Pflfigers Archiv
Pfl/igers Arch. 380, 205-210 (1979)
EuropeanJournal
of Physiology
9 by Springer-Verlag1979
A Multiple Regression Model for Blood Lactate Removal in Man A. Bonen, C. J. Campbell, R. L. Kirby, and A. N. Belcastro School of Physical Education and Department of Medicine, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada
Abstract. After exercise the lactate (La) removal from
blood occurs significantly faster during moderate exercise than at rest. However, under both conditions there are considerable inter-individual differences in La removal. These differences in man may depend on the slow-twitch (ST) fiber content of muscle (X0, the La concentration in blood (Xz), and the intensity of the recovery exercise (X3). Therefore, multiple regression models were obtained to describe La removal rates with these variables. In 10 women La concentrations were increased via a 6min bicycle ergometer ride (87% l)Ozm,x) and blood La concentrations were measured every 5 rain during 20 min resting and active recovery periods ( 2 9 - 4 9 ~ 1202m,x). For resting recovery only the initial La concentration after the 6 min exercise provided a significant description for La removal in 8 subjects (P = 0.03). However, for the active recovery a highly significant description for La removal was obtained: La removal rate (mM/1 - min) = 0.773 • 10-2X1 -k 0.321 x 10-1X2 - 0.120 x 10 1X 3 + 0.202 (R = 0.91; P = 0.01). The statistical independence (P > 0.10) of each of these variables in the model suggests that each is contributing uniquely to the total removal rate of La observed during an active recovery period. The relationship between La removal and % ST fibers may be related to the metabolic and anatomical features of these fibers, the La concentration probably reflects the significance of the mass action effect of La, and the intensity of exercise reflects the role of the muscle's metabolic rate. The present results illustrate that the removal of blood lactate is influenced by the interactive effects of the intensity of the recovery exercise, blood lactate concentration and the ST fiber content of muscle. Key words: Lactate - Muscle fibers exercise - Bicycle ergometer - Women. Send offprint requests to
Recovery
A. Bonen at the above address
Introduction
After intense exercise the lactate (La) that has accumulated in blood is taken up by the liver and skeletal muscle [2,10,19]. However, La removal is accelerated when moderate exercise is performed during the recovery period [4,7,15,17]. Hermansen et al. [17] have found that a significant proportion of blood La is taken up by the exercising muscle during active recovery exercise. In addition, tracer studies with 14C-La in man and animals have also shown that blood La is primarily oxidized in skeletal muscle [8,12,19,20] during exercise. Jorfeldt [20] and others [7] have proposed that La is probably metabolized in the slow-twitch (ST) fibers of human skeletal muscle. These fibers contain approximately twice as much H - L D H as M - L D H [28], and thus the oxidation of La to pyruvate would seem to be facilitated here. We have recently found a moderate correlation between La removal from blood during active recovery exercise and the ST fiber content of the vastus lateralis [8]. However, the moderate correlation in that study suggested that other factors may also be affecting the removal of La from the circulation. These include the La concentration in the blood [19, 20], the bloodflow [20], and the metabolic rate of recovery exercise [4,15,25]. Thus, the considerable interindividual differences in La removal observed in our previous studies [4,6,25] may be related to the interactive effects of these parameters. Since the La concentration in blood accumulated during exercise and the intensity of recovery exercise can be manipulated independently of the muscle fiber composition, each of these variables may also account for a unique proportion of the rate of La removal after exercise. To test this hypothesis the variables under consideration were entered in an additive, least squares, multiple regression model in an attempt to determine the influence of each of these variables on La removal
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Pfltigers Arch. 380 (1979)
206
Table 1. Characteristics of the subjects Subject
Age (years)
Height (cm)
Weight (kg)
/)'02 m,x (ml/kg - min)
ST fibers (%)
Active recovery exercise (% VO~m~x)
1 2 3 4 5 6 7 8 9 10.
19 19 19 19 24 20 19 20 26 23
167 166 152 177 160 161 158 156 176 160
55.6 60.3 46.1 70.8 53.9 47.2 55.1 58.4 68.0 55.0
39.8 43.0 47.3 52.6 39.0 58.5 46.1 52.4 40.6 46.0
40 35 34 61 53 59 59 43 40 28
34 38 29 43 32 41 42 37 49 40
20.8
163
57.0
46.5
45
38
-+0.8
•
•
-+2.0
-+3.8
•
-+ SEM
Table 2. Lactate concentrations (raM/l) in blood during active and resting recovery periods ( ~ + SEM) Recovery Procedure
Recovery time, min 0
5
10
15
20
Active Recovery (38.4 • 1.8% gO2max) (N = 10) Rest Recovery ( N = 10)
13.8 • 14.7 +0.7
12.1 +1.1 13.5 •
7.5 +1.0 12.5 -+0.9
5.4 -+0.9 9.7 +1.0
3.9 -+0.8 7.9 -+0.8
from the blood at rest and when moderate exercise is performed during the recovery period.
Method Ten women participated in this study (Table 1). All were quite active and usually trained 3 days per week. Dietary controls were not imposed in this study. Blood La concentrations were increased by a standardized 6min bicycle ergometer ride at approximately 90 % 1202r,~x. This was followed by a 20rain rest period, and on another occasion by a 20 min active recovery exercise period at approximately 40% VO2max.Blood samples were obtained from a forearm vein immediately after the 6 min exercise bout (t = 0) and at min 5, 10, 15 and 20 during each recovery period. The blood (500pl) was immediately deproteinized in 2 ml of 10 % ice-fold perchloric acid and mixed briefly. After centrifuging the sample, the supernatant fluid was stored at - 2 0 ~C. La concentrations were determined with an enzymatic procedure [25]. The oxygen cost (VO2 re,x) of the standardized and recovery exercise bouts were determined during min 3 - 6 of the 6 min exercise bouts, and during min 1 1 - 1 5 of the recovery periods. In addition, determinations of VO2,,,x were obtained before and after this study via a progressively increased b!cycle ergometer ride (180 kpm/3 rain) to voluntary exhaustion. For VO2maxmeasurements the pulmonary ventilations were recorded from a calibrated dry gas meter (model CD4, Parkinson-Cowan), and gas temperatures were recorded from a calibrated thermister located in the gas meter [6]. Small aliquots of air (250 ml/min) were continuously drawn from the expiratory air stream through calibrated, rapid response 02 (model M14, Beckman), and CO2 (model LB2, Beckman) analyzers [25].
