Lactate removal ability exercise in humans
and graded
S. OYONO-ENGUELLE, J. MARBACH, A. HEITZ, A. PAPE, J. C. VOLLMER, AND H. FREUND Laboratoire de Physiologie Appliquke, 67087 Strasbourg Cedex, France
Groupe de Recherche
OYONO-ENGUELLE, 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(3): 905-911, 1990.-Venous lactate concentrations of nine athletes wererecordedevery 5 s before, during, and after graded exercisebeginning at a work rate of 0 W with an increaseof 50 W every 4th min. The continuous model proposedby Hughson et al. (J. Appl. Physiol. 62: 1975-1981, 1987) was well fitted with the individual blood lactate concentration vs. work rate curves obtained during exercise. Time coursesof lactate concentrations during recovery were accurately describedby a sum of two exponential functions. Significant direct linear relationships were found between the velocity constant (yzv) of the slowly decreasingexponential term of the recovery curves and the times into the exercisewhen a lactate concentration of 2.5 mmol/l wasreached.There wasa significant inverse correlation betweeny2v and the rate of lactate increaseduring the last step of the exercise. In terms of the functional meaning given to y2v, these relationships indicate that the shift to higher work rates of the increaseof the blood lactate concentration during graded exercisein fit or trained athletes, when comparedwith lessfit or untrained ones,is associatedwith a higher ability to remove lactate during the recovery. The results suggestthat the lactate removal ability plays an important role in the evolution pattern of blood lactate concentrations during graded exercise. venous blood lactate; recovery; lactate kinetics
C. OTT, Activitk
M. GARTNER, Physiques
et Sportives,
ing lactate disappearance from venous blood provides dynamic information analogous to that delivered by y2a (21) With this known, it might be expected that the study of venous blood lactate kinetics during recovery from graded muscular exercise can shed light on some of the mechanisms concerning blood lactate variations observed during exercise. Despite the large number of papers devoted to the interpretation of blood lactate patterns during incremental exercise, several questions are still open to controversy. The first objective of the present study is to supply a more precise mathematical description of lactate curves during and after graded exercise by using a continuous blood sampling and analyzing method. The second aim is to look for useful relationships between the pattern of venous lactate concentrations during graded muscular exercise in humans and the overall ability of the organism to remove lactate as assessed from the recovery after the graded exercise. In a recent paper, Hughson et al. (16) have used a continuous model to describe blood lactate changes with work rate during a 50 W/min progressively increasing exercise. Another purpose of our study is to learn if their model is also valid for a different slope. METHODS
COURSES of arterial blood lactate concentrations during recovery from muscular exercise of several work rates or durations are accurately described by a sum of two exponential time functions (7-9). The velocity constants of these functions prove to be indicators of blood lactate recovery kinetics. They supply quantitative information on the body’s overall functional ability to exchange (high-velocity constant rla) and to remove (low-velocity constant yaa) lactate after muscular exercise (8). The similarity between the results of Hubbard (l4), Ryan et al. (24), Mazzeo et al. (18), and Stanley et al. (26) obtained during exercise and those of Freund et al. (7, 8) observed during recovery indicates that the modifications of lactate removal kinetics that take place during the exercise are related to those observed during recovery. In addition, it has been shown recently that a sum of two exponential terms can also be used to describe the venous blood lactate recovery curves and that the velocity constant (y2v) of the exponential term describTIME
Subjects and experimental protocol. Nine athletes (2 females and 7 males) whose anthropometric variables and physiological characteristics are reported in Table 1 participated in the study. Details of experimental procedures and an explanation of the risks involved were provided to the subjects before obtaining their written consent to participate in the experiments. Maximal aerobic power (VO 2 max) was determined for all subjects before the lactate experiment. Subjects were tested in the morning at the normal room temperature of 21-23”C, after a light standard breakfast taken -2 h before. Heart rate was monitored throughout the experiment from a continuous electrocardiogram as a safety and check procedure. The exercise was performed in a seated position on a mechanically braked cycle ergometer (Fleisch ergometer) at a constant pedaling frequency of 60 rpm. During rest and recovery, the subjects were seated in an armchair especially fixed to the cycle that allowed them to maintain a comfortable
0161-7567/90 $1.50 Copyright 0 1990 the American Physiological Society
905
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906 TABLE
LACTATE
REMOVAL
ABILITY
AND
GRADED
EXERCISE
1. Physical and anthropometric characteristics of subjects Subj No.
Sl s2 s3 s4 s5 S6 s7 S8 s9 Mean
t SE
Sex
F M M F M M M M M
Age,
Weight,
Height, cm
Maximal Aerobic Power, W
Yr
kg
22 25 18 24 22 20 29 20 25
56.1 58.7 52.0 61.1 61.1 65.7 68.8 65.7 70.7
164.5 168 173 165.5 178 178 181 172 178
250 300 300 320 320 345 360 385 395
2321
62.2k2.0
173.1k2.0
331+15
VO
2 max
ml/min
ml. kg-’ - min-’
3,250 3,900 3,850 4,180 3,950 4,200 4,560 4,950 5,220
58.0 66.4 73.2 68.4 64.6 63.9 66.3 75.3 73.9
4,229+200
67.8t1.9
position. In view of the close dependence of lactate biochemical analyzer were fed into an analog-to-digital recovery kinetic data on both the work rate (8) and the converter (Scientific-Solutions) and a microcomputer duration (7) of the previously performed exercise, the (M24 Olivetti). Concentrations were recorded every 5 s. subjects were sorted according to the highest work rate Expression of data. Exercise intensity is expressed as that they could complete during the incremental exercise absolute work rate (W or W/kg). The rationale for this test. choice lies in the observation that a more coherent interEach incremental test was divided into rest, exercise, pretation of the lactate data is supplied when the results and recovery phases. The duration of the resting phase are expressed as a function of energy requirement instead depended on the time required by each subject (30-60 of relative work load (%VO 2 max). Other authors (10, 15) min) to reach a steady basal venous lactate concentration also agree with this approach. The following criteria have before the exercise began. Exercise started at 0 W with been selected to characterize the pattern of the blood a 50-W increment every 4th min up to 250 W for subject lactate evolution curves during exercise. I) the time into SI (the least physically fit of all the subjects), up to 300 the exercise (t 2,5,s or min) after which a lactate concenW for the five subjects SZ-S6 (series 300 W), and up to tration of 2.5 mmol/l is reached for each subject; this 350 W for the three subjects S7-S9 (series 350 IV). time could be measured accurately because the lactate Subjects S7 and S8 of this latter group repeated the same concentrations were delivered at 5-s intervals. 