a LIBRARY Mchigan State University This is to certify that the thesis entitled THE RELATIONSHIP BETWEEN RESPIRATORY AND LACTATE BREAKPOINTS DURING SELECTED RUN PROTOCOLS presented by MARTHA JANE ANDREWS has been accepted towards fulfillment of the requirements for _M._A..___degree in W OF HEALTH EDUCATION, COUNSELING PSYCHO OGY // AND HUMA» ERFO' :‘CE , // /1‘ I 1/ L, , I Major professor Date%M/§ 7f Cflp7 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution MSU LIBRARIES .—_—. RETURNING MATERIALS: Piace in book drop to remove this checkout from your record. FINES will be charged if book is returned after the date stamped beiow. THE RELATIONSHIP BETWEEN RESPIRATORY AND LACTATE BREAKPOINTS DURING SELECTED RUN PROTOCOLS Br Martha Jane Andrews A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF ARTS School of Health Education. Counseling Psychology. and Hunan Performance 1987 ABSTRACT THE RELATIONSHIP BETWEEN RESPIRATORY AND LACTATE BREAKPOINTS DURING SELECTED RUN PROTOCOLS 9? 1 Martha Jane Andrews A continuous. incremental treadmill run (ramp) was performed to determine if two respiratory breakpoints could be detected. An 18- minute defined velocity run protocol utilizing six running speeds and a 30-minute interrupted run protocol utilizing four running speeds were performed to evaluate the relationship of the respiratory (Rbk) and lactate (Lbk) breakpoints. High correlations were obtained between Rbkl and Lbkl (r=0.96) and between mm and 1.ka (r=0.89) with sample sizes of 6 and 5. respectively. A paired t-test indicated no significant difference between velocities at Rbkl and Lbkl and no significant difference between velocities at Rbkz and Lbkz. The mean 63/602 plots from the 30-minute interrupted runs show an increase over time while the mean lactate plots do not. These findings suggest factors other than lactate are responsible for the increase in ventilation at the onset of anaerobiosis. DEDICATION To my special friend. David ii ACKNOWLEDGMENTS I would like to thank the graduate assistants. Sharon Evans. Beth Garvy. and Chet Zelaslro for their many hours in lab directing and participating in data collection and the many individuals who willingly gave up their time to assist in data collection. Special thanks is extended to each of the subjects who endured throughout the study and to Bob Wells for helping things run smoothly. I would like to thank Glenna DeJong for her many hours in lab helping to collect data and for her suggestions and comments. Finally. I would also like to thank Dr. Wayne VanI-iuss and Dr. William Heusner for their suggestions and guidance. iii TABLE OF CONTENTS LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . LIST OF FIGURE 0 O O 0 O O O O O O O O O I O O O O O 0 Chapter I. II. III. Iv. THE PROM O O O O O O I O O O O O O O O O O O 0 Need for the Study . Purpose . . . . . . Research Hypothesis Research Plan . . . Definitions . . . . Limitations . . . . REVIEW OR RELATED LITERATURE . . . . . . . . . . . Applications of the AT . . . . . . . . . . . . . . as a measuring tool . . . . . . . . . . . . . . as a predictor of maximal endurance performance Principle Hechanisms of Action . . . . energy substrates . . . . . . blood lactate . . . . . . . . muscle oxidative capacity . . lactate clearance . . . . . muscle fiber composition . . Invasive determination of the AT sources of blood lactate . . . validity of lactate measurement use bicarbonate buffer system . . . . . Noninvasive Determination of the AT . . use of respiratory parameters . . validity of criterion measures . . RESEARCH METHODS . . . . . . . . . . . . . . . . . Subjects . . . . . . . Data Collection . . . Treatment of the Data Footnotes . . . . . . RmULm MD DISCUSSION 0 O I O O O U I I O O O I 0 iv Page vi vii GUIUlehoLOJ s... s) 10 10 11 11 11 12 13 13 15 16 16 16 19 19 19 22 23 24 Results Physical Measurements Design One . 18-minute defined velocities protocol Statistical Analysis . Design Two . intermittent 30-minute Discussion V. SUMMARY. Summary Conclusions Recommendations APPENDIX A . CONCLUSIONS APPENDIX B . . . . . . REFERENCES . AND protocol . . . RECOMMENDATIONS 24 24 24 27 29 33 33 33 42 42 44 44 45 56 57 Table Table Table Table Table Table Table Table Table Table 1A. 2A. 3A. 4A. 5A. 6A. 7A. LIST OF TABLES Physiological Measures . . . . . . . . . . Breakpoint Velocities (mph) and Lactate Concentrations (mM) Mean VE/VO Values and Lactate Concentrations (mM) from Ihe 30-Minute Intermittent Protocol Individual Physical Characteristic Data . . . Max. V02 Values (ml/kg/min) . . . . . . Breakpoint Velocities (mph) . . . . . . . . . 602 (ml/min) and 3 Max. 602 lB-Minute Defined Velocities Protocol Lactate Concentrations (mM) . . . . . . . . . at the Breakpoints Pre- and Post-Exercise Lactate Concentrations (mM) from Ramp 2 and Ramp 3 . . . . . . . . VE/VO Values and Lactate Concentrations (mM) from Ihe 30-Minute Intermittent Protocol vi Page 25 27 30 45 45 46 46 47 47 48 Figure Figure Figure Figure Figure Figure Figure I. 2. 3. LIST OF FIGURES Examples of the ramp curve and breakpoint deter- ”inations I I I I I I I I I I I I I Representative plots of the 18-minute defined velocities protocol data . . . . . The relationship between Lbkl and Rbkl and the relationship between Lbk2 and Rka The mean VE/VO and lactate values from the 30- minute intermigtent runs . . . . . . . . . . . . . A plot indicating the relationship between the ramp curve and the 18-minute defined velocities protocol . . . . . . . . . . . . . . . . . . . . . An example of the training effect occurring between ramp 2 and ramp 3 . . . . . . . . . An uncharacteristic plot of the 18-minute defined velocities run data . . . . . . . . vii Page 26 28 32 34 . 