Muscle samples were obtained at rest with the needle biopsy technique [5] from the vastus lateralis of the right and left legs several weeks prior to, and several weeks after the La removal experiments, respectively. Fast-twitch (FT) and slow-twitch (ST) muscle fiber determinations were identified on the basis of staining intensity for myosin ATPase at pH 10.4 and 4.3 [11]. The percentage of ST fibers was calculated by adding the total number of ST fibers counted in the two biopsies and dividing this by the total number of fibers counted in the two samples. As in other studies [4,15, 25] the La removal rates(mM/I-min) during the recovery periods were calculated from the slope of the regression line between La concentration and time. Then, based on the ST fiber content of the vastus lateral• the La concentration in blood immediately after the 6 min standardized intense exercise bout (t = 0), and the intensity of the recovery exercise, a least squares, multiple regression procedure [24] was used to develop an equation to account for the differences in La removal rates among the subjects.
'Results The standardized 6 min exercise bouts were conducted a t 86.0 + 1 . 6 % ~/'O2max a n d 89.4 + 2 . 3 % ~';rO2max (X + SEM) prior to the resting and active recovery exercise sessions, respectively, and the active recovery exercise was conducted at 29-49% VO2m,x. T h e S T fiber composition in the subjects ranged from 28-61%. L a r e m o v a l o c c u r r e d s i g n i f i c a n t l y f a s t e r ( P < 0.01) during the active recovery than at rest (Table2).
A. Bonen et al. : Blood Lactate Removal in M a n
207
However, the individual removal rates during each recovery condition varied considerably among the subjects (Fig. l). These ranged from 0.773 to 0.269 raM/1, rain during the active recovery, and from 0.667 to 0.052 raM/l-rain during the resting recovery. The linear regression provided a good approximation for the calculation of La removal rates since the correlation coefficients associated with these individual linear regressions (Fig. 1) ranged from 0.94 to 0.99 (P < 0.01) during the active recovery period. In the remaining subject the correlation was 0.87 (P < 0.025). For the resting recoveries similar accuracies (r = 0.86 to r = 0.99) were obtained in 8 subjects, but in two subjects the linear regression between La concentra-
20.0
A
~15.0
z
10.0
5.1)
1;
t5
;o
zo
~5
2'o
RECOVERY TIME (rain) Fig. 1. Individual regression lines of La removal during active recovery exercise (A) and during a resting recovery period (B) following a standardized 6 min intense exercise bout. Heavy line is the mean removal rate. Dashed lines in B represent two instances when the linear regression did not provide an adequate fit (P > 0.10)
tion and recovery time was quite poor, for them the correlation coefficients were 0.33 and 0.28 (P > 0.10). In general, the zero order correlation coefficients between La removal rates during the active recovery period and the variables selected for this investigation were moderate or low (Table3). Significant correlations, however (P < 0.05) were found between the La removal rate and the % ST fibers, and the La concentrations after the 6 min standardized exercise bout (Table 3). With the multiple regression approach a highly significant description for La removal rates during the active recovery period was obtained when the initial post-exercise La concentration, the % ST fibers and the relative cost of the recovery exercise were combined in a prediction equation (Fig. 2). By itself the La concentration at the beginning of the recovery period was only moderately correlated (r = 0.64; P = 0.046) with the La removal rate. With the inclusion of the % ST fibers the multiple correlation coefficient (R) was increased to 0.80 (P = 0.030), and the addition of the intensity of the recovery exercise further increased the multiple R to 0.91 (P = 0.012). With these factors the following multiple regression equation was obtained to describe the net removal rate of La from the blood: La removal rate = 0.773 x 10 -2 % ST fibers + 0.321 x i0-1 initial La concentration (raM/1 9rain) - 0.120 x 10-1 recovery exercise % VO2m,x + 0.202. The coefficient of variations is + 15.1%, and the initial La concentrations, the % ST fibers, and the recovery exercise intensity accounted for 41%, 22 %, and 19% of the total variance associated with La removal rates during active recovery exercise. Although the addition of /'~02max t o the equation improved the overall prediction only slightly (R = 0.93; CV = + 13.9 %), this factor was not significant (P > 0.10) in combination with the other predictors.
Table 3. Intercorrelations of selected variables with La removal rates during an active recovery period (N = 10) J7 _+SEM
La removal rate
La removal rate m M / 1 . rain
0,530 +0.049
-
La concentration at min 0 (raM/l) ST fibers
13,8 +0.9 45.0
0.64*
-
0.54**
0.12
(%) Recovery intensity
(% FO2~.J 1702 m.x (ml/kg-min)
La concentration ST at min 0 fibers
Recovery Intensity
_+3.8 38.4
- 0.23
0.10
0.27
0.26
-0.17
0.42
_+1.8 46.5 _+2.0
*P = 0.023; **P = 0.052 (1-tailed test)
0.19
1202m~x
Pfltigers Arch. 380 (1979)
208 REMOVAL RATE- 0.773x10-2Xl+ 0.321x10-1XsO.120x10-1X3+
--
O.80
E
VOxrlO
0.202~
X~=%ST fibers X2=initial [Lal
E
0.60
/ /
9
0,40
~-
0.20 .