2) the experiment a few days afterward but were asked to lactate increase rate (LIR, mmol .1-l min-‘) during the exercise only up to 300 W. The aim of this additional last step of exercise (increase of lactate concentration measurement was to see the influence of lower work rates between the onset and end of the last step of exercise and hence of shorter graded exercise duration on lactate divided by the duration of this step). recovery kinetics. Subject S9 was not concerned by this Mathematical and statistical analysis. The individual additional experimentation. Indeed, if he had stopped venous lactate recovery curves were fitted by means of the exercise at 300 W, his lactate concentration at the an iterative nonlinear technique to a sum of two expoend of the test would not have been high enough to allow nential terms of the form an accurate study of its evolution during the following recovery. The symbol cy will be used to identify the Lv(t) = Lv(0) + Alv(l - e-ylvt) + Agv(l - e-r2vt) (1) supplementary exercise performed by the subjects ST and S8 up to 300 W (included with the series 300 W). In this equation Lv(t) is the venous blood lactate concentration at time t into the recovery, Lv(0) is the Venous blood lactate concentrations were measured after at the end of each exercise until they returned again to a near steady measured venous lactate concentration exercise, AIv and A2v are the amplitudes, and ylu and basal level (65-120 min depending on the subject and the y2u are the velocity constants of the exponential funcexercise). tions. Blood sampling and analysis. An indwelling l-mmThe continuous model proposed by Hughson et al. (16) diameter polyethylene catheter was placed in an antewas used for fitting the individual curves of lactate cubital vein. After heparinization of the subjects (hepaconcentrations observed at the end of each step in graded rin, 100 IU/kg) to prevent blood clotting, the catheter was connected to an automatic analyzer comprised of a exercise as a function of work rate (W/kg). The form of peristaltic pump (Ismatec), a dialyzer (Technicon), an this model is given by oil bath at 40°C (Technicon), a detector (LKB 2138 Y = a + b exp(cx) (2) Uvicord S; operating wavelength 365 nm), and a stripchart graphic recorder (Hewlett-Packard). Blood was where y is lactate concentration, x is work rate, and a, b, and c are coefficients estimated by minimizing the residdrawn continuously at a rate of 0.32 ml/min throughout ual sum of the squares between lactate concentrations the experiment. Lactate concentrations were measured and the calculated curve. Linear regressions were used by an enzymatic method according to the flow diagram to describe the relationships between data. Statistical described by Freund et al. (6), which is a modification of previously described methods (5, 19). Signals from the significance was set at P < 0.05. l
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LACTATE
REMOVAL
ABILITY
AND GRADED
EXERCISE
907
RESULTS
All the subjects advanced to their required highest work rate. Except for S3 and S4 of series 300 W, who stopped after 3 min, all completed 4 min at the prescribed highest work rate. With respect to these subjects, S3 and S4, the duration of their last step of exercise was nevertheless considered to be near enough to 4 min to allow retaining the parameters chosen for this study. Time courses of the lactate concentrations before, during, and after the exercise are reproduced in Fig. 1. The venous lactate concentrations reached every 4th min during the graded exercise are presented as a function of work rate in Fig. 2. In Table 2 the values of tze5and LIR are given. Compared with the other subjects of series 300 IV (SZS6) who performed the same graded exercise, S7cu and S8cu had the lowest lactate concentrations during and at
o!
1
I
I
1
1
1
1
0
1 2 3 4 5 6 WORK RATE ) We kg-’ FIG. 2. Individual venous lactate concentrations every 4th min during graded exercise as function of absolute work rate normalized to body mass.
12 -
A
I
TABLE
2. Individual
values of selected criteria
Subj
250- W graded Sl
18.75 300- W graded
s2 s3 s4 s5 S6 s7cY S8a
ins5
C
c 1 z E E
8-
1 i
.
OL
!I! I
0
I
,
I
30
I
'
6'0 '
TIME,
' 9'0
'
' 120
'
min
FIG. 1. Individual time courses of venous lactate concentrations before, during, and after graded exercise. A, B, and C: curves of subjects who exercised up to 250, 300, and 350 W, respectively. Vertical dashed lines, 4min periods of exercise beginning with 0 W to maximum work rate, in 50-W steps.
exercise
22.92 21.75 21.83 21.17 22.25 27.50 27.50 350-W
s7 S8 s9
LIR, pmol - 1-l min-’
t2.5,
min
No.
graded
exercise
26.17 26.08 31.25
l
exercise 800 (series 300 W) 1,160 1,330 1,500 1,038 550 270 258 (series 350 W) 838 783 463
the end of this exercise (Fig. 1B). As shown in Table 2, their lactate concentrations increased later (greater t2.J and less sharply during the last exercise step (lower LIR). Their maximal lactate concentrations during the recovery were markedly lower than those of S2-S6 (Fig. 1B). But in the series 350 IV, the same subjects, S7 and S8, reached higher lactate concentrations than S9. Moreover, relative to S9, their lactate concentrations increased sooner (smaller t2.J and more abruptly (higher LIR) during the last step of the 350 W graded exercise (Fig. 1C and Table 2). The parameters of the fits of Eq. 2 to the changes of lactate concentrations with work rate are reported in Table 3. The data were well fitted by Eq. 2 (Fig. 3). There were nevertheless exceptions for which the fits were slightly less accurate, namely as illustrated in Fig. 3 (bottom) when a decrease in lactate concentration occurred at low work rates. Eq. 1 fitted closely the venous lactate concentration curves over the entire recovery (Table 4). The standard deviation (a) between the experimental and predicted curves was small. The accuracy
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LACTATE
908 TABLE
REMOVAL
ABILITY
AND GRADED
EXERCISE
3. Parameters of fits of Eq. 2 to curves of lactate concentration vs. work rate during graded exercise Subj
No.
a
Sl
b
250-W graded 0.06596
0.6927
300-W
s2 s3 s4 s5 S6 S7a S&Y
0.5719 0.6279 1.1726 0.6032 1.2758 0.8188 0.6774
s7 S6 s9
0.7032 0.9265 0.8846
graded
. 1
.
.
2
3
I
4
0.9988
exercise
=
5
1
r
1.2261 0.8628 1.1671 0.9618 1.0415 1.0548 1.1094 exercise
92
0.999
108 153 253 144 61 18 64
0.999 0.998 0.994 0.999 0.999 0.999 0.996
35 59 66
0.999 0.999 0.996
(series 300 W)
(series
0.01463 0.01278 0.00000815
S?
pi&1
exercise
0.01415 0.05233 0.02170 0.07219 0.03607 0.02010 0.01252 350- W graded
I,
c
350 W)
1.1785 1.1409 2.5277
There was a statistically significant relationship between the VO 2max and the corresponding t2.5 (r = 0.901, P < 0.001). For the subjects of series 300 VVthere was further a close correlation between the maximal aerobic power and y2v (r = 0.862, P c 0.013). To study the potential influence of individual removal ability (as supplied by y2v) on the evolution pattern of lactate concentration during a graded exercise test, y2v of the subjects of series 300 VVwas plotted in Fig. 4 against t2.5and LIR. The relationships are both statistically significant.
