Respiratory and cardiac responses to exercise-simulating peripheral perfusion in endurance trained and untrained rats

Summary In endurance trained (TR) and untrained (UTR) rats heart rate (HR) and respiratory rate (RR) were recorded during perfusion of the circulatorily isolated hind leg of the rat with exercise simulating modified tyrode solutions (TR: n=10, UTR: n=10; compare part I). During the 20 min test period and the preceding and succeeding periods of control perfusions with an unmodified tyrode solution, [lactate], pH, [K⁺], [Na⁺], PO₂ and PCO₂ were measured in the outflow of the femoral vein. In 3 experimental series: (1) hypoxic tyrode solution enriched with lactic acid (15 mmol·l^–1), (2) normoxic solution with lactic acid, (3) hypoxic solution without lactic acid, were applied. The outflow parameters were cross correlated with both HR and RR. The analysis revealed a significant temporal relationship between [lactate], pH, PO₂, PCO₂ and [K⁺] and both HR and RR. In the trained rats no temporal correlation between either of the outflow and reflex parameters could be determined. This result was not due to low [lactate], but was also found during perfusion with lactic acid. In all 3 test conditions [lactate] in untrained individuals was best correlated with both HR and RR. Although the correlation peaks of the respiratory response, but not of the HR response were definitely lower in normoxic lactic and perfusion than in the two other experimental conditions, both inter- and intraindividual correlation analyses revealed a high degree of interdependence between respiratory and cardiac responses.Dedicated to J. Stegemann on the occasion of his 60th anniversaryThis work was supported by grants (No. 06/06040/68511) from the Minister für Wissenschaft und Forschung des Landes Nordrhein-Westfalen and the Görres Gesellschaft zur Pflege der WissenschaftPreliminary reports of this work was presented at the spring meetings of the Deutsche Physiologische Gesellschaft, March 1986, in Berlin and March 1987, in Homburg     

Blood lactate accumulation in intermittent supramaximal exercise

Summary Blood lactate accumulation rate and oxygen consumption have been studied in six trained male runners, aged 20 to 30 years. Subjects ran on a treadmill at a rate representing 172±5% for four 45 s sessions, separated by 9 min rest periods. Oxygen consumption was measured throughout. Blood lactate was determined in samples taken from the ear and was measured at the end of each exercise session, and two, five and nine minutes later. After the fourth exercise session, the same measurements were made every five min for 30 min. 4 subjects repeated a single exercise of the same type, duration and intensity and the same measurements were taken. With repetitive intermittent exercise, gradual increases in blood lactate concentration ([LA]b) occurred, whereas its rate of accumulation ([LA]b) decreased. The amount of oxygen consumed during each 45 s exercise session remained unchanged for a given subject. After cessation of intermittent exercise, the half-time of blood lactate was 26 min, whereas it was only 15 min after a single exercise session. values, on the other hand, returned to normal after 15 to 20 min. All other conditions being equal, the gradual decrease in [LA]b during intermittent exercise could be explained if the lactate produced during the first exercise session is used during the second period, and/or if the diffusion space of lactate increases. The diffusion space seems to be multicompartmental on the basis of half-time values noted for [LA]b after intermittent exercise, compared with those noted after a single exercise session. The distinction between the rapid return to normal values and the more gradual return to normal blood lactate levels confirms that there is no simple and direct relationship between oxygen debt and the accumulation of blood lactate after muscular exercise. In practical terms, these results show that the calorific equivalent of lactic acid defined by Margaria et al. (1963) cannot be used in the case of intermittent exercise of supramaximal intensity.     