0.20
.
.
0.40 OBSERVED La
.
.
0.60
0.80
REMOVAL RATE (mMIL. min)
Fig.2. Comparison of observed with predicted La removal rates during active recovery exercise. Predicted values were derived from a multiple regression based on the % ST fibers (X1) initial La concentration during the recovery exercise (22), and the relative intensity of the recovery exercise (X~) (R = 0.91, P = 0.01)
For the resting recovery none of the predictors provided a significant description (P> 0.10) for the La removal rate. However, these data included two subjects for whom the La removal rate did not follow a linear decrement (P > 0.10) during the recovery period. When these two subjects were omitted from the analysis only the initial La concentration during the recovery period was significantly correlated with the La removal rate (r = 0.80; P = 0.03). Addition of the other variables in a multiple regression equation did not improve the prediction significantly (P > 0.10).
Discussion
The findings from the present study indicate that variations in La removal rates among individuals, during an active recovery, may be described by an additive, multiple regression model, from factors with known or hypothesized physiological significance. These were a) the La concentration in blood during the recovery period, b) the ST fiber composition of skeletal muscle, and c) the relative intensity of the recovery exercise. In addition, the algebraic signs associated with these variables appear to correspond with their physiological function. The lack of intercorrelations among these parameters (P > 0.10) indicated their independence from each other (Table 3), and thus the additive regression model is particularly apt for describing the
La removal rates with these variables. The mutual independence of the variables also suggests that each is exerting an independent effect on La removal. The proportion of variance contributed by each factor in the model is dependent on the sequence that it is entered in the equation [24]. Thus, while the relative physiological contribution of the variables cannot be determined from the model, the multiple regression approach does provide an excellent insight into the factors that may account simultaneously for the complex physiological phenomenon of individual differences in La removal rates. Each of the variables employed in the present study contributed significantly to overall description for La removal during active recovery and this further supports their physiological role. La uptake from blood can occur in the liver [27], heart [29], brain [26], kidney [30] and skeletal muscle [1,2,10,11,15,17,19-21]. However, the major proportion of La removal occurs in skeletal muscle, since a large fraction of La is oxidized almost immediately in exercising dogs (74%) [10] and man (52%) [20], and only about 20 % of the hepatic glucose production is derived from lactate [19]. The net removal of La under our experimental conditions is probably closely related to the absolute uptake of La, since at rest or during moderate exercise very little La is produced in skleletal muscle [21]. It has been reported that La uptake during 40 rain of mild exercise (40 % 1202ma0 occurred primarily in non-exercising muscle [1]. However, the metabolic rate of the resting muscle was markedly increased, and the detectable EMG activity in this muscle and its glycogen loss during the experiment indicated that this muscle was not completely at rest. In the experiments by Hermansen et al. [17] it was found that a significant quantity of La was taken up by the exercising muscle during active recovery exercise at 65 % 17Ozmax. The relationship between La removal and the % ST fibers may be related to the metabolic and anatomical features of these fibers. Specifically, the greater capillary density around the ST fibers [3] and their enriched H-LDH isozyme content (LDH-1 + LDH-2) [22, 23, 28] suggest that the delivery, uptake and subsequent oxidation of La is facilitated here. Presumably, the location of H-LDH on the mitochondrial membrane [14] and inside the mitochondrion [28] accounts for the rapid oxidation of La observed in exercising man [20] and dogs [10]. With active recovery exercise the functional significance of the ST fibers for La removal becomes more evident, since these fibers are employed during low intensities of exercise and can therefore rely on La as a substrate. The La removal from blood is directly correlated with the La concentrations in the blood [19]. We used the La concentrations at the beginning of the recovery
A. Bonen et al. : Blood Lactate Removal in Man p e r i o d as as an index for this mass a c t i o n effect o f La. Clearly, the c o r r e l a t i o n (r = 0.64) between this L a c o n c e n t r a t i o n a n d the L a r e m o v a l rate d u r i n g the active recovery p e r i o d suggests t h a t b l o o d L a also exerts a mass a c t i o n effect in m a n . A similar result (r = 0.80) also o c c u r r e d at rest in the eight subjects for w h o m an a c c e p t a b l e linear d e s c r i p t i o n o f L a r e m o v a l was obtained. T h e negative weighting o f the relative intensity o f exercise suggests t h a t the recovery exercise in the p r e s e n t s t u d y r e t a r d e d the o p t i m a l r e m o v a l o f La. In a p r e v i o u s s t u d y we f o u n d t h a t the m o s t effective rem o v a l o f L a d u r i n g bicycle e r g o m e t e r exercise o c c u r r e d at 3 2 % I~Ozma~ [4]. In the present s t u d y the exercise intensity was generally above this optimal w o r k l o a d (range 29-49700 lzO2m,x). Thus, for m o s t subjects net L a r e m o v a l was n o d o u b t s o m e w h a t less than optimal, since L a p r o d u c t i o n was p r o b a b l y slightly a u g m e n t e d . Nevertheless, the r e m o v a l rate o f L a was still significantly m o r e r