6 DISCUSSION
4
EXPERIMENTAL
CURVE
The present study demonstrates that the venous blood lactate recovery curves from graded muscular exercise fit accurately the two exponential time functions in Eq. 1. This result shows that the mathematical model Eq. 1 proposed for the analytical description of the lactate concentration during recovery from constant-load exercise applies also to recovery from exercise of progressively increasing intensity. For clarity of the discussion it may be helpful to recall s9 some basic information that will facilitate the interpretation of the present results. First, for constant work rates ranging almost from 100 to 375 W, the velocity constants of Eq. 1 decreased when work rate increased 1 2 3 4 5 6 (7-9). With respect to yzv, the results of S7 and S6 corroborate this earlier finding, because when they exWORK RATE, W.kg - ’ ercised up to 350 W instead of up to 300 W their 720 was FIG. 3. Examples of fits of Eq. 2 to exercise lactate concentrations lowered (Table 4). Second, as already mentioned, y2v has every 4th min. Bottom: decrease of venous lactate concentration at low been given a functional meaning, namely the ability of work rates is not accounted for by &. 2. the body to remove lactate via metabolic processes (8). (lOOa/average concentration of the recovery) ranged Third, in graded exercise there is a relationship between from 2 to 8%. As shown in Table 4, for eight out of the work rate and exercise duration because the load innine subjects, the y2v of the fits to the venous lactate creases stepwise with time. recovery curves after the prescribed highest work rate A very interesting result of this study is that, for the ranged within 0.038-0.053 min-‘. S9 of series 350 VV subjects placed in the same experimental series 300 W, displayed a higher value (0.077 min-l). Table 4 shows there are statistically significant correlations of the y2v also that S7a and SBa, had decidedly higher y2v (0.078 of the fits to the lactate recovery curves with the time and 0.094 min-‘) when they stopped cycling at 300 W t2 5 and LIR (Fig. 4), as well as with the maximal aerobic than the other subjects of series 300 IV and higher than power (84 and 68% of the variance of ts5 . and LIR are when they were placed in series 350 VV. accounted for by yzv, respectively). However, because dr
FlITED
CURVE
3 3
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LACTATE TABLE
REMOVAL
ABILITY
AND GRADED
EXERCISE
909
4. Parameters of fits of Eq. 1 to venous lactate recovery curves and some other characteristics Subj No.
Lv(O), pmol/l
Alv, pmol/l
&v, pmol/l
Recovery Sl
s2 s3 s4 s5 S6 s7ar S8a
6,340
7,960
8,170 7,790
8,650 5,450 2,820 2,640
7,223
4,280 4,020 3,375 13,285 3,282 1,261 1,050
-12,737 Recovery -11,665 -11,249 -10,366 -21,110
-7,305 -3,542 -3,108 Recovery
s7 S8 s9
6,580 6,470 3,120
4,093
2,834
from
-10,322 -8,867 -4,201
YlV,
Y2V,
w4,
min-’
min-’
pmol/l
from
250- W graded
0.2945
0.04426
300-W
graded
0.03895
0.5388
0.05321
0.6659 0.1490
0.03799 0.04311 0.04891 0.07849 0.09394
0.4800 0.8789
0.6742 from
350-W
graded
0.2564 0.4896
Lvbs), pmol/l
exercise 826
exercise
0.4569
Lv(max), pmol/l
174
9,530
590
78 174 172 141
9,890 9,800
570 880 1,030 760
(series 300 W) 576 941 1,199
824
11,920 7,100
139
1,426 539
62 32
3,350
143 48 71
7,800 7,400 4,200
582
exercise
10,050
1,290 760 670
2,930
(series 350 W)
0.04234 0.05128 0.07674
351 437 614
1,696 1.1580 Lv(=), computed value of lactate concentration at end of recovery (t + 00); Lv(max), highest venous lactate concentration Lv(rs), venous lactate concentration at rest before the exercise.
blood lactate recovery kinetics are closely dependent on the work rate (8) and (although less) on the duration (7) of the previously performed exercise, the validity of the correlations of y2v with t2.5 or LIR requires that the subjects had performed similar graded exercises. Note that, as shown in Table 4, the relations hold true also for the subjects of series 350 VV (S7 and S8 with a 4533% lower y2v than S9 had a 9-30% lower maximal aerobic power, a 16% lower t2.5, and 71-81% higher LIR). Because of the known dependency of y2v on work rate (7, 8, 21) these relationships can be extrapolated to all the subjects. Indeed it is beyond doubt that if S2-SS had stopped cycling at 250 W, they would have reached a higher y2v than that attained respectively after the 300W graded exercise and very likely also a more elevated y2u than the 0.044 min-’ obtained for S1. The same reasoning can hold but stepwise for S9. Thus if the test had been stopped for all the subjects at the end of the 250-W exercise, the y2u reached by S1 would have been lower than that of any of the other subjects. Conversely S9, who displayed a markedly higher y2u than all the other subjects when they cycled up to their highest requested work rate, may preserve the highest y2u (i.e., lactate removal ability) after having cycled at 250 W. Now, as seen in Table 2, S1, with an already low y2v after the lowest work rate, has the lowest maximal aerobic power and t2.5 (19 min), whereas S9 of series 350 W with the highest y2v after the 350-W exercise has the highest maximal aerobic power as well as t2.5 (31 min). Between these two subjects are placed the subjects of series 300 VV in the order given by Fig. 4: the group of subjects (S2-S6) with a t2.5 of ~22 min and then S7 and S8 with a t2 5 of almost 27 min. Likewise the correlations between y2V and LIR reported in Fig. 4 can be extrapolated to S9. Indeed if he had stopped cycling after having completed the 300-W exercise, he would have had a greater y2u than 0.077 min-’ but with only a 108-prnol. 1-l .rnin-’ rate of lactate increase during the 300-W exercise bout. The close direct relationships between y2v and t2.5
990 940 1,040
of each recovery;
y=7013x r =0.918 p ( 0.004
25
Lo ei 4
0
0.02
0.04
0.06
0.08
0.10
Y2v , mid FIG. 4. Relationships between t 2.5and LIR, and y2v. Dashed lines, extrapolations; shaded areas, 95% confidence limits. Number of observations = 7.
suggest that the higher the yzu, the later will lactate concentrations rise clearly over their basal level during the graded exercise. In view of the functional meaning that can be given to yzu (8), these relationships indicate that subjects with a greater ability to remove lactate during the recovery increased their exercise blood lactate concentrations later and to a lesser extent. The shift to the right of the curves of lactate con .centration vs. exercise intensity is associated with an elevated y2v, i.e., a high lactate removal ability during recovery. It is well
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910
LACTATE
REMOVAL
ABILITY
established that the blood lactate curve observed in a physically fit or trained individual lies to the right of the analogous curve from a less-fit or untrained subject (11). Our results are quite in agreement with this finding. Indeed, as shown by the significant positive correlation between VO 2 maxand t2.5, the exercise intensities required to attain the same blood lactate were decidedly higher for our trained or fit athletes compared with the less-fit or less-trained ones. However, still under debate are the reasons for this shift. Because blood lactate depends at the same time on the rates of blood lactate appearance and disappearance, a variation in blood lactate level at similar absolute work rate after training can be due to a change in one or both of these processes. There are two theories to explain this shift. One is that lactate production is reduced in trained individuals as compared with untrained ones. This thesis defended by Holloszy et al. (12, 13) is supported by several results, including 1) the glucogen-sparing effect induced by training (4, 25) with a greater use of fat as illustrated by a lower respiratory exchange ratio (17) and 2) the decrease in glycolytic enzyme activities found after training (22). The second conception is that lactate clearance is increased, as argued by Donovan and Brooks (3). There are also several experimental observations that agree with this point of view: 1) the adaptive increase in mitochondrial respiratory enzyme levels and the ability to oxidize pyruvate in response to endurance training (20); 2) the increment in lactate dehydrogenase isomers LDHl and LDH, in the trained muscles (1); 3) the transfer effects of VO 2 rnaXfrom trained legs to untrained arms observed by Rosier et al. (23), who suggested that