This article was downloaded by: [Temple University Libraries] On: 23 April 2015, At: 06:05 Publisher: Routledge Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Sports Sciences Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/rjsp20
Ventilation and blood lactate increase exponentially during incremental exercise a
a
Steven C. Dennis , Timothy D. Noakes & Andrew N. Bosch
a
a
MRC/UCT Bioenergetics of Exercise Research Unit, Department of Physiology , University of Cape Town Medical School , Observatory, 7925, South Africa Published online: 14 Nov 2007.
To cite this article: Steven C. Dennis , Timothy D. Noakes & Andrew N. Bosch (1992) Ventilation and blood lactate increase exponentially during incremental exercise, Journal of Sports Sciences, 10:5, 437-449, DOI: 10.1080/02640419208729942 To link to this article: http://dx.doi.org/10.1080/02640419208729942
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sublicensing, systematic supply, or distribution in any form to anyone is expressly
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Journal of Sports Sciences, 1992, 10, 437-449
Ventilation and blood lactate increase exponentially during incremental exercise STEVEN C. DENNIS,* TIMOTHY D. NOAKES and ANDREW N. BOSCH MRC/UCT Bioenergetics of Exercise Research Unit, Department of Physiology, University of Cape Town Medical School, Observatory 7925, South Africa
Downloaded by [Temple University Libraries] at 06:06 23 April 2015
Accepted 17 July 1991
Abstract This study examined whether the ventilatory (V) compensation for metabolic acidosis with increasing O2 uptake (VO2) and CO2 output (VCO2) might be more in accord with the theoretical expectation of a progressive acceleration of proton production from carbohydrate oxidation rather than a sudden onset of blood lactate (BLa) accumulation. The interrelationships between V, VO2, VCO2 and BLa concentration, [BLa], were investigated in 10 endurance-trained male cyclists during incremental (120+15 W min -1 ) exercise tests to exhaustion. Regression analyses on the V, VCO2 and [BLa] vs VO2 data revealed that all were better fitted by continuous Y=A. exp. [B.VO 2 ] + C rate laws than by threshold linear rate equations (P< 0.0001). Plots of V vs VCO2 and [BLa] were also non-linear. Ventilation increased as an exponential V= 27 ± 4 . exp . [0.37 ± 0.03 . VCO2] function of VCO2 and as a hyperbolic function of [BLa]. In opposition to the 'anaerobic (lactate) threshold' hypothesis, we suggest these data are more readily explained by a continuous development of acidosis, rather than a sudden onset of BLa accumulation, during progressive exercise. Keywords: Ventilation, blood lactate, anaerobic threshold.
Introduction Bock and Dill (1931) may have been the first to notice that the apparently linear relationship between ventilation (V) and oxygen consumption (VO2) is lost at high work rates (Douglas et al, 1913; Douglas, 1927; Hill and Lupton, 1923). They suggested that this phenomenon was the result of rapid lactic acid accumulation during intense exercise. The FO2 at which the rise in V appears to deviate from linearity was subsequently termed the 'anaerobic threshold' (Wasserman and Mcllroy, 1964) and the lactic acidosis explanation for this phenomenon became widely accepted (Hughes et al., 1968; Sutton and Jones, 1979; Whipp and Ward, 1980; Hughson and Green, 1982; Jones, 1984). Numerous reports have appeared suggesting that the lactate and ventilation thresholds are coincident and causally * To whom all correspondence should be addressed. 0264-0414/92 © 1992 E. & F.N. Spon
Downloaded by [Temple University Libraries] at 06:06 23 April 2015
438
Dennis et al.