a p i d d u r i n g the active recovery t h a n d u r i n g the resting recovery. D u r i n g the resting recovery, differences in L a r e m o v a l rates c o u l d n o t be described with the variables at h a n d ( P > 0.10). This suggests t h a t differences in muscle fiber c o m p o s i t i o n a n d the m e t a b o l i c rates at rest are less significant for the d i s p o s a l o f L a at rest. This m a y be r e l a t e d to r e d u c e d delivery o f L a to the muscle d u r i n g a resting recovery, a n d the inactivity o f muscle, p a r t i c u l a r l y the ST fibers. In addition, the liver m a y also dispose o f relatively m o r e L a at rest t h a n d u r i n g exercise. This w o u l d further reduce the i m p o r t a n c e o f the fiber c o m p o s i t i o n o f skeletal muscle for L a r e m o v a l at rest. It w o u l d seem t h a t L a m a y be a preferential s u b s t r a t e for muscle m e t a b o l i s m d u r i n g active r e c o v e r y exercise. N o r m a l l y m i l d exercise ( 2 4 - 4 8 % J~O 2 max) is fueled b y free fatty acids ( F F A ) [1,2] b u t with o u r e x p e r i m e n t a l p r o c e d u r e s the a c c u m u l a t i o n o f L a at the e n d o f 6 min o f intense exercise also alters the m e t a b olism o f free fatty acids ( F F A ) . Based on the w o r k o f Issekutz a n d Miller [18] the high L a c o n c e n t r a t i o n s m i g h t be e x p e c t e d to i n h i b i t the release o f F F A f r o m their storage sites. A shift t o w a r d s c a r b o h y d r a t e m e t a b o l i s m s h o u l d therefore occur, if exercise is to be m a i n t a i n e d , a n d the presence o f L a in the b l o o d p r o v i d e s the muscle w i t h a c o n v e n i e n t c a r b o h y d r a t e source. Yet, there is also evidence t h a t L a p r o m o t e s the u p t a k e o f F F A in muscle [2, 9]. In this case the muscle w o u l d have b o t h L a a n d F F A to sustain its o x i d a t i v e m e t a b o l i s m . In spite o f the conflicting evidence concerning the effects o f L a o n F F A m e t a b o l i s m [2, 9, 18], it seems r e a s o n a b l e to p r o p o s e t h a t the L a in b l o o d is a c o n v e n i e n t s u b s t r a t e for oxidative m e t a b o l i s m d u r i n g an active r e c o v e r y p e r i o d , especially since L a u p t a k e in muscle is a t t e n u a t e d b y its glycogen c o n t e n t [13].
209
References 1. Ahlborg, G., Hagenfeldt, L., Wahren, J. : Substrate utilization by the inactive leg during one-leg or arm exercise. J. Appl. Physiol. 39, 718-723 (1979) 2. Ahlborg, G., Hagenfeldt, L., Wahren, J.: Influence of lactate infusion on glucose and FFA metabolism in man. Scan& J. Clin. Lab. Invest. 36, 193-201 (1976) 3. Anderson, P. : Capillary distribution in skeletal muscle of man. Acta Physiol. Scand. 95, 203-205 (1975) 4. Belcastro, A. N., Bonen, A.: lactic acid removal rates during controlled and uncontrolled recovery exercise. J. Appl. Physiol. 39, 932-937 (1975) 5. Bergstrom, J. : Muscle electrolytes in man. Scand. J. Clin. Lab. Invest. Suppl. 68 (1962) 6. Bonen, A., Belcastro, A. N.: Accuracy of a dry gas meter to monitor ventilation during exercise. Br. J. Sports Med. 8, 181 182 (1974) 7. Bonen, A., Belcastro, A. N. : Comparison of self-selected recovery methods on lactic acid removal rates. Med. Sci. Sports 8, 176-178 (1976) 8. Bonen, A., Campbell, C. J., Kirby, R. L., Belcastro, A. N.: Relationship between slow-twitch muscle fibers and lactic removal. Can. J. Appl. Sport Sci. 3, 160-162 (1978) 9. Dieterle, P., Banholzer, P., Dieterle, R., Henner, J., Schwartz, K. : The influence of lactate on muscle metabolism. Lactate as a possible regulating factor for the increased energy suppiy during muscular work. Horm. Metab. Res. 3, 340-344 (1971) 10. Depocas, F., Minaire, Y., Chatonnet, J. : Rates of formation and oxidation of lactic acid in dogs at rest and during exercise. Can. J. Physiol. Pharmacol. 47, 603-610 (1969) 11. Dubowitz, V., Brooke, M. H.: Muscle Biopsy: A Modern Approach, pp. 20-33. London: W. B. Saunders 1973 12. Eldridge, F. L. : Relationship between turnover rate and blood concentration of lactate in exercising dogs. J. Appl. Physiol. 39, 231-234 (1975) 13. Essen, B., Pernow, B., Gollnick, P. D., Saltin, B.: Muscle glycogen content and lactate uptake in exercising muscle. In: Metabolic adaptation to prolonged physical exercise. (H. Howald and J. R. Poortmans, eds.), pp. 130- I34. Basel: Birkhauser, 1975 14. Gollnick, P. D., Armstrong, R. B. : Histochemical localization of lactate dehydrogenase isozymes in human skeletal muscle fibers. Life Sci. 18, 23-32 (1976) 15. Hermansen, L., Stensvold, I. : Production and removal of lactate during exercise in man. Acta Physiol. Scand. 86, 191 - 201 (1972) 16. Hermansen, L., Vaage, O. : Lactate disappearance and glycogen synthesis in human muscle after maximal exercise. Am. J. Physiol. 233, E422-E429 (1977) 17. Hermansen, L., Maehlum, S., Pruett, E. D. R., Vaage, O., Waldhum, E., Wessel-Aas~ T.: Lactate removal at rest and during exercise. In: Metabolic adaptation to prolonged physical exercise (H. Howald and J. R. Poortmans, eds.), pp. 101 - 105. Basel: Birkhfiuser 1975 18. Issekutz, B., Miller, H.: Plasma free fatty acids during exercise and the effect of lactic acid. Proc. Soc. Exp. Biol. 110, 237-242 (1962) 19. Issekutz, B., Shaw, W. A. S., Issekutz, A. C. : Lactate metabolism in resting and exercising dogs. J. Appl. Physiol. 40, 312-319 (1976) 20. Jorfeldt, L.: Metabolism of L(+)-lactate in human skeletal muscle during exercise. Acta Physiol. Scand., Suppl. 338 (1970) 21. Jorfeldt, L., Juhlin-Dannfelt, A., Karlsson, J. : Lactate release in relation to tissue lactate in human skeletal muscle during exercise. J. Appl. Physiol. Environ. Exercise Physiol. 44, 350352 (1978)