an increase in net oxidation of lactate may be responsible for the increased arm VOW,,,; and 4) the higher lactate metabolic clearance rate observed by Stanley et al. (26) during incremental exercise in a competitive runner when compared with a recreational swimmer. If, as already pointed out (7, 8), lactate removal ability in the recovery provides information, at least qualitatively, on that prevailing during the exercise, our results are more in line with the second point of view mentioned above according to which physical fitness or training program effectiveness is related to improved lactate removal ability. The close relationship between the maximal aerobic power and y2u, as well as the likelihood that athletes who display a greater ability to remove lactate during recovery also have a higher ability to remove lactate during exercise when compared with less-fit or lesstrained athletes, lend further support to that idea. However, this interpretation does not exclude the possibility of a decreased lactate production in physically fit subjects. With regard to the relationship between vo2,,, and y2u, it can reasonably be interpreted as being the consequence of concomitant respiratory, cardiovascular, and biochemical adaptations induced by training or due to the differences in physical fitness. According to Fig. 2 of Stanley et al. (26), lactate concentrations increased abruptly during graded exercise when the lactate metabolic clearance rate (MCR) and hence the fractional removal rate were decreasing. (MCR is the product of the volume of the lactate distribution
AND
GRADED
EXERCISE
space times the lactate fractional turnover or removal rate.) As already discussed (7, 8), 9/2~ and hence the lactate removal ability are formally comparable to the lactate fractional turnover rate of the recovery, and y2u is closely correlated to y2a. There is a clear analogy between the results of Stanley et al. (26) and an inverse relationship between y2u and LIR. Both indicate that the rate of increase of blood lactate concentration is dependent on the lactate removal ability of the individual. A lowered rate of blood lactate increase in physically well-fit or well-trained subjects can also be explained by a lowered rate of lactate production (4, 12). Therefore one inference that can be drawn from the inverse relationship between LIR and y2u is that the increase in lactate concentration at the highest work rates can be also accounted for by a reduced lactate disappearance rate (Rd) from blood and not only by an elevated lactate appearance rate (R,) in blood. These two processes may act simultaneously. Thus, with respect to the mechanisms underlying the increase in lactate during progressive exercise, although we have no means of estimating lactate production, our results are more in line with the dynamic conception that considers the balance between R, and Rd than with the conception of a sudden onset of lactate production at a critical work rate. Recently Hughson et al. (16) have shown that a continuous model (Ea. 2) better fits lactate curves from progressive exercise with a 50=W/min slope than does the threshold model (2). Another finding of the present study is that the same Eq. 2 works also for a 50-W increment in work rate every 4th min. The goodness of the fits of Eq. 2 to the lactate vs. work rate curves is illustrated in Fig. 3. The standard deviation between the fitted and experimental curves is small, and the regression coefficients are very high (Table 3). Nevertheless, despite the goodness of the fits, the functional form of Eq. 2 cannot account for the decrease of lactate concentration (relative to the preexercise level), which happens sometimes for the low work rates of the incremental exercise, as shown in Fig. 3 (bottom). During these easy exercise steps, depending on the subject, lactate concentrations may increase, remain constant, or even decrease. Curiously enough, the decrease has never deserved special notice by authors. Hughson et al. (16) have mentioned that some subjects appear to maintain a constant lactate concentration probably by increasing Rd to precisely match R, at low work rates. In the same way, when lactate concentration decreases at low work rates, Rd might be greater than R,. This explanation is not speculative because the MCR during exercise was found higher, up to 60-7095 iTOzrnax (26), than at rest. Finally a high lactate removal ability at low work rates and its progressive decrease to lower values with increasing exercise intensities (7, 8), as clearly shown in this study by S7 and S8, seem to be one of the keys in the interpretation of blood lactate patterns in graded exercise. In fit or trained athletes the shift of the increase of the blood lactate to higher work rates during graded exercise is associated with a higher ability to remove lactate during the recovery and very likely also during the exercise.
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LACTATE
REMOVAL
ABILITY
We acknowledge the patient cooperation of the athletes. We particularly thank Prof. B. Metz for continual interest and encouragement. We also thank R. Bucher and J. Becht for help in the preparation of the figures. Address for reprint requests: H. Freund, Groupe de Recherche Activites Physiques et Sportives, 21 Rue Becquerel, 67087 Strasbourg Cedex, France. Received 27 June 1988; accepted in final form 8 November 1989.
F. S., AND M. A. ROGERS. Skeletal muscle lactate dehydrogenase isozyme alterations in men and women marathon runners.
1. APPLE,
J. Appl. Physiol. 61: 477-481, 1986. 2. BEAVER, W. L., K. WASSERMANN,
AND B. J. WHIPP. Improved detection of lactate threshold during exercise using a log-log transformation. J. Appl. Physiol. 59: 1936-1940, 1985. 3. DONOVAN, C. M., AND G. A. BROOKS. Endurance training affects lactate clearance, not lactate production. Am. J. Physiol. 244 (Endocrinol. Metab. 7): E83-E92, 1983. 4. FAVIER, R. J., S. H. CONSTABLE, M. CHEN, AND J. 0. HOLLOSZY. Endurance exercise training reduces lactate production. J. AppZ. 61: 885-889,
911
EXERCISE
endurance exercise in muscle. Annu.
Rev.
Physiol.
38: 273-291,
1976. 13. HOLLOSZY,
J. O., AND E. F. COYLE. Adaptations of skeletal muscle to endurance exercise and their metabolic consequences. J. AppZ.
Physiol. 56: 831-838, 1984. 14. HUBBARD, J. L. The effect of Physiol. Land. 231: 1-18, 1973. 15. HUGHES, E. F., S. C. TURNER,
exercise on lactate metabolism. J.
AND G. A. BROOKS. Effects of glycogen depletion and pedalling speed on anaerobic threshold. J.
AppZ. Physiol. 56: 1598-1607, 1982. 16. HUGHSON, R. L., K. H. WEISIGER,
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H. Dosage automatique continu de l’acide pyruvique. Description de la methode et application aux dosages simultanes de la pyruvicemie, de la lactatemie et de la glycemie. Ann. BioZ.
CZin. 25: 421-437,1967. 6. FREUND, H., P. JAQUOT, INA, AND J. J. VOGT. In
J. MARBACH, A. PELLIER, D. RAMBOARvivo experiments on the autoanalyser in a computerized environment. In: Advances in Automated Analysis. White Plains, NY: Mediad, 1970, vol. 1, p. 195-198. 7. FREUND, H., S. OYONO-ENGUELLE, A. HEITZ, J. MARBACH, C. OTT, AND M. GARTNER. Effect of exercise duration on lactate kinetics after short muscular exercise. Eur. J. AppZ. Physiol. Occup. Physiol. 58: 534-542, 1989. 8. FREUND, H., S. OYONO-ENGUELLE, A. HEITZ, J. MARBACH, C. OTT, P. ZOULOUMIAN, AND E. LAMPERT. Work rate-dependent - lactate kinetic after exercise in humans. J. AppZ. Physiol. 61: 932939,1986. 9. FREUND, H., AND P. ZOULOMIAN. Lactate after exercise in man. I. Evolution kinetics in arterial blood. Eur. J. AppZ. Physiol. Occup. Physiol. 46: 121-133, 1981. 10. GAESSER, G. A., AND D. C. POOLE. Blood lactate during exercise: time course of training adaptation in humans. Int. J. Sports Med. 9: 284-288,1988. 11. GOLLNICK, P. D., W. M. BAYLY, AND D. R. HODGSON. Exercise
intensity, training diet and lactate concentration in muscle and blood. Med. Sci. Sports Exercise 18: 334-340, 1986. 12. HOLLOSZY, J. O., AND F. W. BOOTH. Biochemical adaptations to
AND G. D. SWANSON. Blood lactate concentration increases as a continuous function in progressive exercise. J. AppZ. Physiol. 62: 1975-1981, 1987. 17. HURLEY, B. F., P. M. NEMETH, W. H. MARTIN III, J. M. HAGBERG, G. P. DALSKY, AND J. 0. HOLLOSZY. Muscle triglyceride utilization during exercise: effect of training. J. AppZ. Physiol. 60: 562-567, 1986. 18. MAZZEO, BUDINGER.