Acute altitude exposure and altered acid-base states

Summary This study examined the influence of acute altitude (AL) exposure alone or in combination with metabolic acid-base manipulations on the exercise ventilatory and blood lactate responses. Four subjects performed a 4 min, 30 W incremental test to exhaustion at ground level (GL) and a 4 min, 20 W incremental test during three acute exposures to a simulated altitude of 4200 m; (i) normal (NAL), (ii) following 0.2 g·kg^–1 ingestion of sodium bicarbonate (BAL), and (iii) following 0.5 g·day^–1 ingestion of acetazolamide for 2 days prior to exposure (AAL). increased progressively throughout the incremental tests at AL and the minimum value was not related to a change in the blood lactate response. In contrast, the decreased initially to reach a minimum value at the same power output for each altitude trial and was related to a lactate threshold defined by a log-log transformation (r=0.78). This transformation of the blood lactate data was not influenced by the altered acid-base states. The relative exercise intensity corresponding to both a lactate of 1 mM and an absolute lactate of 4 mM was significantly increased during the AAL (79.9±12.9 and 93.9±13.7% , respectively) compared with NAL (59.1±5.5 and 78.0±5.8% , respectively). These data suggest that strong relationships exist between the ventilatory and blood lactate response during AL exposure and altered acid-base states. Further, it is concluded that, unless the acid-base status is known, the use of an absolute or lactate value to compare submaximal exercise should be interpreted with caution.     

Are oxygen uptake kinetics at the onset of exercise speeded up by local metabolic status in active muscles?

To assess the rate-limiting factor of oxygen uptake ( ) kinetics at the onset of exercise, six healthy male sedentary subjects performed repeated one-legged constant-load cycle exercise. The one-legged constant-load exercise test consisted of two 5-min periods of pedalling at an exercise intensity of 50 W, with a 5-min rest between periods (these exercise periods, i.e. first and second exercises, were performed by the same leg). The exercise was then repeated using the other leg. In addition, two-legged incremental exercise was investigated to establish whether kinetics were affected by slower heart rate kinetics. The incremental exercise test consisted of two-legged pedalling first with the cycle unloaded as a warm-up for 5 min followed by 50-W exercise for 5 min. The exercise intensity was then increased to 100 W for 5 min. During exercise, gas exchange parameters were determined by the breath-by-breath method and cardiac output ( ) was determined continuously by an impedance technique with a computer-based automated system. To determine the kinetics of heart rate (HR), and , a best fit procedure was employed using least-squares criteria with a time delay, except during the initial increase. During the one-legged constant-load exercise test, kinetics were significantly accelerated by repeated exercise using the same leg. On the other hand, when the exercise was changed to the other leg, kinetics were significantly slower, although kinetics continued to be faster. During the incremental exercise test, although the HR response was slower at the transition from 50-W to 100-W exercise than at the transition from warm-up to 50-W exercise, there were no significant changes in kinetics. These findings suggest that kinetics may be affected by metabolic conditions in the muscle, but not by blood flow ( and/or HR) kinetics.     

A method for determining the maximal steady state of blood lactate concentration from two levels of submaximal exercise

The aim of this study was to estimate the characteristic exercise intensity _CL which produces the maximal steady state of blood lactate concentration (MLSS) from submaximal intensities of 20 min carried out on the same day and separated by 40 min. Ten fit male adults [maximal oxygen uptake _max 62 (SD 7) ml · min^–1 · kg^–1] exercisOed for two 30-min periods on a cycle ergometer at 67% (test 1.1) and 82% of _max (test 1.2) separated by 40 min. They exercised 4 days later for 30 min at 82% of _max without prior exercise (test 2). Blood lactate was collected for determination of lactic acid concentration every 5 min and heart rate and O₂ uptake were measured every 30 s. There were no significant differences at the 5th, 10th, 15th, 20th, 25th, or 30th min between , lactacidaemia, and heart rate during tests 1.2 and 2. Moreover, we compared the exercise intensities _CL which produced the MLSS obtained during tests 1.1 and 1.2 or during tests 1.1 and 2 calculated from differential values of lactic acid blood concentration ([1a^–]_b) between the 30th and the 5th min or between the 20th and the 5th min. There was no significant difference between the different values of _CL [68 (SD 9), 71 (SD 7), 73 (SD 6),71 (SD 11) % of _max (ANOVA test,P<0.05). Four subjects ran for 60 min at their _CL determined from periods performed on the same day (test 1.1 and 1.2) and the difference between the [la^–]_b at 5 min and at 20 min ( ([la^–]_b)) was computed. The [la^–]_b remained constant during exercise and ranged from 2.2 to 6.7 mmol · l^–1 [mean value equal to 3.9 (SD 1) mmol · l^–1]. These data suggest that the _CL protocol did not overestimate the exercise intensity corresponding to the maximal fractional utilization of _max at MLSS. For half of the subjects the _CL was very close to the higher stage (82% of _max where an accumulation of lactate in the blood with time was observed. It can be hypothesized that _CL was very close to the real MLSS considering the level of accuracy of [la^–]_b measurement. This study showed that exercise at only two intensities, performed at 65% and 80% of _max and separated by 40 min of complete rest, can be used to determine the intensity yielding a steady state of [la^–1]_b near the real MLSS workload value.     

