training. The faster decline previously reported for trained subjectsmay be due to the useof a linear rather than a biexponential curve fit. l

l

Ability to remove lactate in endurance-trained and -untrained humans 2’0 the Editor: An enhanced efficiency of lactate removal has been reported in response to endurance training in several studies in animals (3-6) and in humans (12-14). In a recent study, however, Bassett et al. (1) concluded that “the rate of lactate decline after exercise was similar in trained and untrained human subjects.” Their conclusion was based on the fact that when untrained and trained subjects exercise for the same duration at almost the same relative work rate, 80 and 85% of maximal 0, uptake (vo 2 maX),respectively, there was no difference in the velocity constant for lactate removal (y2) (7). Once more, the study of Bassett et al. (1) opens the old debate on whether the exercise intensity should be expressed in terms of absolute or relative work rate. An important disadvantage in interpreting the data as a function of the relative work rate is that the reference variable used to normalize the exercise intensity depends itself on the training status of the subjects. Indeed, it is well established that VO 2 max, which is extensively used as reference, increases in response to endurance training. Therefore expressing the results as a function of VO,,, consists inevitably in comparing two groups of subjects (trained and untrained) who work at two different metabolic rates, as in the study of Bassett et al. (1). Being aware of this point, we already reported (12) that “a more coherent interpretation of lactate data is supplied when the results are expressed as a function of the energy re396

quirement instead of relative work load.” In a recent review, Booth and Thomason (2) mention that “physical exercise disrupts the milieu interieur” and that “a function of exercise adaptations seems to be to minimize disruption of homeostasis during an exercise bout” to “permit the animal or human to undergo physical work for longer duration at the same absolute power before fatigue” or (our conclusion) at higher absolute work rate for the same duration. Our interpretation of lactate kinetic data is in line with the conceptual dynamic view of Booth and Thomason (2) on the functional and structural adaptations induced by training. The real question is why the trained subjects of Bassett et al. (1) had the same y2 as the untrained subjects even though they brought into play a larger flux of biochemical reactions for covering the 43% higher energy expenditure in which they were involved, To provide an adequate answer, it is necessary to investigate the functional differences that exist between trained and untrained subjects when they are performing the same absolute work rate but not when they are in the same physiological state (relative to their . vo 2max) as in the study of Bassett et al. (1). Contrary to the claim of Bassett et al. (l), their results are in accordance with ours (12). We observed that after an incremental bicycle exercise, eight of nine subjects, independently of their training status, displayed practically the same y2 (0.04-0.05 min-‘) when they advanced to their required highest sustainable work rate. However, we emphasized that the same y2 was reache.d after an incremental exercise up to only 250 W (100% VO, max)for the less fit subject, up to 300 W (87-100% To2 ,,) for the five more fit subjects, and finally up to 350 W (91-97% 60,~~) for the most fit subjects. Moreover we showed that when two subjects able to exercise up to 350 W stopped cycling at 300 W, they both displayed a markedly higher T? (0.086 t 0.011 min-‘) than all the subjects able to exercise only up to 300 W (0.044 t 0.007 min-I). Because it is obvious that individuals who reach a higher absolute work rate are more fit or trained than others who are exhausted at lower work loads, we concluded that trained or physically fit subjects had a higher lactate removal ability than the others. However, Bassett et al. (1) reported that this difference in y2 might result from differences in blood lactate levels (8 vs. 3 mmol/l) that were reached at the end of exercise in response to the different relative work rates (95 t 5% VO, maxfor the less fit and 81 t 5% voarnar for the trained). In view of the biexponential evolution of the lactate recovery curves, our group has proposed a mathematical two-compartment model for representing the movements of lactate after muscular exercise and has illustrated the behavior of this system by means of a hydraulic analogue (7). Thus we are aware that blood lactate concentrations at any moment are the result of the dynamic interactions between rates of lactate appearance and lactate disappear-