related (Wasserman et al, 1967,1973,1990; Wasserman, 1978,1984a,b; Whipp et al, 1984; Beaver et al., 1986a,b). More recently, however, the validity of the lactate (anaerobic) threshold has become an issue of concern (Brooks, 1985; Walsh and Banister, 1988). First, several investigators have shown that the lactate and ventilation thresholds can be dissociated (Hagberg et al, 1982; Hughes et al, 1982; Heigenhauser et al, 1983; Yamamoto and Hughson, 1989) and, secondly, both muscle (Green et al, 1983; Connett et al, 1986) and 'arterialized' venous blood (Hughson et al, 1987; Campbell et al, 1989) lactate concentrations have been found to increase as continuous, rather than threshold, functions of ^O 2 . Furthermore, the connection between the respiratory compensation for metabolic acidosis and the accumulation of lactate in the blood has also been questioned on theoretical grounds (Walsh and Banister, 1988). When glycolytic ATP formation is taken into consideration and the likely electrical charges at intracellular pH are summed, the breakdown of glucose or glycogen to lactate does not produce a net gain of protons (Gevers, 1977; Walsh and Banister, 1988): Glucose + 2 MgADP" +2 P, 2 -->2 lactate" +2 MgATP2"
(1)
Instead, the metabolic generation of protons during progressive exercise is more a consequence of the rise in glycolytic ATP turnover with increasing work rate. When ATP is resynthesized by glycolysis, rather than by oxidative phosphorylation or creatine phosphate hydrolysis, the protons produced by its hydrolysis are not re-consumed. Protons are therefore generated irrespective of whether lactate is formed or pyruvate is delivered to the mitochondria for oxidation: 2
MgATP2> MgADP pyruvate | | or < glycolysis lactate
|
glucose or glycogen
^'
Since any increase in carbohydrate metabolism would be expected to accelerate proton formation, the presence of a ventilation threshold is open to doubt. Like the blood lactate threshold (Beaver et al, 1985), the ventilation threshold (Orr et al, 1982; Beaver et al., 1986b) could also be a result of the inappropriate use of linear regressions to define an exponential function. Accordingly, we have employed linear and non-linear least-squares analyses to determine whether V shows a threshold effect or increases as a continuous function of VO2 during cycling exercise of progressively increasing intensity. The same procedures have also been used to investigate the interrelationships between the rises in V and the increases in CO 2 expiration (FCO2) and [BLa] with exercise. Materials and methods The rises in V, KCO2 and [BLa] with increasing VO2 were examined in 10 endurancetrained male subjects during progressive cycling exercise to exhaustion. The study was approved by the Research and Ethics Committee of the Faculty of Medicine of the University of Cape Town.
Ventilation during incremental exercise
439
Exercise protocol The subjects reported to the laboratory in the fasted state. The exercise was performed on a Tunturi EL 400 cycle ergometer (Tunturipyora, Piisparisti, Finland). Unless stated otherwise (Table 1), the starting workload was 120 W with increases of 15 W every 60 s until the subject could no longer continue the test. The electrocardiogram was monitored throughout the test by attaching RA, LA and V5 leads to the subjects and displaying the signal on a Lohmeier Model 607 oscilloscope (Lohmeier, Germany).
Downloaded by [Temple University Libraries] at 06:06 23 April 2015
Table 1. The subject's details and exercise protocols Age (years)
Body mass (kg)
Workload range (W)
$OZ max (lmin" 1 )
L.D. G.H. R.S. J.P. K.H. S.L. J.S. A.P. Y.C. M.K.
32 33 25 37 34 20 26 27 32 27
80 68 76 59 70 95 77 74 74 58
120-405 120-300 120-405 120-300 120-315 165-390 120-330 150-375 120-375 120-390
4.87 4.29 4.50 3.44 3.52 4.71 4.05 4.43 3.89 3.70
Mean
29 2
73 3
128-359 5-14
4.14 0.16
Subject
S.E.M.