Metabolic responses to light arm and leg exercise when sitting

Summary Seven male subjects performed progressive exercises with a light work load on an upper limb or bicycle ergometer in the sitting position. At any comparable work load above zero, arm exercise induced higher oxygen uptake, ventilation, heart rate, oxygen pulse, respiratory rate and tidal volume than leg exercise. At similar levels of above 0.45 1 · min^–1, heart rate and ventilation were higher during arm exercise. A close linear relationship between carbon dioxide output and oxygen uptake was observed during both arm and leg exercises, the slope for arm work being steeper. The ventilatory equivalent for gradually decreased during both types of exercise. The ventilatory equivalent for remained constant (arm) while it rose (leg) to a peak at 9.8 W and then gradually decreased. Ventilation in relation to tidal volume had a linear relationship with leg exercise, but became curvilinear with arm exercise after tidal volume exceeded 1100ml. The observed differences in response between arm and leg exercises at a given work load appear to be influenced by differences in sympathetic outflow due to the greater level of static contraction of the relatively small muscle groups required by arm exercise.     

Effect of high intensity interval training on 2,3-diphosphoglycerate at rest and after maximal exercise

Summary The purpose of this study was to examine the effect of intense interval training on erythrocyte 2,3-diphosphoglycerate (2,3-DPG) levels at rest and after maximal exercise. Eight normal men, mean ± SE=24.2±4.3 years, trained 4 days·week^–1 for a period of 8 weeks. Each training session consisted of eight maximal 30-s rides on a cycle ergometer, with 4 min active rest between rides. Prior to and after training the subjects performed a maximal 45-s ride on an isokinetic cycle ergometer at 90 rev·min^–1 and a graded leg exercise test (GLET) to exhaustion on a cycle ergometer. Blood samples were obtained from an antecubital vein before, during and after the GLET only. Training elicited significant increases in the amount of work done during the 45-s ride (P<0.05), and also in maximal oxygen uptake ( max: Pre=4.01±0.13; Post=4.29±0.07 l·min^–1;P<0.05) during exercise and total recovery (Pre=19.14±0.09; Post=21.45±0.10 l·30 min^–1;P<0.05) after the GLET. After training blood lactate was higher, base excess lower and pH lower during and following the GLET (P<0.05 for all variables). Training caused no significant differences in erythrocyte 2,3-DPG levels at rest (Pre=11.8±0.7; Post=12.1±0.7 mol·g^–1 hemoglobin (Hb);P>0.05), at exhaustion (Pre=12.0±0.8; Post=11.2±0.8 mol·g^–1 Hb;P>0.05) or during 30 min of recovery from the GLET. Additionally, acute exercise (pre-training GLET) did not effect any change in 2,3-DPG at exhaustion or during recovery from exercise compared to resting values. The higher max and total recovery values observed after training appear to be unrelated to 2,3-DPG levels. Under the present conditions, the role, if any, of 2,3-DPG in enhancing tissue oxygenation during increased metabolic demand remains obscure.Supported by grants from Miles Laboratories, Elkhart, Indiana, and the Ball State Graduate Student Research Fund     

Respiratory and cardiac responses to exercise — simulating peripheral perfusion in endurance trained and untrained rats