210 22. Karlsson, J., Frith, K., Sj6din, B., Gollnick, P. D., Saltin, B. : Distribution of LDH isozymes in human skeletal muscle. Scand. J. Clin. Lab. Invest. 33, 307-312 (1974) 23. Karlsson, J., Sj6din, B., Thorstensson, A., Hulten, B., Frith, K. : LDH isozymes in skeletal muscle of endurance and strength trained athletes. Acta Physiol. Scand. 93, 150-156 (1975) 24. Kerlinger, F. N., Pedhazur, E. J. : Multiple Regression in Behavioral Research, pp. 5 3 - 8 1 . New York: Holt, Rinehart and Winston 1973 25. McGrail, J. C., Bonen, A., Belcastro, A. N. : Dependence of La removal on muscle metabolism in man. Eur. J. Appl. Physiol. 39, 8 7 - 9 7 (1978) 26. Nemoto, E. M., Hoff, J. T., Severinghaus, J. W. : Lactate uptake and metabolism by brain during hyperlactataemia and hypoglycemia. Stroke 5, 4 8 - 5 3 (1974)
Pfliigers Arch. 380 (1979) 27. Rowel1, L. B., Kraning II, K. K., Evans, T. O., Kennedy, J. W., Blackmon, J, R., Kusmi, F. : Splanchnic removal of lactate and pyruvate during exercise in man. J. Appl. Physiol. 21, 17731783 (1966) 28. Sj6din, B. : Lactate dehydrogenase in human skeletal muscle. Acta Physiol. Scand., Suppl. 436 (1976) 29. Spitzer, J. J. : Effect of lactate infusion on canine myocardial free fatty acid metabolism in vivo. Am. J. Physiol. 226, 213-217 (1974) 30. Yudkin, J., Cohen, R. D. : The contribution of the kidney to the removal of lactic acid under load under normal and acidotic conditions in the conscious cat. Clin. Sci. Mol. Med. 46, 8P (1974)
Received January 2, 1979
Pfl/igers Arch. 380, 205-210 (1979)
EuropeanJournal
of Physiology
9 by Springer-Verlag1979
A Multiple Regression Model for Blood Lactate Removal in Man A. Bonen, C. J. Campbell, R. L. Kirby, and A. N. Belcastro School of Physical Education and Department of Medicine, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada
Abstract. After exercise the lactate (La) removal from
blood occurs significantly faster during moderate exercise than at rest. However, under both conditions there are considerable inter-individual differences in La removal. These differences in man may depend on the slow-twitch (ST) fiber content of muscle (X0, the La concentration in blood (Xz), and the intensity of the recovery exercise (X3). Therefore, multiple regression models were obtained to describe La removal rates with these variables. In 10 women La concentrations were increased via a 6min bicycle ergometer ride (87% l)Ozm,x) and blood La concentrations were measured every 5 rain during 20 min resting and active recovery periods ( 2 9 - 4 9 ~ 1202m,x). For resting recovery only the initial La concentration after the 6 min exercise provided a significant description for La removal in 8 subjects (P = 0.03). However, for the active recovery a highly significant description for La removal was obtained: La removal rate (mM/1 - min) = 0.773 • 10-2X1 -k 0.321 x 10-1X2 - 0.120 x 10 1X 3 + 0.202 (R = 0.91; P = 0.01). The statistical independence (P > 0.10) of each of these variables in the model suggests that each is contributing uniquely to the total removal rate of La observed during an active recovery period. The relationship between La removal and % ST fibers may be related to the metabolic and anatomical features of these fibers, the La concentration probably reflects the significance of the mass action effect of La, and the intensity of exercise reflects the role of the muscle's metabolic rate. The present results illustrate that the removal of blood lactate is influenced by the interactive effects of the intensity of the recovery exercise, blood lactate concentration and the ST fiber content of muscle. Key words: Lactate - Muscle fibers exercise - Bicycle ergometer - Women. Send offprint requests to
Recovery
A. Bonen at the above address
Introduction
After intense exercise the lactate (La) that has accumulated in blood is taken up by the liver and skeletal muscle [2,10,19]. However, La removal is accelerated when moderate exercise is performed during the recovery period [4,7,15,17]. Hermansen et al. [17] have found that a significant proportion of blood La is taken up by the exercising muscle during active recovery exercise. In addition, tracer studies with 14C-La in man and animals have also shown that blood La is primarily oxidized in skeletal muscle [8,12,19,20] during exercise. Jorfeldt [20] and others [7] have proposed that La is probably metabolized in the slow-twitch (ST) fibers of human skeletal muscle. These fibers contain approximately twice as much H - L D H as M - L D H [28], and thus the oxidation of La to pyruvate would seem to be facilitated here. We have recently found a moderate correlation between La removal from blood during active recovery exercise and the ST fiber content of the vastus lateralis [8]. However, the moderate correlation in that study suggested that other factors may also be affecting the removal of La from the circulation. These include the La concentration in the blood [19, 20], the bloodflow [20], and the metabolic rate of recovery exercise [4,15,25]. Thus, the considerable interindividual differences in La removal observed in our previous studies [4,6,25] may be related to the interactive effects of these parameters. Since the La concentration in blood accumulated during exercise and the intensity of recovery exercise can be manipulated independently of the muscle fiber composition, each of these variables may also account for a unique proportion of the rate of La removal after exercise. To test this hypothesis the variables under consideration were entered in an additive, least squares, multiple regression model in an attempt to determine the influence of each of these variables on La removal
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206
Table 1. Characteristics of the subjects Subject
Age (years)
Height (cm)
Weight (kg)
/)'02 m,x (ml/kg - min)
ST fibers (%)
Active recovery exercise (% VO~m~x)
1 2 3 4 5 6 7 8 9 10.