0161-7567/92 $2.00 Copyright 0 1992the American Physiological Society

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LETTERS

397

TO THE EDITOR

ante. In our opinion, the lower lactate concentration that is reached at the end of exercise by the trained subjects when they cycle at the same absolute work rate as lesstrained subjects may be the result of 1) a reduced lactate production by the trained individuals compared with the less-trained ones (10) and 2) a higher efficiency in lactate removal as indicated by the increased yz of the welltrained athletes. We do not believe, however, that y2 depends on the lactate concentration reached at the end of exercise. The ability to remove lactate depends on the physiological state of the organism. For instance, significantly lower y2 (impaired ability to remove lactate) were obtained after 60 min than after 3 min of bicycle exercise (9), even though the lactate concentrations reached at the end of the exercises were the same. With respect to the data of Bassett et al. (l), a similar yz was reached by their trained and untrained subjects, but after an exercise of only 221 W (2.49 W/kg) for the untrained group and 315 W (4.36 W/kg), i.e., an exercise involving a 43% higher energy expenditure, for the trained group. In view of the statistically significant inverse relationships between y2 and absolute work rate (7), if the trained subjects of Bassett et al. (1) had performed their exercise at the same work rate of 221 W as the untrained subjects, their yz would have been higher than after 315 W and also higher than the y2 of 0.06 mine1 of the untrained subjects. If the authors had included this situation in their experimental protocol, they could have clearly demonstrated that the trained subjects display a higher y2 (a higher ability to remove lactate) than the untrained individuals at the same absolute work rate. The lack of statistically significant differences observed by Bassett et al. (1) between yz when the trained and untrained individuals undergo the same relative work load indicates, at least for their population of subjects, that the modifications induced by training on the ability to remove lactate are proportionally of the same magnitude as those induced on 00, mBx.It is nevertheless worth mentioning that many studies have shown that changes in lactate-related variables may be larger than changes in VO, max(for references, see Ref. 15). For instance, the functional and structural improvements that facilitate the redistribution of lactate between the muscles and the blood of trained subjects may be proportionally larger than those observed for the VO, max, as shown by the significantly decreased time-to-peak lactate found by Bassett et al. (1) for the trained subjects. The several questions raised by the present discussion emphasize the importance of the metabolism of lactate in exercise physiology. Nevertheless, studies on lactate kinetics are rather scarce in humans. Stanley et al. (13) reported that, for a given arterial lactate concentration, the rate of lactate disposal (and hence the lactate metabolic clearance rate) was higher in a well-trained competitive long distance runner than in a recreational swimmer. In further data of Stanley et al. (14) during exercise at near the same absolute and relative work rate, the lactate metabolic clearance rate was higher on the average in competitive athletes than in recreational sportsmen. It was pointed out (8) that the relationships observed during exercise by Stanley et al. (13) and Mazzeo et al. (11) between the lactate metabolic clearance rate and work

rate displayed patterns similar to those between the lactate metabolic rate of the recovery (computed by means of yz) and work rate of the preceding exercise. As regards the influence of training on the efficiency of lactate removal, our results observed during recovery (12) with endogenous lactate are consistent with those of Stanley et al. (13, 14) obtained during the exercise with isotopic lactate. In summary, the interpretation of the lactate kinetic data as a function of the absolute work rate reconciles the results of Bassett et al. (1) with the data of Stanley et al. (13, 14) and with our data in humans (l2), as well as with those of Freminet et al. (6), Donovan and Brooks (3), and Donovan and Pagliassotti (4,5) in animals. It is in line with the concept of molecular and cellular adaptations that occur as a result of exercise training (2). A comparatively higher efficiency of lactate removal at the same absolute work rate may be indicative of functional and structural adaptations that allow the trained subjects to perform higher absolute work rates before becoming exhausted when compared with nonconditioned subjects. REFERENCES 1. BASSETT, D. R. SAMPEDRO.

R., JR., P. W. MERRILL, F. J. NAGLE, J. C. AGRE, AND Rate of decline in blood lactate after cycling exercise in endurance-trained and -untrained subjects. J. A&. Physiol.

70: 1816-1820,199l. 2. BOOTH, F. W., AND D.

B. THOMASON. Molecular and cellular adaptation of muscle in response to exercise: perspectives of various models. Physiol. Rev. 71: 541-585, 1991. 3. DONOVAN, C. M., AND G. A. BROOKS. Endurance training affects lactate clearance, not lactate production. Am. J. Physiol. 244 (Enducrinol. Metab. 4. DONOVAN, C.

7): E83-E92,

257 (Endocrinol. 5. DONOVAN, C.

Metab.

1983.

M., AND M. J. PAGLIASSOTTI. Endurance training enhances lactate clearance during hyperlactatemia. Am. J. Physiol. 20): E782-E789,

1989.

M., AND M. J. PAGLIASSOTTI. Enhanced efficiency of lactate removal after endurance training. J. Appl. Physiol. 68:

1053-1058, 6. FREMINET,

1990.