Summary Ventilatory and circulatory drives elicited by exercise-simulating perfusion of the circulatory isolated hindleg were examined in 10 trained (TR) and untrained (UTR) rats. TR were submitted to endurance training on a motordriven treadmill (30·min^–1 at a grade of 10%, 5 days a week for 30 min). Exercise was simulated by perfusion with modified tyrode solutions:I.) hypoxic, enriched with lactic acid (15 mmol·l^–1), II.) normoxic, enriched with lactic acid. III.) hypoxic without lactic acid. Perfusion was performed in anaesthetized animals through cannulae in the femoral artery and vein; the hindled was connected to the rest of the body only by nerve and bone. 10 min of control perfusion (normoxic tyrode solution) was followed by a 20 min test period and another 10 min control perfusion. Apart from heart rate (HR), respiratory rate (RR) and several outflow parameters were measured ([K⁺], [Na⁺], [lactate], pH, PO₂, PCO₂). During control periods HR was slightly higher in UTR than in TR (375.5±3.9 (SE) vs. 364.1±5.5 beats/min^–1,p<0.6 n.s.), and RR in UTR was significantly higher than those in TR (61.5±0.4 bpm vs. 55.5±3.9 breaths·min^–1,p<0.001). During the test periods both HR and RR in UTR increased significantly while in TR they did not (e.g. in series I mean HR and RR in UTR increased by 8.9±1.2 beats·min^–1 and 1.4±0.1 breaths·min^–1 respectively, whereas in TR the changes were-2.9±1.5 beats·min^–1 and -0.8±0.2 breaths·min^–1. A significant difference between UTR and TR can only partly be due to diminished venous [H⁺] caused by better H⁺ buffering in TR. Particularly in the tests with lactic acid, lactate was far above threshold level. It can be concluded that the metabolic stimulus and the afferent branch of the cardiorespiratory reflex have been attenuated by endurance training.Dedicated to J. Stegemann on the occasion of his 60^th anniversary     

Sex differences in endurance capacity and metabolic response to prolonged,heavy exercise

Summary In order to test for possible sex differences in endurance capacity, groups of young, physically active women (n=6) and men (n=7) performed bicycle ergometer exercise at 80% and 90% of their maximal oxygen uptakes ( ). The groups were matched for age and physical activity habits. At 80% the women performed significantly longer (P<0.05), 53.8±12.7 min vs 36.8±12.2 min, respectively (means ± SD). Mid-exercise and terminal respiratory exchange ratio (R) values were significantly lower in women, suggesting a later occurrence of muscle glycogen depletion as a factor in their enhanced endurance. At 90% the endurance times were similar for men and women, 21.2±10.3 min and 22.0±5.0 min, respectively. The blood lactate levels reached in these experiments were only marginally lower (mean differences 1.5 to 2 mmol·l^–1) than those obtained at , suggesting high lactate levels as a factor in exhaustion. The changes in body weight during the 80% experiments and the degree of hemoconcentration were not significantly different between men and women.     

CO2-dependent component of the neurogenic vascular tone in the cat

Complete vascular isolation of the hindlimbs was performed in vagotomized cats under Sodium Pentobarbital anesthesia. The hindlimbs were perfused at constant flow with blood kept at a constant and physiological , , and pH values by means of a specially designed pump-oxygenator system. The animals were hyperventilated with different CO₂ mixtures (0%, 5%, 7% and 10% in O₂) thereby changing blood gases and pH levels in the upper body but not in the hindlimb vascular bed. At body (mm Hg) of 13.7 ±1.0 (means±SE), 30.6±1.05, 40,4±0,9 and 58.4 ±2.9 the hindlimb perfusion pressure (mm Hg) was, respectively 124±7.6, 138±7.4, 156±11.9 and 187 ±15.1. These changes in perfusion pressure were still present after complete peripheral chemoreceptor denervation but were abolished after section of the spinal cord at the T₅ level. Since hindlimb perfusion pressure fell when body was lowered below physiological levels it is concluded that part of the neurogenic vascular tone of the hindlimbs is maintained by a CO₂ mediated stimulation of supraspinal structures.Supported by Grants of the British Columbia Heart Foundation and the Medical Research Council of Canada.     