19 19 19 19 24 20 19 20 26 23
167 166 152 177 160 161 158 156 176 160
55.6 60.3 46.1 70.8 53.9 47.2 55.1 58.4 68.0 55.0
39.8 43.0 47.3 52.6 39.0 58.5 46.1 52.4 40.6 46.0
40 35 34 61 53 59 59 43 40 28
34 38 29 43 32 41 42 37 49 40
20.8
163
57.0
46.5
45
38
-+0.8
•
•
-+2.0
-+3.8
•
-+ SEM
Table 2. Lactate concentrations (raM/l) in blood during active and resting recovery periods ( ~ + SEM) Recovery Procedure
Recovery time, min 0
5
10
15
20
Active Recovery (38.4 • 1.8% gO2max) (N = 10) Rest Recovery ( N = 10)
13.8 • 14.7 +0.7
12.1 +1.1 13.5 •
7.5 +1.0 12.5 -+0.9
5.4 -+0.9 9.7 +1.0
3.9 -+0.8 7.9 -+0.8
from the blood at rest and when moderate exercise is performed during the recovery period.
Method Ten women participated in this study (Table 1). All were quite active and usually trained 3 days per week. Dietary controls were not imposed in this study. Blood La concentrations were increased by a standardized 6min bicycle ergometer ride at approximately 90 % 1202r,~x. This was followed by a 20rain rest period, and on another occasion by a 20 min active recovery exercise period at approximately 40% VO2max.Blood samples were obtained from a forearm vein immediately after the 6 min exercise bout (t = 0) and at min 5, 10, 15 and 20 during each recovery period. The blood (500pl) was immediately deproteinized in 2 ml of 10 % ice-fold perchloric acid and mixed briefly. After centrifuging the sample, the supernatant fluid was stored at - 2 0 ~C. La concentrations were determined with an enzymatic procedure [25]. The oxygen cost (VO2 re,x) of the standardized and recovery exercise bouts were determined during min 3 - 6 of the 6 min exercise bouts, and during min 1 1 - 1 5 of the recovery periods. In addition, determinations of VO2,,,x were obtained before and after this study via a progressively increased b!cycle ergometer ride (180 kpm/3 rain) to voluntary exhaustion. For VO2maxmeasurements the pulmonary ventilations were recorded from a calibrated dry gas meter (model CD4, Parkinson-Cowan), and gas temperatures were recorded from a calibrated thermister located in the gas meter [6]. Small aliquots of air (250 ml/min) were continuously drawn from the expiratory air stream through calibrated, rapid response 02 (model M14, Beckman), and CO2 (model LB2, Beckman) analyzers [25].
Muscle samples were obtained at rest with the needle biopsy technique [5] from the vastus lateralis of the right and left legs several weeks prior to, and several weeks after the La removal experiments, respectively. Fast-twitch (FT) and slow-twitch (ST) muscle fiber determinations were identified on the basis of staining intensity for myosin ATPase at pH 10.4 and 4.3 [11]. The percentage of ST fibers was calculated by adding the total number of ST fibers counted in the two biopsies and dividing this by the total number of fibers counted in the two samples. As in other studies [4,15, 25] the La removal rates(mM/I-min) during the recovery periods were calculated from the slope of the regression line between La concentration and time. Then, based on the ST fiber content of the vastus lateral• the La concentration in blood immediately after the 6 min standardized intense exercise bout (t = 0), and the intensity of the recovery exercise, a least squares, multiple regression procedure [24] was used to develop an equation to account for the differences in La removal rates among the subjects.
'Results The standardized 6 min exercise bouts were conducted a t 86.0 + 1 . 6 % ~/'O2max a n d 89.4 + 2 . 3 % ~';rO2max (X + SEM) prior to the resting and active recovery exercise sessions, respectively, and the active recovery exercise was conducted at 29-49% VO2m,x. T h e S T fiber composition in the subjects ranged from 28-61%. L a r e m o v a l o c c u r r e d s i g n i f i c a n t l y f a s t e r ( P < 0.01) during the active recovery than at rest (Table2).