R. S., G. A. BROOKS, D. A. SCHOELLER, AND T. F. Disposal of [l-13C]lactate in humans during rest and
exercise. J. AppZ. Physiol. 60: 232-241, 1986. Y., C. STUDIEVIC, AND F. FOUCHERAND. Dosage automatique de l’acide lactique. Possibilites d’utilisation en continu.
19. MINAIRE,
Pczthol. BioZ. 13: 1170-1173, 1965. 20. MORGAN, T. E., L. A. COBB, F. A. SHORT, R. Ross, AND D. R. GUNN. Effect of long-term exercise on human muscle mitochondria. In: Muscle Metabolism During Exercise, edited by B. Pernow
and B. Saltin. New York: Plenum, 1971, p. 87-95. M. GARTNER, J. MARBACH, A. HEITZ, C. Comparison of arterial and venous blood lactate kinetics after short exercise. Int. J. Sports Med. 10: 16-24,
21. OYONO-ENGUELLE, S., OTT, AND H. FREUND. 1989. 22. REICHMANN, BERGEN, AND
H., H. HOPPELER, 0. MATHIEU COSTELLO, F. VAN D. PETTE. Biochemical and ultrastructural changes of skeletal muscle mitochondria after chronic electric stimulation in rabbits. Pfluegers Arch. 401: l-9, 1985. 23. R~SLER, K., H. HOPPELER, K. E. CONLEY, H. CLAASSEN, P. GEHR, AND H. HOWALD. Transfer effects in endurance exercise: adaptations in trained and untrained muscles. Eur. J. AppZ. Physiol. Occup. Physiol. 24. RYAN, W. J.,
Metabolism
54: 355-362,
1985.
J. R. SUTTON, C. J. TOEWS, AND N. L. JONES. of infused L( +)-lactate during exercise. CZin. Sci. 56:
139-149,1979. 25. SALTIN, B., AND
J. KARLSSON. Muscle glycogen utilization during work at different intensities. In: Muscle MetuboZism During Exercise, edited by B. Pernow and B. Saltin. New York: Plenum, 1971, p. 286-299. 26. STANLEY, W. C., E. W. GERTZ, J. A. WISNESKI, D. L. MORRIS, R. A. NEESE, AND G. A. BROOKS. Systemic lactate kinetics during graded exercise in man. Am. J. Physiol. 249 (EndocrinoZ. Metab. 12): E595-E602,1985.
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and graded
S. OYONO-ENGUELLE, J. MARBACH, A. HEITZ, A. PAPE, J. C. VOLLMER, AND H. FREUND Laboratoire de Physiologie Appliquke, 67087 Strasbourg Cedex, France
Groupe de Recherche
OYONO-ENGUELLE, 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(3): 905-911, 1990.-Venous lactate concentrations of nine athletes wererecordedevery 5 s before, during, and after graded exercisebeginning at a work rate of 0 W with an increaseof 50 W every 4th min. The continuous model proposedby Hughson et al. (J. Appl. Physiol. 62: 1975-1981, 1987) was well fitted with the individual blood lactate concentration vs. work rate curves obtained during exercise. Time coursesof lactate concentrations during recovery were accurately describedby a sum of two exponential functions. Significant direct linear relationships were found between the velocity constant (yzv) of the slowly decreasingexponential term of the recovery curves and the times into the exercisewhen a lactate concentration of 2.5 mmol/l wasreached.There wasa significant inverse correlation betweeny2v and the rate of lactate increaseduring the last step of the exercise. In terms of the functional meaning given to y2v, these relationships indicate that the shift to higher work rates of the increaseof the blood lactate concentration during graded exercisein fit or trained athletes, when comparedwith lessfit or untrained ones,is associatedwith a higher ability to remove lactate during the recovery. The results suggestthat the lactate removal ability plays an important role in the evolution pattern of blood lactate concentrations during graded exercise. venous blood lactate; recovery; lactate kinetics
C. OTT, Activitk
M. GARTNER, Physiques
et Sportives,
ing lactate disappearance from venous blood provides dynamic information analogous to that delivered by y2a (21) With this known, it might be expected that the study of venous blood lactate kinetics during recovery from graded muscular exercise can shed light on some of the mechanisms concerning blood lactate variations observed during exercise. Despite the large number of papers devoted to the interpretation of blood lactate patterns during incremental exercise, several questions are still open to controversy. The first objective of the present study is to supply a more precise mathematical description of lactate curves during and after graded exercise by using a continuous blood sampling and analyzing method. The second aim is to look for useful relationships between the pattern of venous lactate concentrations during graded muscular exercise in humans and the overall ability of the organism to remove lactate as assessed from the recovery after the graded exercise. In a recent paper, Hughson et al. (16) have used a continuous model to describe blood lactate changes with work rate during a 50 W/min progressively increasing exercise. Another purpose of our study is to learn if their model is also valid for a different slope. METHODS
COURSES of arterial blood lactate concentrations during recovery from muscular exercise of several work rates or durations are accurately described by a sum of two exponential time functions (7-9). The velocity constants of these functions prove to be indicators of blood lactate recovery kinetics. They supply quantitative information on the body’s overall functional ability to exchange (high-velocity constant rla) and to remove (low-velocity constant yaa) lactate after muscular exercise (8). The similarity between the results of Hubbard (l4), Ryan et al. (24), Mazzeo et al. (18), and Stanley et al. (26) obtained during exercise and those of Freund et al. (7, 8) observed during recovery indicates that the modifications of lactate removal kinetics that take place during the exercise are related to those observed during recovery. In addition, it has been shown recently that a sum of two exponential terms can also be used to describe the venous blood lactate recovery curves and that the velocity constant (y2v) of the exponential term describTIME
Subjects and experimental protocol. Nine athletes (2 females and 7 males) whose anthropometric variables and physiological characteristics are reported in Table 1 participated in the study. Details of experimental procedures and an explanation of the risks involved were provided to the subjects before obtaining their written consent to participate in the experiments. Maximal aerobic power (VO 2 max) was determined for all subjects before the lactate experiment. Subjects were tested in the morning at the normal room temperature of 21-23”C, after a light standard breakfast taken -2 h before. Heart rate was monitored throughout the experiment from a continuous electrocardiogram as a safety and check procedure. The exercise was performed in a seated position on a mechanically braked cycle ergometer (Fleisch ergometer) at a constant pedaling frequency of 60 rpm. During rest and recovery, the subjects were seated in an armchair especially fixed to the cycle that allowed them to maintain a comfortable