36 37 I 38 CHAPTER I THE PROBLEM With progressive exercise the amount of carbon dioxide (002) expired exhibits a continuous increase but there comes a point when CO2 expired exhibits a slight increase in slope followed by a more abrupt increase in slope. This first increase. also known as the aerobic threshold. will be referred to as the first breakpoint (bkl) while the second increase will be called the second breakpoint (bk2). This abrupt increase or second breakpoint is identified as the onset of metabolic acidosis. and this breakpoint was first termed the "anaerobic threshold” (AT) by Hasserman et al. (63). The theory behind the AT states that when a high work rate is achieved during a progressive exercise test. the amount of oxygen supplied to the mitochondria may not meet the requirements of the working muscle. This imbalance results in an increase in anaerobic glycolysis which. in turn. causes an increase in pyruvic acid which is reduced to lactic acid in the cytosol. Because of the bicarbonate buffering system. the lactic acid is converted to sodium lactate and carbonic acid. and the carbonic acid dissociates to CO2 and water. As a result. ventilation increases in order to rid the body of the excess CO produced. By measuring the 2 gas exchange. the onset of metabolic acidosis or the AT can be detected ( 13. 56.59). 2 Green et al. (22). Yeh et al. (66) and Knuttgen and Saltin (39) accept the concept of the AT but are unable to accept the use of ventilation to define the AT as this is based on several assumptions. Therefore. the validity of predicting the onset of metabolic acidosis from an increase in ventilation is questionable (3). Because of the inability to confirm these assumptions and predictions. many investigators (3.24.29.36.63) are in opposition to the AT hypothesis. In a study by Gladden et al. (20) it was found that the AT is not very reproducible and there is little agreement between the Rbk2 (respiratory breakpoint 2) and 1.ka (lactate breakpoint 2). However. they did find strong correlations (r = 0.87 - 0.96) between the Rka as a dependent variable and the [.ka as the independent variable. This was also seen in many other studies (5.14.41.47.67). Gladden et al. (20) concluded that the ventilatory measurements and lactate measurements do not elicit the same AT. The Rka was found to occur at a higher intensity than the Lka. This conclusion was drawn by other investigators including Green et al. (23) and Yeh et al. (66) but this disagrees with previous research (5. 14.134.47.67) due to the methods of evaluation. 7 Despite the questions of validity concerning the assumptions made by Brooks (2) and the studies reporting a significant difference in work intensity between the Lka and Rka. numerous investigators (s. 11. l4.34.38.4l.47.48.63.67) have concluded that there at. no significant differences in the to at the m2 and Rka. Gladden et 2 al. (20) reported no significant difference between the mean 12ka and Lbk2 work intensities when evaluated by 8 different evaluators in addition to computer analysis. In studies by Caiozzo et al. (5). Davis et al. (12). and Reybrouck et al. (48) correlations of r = 0.93 - 0.98 3 between the Lbk2 and 12ka were reported. The Rbk2 reproducibility was investigated with the test-retest correlation in excellent agreement during incremental exercise (12.45). Furthermore. test-retest correlations ranging from r = 0.72 to r = 0.93 were reported in two studies (5.14) between the Rka and Lbk2. Significant correlations of r = 0.866 and r = 0.912 were determined between the 1.ka and 11ka when expressed in V0 values (36.69). 2 The methods of evaluation and the test protocol are critical factors in determining the relationship of the blood lactate concentration and the AT determined via gas exchange. According to Hughson and Green (30) the close relationship ”between the blood lactate concentration and the AT may be somewhat fortuitous and dependent on the ~rate of increase of work.” It is the various evaluation methods and test protocols which have led to conflicting. non-reproducible data causing some investigators to question the AT theory. Need for the study The AT has use as a predictor of maximal endurance performance as well as in exercise prescription (16) and routine clinical evaluation (20). with the ease in determining this measure via gas exchange methods. it is a simple measure with powerful. practical implications. A few studies have reported the AT occurring at the same work intensity when determined invasively and noninvasively: while. other studies have concluded just the opposite. These discrepancies center around differing protocols. exercise modes. and methods and criteria of measurement. Because of the power and practical implications 4 associated with the AT. the need for a protocol and criteria delivering valid determinations. both invasively and noninvasively. is necessary and critical. Purpose of the study The purpose of this study is to examine the relationship between Lbkl and Rbkl and the relationship between Lbk2 and Rka. Theoretically. Lbkl should occur at the same work intensity as Rbkl. and Lbk2 should occur at the same work intensity as Rka. It is the intent of this study to see if the theoretical considerations supporting the AT concept can be upheld. Research Hypotheses The hypotheses for the proposed study are: 1. There are two defined breakpoints in runners which occur over the course of a continuous. incremental treadmill test. 2. The velocity at which breakpoint 1 occurs is not significantly different when determined by respiratory parameters and lactate measurements. 