A. Bonen et al. : Blood Lactate Removal in M a n
207
However, the individual removal rates during each recovery condition varied considerably among the subjects (Fig. l). These ranged from 0.773 to 0.269 raM/1, rain during the active recovery, and from 0.667 to 0.052 raM/l-rain during the resting recovery. The linear regression provided a good approximation for the calculation of La removal rates since the correlation coefficients associated with these individual linear regressions (Fig. 1) ranged from 0.94 to 0.99 (P < 0.01) during the active recovery period. In the remaining subject the correlation was 0.87 (P < 0.025). For the resting recoveries similar accuracies (r = 0.86 to r = 0.99) were obtained in 8 subjects, but in two subjects the linear regression between La concentra-
20.0
A
~15.0
z
10.0
5.1)
1;
t5
;o
zo
~5
2'o
RECOVERY TIME (rain) Fig. 1. Individual regression lines of La removal during active recovery exercise (A) and during a resting recovery period (B) following a standardized 6 min intense exercise bout. Heavy line is the mean removal rate. Dashed lines in B represent two instances when the linear regression did not provide an adequate fit (P > 0.10)
tion and recovery time was quite poor, for them the correlation coefficients were 0.33 and 0.28 (P > 0.10). In general, the zero order correlation coefficients between La removal rates during the active recovery period and the variables selected for this investigation were moderate or low (Table3). Significant correlations, however (P < 0.05) were found between the La removal rate and the % ST fibers, and the La concentrations after the 6 min standardized exercise bout (Table 3). With the multiple regression approach a highly significant description for La removal rates during the active recovery period was obtained when the initial post-exercise La concentration, the % ST fibers and the relative cost of the recovery exercise were combined in a prediction equation (Fig. 2). By itself the La concentration at the beginning of the recovery period was only moderately correlated (r = 0.64; P = 0.046) with the La removal rate. With the inclusion of the % ST fibers the multiple correlation coefficient (R) was increased to 0.80 (P = 0.030), and the addition of the intensity of the recovery exercise further increased the multiple R to 0.91 (P = 0.012). With these factors the following multiple regression equation was obtained to describe the net removal rate of La from the blood: La removal rate = 0.773 x 10 -2 % ST fibers + 0.321 x i0-1 initial La concentration (raM/1 9rain) - 0.120 x 10-1 recovery exercise % VO2m,x + 0.202. The coefficient of variations is + 15.1%, and the initial La concentrations, the % ST fibers, and the recovery exercise intensity accounted for 41%, 22 %, and 19% of the total variance associated with La removal rates during active recovery exercise. Although the addition of /'~02max t o the equation improved the overall prediction only slightly (R = 0.93; CV = + 13.9 %), this factor was not significant (P > 0.10) in combination with the other predictors.
Table 3. Intercorrelations of selected variables with La removal rates during an active recovery period (N = 10) J7 _+SEM
La removal rate
La removal rate m M / 1 . rain
0,530 +0.049
-
La concentration at min 0 (raM/l) ST fibers
13,8 +0.9 45.0
0.64*
-
0.54**
0.12
(%) Recovery intensity
(% FO2~.J 1702 m.x (ml/kg-min)
La concentration ST at min 0 fibers
Recovery Intensity
_+3.8 38.4
- 0.23
0.10
0.27
0.26
-0.17
0.42
_+1.8 46.5 _+2.0
*P = 0.023; **P = 0.052 (1-tailed test)
0.19
1202m~x
Pfltigers Arch. 380 (1979)
208 REMOVAL RATE- 0.773x10-2Xl+ 0.321x10-1XsO.120x10-1X3+
--
O.80
E
VOxrlO
0.202~
X~=%ST fibers X2=initial [Lal
E
0.60
/ /
9
0,40
~-
0.20 .
0.20
.
.
0.40 OBSERVED La
.
.
0.60
0.80
REMOVAL RATE (mMIL. min)
Fig.2. Comparison of observed with predicted La removal rates during active recovery exercise. Predicted values were derived from a multiple regression based on the % ST fibers (X1) initial La concentration during the recovery exercise (22), and the relative intensity of the recovery exercise (X~) (R = 0.91, P = 0.01)
For the resting recovery none of the predictors provided a significant description (P> 0.10) for the La removal rate. However, these data included two subjects for whom the La removal rate did not follow a linear decrement (P > 0.10) during the recovery period. When these two subjects were omitted from the analysis only the initial La concentration during the recovery period was significantly correlated with the La removal rate (r = 0.80; P = 0.03). Addition of the other variables in a multiple regression equation did not improve the prediction significantly (P > 0.10).
Discussion
The findings from the present study indicate that variations in La removal rates among individuals, during an active recovery, may be described by an additive, multiple regression model, from factors with known or hypothesized physiological significance. These were a) the La concentration in blood during the recovery period, b) the ST fiber composition of skeletal muscle, and c) the relative intensity of the recovery exercise. In addition, the algebraic signs associated with these variables appear to correspond with their physiological function. The lack of intercorrelations among these parameters (P > 0.10) indicated their independence from each other (Table 3), and thus the additive regression model is particularly apt for describing the
La removal rates with these variables. The mutual independence of the variables also suggests that each is exerting an independent effect on La removal. The proportion of variance contributed by each factor in the model is dependent on the sequence that it is entered in the equation [24]. Thus, while the relative physiological contribution of the variables cannot be determined from the model, the multiple regression approach does provide an excellent insight into the factors that may account simultaneously for the complex physiological phenomenon of individual differences in La removal rates. Each of the variables employed in the present study contributed significantly to overall description for La removal during active recovery and this further supports their physiological role. La uptake from blood can occur in the liver [27], heart [29], brain [26], kidney [30] and skeletal muscle [1,2,10,11,15,17,19-21]. However, the major proportion of La removal occurs in skeletal muscle, since a large