0161-7567/90 $1.50 Copyright 0 1990 the American Physiological Society
905
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906 TABLE
LACTATE
REMOVAL
ABILITY
AND
GRADED
EXERCISE
1. Physical and anthropometric characteristics of subjects Subj No.
Sl s2 s3 s4 s5 S6 s7 S8 s9 Mean
t SE
Sex
F M M F M M M M M
Age,
Weight,
Height, cm
Maximal Aerobic Power, W
Yr
kg
22 25 18 24 22 20 29 20 25
56.1 58.7 52.0 61.1 61.1 65.7 68.8 65.7 70.7
164.5 168 173 165.5 178 178 181 172 178
250 300 300 320 320 345 360 385 395
2321
62.2k2.0
173.1k2.0
331+15
VO
2 max
ml/min
ml. kg-’ - min-’
3,250 3,900 3,850 4,180 3,950 4,200 4,560 4,950 5,220
58.0 66.4 73.2 68.4 64.6 63.9 66.3 75.3 73.9
4,229+200
67.8t1.9
position. In view of the close dependence of lactate biochemical analyzer were fed into an analog-to-digital recovery kinetic data on both the work rate (8) and the converter (Scientific-Solutions) and a microcomputer duration (7) of the previously performed exercise, the (M24 Olivetti). Concentrations were recorded every 5 s. subjects were sorted according to the highest work rate Expression of data. Exercise intensity is expressed as that they could complete during the incremental exercise absolute work rate (W or W/kg). The rationale for this test. choice lies in the observation that a more coherent interEach incremental test was divided into rest, exercise, pretation of the lactate data is supplied when the results and recovery phases. The duration of the resting phase are expressed as a function of energy requirement instead depended on the time required by each subject (30-60 of relative work load (%VO 2 max). Other authors (10, 15) min) to reach a steady basal venous lactate concentration also agree with this approach. The following criteria have before the exercise began. Exercise started at 0 W with been selected to characterize the pattern of the blood a 50-W increment every 4th min up to 250 W for subject lactate evolution curves during exercise. I) the time into SI (the least physically fit of all the subjects), up to 300 the exercise (t 2,5,s or min) after which a lactate concenW for the five subjects SZ-S6 (series 300 W), and up to tration of 2.5 mmol/l is reached for each subject; this 350 W for the three subjects S7-S9 (series 350 IV). time could be measured accurately because the lactate Subjects S7 and S8 of this latter group repeated the same concentrations were delivered at 5-s intervals. 2) the experiment a few days afterward but were asked to lactate increase rate (LIR, mmol .1-l min-‘) during the exercise only up to 300 W. The aim of this additional last step of exercise (increase of lactate concentration measurement was to see the influence of lower work rates between the onset and end of the last step of exercise and hence of shorter graded exercise duration on lactate divided by the duration of this step). recovery kinetics. Subject S9 was not concerned by this Mathematical and statistical analysis. The individual additional experimentation. Indeed, if he had stopped venous lactate recovery curves were fitted by means of the exercise at 300 W, his lactate concentration at the an iterative nonlinear technique to a sum of two expoend of the test would not have been high enough to allow nential terms of the form an accurate study of its evolution during the following recovery. The symbol cy will be used to identify the Lv(t) = Lv(0) + Alv(l - e-ylvt) + Agv(l - e-r2vt) (1) supplementary exercise performed by the subjects ST and S8 up to 300 W (included with the series 300 W). In this equation Lv(t) is the venous blood lactate concentration at time t into the recovery, Lv(0) is the Venous blood lactate concentrations were measured after at the end of each exercise until they returned again to a near steady measured venous lactate concentration exercise, AIv and A2v are the amplitudes, and ylu and basal level (65-120 min depending on the subject and the y2u are the velocity constants of the exponential funcexercise). tions. Blood sampling and analysis. An indwelling l-mmThe continuous model proposed by Hughson et al. (16) diameter polyethylene catheter was placed in an antewas used for fitting the individual curves of lactate cubital vein. After heparinization of the subjects (hepaconcentrations observed at the end of each step in graded rin, 100 IU/kg) to prevent blood clotting, the catheter was connected to an automatic analyzer comprised of a exercise as a function of work rate (W/kg). The form of peristaltic pump (Ismatec), a dialyzer (Technicon), an this model is given by oil bath at 40°C (Technicon), a detector (LKB 2138 Y = a + b exp(cx) (2) Uvicord S; operating wavelength 365 nm), and a stripchart graphic recorder (Hewlett-Packard). Blood was where y is lactate concentration, x is work rate, and a, b, and c are coefficients estimated by minimizing the residdrawn continuously at a rate of 0.32 ml/min throughout ual sum of the squares between lactate concentrations the experiment. Lactate concentrations were measured and the calculated curve. Linear regressions were used by an enzymatic method according to the flow diagram to describe the relationships between data. Statistical described by Freund et al. (6), which is a modification of previously described methods (5, 19). Signals from the significance was set at P < 0.05. l
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LACTATE
REMOVAL
ABILITY
AND GRADED
EXERCISE
907
RESULTS
All the subjects advanced to their required highest work rate. Except for S3 and S4 of series 300 W, who stopped after 3 min, all completed 4 min at the prescribed highest work rate. With respect to these subjects, S3 and S4, the duration of their last step of exercise was nevertheless considered to be near enough to 4 min to allow retaining the parameters chosen for this study. Time courses of the lactate concentrations before, during, and after the exercise are reproduced in Fig. 1. The venous lactate concentrations reached every 4th min during the graded exercise are presented as a function of work rate in Fig. 2. In Table 2 the values of tze5and LIR are given. Compared with the other subjects of series 300 IV (SZS6) who performed the same graded exercise, S7cu and S8cu had the lowest lactate concentrations during and at
o!
1
I
I
1
1
1
1
0
1 2 3 4 5 6 WORK RATE ) We kg-’ FIG. 2. Individual venous lactate concentrations every 4th min during graded exercise as function of absolute work rate normalized to body mass.
12 -
A
I
TABLE
2. Individual
values of selected criteria
Subj
250- W graded Sl
18.75 300- W graded
s2 s3 s4 s5 S6 s7cY S8a
ins5
C
c 1 z E E
8-
1 i
.
OL
!I! I
0
I
,
I
30
I
'
6'0 '
TIME,
' 9'0
'
' 120
'
min
FIG. 1. Individual time courses of venous lactate concentrations before, during, and after graded exercise. A, B, and C: curves of subjects who exercised up to 250, 300, and 350 W, respectively. Vertical dashed lines, 4min periods of exercise beginning with 0 W to maximum work rate, in 50-W steps.
exercise
22.92 21.75 21.83 21.17 22.25 27.50 27.50 350-W
s7 S8 s9
LIR, pmol - 1-l min-’
t2.5,
min
No.
graded
exercise
26.17 26.08 31.25
l
exercise 800 (series 300 W) 1,160 1,330 1,500 1,038 550 270 258 (series 350 W) 838 783 463
the end of this exercise (Fig. 1B). As shown in Table 2, their lactate concentrations increased later (greater t2.J and less sharply during the last exercise step (lower LIR). Their maximal lactate concentrations during the recovery were markedly lower than those of S2-S6 (Fig. 1B). But in the series 350 IV, the same subjects, S7 and S8, reached higher lactate concentrations than S9. Moreover, relative to S9, their lactate concentrations increased sooner (smaller t2.J and more abruptly (higher LIR) during the last step of the 350 W graded exercise (Fig. 1C and Table 2). The parameters of the fits of Eq. 2 to the changes of lactate concentrations with work rate are reported in Table 3. The data were well fitted by Eq. 2 (Fig. 3). There were nevertheless exceptions for which the fits were slightly less accurate, namely as illustrated in Fig. 3 (bottom) when a decrease in lactate concentration occurred at low work rates. Eq. 1 fitted closely the venous lactate concentration curves over the entire recovery (Table 4). The standard deviation (a) between the experimental and predicted curves was small. The accuracy
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LACTATE
908 TABLE
REMOVAL
ABILITY
AND GRADED
EXERCISE
3. Parameters of fits of Eq. 2 to curves of lactate concentration vs. work rate during graded exercise Subj
No.
a
Sl
b
250-W graded 0.06596
0.6927
300-W
s2 s3 s4 s5 S6 S7a S&Y
0.5719 0.6279 1.1726 0.6032 1.2758 0.8188 0.6774
s7 S6 s9
0.7032 0.9265 0.8846
graded
. 1
.