3. The velocity at which breakpoint 2 occurs is not significantly different when determined by respiratory parameters and lactate measurements. Research Plan Nine actively training male runners were volunteer participants in this study. Each subject was initially tested twice on a continuous. incremental treadmill run called a ramp. From the second ramp respiratory breakpoints were determined. and these were used in the determination of the subsequent 18-minute defined velocity runs. Upon completion of this series of runs. a third ramp was performed. The next series of run velocities for the 30-minute intermittent protocol were ascertained from this ramp. Throughout every run expired gases were collected in 30 second intervals and analyzed for the percentage of 02 and 602. Venous lactate measurements were taken prior to each warm-up. 2 minutes after completion of the ramp protocol. 2 minutes after completion of each interval of the 18-minute defined velocities protocol. and immediately upon completion of each interval of the 30- minute intermittent protocol. Definitions Anaerobic threshold (AT) - V02 just below that at which metabolic acidosis and associated changes in gas exchange occur Lactate breakpoint 1 (Lbkl) - the work intensity in an incremental test at which lactate shows a sudden increase above resting levels Lactate breakpoint 2 (Lbk2) - the work intensity in an incremental test at which lactate shows a second abrupt increase above resting levels Respiratory breakpoint 1 (Rbkl) - the work intensity in an incremental test at which VE/VO2 shows an increase above resting levels Respiratory breakpoint 2 (Rka) - the work intensity in an incremental test at which VE/VO shows an abrupt 2 increase without a simultaneous increase in VE/VCO2 2 - the volume of oxygen consumed in liters per minute VCO2 - the volume of carbon dioxide exhaled in liters per minute (10 Limitations The results of this study apply only to reasonably fit male runners between the ages of 23 - 40. Each subject underwent a training effect in learning ‘to run on the treadmill. Also. motivational factors differed for each subject during each run. CHAPTER II REVIEW OR RELATED LITERATURE In the early 1930's Douglas and his colleague Owles (6.44) saw that an individual could exercise at particular work rates without showing an increase in lactate. However. upon reaching a certain level. the blood lactic acid concentration progressively increased. the bicarbonate ion concentration decreased. CO2 excretion increased. and ventilation was stimulated. These indicators of metabolic acidosis led Douglas and Owles to put forth a threshold concept in which exercise above this threshold would result in muscular lactic acid production (36). The term ”anaerobic threshold” (AT) was first coined by Wasserman et al. (63) in the early 1960s in response to an increase in the ventilatory equivalent (VB) and plasma lactate levels greater than the increase in oxygen uptake '(VOZ) at a given work rate. These events were seen in graded exercise with work increments between 1-4 minutes (48). The AT is the V02 at which muscle and blood lactate increase simultaneously (9) and the associated changes in gas exchange occur (30). This breakpoint has been defined by Wasserman et al. (61) as the "V02 at which aerobic metabolic processes can no longer meet the skeletal muscle requirements for ATP." In studies by Wasserman and McIlroy (60) and Vasserman (63) an increase in lactate accumulation after a specific work rate in 8 progressive exercise is seen. and it is believed that anaerobic metabolism occurs at this point of accumulation. and above the AT. anaerobic glycolysis must increase in order to supply muscle with the necessary ATP. Because the rate of anaerobic glycolysis increases. muscle lactate concentration increases. resulting in metabolic acidosis (22.51). Many other names have been given to the AT including. the onset of blood lactic acid (OBLA) (36.53). 4.0 mM threshold (25). lactate breakpoint (22) and the individual anaerobic threshold (38.55). Applications of the AT The AT is used by exercise scientists (5.17.45) as well as by cardiologists (8.41) and pulmonary physiologists (8.59) for use in exercise prescription (16). training studies. and routine clinical evaluation (20). In patients with cardiac and pulmonary problems. a low AT can be diagnostic (8.41) as it is believed the AT is a direct measure of the ”workload at which the cardiovascular system fails to supply adequate oxygen to the body tissues” (66). Another use of the AT measure is in determining cardiorespiratory endurance capacity (49.65) which is useful in ascertaining whether or not an individual has a large enough cardiopulmonary reserve so that he/she may be able to perform his/her job over an 8 hour shift (8). The use of the AT as a criterion measure has been gaining support in occupational medicine because individuals can be equated better by using their AT as compared to a specific percentage of the 702 max (8). 9 Furthermore. other applications of the AT include studying the effects of drugs on exercise tolerance (5.31). correlating the AT with biochemical properties and fiber composition of muscle (17.34.50.53). characterising endurance athletes (5.12). determining the optimal training intensity for endurance training (4.38.49.67). and predicting endurance performance (5.12.14.17.40.45.53.58.62.63.65.66). As a predictor of maximal endurance performance. the AT is better than the sex. to (40.49.64) although there is a significant 2 correlation between the AT and max. V0 . Individuals with similar max. 2 V02 values often exhibit different performances during an endurance event and with training. an individual's max. V02 may reach a plateau while his endurance performance continues to improve (12). The training stimulus is not individualised enough to minimise the variability witnessed when intensity is expressed as a percentage of max. V02. A particular percentage may be a high intensity for one person but a moderate intensity for another based on the lactate response; therefore. using the work intensity or the V02 where the AT occurs may be a better predictor of endurance performance capacity than max. lilo2 because the AT is more sensitive to interindividual differences such as training intensity and muscle fiber type (42.52). This suggests that good endurance performers could work at a greater submaximal load without an increase in blood lactate as compared to poor endurance performers (4.67). Rumagai et al. (40) used 17 runners to compare 5 and 10 km times to the AT and found a correlation of r = 0.95 while Powers et al. (45) used 9 runners and found a correlation of r = 0.94 between the AT and 10 km racing times. 