The effect of O2 breathing on maximal aerobic power

Summary Time of performance, blood lactic acid concentration (L.A.), heart rate (H.R.) and maximal oxygen consumption ( ) were measured during air and oxygen breathin in 11 subjects performing a supramaximal exercise with an O₂ requirement of 70 to 80 ml/kg·min to exhaustion. In addition the subjects were tested for maximal aerobic power with an indirect method. In one subject the rate of lactic acid increase in blood was also measured.The measured with both the direct and the indirect method appears to be about 8% higher when breathing pure oxygen; lactic acid production rate decreases correspondingly. Maximal H.R. and maximal L.A. concentration were found to be the same.In submaximal exercise steady state H.R. is lower by about 8–9 beats/min when breathing oxygen. Also when breathing oxygen H.R. is a linear function of the work load.From experimental data obtained in subjects of different , breathing both air or O₂, the energy equivalent of L.A. could be calculated as amounting to about 47 ml of O₂ or 235 cal per g of L.A. produced.This work was supported by a grant from the National Research Council of Italy (C.N.R.)     

The effect of one-legged sprint training on intramuscular pH and nonbicarbonate buffering capacity

Summary To determine the effect of one-legged sprint training on muscle pH and nonbicarbonate buffering capacity (BC), 9 subjects completed 15 to 20 intervals at 90 RPM, 4 days a week for 7 weeks on a bicycle ergometer adapted for one-legged pedaling. Needle biopsies from the vastus lateralis and blood samples from an antecubital vein were taken at rest and twice during recovery (1 and 4 minutes) from a 60 s one-legged maximal power test on a cycle ergometer. pH one minute after exercise in both the trained and untrained legs following the training period was not different but both were higher than before training. BC increased from 49.9 to 57.8 mol HCl×g^–1×pH^–1 after training (p<0.05). Blood lactate levels after exercise were significantly higher for the trained leg when compared to the untrained leg after sprint training. Peak and average power output on the 60 s power test increased significantly after training. One-legged aerobic power ( ) significantly increased in the untrained and trained legs. Two-legged also improved significantly after training. These data suggest that nonbicarbonate buffering capacity and power output can be enhanced with one-legged sprint training. Also, small but significant improvements in were also observed.     

Influence of cold exposure on blood lactate response during incremental exercise

Summary This study examined the effect of acute exposure of the whole body to cold on blood lactate response during incremental exercise. Eight subjects were tested with a cycle ergometer in a climatic chamber, room temperature being controlled either at 24° C (MT) or at –2° C (CT). The protocol consisted of a step increment in exercise intensity of 30 W every 2 min until exhaustion. Oxygen consumption ( ) was measured at rest and during the last minute of each exercise intensity. Blood samples were collected at rest and at exhaustion for estimations of plasma norepinephrine (NE), epinephrine (E), free fatty acid (FFA) and glucose concentrations, during the last 15 s of each exercise step and also during the 1^st, 4^th, 7^th, and the 10^th min following exercise for the determination of blood lactate (LA) concentration. The , was higher during CT than during MT at rest and during nearly every exercise intensity. At CT, lactate anaerobic threshold (LAT), determined from a marked increase of LA above resting level, increased significantly by 49% expressed as absolute , and 27% expressed as exercise intensity as compared with MT. The LA tended to be higher for light exercise intensities and lower for heavy exercise intensities during CT than during MT. The E and NE concentrations increased during exercise, regardless of ambient temperature. Furthermore, at rest and at exhaustion E concentrations did not differ between both conditions, while NE concentrations were greater during CT than during MT. Moreover, an increase of FFA was found only during CT. The difference in FFA level suggests that alterations in fat metabolism, possibly initiated by an enhanced secretion of NE, may have contributed to a decrease in lactate production.     

Times to exhaustion at 100% of velocity at\dot V{\text{O}}_{\text{2}} max and modelling of the time-limit / velocity relationship in elite long-distance runners

The aim of this study was to measure running times to exhaustion (Tlim) on a treadmill at 100% of the minimum velocity which elicits _{max max} in 38 elite male long - distance runners _max = 71.4 ± 5.5 ml.kg^–1.min^–1 and _max = 21.8 ± 1.2 km.h^–1). The lactate threshold (LT) was defined as a starting point of accelerated lactate accumulation around 4 mM and was expressed in _max. Tlim value was negatively correlated with _max (r = -0.362, p< 0.05) and _max (r = –0.347, p< 0.05) but positively with LT (%v _max) (r = 0.378, p < 0.05). These data demonstrate that running time to exhaustion at _max in a homogeneous group of elite male long-distance runners was inversely related to _max and experimentally illustrates the model of Monod and Scherrer regarding the time limit-velocity relationship adapted from local exercise for running by Hughson et al. (1984) .     