.
2
3
I
4
0.9988
exercise
=
5
1
r
1.2261 0.8628 1.1671 0.9618 1.0415 1.0548 1.1094 exercise
92
0.999
108 153 253 144 61 18 64
0.999 0.998 0.994 0.999 0.999 0.999 0.996
35 59 66
0.999 0.999 0.996
(series 300 W)
(series
0.01463 0.01278 0.00000815
S?
pi&1
exercise
0.01415 0.05233 0.02170 0.07219 0.03607 0.02010 0.01252 350- W graded
I,
c
350 W)
1.1785 1.1409 2.5277
There was a statistically significant relationship between the VO 2max and the corresponding t2.5 (r = 0.901, P < 0.001). For the subjects of series 300 VVthere was further a close correlation between the maximal aerobic power and y2v (r = 0.862, P c 0.013). To study the potential influence of individual removal ability (as supplied by y2v) on the evolution pattern of lactate concentration during a graded exercise test, y2v of the subjects of series 300 VVwas plotted in Fig. 4 against t2.5and LIR. The relationships are both statistically significant.
6 DISCUSSION
4
EXPERIMENTAL
CURVE
The present study demonstrates that the venous blood lactate recovery curves from graded muscular exercise fit accurately the two exponential time functions in Eq. 1. This result shows that the mathematical model Eq. 1 proposed for the analytical description of the lactate concentration during recovery from constant-load exercise applies also to recovery from exercise of progressively increasing intensity. For clarity of the discussion it may be helpful to recall s9 some basic information that will facilitate the interpretation of the present results. First, for constant work rates ranging almost from 100 to 375 W, the velocity constants of Eq. 1 decreased when work rate increased 1 2 3 4 5 6 (7-9). With respect to yzv, the results of S7 and S6 corroborate this earlier finding, because when they exWORK RATE, W.kg - ’ ercised up to 350 W instead of up to 300 W their 720 was FIG. 3. Examples of fits of Eq. 2 to exercise lactate concentrations lowered (Table 4). Second, as already mentioned, y2v has every 4th min. Bottom: decrease of venous lactate concentration at low been given a functional meaning, namely the ability of work rates is not accounted for by &. 2. the body to remove lactate via metabolic processes (8). (lOOa/average concentration of the recovery) ranged Third, in graded exercise there is a relationship between from 2 to 8%. As shown in Table 4, for eight out of the work rate and exercise duration because the load innine subjects, the y2v of the fits to the venous lactate creases stepwise with time. recovery curves after the prescribed highest work rate A very interesting result of this study is that, for the ranged within 0.038-0.053 min-‘. S9 of series 350 VV subjects placed in the same experimental series 300 W, displayed a higher value (0.077 min-l). Table 4 shows there are statistically significant correlations of the y2v also that S7a and SBa, had decidedly higher y2v (0.078 of the fits to the lactate recovery curves with the time and 0.094 min-‘) when they stopped cycling at 300 W t2 5 and LIR (Fig. 4), as well as with the maximal aerobic than the other subjects of series 300 IV and higher than power (84 and 68% of the variance of ts5 . and LIR are when they were placed in series 350 VV. accounted for by yzv, respectively). However, because dr
FlITED
CURVE
3 3
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LACTATE TABLE
REMOVAL
ABILITY
AND GRADED
EXERCISE
909
4. Parameters of fits of Eq. 1 to venous lactate recovery curves and some other characteristics Subj No.
Lv(O), pmol/l
Alv, pmol/l
&v, pmol/l
Recovery Sl
s2 s3 s4 s5 S6 s7ar S8a
6,340
7,960
8,170 7,790
8,650 5,450 2,820 2,640
7,223
4,280 4,020 3,375 13,285 3,282 1,261 1,050
-12,737 Recovery -11,665 -11,249 -10,366 -21,110
-7,305 -3,542 -3,108 Recovery
s7 S8 s9
6,580 6,470 3,120
4,093
2,834
from
-10,322 -8,867 -4,201
YlV,
Y2V,
w4,
min-’
min-’
pmol/l
from
250- W graded
0.2945
0.04426
300-W
graded
0.03895
0.5388
0.05321
0.6659 0.1490
0.03799 0.04311 0.04891 0.07849 0.09394
0.4800 0.8789
0.6742 from
350-W
graded
0.2564 0.4896
Lvbs), pmol/l
exercise 826
exercise
0.4569
Lv(max), pmol/l
174
9,530
590
78 174 172 141
9,890 9,800
570 880 1,030 760
(series 300 W) 576 941 1,199
824
11,920 7,100
139
1,426 539
62 32
3,350
143 48 71
7,800 7,400 4,200
582
exercise
10,050
1,290 760 670
2,930
(series 350 W)
0.04234 0.05128 0.07674
351 437 614
1,696 1.1580 Lv(=), computed value of lactate concentration at end of recovery (t + 00); Lv(max), highest venous lactate concentration Lv(rs), venous lactate concentration at rest before the exercise.
blood lactate recovery kinetics are closely dependent on the work rate (8) and (although less) on the duration (7) of the previously performed exercise, the validity of the correlations of y2v with t2.5 or LIR requires that the subjects had performed similar graded exercises. Note that, as shown in Table 4, the relations hold true also for the subjects of series 350 VV (S7 and S8 with a 4533% lower y2v than S9 had a 9-30% lower maximal aerobic power, a 16% lower t2.5, and 71-81% higher LIR). Because of the known dependency of y2v on work rate (7, 8, 21) these relationships can be extrapolated to all the subjects. Indeed it is beyond doubt that if S2-SS had stopped cycling at 250 W, they would have reached a higher y2v than that attained respectively after the 300W graded exercise and very likely also a more elevated y2u than the 0.044 min-’ obtained for S1. The same reasoning can hold but stepwise for S9. Thus if the test had been stopped for all the subjects at the end of the 250-W exercise, the y2u reached by S1 would have been lower than that of any of the other subjects. Conversely S9, who displayed a markedly higher y2u than all the other subjects when they cycled up to their highest requested work rate, may preserve the highest y2u (i.e., lactate removal ability) after having cycled at 250 W. Now, as seen in Table 2, S1, with an already low y2v after the lowest work rate, has the lowest maximal aerobic power and t2.5 (19 min), whereas S9 of series 350 W with the highest y2v after the 350-W exercise has the highest maximal aerobic power as well as t2.5 (31 min). Between these two subjects are placed the subjects of series 300 VV in the order given by Fig. 4: the group of subjects (S2-S6) with a t2.5 of ~22 min and then S7 and S8 with a t2 5 of almost 27 min. Likewise the correlations between y2V and LIR reported in Fig. 4 can be extrapolated to S9. Indeed if he had stopped cycling after having completed the 300-W exercise, he would have had a greater y2u than 0.077 min-’ but with only a 108-prnol. 1-l .rnin-’ rate of lactate increase during the 300-W exercise bout. The close direct relationships between y2v and t2.5
990 940 1,040
of each recovery;
y=7013x r =0.918 p ( 0.004
25
Lo ei 4
0
0.02
0.04
0.06
0.08
0.10
Y2v , mid FIG. 4. Relationships between t 2.5and LIR, and y2v. Dashed lines, extrapolations; shaded areas, 95% confidence limits. Number of observations = 7.