10 The AT has been shown to be highly correlated to marathon performance. In a study by Farrell et al. (17) thirteen marathon runners ran a marathon. and their treadmill velocities which corresponded to the Lbk2 yielded a correlation of r = 0.98. Their average race pace was within 8 m/min of their running velocity at their AT. This led Farrell et al. to conclude that marathon runners run within 5% of their AT as opposed to some specific percentage of their V02 max. In another study by Tanaka et al. (57) it was determined that the average marathon running speed is almost the same as that determined on a treadmill at the AT. The concept of the AT is important in order to optimize both the cardiopulmonary and metabolic benefits of chronic exercise. Principle Mechanisms of Action According to Davis (68) there are five principles of action underlying the concept of the AT. They include the use of different metabolic substrates for energy production. an oxygen deficiency in muscle. the exceedence of the muscle oxidative capacity. a decrease in hepatic lactate clearance. and muscle fiber type recruitment. In terms of energy substrates. a study (33) was performed by Ivy et al. in which the subjects were given a fatty meal 5 hours before they were to perform an incremental bike test. The results show a small increase in both the Rka and Lbk2. so it has been suggested that the onset of metabolic acidosis is due to more than just an oxygen deficiency. A decrease in lactate is seen during exercise resulting from an increase in free fatty acid levels (8). 11 Many investigators (2.8.9.26) have indicated that an increase in blood lactate concentration occurs at the AT in response to a lack of oxygen to the exercising muscle. Wasserman. and McIlroy' (60). when initially using the term ”anaerobic threshold". assumed that there was a lack of oxygen in the working muscle causing in an increase in lactate as well as the lactate/pyruvate ratio (63). Another explanation given is that at the AT. it is believed oxygen delivery is adequate but that the oxidative capacity of the muscle is exceeded. In other words. the mmscle cannot process this oxygen fast enough. With endurance training the capacity of the oxidative enzymes increases (28) and the number and size of the mitochondria increase therefore. these changes may be responsible for the increase in the AT that is seen with training (8). Furthermore. when an individual is working at greater than 50-60% of his/her V02 max. there is a systemic increase in blood lactate (37.39.63). This may result. not because of an increase in lactate production. but because of a decrease in hepatic clearance (8). 0n the other hand. during exercise both production and clearance increase. but when the production rate increases steeply there is only a small blood concentration increase because of the clearance rate efficiency (66). According to Brooks (3) and Donovan. and Brooks (15) with intense exercise the tflood flow to the liver decreases because of an increase in vasoconstriction. Consequently. the lactate production is higher than lactate removal. At a work intensity at or above the AT. muscle lactate production exceeds its elimination so a continuous increase in blood lactate appears (1.55.61). 1.2 The type of muscle fiber that is recruited influences the production. release. and oxidation of lactate by muscle which. in turn. influences the blood lactate levels. Type I or slow twitch oxidative (SO) fibers contain low glycogen stores. have a high oxidative enzyme capacity. are fatigue resistant. are predominantly recruited at low to moderate work rates. and exhibit high H-LDH enzyme activity. Type II or fast twitch glycolytic (FG) fibers are highly glycolytic in nature and have 3 times the M-LDH activity of type I fibers. These fibers have a high glycogen content and are quick to fatigue. Fast twitch oxidative glycolytic (FOG) fibers are fatigue resistant. have a greater myoglobin content than FG fibers. and exhibit lower total LDH activity than FG fibers (32). M-LDH is most frequently found in muscle whereas H-LDH is most frequently found in heart. Because of the kinetic properties of the LDH isozymes. under physiological conditions. the muscle form favors the reduction of pyruvate to lactate while the heart form favors the oxidation of lactate to pyruvate. LDH is a near equilibrium enzyme so that when the rate of pyruvate formation from glycolysis exceeds the rate of pyruvate oxidation to acetyl CoA pyruvate accumulates and lactate is produced (21.36). At higher work rates. fast-twitch fibers are predominantly recruited. The recruitment of ‘these .highly glycolytic fibers could explain the increase in lactate production seen during a progressive exercise test. (8.54). There is a significant correlation between the percentage of slow-twitch fibers and the lactate AT (34). l3 Invasive Determination of the AT The Lbk2 has been determined by blood lactate measurements from various sources of blood including arterial samples (63.67). capillary measurements (38.47). the pulmonary artery (66) and the most common source. venous blood (5.7.14.24.34.54). The lactate levels may be different in each of these blood sources according to Green et al. (23) possibly because of a delay in the diffusion of lactate from muscle to