Ventilation and gas exchange measurements During the exercise, the subjects wore a nose-clip and inspired air from a Hans Rudolph 2700 one-way valve connected to a Mijnhardt dry gas meter (Vacumed, Ventura, U.S.A.). Expired air was passed through a 15-litre baffled mixing chamber and a condensation coil to Ametek N-22M O 2 and CD-3A CO 2 analysers (Thermox Instruments, Pittsburgh, U.S.A.). Before every test, the gas meter was calibrated with a Hans Rudolph 5530 3-litre syringe and the analysers were set with air and a 4% CO 2 /16% O 2 /80% N 2 mixture. Instrument outputs were processed by an on-line IBM PC computer which calculated the average V, VO2 and KCO2 over each minute using conventional equations (Noakes, 1988).
Blood lactate assays Rises in circulating [BLa] with increasing VO2 were determined in successive 1-min blood samples drawn continuously from a forearm vein via a Jelco catheter and Eyela Microtube pump (Rakakekai, Japan). Blood leaving the pump (1 ml min~ *) was deproteinized in 0.6 M ice-cold HC1O4 (2 ml), centrifuged at 500 # for 15 min and stored at - 2 0 ° C for later enzymatic assay (Bergmeyer, 1981).
440
Dennis et al.
Downloaded by [Temple University Libraries] at 06:06 23 April 2015
Model comparisons Interrelationships between the rises in V, FCO2 and [BLa] with increasing VO2 were investigated with the ISI Graph Pad linear and non-linear regression program (Institute for Scientific Information, Philadelphia, U.S.A.). Using this program, two models were tested. In one, the rises in V, FCO2 and [BLa] were treated as continuous exponential functions and a single Y=A • exp • [2? • KO2] + C rate law was fitted to the data. In the other model, the conventional threshold responses were identified by two impartial observers and multiple Y=D- VO2 + E rate equations were fitted between the predicted inflection points. The models were compared by dividing the sum of the squares of the differences between the observed and computed values by the degrees of freedom. Unlike the correlation coefficient (R2), a mean of the residual variance (MRV) makes allowance for differences in the number of fitting parameters in the least-squares analyses. Statistical analyses Statistical significances (P
Journal of Sports Sciences Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/rjsp20
Ventilation and blood lactate increase exponentially during incremental exercise a
a
Steven C. Dennis , Timothy D. Noakes & Andrew N. Bosch
a
a
MRC/UCT Bioenergetics of Exercise Research Unit, Department of Physiology , University of Cape Town Medical School , Observatory, 7925, South Africa Published online: 14 Nov 2007.
To cite this article: Steven C. Dennis , Timothy D. Noakes & Andrew N. Bosch (1992) Ventilation and blood lactate increase exponentially during incremental exercise, Journal of Sports Sciences, 10:5, 437-449, DOI: 10.1080/02640419208729942 To link to this article: http://dx.doi.org/10.1080/02640419208729942
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sublicensing, systematic supply, or distribution in any form to anyone is expressly
Downloaded by [Temple University Libraries] at 06:06 23 April 2015
forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Journal of Sports Sciences, 1992, 10, 437-449
Ventilation and blood lactate increase exponentially during incremental exercise STEVEN C. DENNIS,* TIMOTHY D. NOAKES and ANDREW N. BOSCH MRC/UCT Bioenergetics of Exercise Research Unit, Department of Physiology, University of Cape Town Medical School, Observatory 7925, South Africa
Downloaded by [Temple University Libraries] at 06:06 23 April 2015
Accepted 17 July 1991
Abstract This study examined whether the ventilatory (V) compensation for metabolic acidosis with increasing O2 uptake (VO2) and CO2 output (VCO2) might be more in accord with the theoretical expectation of a progressive acceleration of proton production from carbohydrate oxidation rather than a sudden onset of blood lactate (BLa) accumulation. The interrelationships between V, VO2, VCO2 and BLa concentration, [BLa], were investigated in 10 endurance-trained male cyclists during incremental (120+15 W min -1 ) exercise tests to exhaustion. Regression analyses on the V, VCO2 and [BLa] vs VO2 data revealed that all were better fitted by continuous Y=A. exp. [B.VO 2 ] + C rate laws than by threshold linear rate equations (P< 0.0001). Plots of V vs VCO2 and [BLa] were also non-linear. Ventilation increased as an exponential V= 27 ± 4 . exp . [0.37 ± 0.03 . VCO2] function of VCO2 and as a hyperbolic function of [BLa]. In opposition to the 'anaerobic (lactate) threshold' hypothesis, we suggest these data are more readily explained by a continuous development of acidosis, rather than a sudden onset of BLa accumulation, during progressive exercise. Keywords: Ventilation, blood lactate, anaerobic threshold.