Effect of an increase in{\text{Hb}}_{{\text{O}}_{\text{2}} } affinity on the calculated capillary recruitment of an isolated rat heart

The effect of an increase in hemoglobin O₂ affinity on myocardial O₂ delivery was studied in a blood perfused working rat heart preparation. In a first series of experiments P₅₀ ( for which saturation is 50%) was lowered by use of carbon monoxide. The heart was alternatively perfused with the blood sample of P₅₀=32 mm Hg and the blood sample of P₅₀=17 mm Hg. O₂ capacity of both samples was kept the same by appropriate hemodilution. In a second serie of experiments change of P₅₀ was obtained by the use of adult human erythrocytes containing hemoglobin creteil with a P₅₀ of 13.6 mm Hg. As P₅₀ decreased from 25 to 10 mm Hg, coronary sinus ( ) diminished from 26±2 to 18±2 mm Hg (–29±2%), coronary sinus O₂ content ( ) increased by 15±3%, myocardial oxygen consumption did not change significantly. The percentage of increase of coronary flow was 23±4%.Analysis of these results with a simple mathematical model of O₂ delivery suggest that increase in affinity is corrected by a simultaneous increase in coronary flow and capillary recruitment.This study was supported by contracts 74-7-0274 from D.G.R.S.T., 76-1-1755 from I.N.S.E.R.M. and a grant from the University of Paris VII     

The effects of dietary manipulation upon the respiratory exchange ratio as a predictor of maximum oxygen uptake during fixed term maximal incremental exercise in man

Summary This study examined the effects of dietary manipulation upon the respiratory exchange ratio ( ) as a predictor of maximum oxygen uptake ( ). Seven healthy males performed fixed term maximal incremental treadmill exercise after an overnight fast on three separate occasions. The first test took place after the subjects had consumed their normal mixed diet (45±5% carbohydrate (CHO)) for a period of three days. This test protocol was then repeated after three days of a low CHO diet (3±2% CHO), and again after three days of a high CHO diet (61±5% CHO). Respiratory gases were continuously monitored during each test using an online system. No significant changes in mean exercise oxygen uptake ( ), or maximum functional heart rate (FHR_max) were found between tests. Mean exercise carbon dioxide output ( ) and R were significantly lower than normal after the low CHO diet (bothp<0.001) and significantly higher than normal after the high CHO diet (bothp<0.05). Moreover, compared with the normal CHO diet, the R-time relationship during exercise was at all times significantly (p<0.001) shifted to the right after the low CHO diet, and shifted to the left, being significantly so (p<0.05) over the final 5 min of exercise, after the high CHO diet. As a result, predictions of based on the R-time relationship were similar to recorded after the normal CHO dietary condition (-1.5±1.9%), but higher after the low CHO diet (+14.8±3.9%,p<0.001) and lower after the high CHO diet (–7.0±4.5%,p<0.01). These results indicate that dietary manipulation can significantly affect respiratory gas exchanges during fixed term maximal incremental exercise, and by doing so can significantly influence predictions of based on R.     

Influence of a 24 h fast on high intensity cycle exercise performance in man

Summary The influence of a 24 h fast on endurance performance and the metabolic response to maximal cycle exercise was investigated in 6 healthy men (mean±SD: age = 21±7 years; weight = 73±10 kg; = 46±10 ml·kg^–1·min^–1). Subjects performed in randomised order two exercise bouts to exhaustion separated by one week. Test rides were performed in fasted (F) and post-absorptive (normal-diet, ND) conditions on an electrically braked cycle ergometer at a workload equivalent to 100% of . Acid-base status and selected metabolites were measured on arterialised venous blood at rest prior to exercise and at intervals for 15 mins following exercise. Exercise time to exhaustion was shorter after F compared with ND (p<0.01). Pre-exercise blood bicarbonate (HCO₃ ^–) concentration, and base excess (BE) were lower after F compared with ND (p<0.05). Prior to exercise, circulating concentrations of free fatty acids (FFA), gb-hydroxybutyrate (B-HB) and glycerol were higher after F compared with ND (p<0.01) but blood glucose and lactate concentration were not different. On the F treatment, after exercise, blood pH, HCO₃ ^–, and BE were all significantly higher (p<0.01) than on ND; blood lactate concentration was significantly lower for the whole of the post-exercise period after F compared with ND (p<0.01). Circulating levels of FFA and B-HB after exercise on the F treatment fell but levels of these substrates were not altered by exercise after ND. Blood glucose and glycerol concentrations increased following exercise on both treatments. The present study provides evidence that a 24 h fast is detrimental to high-intensity exercise performance and possibly influences the metabolic response following maximal cycle exercise. These changes may be related to the altered pre-exercise acid-base status and/or a change in the pattern of substrate utilisation.     