blood due to translocation hindrances or because of the potential dissociation of lactate and hydrogen ion remval from muscle. Determining the AT via lactate measurements assumes that muscle and blood lactate concentrations increase at the same time although it does not necessarily have to be a quantitative relationship as the site where the blood sample was taken is not in the same area where the lactate was produced. As a consequence. some of the organs in between the sites of lactate production and measurement metabolize lactate (9). Yeh et al. (68) reported a 1.5 minute delay between arterial and venous lactate levels but similar breakpoints have been shown for muscle and arterial blood (37.39). and a correlation of r = 0.89 is seen at OBLA between blood and muscle lactates (l). Owles (44). in his early work. reported that the plasma lactate concentration was the balance between the entry and exit of lactate into the plasma. In other “words. the blood lactate concentration is dependent upon the rate of production. the rate of removal. and the rate of diffusion from the cells into the blood. Muscle lactate production occurs at rest as well as during exercise so lactate production is not the best indicator of the anaerobic state. 14 Factors regulating lactate production include LDH activity. the pyruvate concentration. and the extra-mitochondrial concentration of NADH (1.36). During its removal. plasma lactate undergoes one of two fates. First. muscle with a low lactate concentration takes up lactate and converts it to pyruvate which is used as a substrate in the TCA cycle during aerobic metabolism. Second. lactate is converted to glucose through the Cori cycle in the liver and kidney (36). Lactate is a small. easily diffusible molecule that rapidly diffuses from its cellular production site to all the water compartments of the body. A 5-10 minute period is necessary in order for muscle and blood lactate concentrations to reach equilibrium (21). A common misconception is that lactate is removed from muscle as fast as it is produced. so the point called the AT is just the point where lactate production exceeds removal. This is a remote possibility according to Davis et al. (14) since lactate rapidly diffuses into the water compartments of the body so even with very active lactate removal some of the lactate produced at the AT by exercising muscle will reach venous blood. Jones and Ehsram (36) have expressed similar views stating that changes in the plasma lactate concentration may not show a quantitative relationship to the efflux of hydrogen ions from muscle. A study by Jorfeldt et al. (37) shows that lactate released from exercising muscle levels off with increased muscle lactate concentration thus indicating a translocation hindrance for lactate in exercising muscle. The site of these hindrances may be extracellular or involve the cell membrane. Maximal muscular lactate release occurs at approximately the 4-5 mM concentration. 15 Another factor which influences lactate production is the intensity of the work load. Light to moderately heavy work (up to 50% 2 max.) leads to a blood lactate concentration that either remains unchanged or decreases slightly. Moderately heavy to heavy of the to work (50-85% of the V0 max.) shows a rapid increase in lactate during 2 the first 5-10 minutes of work followed by a leveling off or decline. A continuous increase in the lactate concentration until exhaustion or fatigue is seen in heavy work which is greater than 90% of the V02 max. (21). Aunola and Rusko (1) have suggested that at a work intensity less than that where OBLA occurs. lactate clearance from muscle is greater than the rate of diffusion into the blood. At an intensity greater than that of OBLA. muscle lactate production is greater than its elimination hence. a continuous increase in blood lactate appears. The use of blood lactate measures as an indicator of the work intensity where the AT occurs is based on the knowledge that. at low work levels during an incremental test. blood lactate remains at resting level values. but at some intensity lactate begins to increase and keeps increasing throughout the remainder of the exercise period. Various indices of lactate measure have been utilized in determining at what work intensity the AT occurs. This includes a slight increase in capillary lactate concentration (38.66). the nonlinear rise in venous lactate (66). the start of an exponential rise in venous lactate (66). and most commonly. the abrupt increase in venous lactate (14). Since the pKa of lactic acid is 3.8. almost all of it is ionized to lactate and hydrogen ion at cellular pH (59.60.61). A hydrogen ion from lactic acid is buffered by the bicarbonate system 16 thereby causing the cessation of a decrease in cellular pH. The buffer system consists of the following reactions: A lactic acid + NaHC03 : NaLA + H2003 ‘__ (:02 + azo (59). The lactic acid produced reacts with the bicarbonate ion forming carbonic acid. The enzyme carbonic anhydrase catalyzes the breakdown of carbonic acid to carbon dioxide and water. This reaction occurs intracellularly as well as on the endothelial surface of the muscle vasculature as this is where carbonic anhydrase is located (8). The carbon dioxide produced does not accumulate because when the buffer system is exceeded the respiratory chemoreceptors' are stimulated resulting in an increase in ventilation (18.30). In a study performed by Reybrouck et al. (48) long-term exercise was performed both above and below Rbk2. Throughout 40 minutes of exercise the pH remains constant at both exercise intensities while lactate accumulates at the work intensity performed above the Rbk2. In patients with no carotid bodies. elevated arterial P002 and a decreased pH during long-term exercise above the Rbk2 is seen. This study illustrates the