A., C. POYART, E. BURSAIJX, AND T. TABLON. Effect of physical training on the rates of lactate turnover and oxydation in rats. In: Metabolic Adaptations to Prolonged Physical Exercise, edited by H. Howald and J. R. Poortmans. Basel: Birkhauser, 1975, p. 113-118. 7. FREUND, H., S. OYONO-ENGUELLE, A. HEITZ, J. MARBACH, C. OTT, P. ZOULOUMIAN, AND E. LAMPERT. Work rate-dependent lactate kinetics after exercise in humans. J. Appl. Physiol. 61: 932-939, 1986. 8. FREUND, OTT, AND

H., S. OYONO-ENGUELLE, A. HEITZ, J. MARBACH, C, M. GARTNER. Effect of exercise duration on lactate kinetics after short muscular exercise. Eur. J. Appl. Physiol. Occup. Physiol. 58: 534-542, 1989. 9. FREUND, H., S. OYONO-ENGUELLE, A. HEITZ, C. OTT, J. MARBACH, M. GARTNER, AND A. PAPE. Comparative lactate kinetics after short and prolonged submaximal exercise. Int. J. Sports Med. 11: 284-288,199O. 10. HOLLOSZY, J.

O., AND E. F. COYLE. Adaptations of skeletal muscle to endurance exercise and their metabolic consequences. J. Appl.

Physiol. 56: 831-838, 1984. 11. MAZZEO, R. S., G. A. BROOKS, D. A. SCHOELLER, AND T. F. BUDINGER. Disposal of blood [l-13C]lactate in humans during rest and exercise. J. Appl. Physiol. 60: 232-241, 1986. 12. OYONO-ENGIJELLE, S., J. MARBACH, A. HEITZ, C. OTT, M. GARTNER, A. PAPE, J. C. VOLLMER, AND H. FREUND. Lactate removal ability and graded exercise in humans. J. Appl. Physiol. 68: 905-911,199o. 13. STANLEY, W. C., E. W. GERTZ, J. A. WISNESKI, D. L. MORRIS, R. A. NEESE, AND G. A. BROOKS. Systemic lactate kinetics during graded

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LETTERS

398

TO THE EDITOR

exercise in man. Am. J. Physiol. 249 (Endocrinot. Metub. 12): E595E602,1985. 14. STANLEY, W. C., J. A. WISNESKI, E. W. GERTZ, R. A. NEESE, AND G. A. BROOKS. Glucose and lactate interrelations during moderateintensity exercise in humans. Metabolism 37: 850-858, 1988. 15. TANAKA, K. Lactate-related factors as a critical determinant of endurance. Ann. Physiol. Anthrop. 9: 191-202, 1990.

Samuel Oyono-Engu6116 Laboratoire de Physiologic Appliqu& FacuLte’de Mbdecine Universitk Louis Pasteur F-67085 Strasbourg Cedes France Hubert

Freund

Laboratoire de Pharmacolugie Mule’culaire et Cellulaire Fuculte’ de Pharmacie Universite’ Louis Pasteur F-67400 Illkirch-Graffenstuden, France REPLY

To the Editor: Drs. Oyono-Enguelle and Freund have raised some points of concern regarding the different conclusions reached by their study (16) and ours (1). We agree that the disparity is due to the choice of exercise

protocols,

which equated trained

and untrained

subjects

on the basis of either absolute or relative work rates. However, we maintain that our use of similar relative

work rates is appropriate, below.

for the reasons explained

achieved after exercise. This raises the possibility that the trained subjects in the study of Oyono-Enguelle et al. had elevated yZ values as a result of lower blood lactate levels at the start of recovery. 3) Finally, Oyono-Enguelle and Freund have noted that the trained group in our study had a 43% higher energy expenditure than the untrained group during exercise. Despite this, our results show that by the 2nd min of recovery, 0, uptake in the trained group had returned to levels that were identical to the untrained group. By the 5th min of recovery, both groups had returned to rest levels. It is therefore unlikely that a difference in metabolic rate affected the results during the 60-min recovery period. A much debated topic in the literature concerns the argument over whether training decreases blood lactate levels at a given absolute work rate via decreased production (7,12-13,18) or increased removal (3-5). In support of decreased production, Favier et al. (7) showed a decreased lactate accumulation in isolated muscles of trained vs. control animals. In addition, other investigators (l2,18) have demonstrated a reduced arteriovenous lactate difference in humans after training, again indicative of decreased lactate production. Studies employing carbon-labeled lactate tracers are frequently used to provide support for a training enhancement of lactate removal (3, 8). However, recent