Introduction Bock and Dill (1931) may have been the first to notice that the apparently linear relationship between ventilation (V) and oxygen consumption (VO2) is lost at high work rates (Douglas et al, 1913; Douglas, 1927; Hill and Lupton, 1923). They suggested that this phenomenon was the result of rapid lactic acid accumulation during intense exercise. The FO2 at which the rise in V appears to deviate from linearity was subsequently termed the 'anaerobic threshold' (Wasserman and Mcllroy, 1964) and the lactic acidosis explanation for this phenomenon became widely accepted (Hughes et al., 1968; Sutton and Jones, 1979; Whipp and Ward, 1980; Hughson and Green, 1982; Jones, 1984). Numerous reports have appeared suggesting that the lactate and ventilation thresholds are coincident and causally * To whom all correspondence should be addressed. 0264-0414/92 © 1992 E. & F.N. Spon
Downloaded by [Temple University Libraries] at 06:06 23 April 2015
438
Dennis et al.
related (Wasserman et al, 1967,1973,1990; Wasserman, 1978,1984a,b; Whipp et al, 1984; Beaver et al., 1986a,b). More recently, however, the validity of the lactate (anaerobic) threshold has become an issue of concern (Brooks, 1985; Walsh and Banister, 1988). First, several investigators have shown that the lactate and ventilation thresholds can be dissociated (Hagberg et al, 1982; Hughes et al, 1982; Heigenhauser et al, 1983; Yamamoto and Hughson, 1989) and, secondly, both muscle (Green et al, 1983; Connett et al, 1986) and 'arterialized' venous blood (Hughson et al, 1987; Campbell et al, 1989) lactate concentrations have been found to increase as continuous, rather than threshold, functions of ^O 2 . Furthermore, the connection between the respiratory compensation for metabolic acidosis and the accumulation of lactate in the blood has also been questioned on theoretical grounds (Walsh and Banister, 1988). When glycolytic ATP formation is taken into consideration and the likely electrical charges at intracellular pH are summed, the breakdown of glucose or glycogen to lactate does not produce a net gain of protons (Gevers, 1977; Walsh and Banister, 1988): Glucose + 2 MgADP" +2 P, 2 -->2 lactate" +2 MgATP2"
(1)
Instead, the metabolic generation of protons during progressive exercise is more a consequence of the rise in glycolytic ATP turnover with increasing work rate. When ATP is resynthesized by glycolysis, rather than by oxidative phosphorylation or creatine phosphate hydrolysis, the protons produced by its hydrolysis are not re-consumed. Protons are therefore generated irrespective of whether lactate is formed or pyruvate is delivered to the mitochondria for oxidation: 2
MgATP2> MgADP pyruvate | | or < glycolysis lactate
|
glucose or glycogen
^'
Since any increase in carbohydrate metabolism would be expected to accelerate proton formation, the presence of a ventilation threshold is open to doubt. Like the blood lactate threshold (Beaver et al, 1985), the ventilation threshold (Orr et al, 1982; Beaver et al., 1986b) could also be a result of the inappropriate use of linear regressions to define an exponential function. Accordingly, we have employed linear and non-linear least-squares analyses to determine whether V shows a threshold effect or increases as a continuous function of VO2 during cycling exercise of progressively increasing intensity. The same procedures have also been used to investigate the interrelationships between the rises in V and the increases in CO 2 expiration (FCO2) and [BLa] with exercise. Materials and methods The rises in V, KCO2 and [BLa] with increasing VO2 were examined in 10 endurancetrained male subjects during progressive cycling exercise to exhaustion. The study was approved by the Research and Ethics Committee of the Faculty of Medicine of the University of Cape Town.