importance of the carotid bodies as mediators of the ventilatory' response in response to metabolic acidosis. The effectiveness of this system produces only a small change in pH. There is a quick lung gas exchange so the CO2 produced is quickly blown off (59). Noninvasive Determination of the AT There have been numerous respiratory parameters used to identify the AT such as the nonlinear increase in the minute l7 ventilation (VE) (14.31.34.45). the nonlinear increase in \ICO2 (14.45.62). an abrupt increase in the respiratory quotient (VCOZ/VOZ) (14.43..59.60) and an increase in the ventilatory equivalent for osygen (VB/V02) without a simultaneous increase in the ventilatory equivalent for carbon dioxide (VE/RCOZ) (12.47.49). Wasserman and McIlroy (60) were the first investigators to indicate that measuring the pulmonary gas exchange via the mouth could be used to observe the commencement of metabolic acidosis. Since this time several groups of investigators (14.61.62) have indicated the use of gas exchange as an important and valid method of determining the AT and the onset of metabolic acidosis. The nonlinear increase in VB or ('002 used to detect the AT was first used by Wasserman et al. (63) in 1973. These were determined to be poor markers as it was difficult to identify just where an abrupt increase begins. A better detection measure for defining the AT established by Davis et al. (12) and Wasserman and Whipp (62) includes the increase in {IE/V02 without a simultaneous increase in VE/VCO2 because the increase in both measures occurs either after a period of no rate change or a decrease in rate change. This dual measure is specific in nature as 73/202 may increase in response to anxiety. pain. or hyperventilation but at the AT. {IE/\ICO2 remains stable due to isocapnic buffering (5.8.49.59). Caiozzo et al. (5) determined that of all the gas measures. an increase in {IE/VG2 without the simultaneous increase in {IE/{7C02 gave the best agreement with blood lactates in estimating the AT. Although the concept of the AT is well accepted. a few doubters remain. The protocol. exercise mode. and methods of evaluation all play a critical role in the determination of the AT. Therefore. it 18 is necessary for a protocol and criteria measurements that give rise to a valid and reproducible AT measure be established and reported. ‘The intent of this study is to compare the velocity at Lbkl with the velocity at Rbkl and the velocity at Lbk2 with the velocity at Rbk2 in an effort to determine if the protocol and evaluation criteria utilized produce a valid test for predicting the onset of metabolic acidosis in runners . CHAPTER III RESEARCH METHODS This study was performed with the intention of evaluating the relationship between Lbkl and Rbkl and between Lbk2 and Rbk2 in terms of the velocities at which these breakpoints were detected. Subjects Nine actively training male runners between the ages of 23 and 40 volunteered to be subjects for this study. Each subject completed an informed consent form upon receiving an explanation of the purpose and I risks involved during testing. Data Collection All testing was performed at the Center for the Study of Human Performance at Michigan State University. To determine at what velocity the subjects' breakpoints occurred. a continuous. incremental treadmill run to exhaustion was completed. This ramp protocol was done in duplicate. The run began at 5.1 mph and 0% grade. Every minute the speed was increased 0.3 mph until volitional exhaustion. The grade remained at 0% throughout the test. 19 20 Once 'the breakpoints were identified on. a ‘plot of VE/Vflh vs. velocity from the second ramp. it was possible to determine the velocity for each of the six subsequent 18-minute defined velocity runs. Rbkl was defined as the velocity where there is a slight increase in slope of {IE/1.102. while Rbk2 was defined as the velocity where VE/VO exhibits a second. more abrupt increase in slope. The run 2 speeds were determined as follows: 75% below Rbkl is Al run 25% below Rbkl is A2 run 25% above Rbkl is Bl run 25% below Rbk2 is B2 run 25% above Rbk2 is Cl run 75% above Rbk2 is C2 run. A latin square arrangement was used to determine run. order. Because of the ease of the A and 8 runs. an A run was combined with a 8 run during a single testing session. After an A run the subject was not able to begin the 8 run until his blood lactate concentration was at resting level or below. The C runs were not combined with any other run during a testing session. All runs were performed in duplicate with the exception of subjects C and I who were unable to complete runs 82. Cl. and CZ. The protocol for the above runs (18-minute defined velocities) consisted of. after a 5 minute warm-up at 5 mph. 3 minutes of running followed by 3 minutes of rest. This was repeated 3 times for a total of 9 minutes of work at the defined velocity and 9 minutes of rest. 21 A venous f ingerstick lactate sample was taken prior to warm-up. two minutes post warm-up. and two minutes into each rest period. When the six l8-minute defined velocity runs were completed in duplicate. a third ramp test was performed in order to examine any training effects. From this ramp the next set of run speeds were determined using the same criteria as before. The run speeds were determined by the following: 10% below Rbkl is A run 10% above Rbkl is Bl run 10% below Rbk2 is 82 run 10% above Rbk2 is C run. The protocol of the 30-minute intermittent runs consisted of a 5 minute warm-up at 6 miles per hour. followed by a 5 minute bout of work at the appropriate speed. Run order was again determined by a Latin square arrangement. At the end of the initial work period the subject was given 1 minute of rest. This procedure (5 minutes of work/ 1 minute of rest) was followed until 6 bouts of work were performed