studies have suggested that labeled lactate undergoes an exchange with intracellular lactate and pyruvate (14,17, 1) The rate of lactate removal may be dependent on 19). Thus, tracer techniques may not adequately discriminate between pyruvate and lactate turnover (14,17). Bethe blood lactate concentration. Hence, most studies that cause of these limitations, Donovan and Pagliassotti (4, have examined the effects of training on blood lactate 5) conducted a study in which they infused “cold” exogedecline have attempted to equalize the levels of blood lactate by expressing the work rate as a percentage of nous lactate into resting rats until new steady-state levels were achieved. They reported a twofold increase in maximal aerobic capacity (%$$ m,). For instance, Bonen and co-workers (2,15) compared trained and un- lactate removal with training. In our view, this question cannot be definitively antrained subjects after exercise at 90 and 89% vo, maX, respectively. In a study by Evans and Cureton (6), sub- swered by studying blood lactate recovery data. The biexponential model developed by Freund and cojects cycled to exhaustion at 110% voz m8x. In contrast, in the study of Oyuno-Enguelle et al. (16) workers (9-11, 16) provides a more accurate description trained and untrained subjects exercised at a fixed abso- of recovery lactate data than the linear model used in lute work rate (300 W). The oxygen requirement was 3.97 previous studies (2,15). However, it is limited by the fact l/min and Vozrnax ranged from 3.25 to 5.22 l/min. The that in most instances the “dose” of lactate formed in the compartment is unknown. When our range in relative work rates (76-122% VO, ,,) resulted in intramuscular lower blood lactate levels for the trained subjects (3 vs. 8 trained and untrained subjects performed exercise resulting in similar blood lactate concentrations, the demM). In our view, it makes more sense to compare cline in blood lactate was not significantly different,. trained and untrained subjects at similar blood lactate concentrations, given that most metabolic processes are Thus, we do not believe that recovery lactate data prodependent on the level of substrate present. Studies us- vide support for a training enhancement of lactate reing isotopic tracers (3, 8) and infusions of “cold” exoge- moval. nous lactate (4, 5) have also consistently compared trained and untrained groups at the same blood lactate REFERENCES concentration. BASSETT,D. R., JR., P.W. MERRILL, F. LNAGLE, J.C. AGRE,AND 2) In designing their study, Oyono-Enguelle et al. (16) R. SAMPEDRO. Rate of decline in blood lactate after cycling exerchose to compare trained and untrained subjects at the cise in endurance-trained and -untrained subjects. J. Appl. Physiol. same absolute intensity. The rationale for this protocol 70: 1816-1820,199l. BELCASTRO, A. N., AND A. BONEN. Lactic acid removal rates durwas based on previous work by Freund et al. (11) demoning controlled and uncontrolled recovery exercise. J. Appl. Physiol. strating that y2 (the velocity constant expressing the rate 39: 932-936, 1975. of blood lactate decline) was inversely related to the abDONOVAN, C. M., AND G. A. BROOKS. Endurance training affects solute work rate of the preceding bout. However, yZ was lactate clearance, not lactate production. Am. J. Physiol. 244 (Endocrinol. Metab. 7): E83-E89, 1983. also inversely related to the level of blood lactate Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (129.081.226.078) on January 12, 2019.

LETTERS

TO THE

4. DONOVAN, C. M., AND M. J. PAGLJASSOTTI. Endurance training enhances lactate clearance during hyperlactatemia. Am. J. Physiol. 257 (Endocrinol. Metub, 20): E782-789, 1989. 5. DONOVAN, C. M., AND M. J. PAGLIASSOTTI. Enhanced efficiency of lactate removal after endurance training. J. Appl. Physiol. 68:

Ellis (1) inverted this equation PO, from S using PO 2

1053-1058,199O.

6. EVANS, B. W., AND K. J. CURETON. Effect of physical conditioning on blood lactate disappearance after supramaximal exercise. Br. J. Sports Med. 17: 40-45, 1983. 7. FAVIER, R. J., S. H. CONSTABLE, M. CHEN, AND J. 0. HOLLOSZY. Endurance exercise training reduces lactate production. J. Appl. Physiol. 61: 885-889, 1986. 84 FREMINET, A., C. POYART, E. BURSAIJX, AND T. TABLON. Effect of physical training on the rates of lactate turnover and oxidation in rats. In: Metabolic Adaptations to Prolonged Physical Exercise, edited by H. Howald and J. R. Portmans. Basel: Birkhauser, 1975, p. 113-118. 9. FREUND, H., AND P. ZOULOUMIAN. Lactate after exercise in man: I. Evolution kinetics in arterial blood. Eur. J. Appl. Physiol. Occup. Physiol. 46: 121-133, 1981. 10. FREIJND, H., AND P. ZOULOUMIAN. Lactate after exercise in man. IV. Physiological observations and model predictions. Eur. J. Appl. Physiol. Occup. Physiol. 46: 161-176, 1981. 11. FREIJND, H., S. OYONO-ENGUELLE, A. HEITZ, J. MARBACH, C. OTT, P. ZOULOUMIAN, AND E. LAMPORT. Work rate-dependent lactate kinetics after exercise in humans. J. Appl. Physiol. 61: 932-939, 1986. 12. HENRICKSON, J. Training induced adaptations of skeletal muscle and metabolism during submaximal exercise. J. Physiol. Land. 270: 661-675,1977.