suggest that the higher the yzu, the later will lactate concentrations rise clearly over their basal level during the graded exercise. In view of the functional meaning that can be given to yzu (8), these relationships indicate that subjects with a greater ability to remove lactate during the recovery increased their exercise blood lactate concentrations later and to a lesser extent. The shift to the right of the curves of lactate con .centration vs. exercise intensity is associated with an elevated y2v, i.e., a high lactate removal ability during recovery. It is well
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910
LACTATE
REMOVAL
ABILITY
established that the blood lactate curve observed in a physically fit or trained individual lies to the right of the analogous curve from a less-fit or untrained subject (11). Our results are quite in agreement with this finding. Indeed, as shown by the significant positive correlation between VO 2 maxand t2.5, the exercise intensities required to attain the same blood lactate were decidedly higher for our trained or fit athletes compared with the less-fit or less-trained ones. However, still under debate are the reasons for this shift. Because blood lactate depends at the same time on the rates of blood lactate appearance and disappearance, a variation in blood lactate level at similar absolute work rate after training can be due to a change in one or both of these processes. There are two theories to explain this shift. One is that lactate production is reduced in trained individuals as compared with untrained ones. This thesis defended by Holloszy et al. (12, 13) is supported by several results, including 1) the glucogen-sparing effect induced by training (4, 25) with a greater use of fat as illustrated by a lower respiratory exchange ratio (17) and 2) the decrease in glycolytic enzyme activities found after training (22). The second conception is that lactate clearance is increased, as argued by Donovan and Brooks (3). There are also several experimental observations that agree with this point of view: 1) the adaptive increase in mitochondrial respiratory enzyme levels and the ability to oxidize pyruvate in response to endurance training (20); 2) the increment in lactate dehydrogenase isomers LDHl and LDH, in the trained muscles (1); 3) the transfer effects of VO 2 rnaXfrom trained legs to untrained arms observed by Rosier et al. (23), who suggested that an increase in net oxidation of lactate may be responsible for the increased arm VOW,,,; and 4) the higher lactate metabolic clearance rate observed by Stanley et al. (26) during incremental exercise in a competitive runner when compared with a recreational swimmer. If, as already pointed out (7, 8), lactate removal ability in the recovery provides information, at least qualitatively, on that prevailing during the exercise, our results are more in line with the second point of view mentioned above according to which physical fitness or training program effectiveness is related to improved lactate removal ability. The close relationship between the maximal aerobic power and y2u, as well as the likelihood that athletes who display a greater ability to remove lactate during recovery also have a higher ability to remove lactate during exercise when compared with less-fit or lesstrained athletes, lend further support to that idea. However, this interpretation does not exclude the possibility of a decreased lactate production in physically fit subjects. With regard to the relationship between vo2,,, and y2u, it can reasonably be interpreted as being the consequence of concomitant respiratory, cardiovascular, and biochemical adaptations induced by training or due to the differences in physical fitness. According to Fig. 2 of Stanley et al. (26), lactate concentrations increased abruptly during graded exercise when the lactate metabolic clearance rate (MCR) and hence the fractional removal rate were decreasing. (MCR is the product of the volume of the lactate distribution
AND
GRADED
EXERCISE
space times the lactate fractional turnover or removal rate.) As already discussed (7, 8), 9/2~ and hence the lactate removal ability are formally comparable to the lactate fractional turnover rate of the recovery, and y2u is closely correlated to y2a. There is a clear analogy between the results of Stanley et al. (26) and an inverse relationship between y2u and LIR. Both indicate that the rate of increase of blood lactate concentration is dependent on the lactate removal ability of the individual. A lowered rate of blood lactate increase in physically well-fit or well-trained subjects can also be explained by a lowered rate of lactate production (4, 12). Therefore one inference that can be drawn from the inverse relationship between LIR and y2u is that the increase in lactate concentration at the highest work rates can be also accounted for by a reduced lactate disappearance rate (Rd) from blood and not only by an elevated lactate appearance rate (R,) in blood. These two processes may act simultaneously. Thus, with respect to the mechanisms underlying the increase in lactate during progressive exercise, although we have no means of estimating lactate production, our results are more in line with the dynamic conception that considers the balance between R, and Rd than with the conception of a sudden onset of lactate production at a critical work rate. Recently Hughson et al. (16) have shown that a continuous model (Ea. 2) better fits lactate curves from progressive exercise with a 50=W/min slope than does the threshold model (2). Another finding of the present study is that the same Eq. 2 works also for a 50-W increment in work rate every 4th min. The goodness of the fits of Eq. 2 to the lactate vs. work rate curves is illustrated in Fig. 3. The standard deviation between the fitted and experimental curves is small, and the regression coefficients are very high (Table 3). Nevertheless, despite the goodness of the fits, the functional form of Eq. 2 cannot account for the decrease of lactate concentration (relative to the preexercise level), which happens sometimes for the low work rates of the incremental exercise, as shown in Fig. 3 (bottom). During these easy exercise steps, depending on the subject, lactate concentrations may increase, remain constant, or even decrease. Curiously enough, the decrease has never deserved special notice by authors. Hughson et al. (16) have mentioned that some subjects appear to maintain a constant lactate concentration probably by increasing Rd to precisely match R, at low work rates. In the same way, when lactate concentration decreases at low work rates, Rd might be greater than R,. This explanation is not speculative because the MCR during exercise was found higher, up to 60-7095 iTOzrnax (26), than at rest. Finally a high lactate removal ability at low work rates and its progressive decrease to lower values with increasing exercise intensities (7, 8), as clearly shown in this study by S7 and S8, seem to be one of the keys in the interpretation of blood lactate patterns in graded exercise. In fit or trained athletes the shift of the increase of the blood lactate to higher work rates during graded exercise is associated with a higher ability to remove lactate during the recovery and very likely also during the exercise.
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LACTATE
REMOVAL
ABILITY
We acknowledge the patient cooperation of the athletes. We particularly thank Prof. B. Metz for continual interest and encouragement. We also thank R. Bucher and J. Becht for help in the preparation of the figures. Address for reprint requests: H. Freund, Groupe de Recherche Activites Physiques et Sportives, 21 Rue Becquerel, 67087 Strasbourg Cedex, France. Received 27 June 1988; accepted in final form 8 November 1989.
F. S., AND M. A. ROGERS. Skeletal muscle lactate dehydrogenase isozyme alterations in men and women marathon runners.
1. APPLE,
J. Appl. Physiol. 61: 477-481, 1986. 2. BEAVER, W. L., K. WASSERMANN,
AND B. J. WHIPP. Improved detection of lactate threshold during exercise using a log-log transformation. J. Appl. Physiol. 59: 1936-1940, 1985. 3. DONOVAN, C. M., AND G. A. BROOKS. Endurance training affects lactate clearance, not lactate production. Am. J. Physiol. 244 (Endocrinol. Metab. 7): E83-E92, 1983. 4. FAVIER, R. J., S. H. CONSTABLE, M. CHEN, AND J. 0. HOLLOSZY. Endurance exercise training reduces lactate production. J. AppZ. 61: 885-889,
911
EXERCISE
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