or until exhaustion. whichever came first. Venous fingerstick lactate samples were drawn prior to warm-up. immediately after the completion of each work bout. and 5 minutes after completion of the final work bout. Each run was performed during 1 testing session and on only 1 occasion. During the ramp tests and the l8-minute defined velocity runs. expired gases were collected in neoprene weather balloons in 30 second intervals using the open circuit Douglas bag method. In the 30-minute intermittent runs expired gases were collected in one minute intervals 22 until bag volume was met. At this point gases were collected in 30 second bags. A 2-way Daniels respiratory valve]. through which the subjects inspired. was connected to a 4-way automated switching valve2 by 2 feet of corrugated tubing with a 1.25 inch internal diameter. The percentage of CO and 02 in each of the bags was determined 2 using an infrared CO2 analyzer3 (Applied Electrochemistry CD-3A) and an electrochemical O2 analyzer (Applied Electrochemistry S-3A). A MM- 1154 dry gas meter was used to measure gas volumes. The gas was pumped through the meter at a rate of 50 liters per minute. Prior to each run the analyzers were zeroed using helium and then calibrated using a standard gas sample that had been verified for CO2 and 02 with a Haldane Chemical Analyzers. The blood samples were analyzed for their lactate concentration using an enzymatic-amperometric measurement with the Roche Model 640 Lactate Analyzer6. Treatment of the Data A paired t-test was utilized to detect any statistical significance between velocities at Lbkl and Rbkl as well as any statistical significance between velocities at Lbk2 and Rbk2. The relationship between velocities at the first breakpoint. determined by both respiratory parameters and blood lactate analysis. was examined by calculating the correlation coefficient. A correlation was also calculated between the paired velocities at which Rbk2 and Lbk2 were detected. 1 2 3 23 Footnotes RPel Company. Los Altos. CA. Van HussWells Automated Switching Valve. Applied Electrochemistry. Inc.. Sunnyvale. CA. 4 American Meter Co. (Singer). 5 6 Arthur H. Thomas C0.. Philadelphia. PA. Roche Bio-Electronics. Basel. Switzerland. CHAPTER IV RESULTS AND DISCUSSION The results of the study will be presented in the following order: physical measurements. the first design including ramp 2 and the 18-minute defined velocities protocol. and the second design including ramp 3 and the 30-minute intermittent protocol. A discussion of the results will follow. Physical Measurements In design one (n=9) the mean age (years). weight (kg). maximal heart rate (bpm). and maximal V02 (ml/minlkg) were 30.0 1 6.1. 73.2 t; 7.7. 180 t 15. and 61.4 :_4.3. respectively. The mean values for the same parameters for the subjects participating in design two were 30.9 1- 5.9. 73.3 t 8.2. 185 t 13. and 61.4 i 4.8. respectively. Table 1 contains the physical measurement data. Design One Respiratory breakpoint 1 and respiratory breakpoint 2 were determined from ramp 2 using the VE/VO vs. velocity plot. Three lines 2 were drawn on the curve following the increases in VE/VOZ. The intersection of the first two lines was termed the first breakpoint 24 25 Table 1 Physiological Measures. Design One (n=9) Age (yrs) 30.0 1 6.1 Weight (kg) 73.2 1_7.7 Max. Heart Rate (bpm) 180 + 15 Max. V02 (ml/kg/min) 59.7 1 4.6 Ramp 2 (n=9) v02 (ml/kg/min) Rbkl 42.5 i 6.4 Rbk2 53.7 i 5.5 % Max. V02 Rbkl 71 i 9 11ka 90 1 5 Design Two (n=8) 30.9 15.9 73.3 18.2 185 115 59.4 16.6 Ramp 3 (n=8) 47.7 14.9 55.5 H- 6.9 81 + 4 94 + 5 (Rbkl). and the intersection between the second and third lines was termed the second breakpoint (Rbk2) as Figure 1 illustrates. U.E/U.OZ i‘iPHi J 351 Subject D f- 30“ \\N¢ a. Rbk2 N 204 Rbkl O S 3 a. ma urn: '517'613'529'7Is'eIi'alrr313'sisiaIs' f Subject F 4.7—" . —.-——.—-.-_I. -..- - -- N tn 1 IN) 0 _.l._ ....- ..._- 15- 18- ‘sL7‘513‘ 6:9r7:518.1‘ at?“ 9.3!9.9'18:5'11:111:7712231 Figure 1 Examples of the ramp curve and breakpoint determinations. (The top two curves on either plot are not on scale.) 27 The mean velocity (mph). seen in Table 2. at Rbkl was 8.2 i 1.4 and at Rbk2. 10.5 i 1.0. From Table 1 it can be seen that the mean V02 (ml/min/kq) at Rbkl was 42.5 t 6.4 while at Rbk2 it was 53.7 1; 5.5. The mean % max. V02 (ml/min/kg) at Rbkl and Rbk2 was 71 1_9 and 90 1 5. respectively. Table 2 Breakpoint Velocities (mph) and Lactate Concentrations (mM). Ramp 2 Ramp 3 18-Minute Defined Lactate Velocities (n=9) (n=8) (n=9) (n=9) Rbkl 8.4 1 1.4 9.3 i 0.9 8.2 i 1.3 ---- Rbk2 10.5 i 1.0 10.8 i 1.1 9.9 11.0 --- Lbkl ---- --- 8.4 i 1.6 1.9 1 0.6 Lbk2 ---- ---- 10.2 1 0.9 3.2 2.1-2 ---- data not available lB-Minute Defined Velocities Protocol The VE/VO2 values were plotted vs. time at the six different testing speeds as shown in Figure 2. The corresponding lactate values obtained are also shown in Figure 2. 28 III-I “uni .mumv Hooououa mofiufiuoam> vocfiwoc ouscaeiwa on» we Amen“ CLUE:- o. a a k a _ u n a. a n a 1d I. on n a I l a I u .a t a a an o. a. 2 u. S I a. 0 z a~ an an .733 . I 2 ~33. . O a .ua.aau l a_ . an muoaa m>Humucomounmm N omswwm all-v Fu~UOJl> =15... . C ao-eaa . nu < ova—Jam l ‘otlan 29 As discussed before. three straight lines were drawn and the intersection of any two lines was determined to be a breakpoint. The first two points were connected to obtain the first line. points three and four were connected to obtain the second line. and the last two points were connected to obtain the third line. This is illustrated in Figure 2. Table 2 contains the 18-minute defined velocities breakpoint velocities. The mean velocities (mph) at Rbkl and Rbk2 were 8.2 1 1.3 and 9.9 1 1.0. respectively. A Lbkl mean value (mph) of 8.4 1 1.6 was obtained while the Lbk2 mean was determined to be 10.2 1 0.9. The lactate (mM) concentrations at Lbkl and Lbk2 are shown in Table 3. The mean lactate (mM) concentration at Lbkl was 1.9 1 0.6 and at Lbk2. 