13. HOLLOSZY, J. O., AND E. F. COYLE. Adaptations of skeletal muscle to endurance exercise and their metabolic consequences. J. Appl. Physiol. 56: 831-838, 1984. 14, KATZ, A., AND K. SAHLIN. Role of oxygen in regulation of glycolysis and lactate production in human skeletal muscle. Exercise Sport Sci. Rev. 18: l-28, 1990. 15. M&RAIL, J.C.,A. BONEN,AND A.N. BELGASTRO. Dependenceof lactate removal on muscle metabolism in man. Eur. J. Appl. Physiol. Occup. Physiol. 39: 89-97, 1978. 16. OYONO-ENGIJELLE, S., J. MARBAGH, A. HEITZ, C. OTT, M. GARTNER, A. PAPE, J. C. VOLLMER, AND H. FREIJND. Lactate removal ability and graded exercise in humans. J. Appl. Physiol. 68: 905-911,199o. 17. SAHLIN, K, Lactate production cannot be measured with tracer techniques. Am. J. Physiol. 252 (Endocrinol. 1Metab. 15): E439E440,1987. 18. SALTIN, B., ESSEN, AND

K. NAZAR, D. L. COSTILL, E. STEIN, E. JANSSON, B. P. D. GOLLNIGK. The nature of the training response: peripheral and central adaptations in one-legged exercise. Actu Physiol. Stand. 96: 289-305,1976. 19. WOLFE, R. R., F. JAHOOR, M. MIYOSHI. Evaluation of isotopic equilibration between lactate and pyruvate. Am. J. Physiol. 254 (Endocrinol. Metab. 17): 532435, 1988.

David R. Bassett, Jr. Department of Human

399

EDITOR

to enable calculation

of

11,700 + [503 + (~)yy~ = I (l/S - 1) + [ (;;7yl)

-

[503

+ (~)2]1/2)1/3

The equations In 2 = 0.3923(1n Po,)~ - 4.266 and In PO, = (2.549 In 2 + 10.87)Om5 where 2 = S/(1 - S) allow calculation of S from PO,, and PO, from S, with a maximum deviation of S from the standard curve of to.0092 over the range 0.006 < S < 1 (Fig. 1). Although these equations do not achieve quite the accuracy of those described by Severinghaus and Ellis, they may be useful if a rapid and simple method of conversion between PO, and S, and vice versa, is required. REFERENCES

R. K. Determination of PO, from saturation (Letter to the Editor). J. Appl. Physiol. 67: 902, 1989. 2. SEVERINGHAUS, J. W. Simple, accurate equations for human blood 0, dissociation computations. J. Appl. Physiol. 46: 599-602, 1979. 1. ELLIS,

G. C. G. Watney Department of Large Animal

Clinical Sciences

Health Science Center Collegeof Veterinary Medicine University of Florida Gainesville, Florida 32610 REPLY

To the Editor: Although Watney’s equation is simpler than mine, the difference is hardly worth loss of accuracy. The upper two-thirds of the standard human 0, dissociation curve closely follows a single exponential. For buffs who want even greater simplicity with less error, the following reversible relationship handles the

Performance

and Sport Studies

University of Tennessee-Knoxville Knoxville, Tennessee 3 7996

Calculation

of saturation

and PO,

To the Editor: Severinghaus (2) has described the following simple equation, which fits the standard human blood oxygen dissociation curve to within t_O.OO% of the fractional saturation (S) over the range 0 < S < 1

S = [23,4OO/(Po;

+ 150 PO,) + 11-l

I

0.25

I

0.50 Saturation

1

0.75

I

1.00

FIG. 1. Error in saturation calculated using Severinghaus’ equation (e) and equation described here (+).

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400

LETTERS

range 0.35 < S

Ability to remove lactate in endurance-trained and -untrained humans.

The following is the abstract of the article discussed in the subsequent letter: BASSETT, DAVID R., JR., PETER W. MERRILL, FRANCIS J. NAGLE, JAMES C...
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