Ventilation during incremental exercise
439
Exercise protocol The subjects reported to the laboratory in the fasted state. The exercise was performed on a Tunturi EL 400 cycle ergometer (Tunturipyora, Piisparisti, Finland). Unless stated otherwise (Table 1), the starting workload was 120 W with increases of 15 W every 60 s until the subject could no longer continue the test. The electrocardiogram was monitored throughout the test by attaching RA, LA and V5 leads to the subjects and displaying the signal on a Lohmeier Model 607 oscilloscope (Lohmeier, Germany).
Downloaded by [Temple University Libraries] at 06:06 23 April 2015
Table 1. The subject's details and exercise protocols Age (years)
Body mass (kg)
Workload range (W)
$OZ max (lmin" 1 )
L.D. G.H. R.S. J.P. K.H. S.L. J.S. A.P. Y.C. M.K.
32 33 25 37 34 20 26 27 32 27
80 68 76 59 70 95 77 74 74 58
120-405 120-300 120-405 120-300 120-315 165-390 120-330 150-375 120-375 120-390
4.87 4.29 4.50 3.44 3.52 4.71 4.05 4.43 3.89 3.70
Mean
29 2
73 3
128-359 5-14
4.14 0.16
Subject
S.E.M.
Ventilation and gas exchange measurements During the exercise, the subjects wore a nose-clip and inspired air from a Hans Rudolph 2700 one-way valve connected to a Mijnhardt dry gas meter (Vacumed, Ventura, U.S.A.). Expired air was passed through a 15-litre baffled mixing chamber and a condensation coil to Ametek N-22M O 2 and CD-3A CO 2 analysers (Thermox Instruments, Pittsburgh, U.S.A.). Before every test, the gas meter was calibrated with a Hans Rudolph 5530 3-litre syringe and the analysers were set with air and a 4% CO 2 /16% O 2 /80% N 2 mixture. Instrument outputs were processed by an on-line IBM PC computer which calculated the average V, VO2 and KCO2 over each minute using conventional equations (Noakes, 1988).
Blood lactate assays Rises in circulating [BLa] with increasing VO2 were determined in successive 1-min blood samples drawn continuously from a forearm vein via a Jelco catheter and Eyela Microtube pump (Rakakekai, Japan). Blood leaving the pump (1 ml min~ *) was deproteinized in 0.6 M ice-cold HC1O4 (2 ml), centrifuged at 500 # for 15 min and stored at - 2 0 ° C for later enzymatic assay (Bergmeyer, 1981).
440
Dennis et al.
Downloaded by [Temple University Libraries] at 06:06 23 April 2015
Model comparisons Interrelationships between the rises in V, FCO2 and [BLa] with increasing VO2 were investigated with the ISI Graph Pad linear and non-linear regression program (Institute for Scientific Information, Philadelphia, U.S.A.). Using this program, two models were tested. In one, the rises in V, FCO2 and [BLa] were treated as continuous exponential functions and a single Y=A • exp • [2? • KO2] + C rate law was fitted to the data. In the other model, the conventional threshold responses were identified by two impartial observers and multiple Y=D- VO2 + E rate equations were fitted between the predicted inflection points. The models were compared by dividing the sum of the squares of the differences between the observed and computed values by the degrees of freedom. Unlike the correlation coefficient (R2), a mean of the residual variance (MRV) makes allowance for differences in the number of fitting parameters in the least-squares analyses. Statistical analyses Statistical significances (P