3.2 t 1.2. Statistical Analysis A correlation of 0.96 was determined between the velocities at Rbkl and Lbkl. and a correlation of 0.89 was calculated between the velocities at Rbk2 and Lbk2. Figure 3 shows the relationship between the velocities at Rbkl and Lbkl and the relationship between the velocities at Rbk2 and Lbk2. A paired t-test analysis between velocities at Rbkl and Lbkl indicated no significant difference. A paired t-test analysis between velocities at Rbk2 and Lbk2 also showed no significant difference. In both cases a probability level of .05 was accepted as significant. If a difference between mean velocities of 0.1 mph were to be considered an important difference such as in the case of breakpoint l. the probability of detecting significance with 6 subjects becomes less than 30 Table 3 Mean VE/VO Values and Lactate Concentrations (mM) from the 30-Minute Intermittent Protocol. RUN A B ZB C * data from one subject 24.2 t 1.3 21.2 12.7 22.4 1 1.2 27.1 14.7 k inte val 22.0 i 2.2 23.1 + 1.8 26.7 13.2 29.0 VE/VO 2 22.4 + 2.3 24.5 28.4* 23.4 + 1.9 25.8 + 2.4 27.9 + 4.9 23.6 1 1.7 27.1 Table 3 - Continued RUN 18 2B 2.4 10.6 5.7 l+ 1.9 8.4 2.5 l+ 2.8 H- 1.0 3.3 + 0.8 6.9 + 3.0 9.5 + 2.5 31 LACTATE (mM) work interval 3.5 H- 1.0 7.0 2.6 H- 3.8 : 1.2 7.1 12.5 5. 4* |+ H- |+ 2.5 1.2 1.3 7.0 2.5 2.5 11.1 4.2 i 1.3 7.5 12.6 * data from one subject Rbkl VELOCITY (mph) Rbk2 VELOCITY (mph) 11 10 11 10 32 7 8 9 10 11 Lbkl VELOCITY (mph) l l l l 7 8 9 10 11 Lbk2 VELOCITY (mph) Figure 3 The relationship between Lbkl and Rbkl and the relationship between Lbk2 and Rbk2. 33 4%. From a measurement standpoint detecting such a small difference is impractical but if one considers this from a performance standpoint. over the course of a 2.5 hour marathon this difference would amount to 440 yards. Design Two As before Rbkl and Rbk2 were determined from ramp 3 via the VE/Voz vs. velocity plot. Figure 1 indicates such a plot. To aid in a better. more accurate fit of the three straight lines. a smoothed curve was generated from the original plot. This was accomplished by taking a single data point and averaging this point with the data point immediately on either side of it. Using the same procedure and the newly generated curve. a second smoothed curve was produced. Over all subjects a mean Rbkl (mph) of 9.3 1 0.9 was obtained while the mean Rbk2 (mph) was determined to be 10.8 1 1.1 as seen in Table 2. 30-Minute Intermittent Protocol The second part of design two consisted of the 30-minute intermittent runs. Figure 4 shows the plot of the mean VEIVO vs. 2 time as well as the mean lactate vs. time for each of the four test runs. The mean respiratory and lactate values are found in Table 3. DISCUSSION During ramp 2 all subjects exhibited two obvious breakpoints. The same was also true of ramp 3. This fact is in agreement with many LACTATE (mM) ve/vo7 11 10 32 31 3O 29 28 27 26 24 23 22 21 3A C] [J- c r. .‘28 C)- 18 .. .‘A E] C] II c . I - I _ O o C) (3 (D e . e O O b l l i l l l 44 5 10 15 20 25 30 35 TIME (minutes) 8 single subject I - II t C] [:1 0* _ II II II r C) II L- D O _ I. C) L C) q. (I - C) 0 I ' 4| j- (I 1' .L l 1 L 1— l J 5 10 15 20 25 30 33 TIME (minutes) * single subject Figure 4 The mean VE/VO and lactate values from the 30-minute intermittent ITUIIS. 35 investigators who have reported the occurrence of two breakpoints during a progressive. incremental treadmill run. The 18-minute defined velocity runs when designed were expected to simulate the ramp curve and thus. would be another method of determining breakpoints. Figure 5 shows that this design may have entertained some validity; however. the six run velocities did not always conform to the ramp curve. At this point it is important to note the training effect that transpired over the course of the study. Figure 6 shows two ramp curves for subject G which portray a shift in the VE/VO2 providing evidence for a training effect. No restrictions were placed on the subjects in terms of their daily training. The study took place over a period of 3 months (March-May) when the subjects were preparing for the upcoming outdoor racing season. Interestingly. although a training effect can be seen between ramps 2 and 3 in terms of submaximal VE/VOZ. no significant change in the meanmax. 1.702 between ramps 2 and 3 was seen. For the subjects who did not show a significant training effect between ramp 2 and ramp 3. plotting the data from the six 18-minute defined velocity runs suggests that it may be possible to use such a protocol to determine breakpoints. However. as Figure 7 indicates. this may not be true for all subjects. In addition to training. there may be other factors limiting the use of this protocol. From the paired t-test analyses between velocities at Lbkl and Rbkl and between velocities at Lbk2 and Rbk2. it was determined that there was no significant difference in velocity at the running speeds where these breakpoints occurred. This disagrees with the conclusions stated by Powers et al. (45) who suggests that Rbk2 and Lbk2 do not 36 .mcou moauaooao> commune ouocfieiwa ecu com o>moo damn one monsoon mane icoaumaom ecu wcfiumoficcfi moan < m omswam «Jamdumd m6 n6 «.a m.~. m6 mé p _ p . _ r .L _ . . . m _ p . F . . Ln t. . cam \ .333; oooamoa ooocazima u. m ooohoom h.m L no.“ rma -QN -mN tom rmm 2m: 20'0/3'0 II 111 II: rt- 4‘ Isa 0 1'1." . M J L}. (L1 01 L. LI.) Lil p... (m 37 7 i f 1 $ ! -j; l l J ranu) 3 3 a rang) 3 j _.'i . I '517‘ 6.3] 6.9’ 715' aifefi' 9:3' 91.91815 Figure 6 An example of the training effect occurring between ramp 2 and ramp 3. 38 (H') ELVLDV'I muncHEImH mzu mo uoHa owumwumuumumsocs a< ~— .Mumv can mmwuwuon> tweammv Agnew rafioogu> Ad on o m ouswwm ~12.— 1 d A uh