fraction of La is oxidized almost immediately in exercising dogs (74%) [10] and man (52%) [20], and only about 20 % of the hepatic glucose production is derived from lactate [19]. The net removal of La under our experimental conditions is probably closely related to the absolute uptake of La, since at rest or during moderate exercise very little La is produced in skleletal muscle [21]. It has been reported that La uptake during 40 rain of mild exercise (40 % 1202ma0 occurred primarily in non-exercising muscle [1]. However, the metabolic rate of the resting muscle was markedly increased, and the detectable EMG activity in this muscle and its glycogen loss during the experiment indicated that this muscle was not completely at rest. In the experiments by Hermansen et al. [17] it was found that a significant quantity of La was taken up by the exercising muscle during active recovery exercise at 65 % 17Ozmax. The relationship between La removal and the % ST fibers may be related to the metabolic and anatomical features of these fibers. Specifically, the greater capillary density around the ST fibers [3] and their enriched H-LDH isozyme content (LDH-1 + LDH-2) [22, 23, 28] suggest that the delivery, uptake and subsequent oxidation of La is facilitated here. Presumably, the location of H-LDH on the mitochondrial membrane [14] and inside the mitochondrion [28] accounts for the rapid oxidation of La observed in exercising man [20] and dogs [10]. With active recovery exercise the functional significance of the ST fibers for La removal becomes more evident, since these fibers are employed during low intensities of exercise and can therefore rely on La as a substrate. The La removal from blood is directly correlated with the La concentrations in the blood [19]. We used the La concentrations at the beginning of the recovery
A. Bonen et al. : Blood Lactate Removal in Man p e r i o d as as an index for this mass a c t i o n effect o f La. Clearly, the c o r r e l a t i o n (r = 0.64) between this L a c o n c e n t r a t i o n a n d the L a r e m o v a l rate d u r i n g the active recovery p e r i o d suggests t h a t b l o o d L a also exerts a mass a c t i o n effect in m a n . A similar result (r = 0.80) also o c c u r r e d at rest in the eight subjects for w h o m an a c c e p t a b l e linear d e s c r i p t i o n o f L a r e m o v a l was obtained. T h e negative weighting o f the relative intensity o f exercise suggests t h a t the recovery exercise in the p r e s e n t s t u d y r e t a r d e d the o p t i m a l r e m o v a l o f La. In a p r e v i o u s s t u d y we f o u n d t h a t the m o s t effective rem o v a l o f L a d u r i n g bicycle e r g o m e t e r exercise o c c u r r e d at 3 2 % I~Ozma~ [4]. In the present s t u d y the exercise intensity was generally above this optimal w o r k l o a d (range 29-49700 lzO2m,x). Thus, for m o s t subjects net L a r e m o v a l was n o d o u b t s o m e w h a t less than optimal, since L a p r o d u c t i o n was p r o b a b l y slightly a u g m e n t e d . Nevertheless, the r e m o v a l rate o f L a was still significantly m o r e r a p i d d u r i n g the active recovery t h a n d u r i n g the resting recovery. D u r i n g the resting recovery, differences in L a r e m o v a l rates c o u l d n o t be described with the variables at h a n d ( P > 0.10). This suggests t h a t differences in muscle fiber c o m p o s i t i o n a n d the m e t a b o l i c rates at rest are less significant for the d i s p o s a l o f L a at rest. This m a y be r e l a t e d to r e d u c e d delivery o f L a to the muscle d u r i n g a resting recovery, a n d the inactivity o f muscle, p a r t i c u l a r l y the ST fibers. In addition, the liver m a y also dispose o f relatively m o r e L a at rest t h a n d u r i n g exercise. This w o u l d further reduce the i m p o r t a n c e o f the fiber c o m p o s i t i o n o f skeletal muscle for L a r e m o v a l at rest. It w o u l d seem t h a t L a m a y be a preferential s u b s t r a t e for muscle m e t a b o l i s m d u r i n g active r e c o v e r y exercise. N o r m a l l y m i l d exercise ( 2 4 - 4 8 % J~O 2 max) is fueled b y free fatty acids ( F F A ) [1,2] b u t with o u r e x p e r i m e n t a l p r o c e d u r e s the a c c u m u l a t i o n o f L a at the e n d o f 6 min o f intense exercise also alters the m e t a b olism o f free fatty acids ( F F A ) . Based on the w o r k o f Issekutz a n d Miller [18] the high L a c o n c e n t r a t i o n s m i g h t be e x p e c t e d to i n h i b i t the release o f F F A f r o m their storage sites. A shift t o w a r d s c a r b o h y d r a t e m e t a b o l i s m s h o u l d therefore occur, if exercise is to be m a i n t a i n e d , a n d the presence o f L a in the b l o o d p r o v i d e s the muscle w i t h a c o n v e n i e n t c a r b o h y d r a t e source. Yet, there is also evidence t h a t L a p r o m o t e s the u p t a k e o f F F A in muscle [2, 9]. In this case the muscle w o u l d have b o t h L a a n d F F A to sustain its o x i d a t i v e m e t a b o l i s m . In spite o f the conflicting evidence concerning the effects o f L a o n F F A m e t a b o l i s m [2, 9, 18], it seems r e a s o n a b l e to p r o p o s e t h a t the L a in b l o o d is a c o n v e n i e n t s u b s t r a t e for oxidative m e t a b o l i s m d u r i n g an active r e c o v e r y p e r i o d , especially since L a u p t a k e in muscle is a t t e n u a t e d b y its glycogen c o n t e n t [13].
209
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210 22. Karlsson, J., Frith, K., Sj6din, B., Gollnick, P. D., Saltin, B. : Distribution of LDH isozymes in human skeletal muscle. Scand. J. Clin. Lab. Invest. 33, 307-312 (1974) 23. Karlsson, J., Sj6din, B., Thorstensson, A., Hulten, B., Frith, K. : LDH isozymes in skeletal muscle of endurance and strength trained athletes. Acta Physiol. Scand. 93, 150-156 (1975) 24. Kerlinger, F. N., Pedhazur, E. J. : Multiple Regression in Behavioral Research, pp. 5 3 - 8 1 . New York: Holt, Rinehart and Winston 1973 25. McGrail, J. C., Bonen, A., Belcastro, A. N. : Dependence of La removal on muscle metabolism in man. Eur. J. Appl. Physiol. 39, 8 7 - 9 7 (1978) 26. Nemoto, E. M., Hoff, J. T., Severinghaus, J. W. : Lactate uptake and metabolism by brain during hyperlactataemia and hypoglycemia. Stroke 5, 4 8 - 5 3 (1974)
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Received January 2, 1979