Oxygen debt: Involvement of the Cori cycle

Summary Tryptophan and quinolinic acid, inhibitors of gluconeogenesis, were used to block the removal of lactate by the liver in order to investigate the involvement of the Cori cycle in oxygen debt. Five male, mongrel dogs were run on a treadmill at 4 mph with a 20 percent grade for 19 min. The mean exercise was 80.67±3.11 ml/kg/min for the control tests while peak arterial lactate values ranged from 3.83 to 4.98 mM/l. When removal of lactate by the liver was blocked, oxygen debt showed a mean reduction of 44 percent. Moreover, oxygen consumption during the last minute of exercise was reduced by 11 percent.Fasting (72 h) was used in 1 dog to prevent the accumulation of lactate during exercise. This procedure reduced oxygen debt to the same level as when the removal of lactate by the liver was blocked with tryptophan and quinolinic acid.The data show that the lactacid as well as the alactacid component is involved in oxygen debt when lactate is being removed by the liver during the recovery period following exercise.     

Exercise-induced changes in blood ammonia levels in humans

Summary Five male and two female subjects each performed a maximal aerobic capacity ( ) test, and two to four submaximal aerobic exercise bouts (requiring approximately 50 and 80% of the individual's measured ) on a motor-driven treadmill. Pre-exercise resting oxygen uptakes ( ) and heart rates were determined and a venous blood sample drawn prior to each work session. These same measurements were repeated at 4, 15, 30, and 45 min of the resting recovery period that followed each exercise experiment. Additionally, at the 30th min of each 45-min submaximal exercise, another peripheral venous blood sample was drawn following determination of and heart rate. In all blood samples, the hematocrit and concentrations of ammonia, lactate, pyruvate, glucose, hemoglobin, and total plasma proteins were measured.A significant exponential relationship was observed betwen blood ammonia levels and for all sample periods (pre-exercise rest, exercise, and post-exercise recovery). Peripheral venous blood ammonia levels were significantly correlated with levels of pyruvate and lactate, as these latter substrates exhibited a similar exponential relationship with as was observed with ammonia.This work was supported in part by the Air Force Office of Scientific Research, Air Force Systems Command, Grant AFOSR 73-2455 and by the National Institutes of Health, Grant NIH HD00235-6     

Effects of previous exercise on the ventilatory determination of the aerobic threshold

Summary To study the effects of previous submaximal exercise on the ventilatory determination of the Aerobic Threshold (AeT), 16 men were subjected to three maximal exercise tests (standard test = ST, retest = RT, and test with previous exercise = TPE) on a cycle ergometer. The protocol for the three tests consisted of 3 min pedalling against 25 W, followed by increments of 25 W every minute until volitional fatigue. TPE was preceded by 10 min cycling at a power output corresponding to the AeT as determined in ST, followed by a recovery period pedalling against 25 W until returned to values consistent with the initial response to 25 W. AeT was determined from the gas exchange curves (ventilatory equivalent for O₂, fraction of expired O₂, excess of , ventilation, and respiratory gas exchange ratio) printed every 30 s. The results showed good ST×RT reliability (r=0.89). TPE showed significantly higher AeT values (2.548±0.44 l·min^–1) when compared with ST (2.049±0.33 l·min^–1) and RT (2.083±0.30 l·min^–1). There were no significant differences for the sub-threshold respiratory gas exchange ratios among the trials. The sub-threshold response showed significantly higher values for TPE at power outputs above 50 W. It was concluded that the performance of previous exercise can increase the value for the ventilatory determination of the AeT due to a faster sub-threshold response.Supported by fellowship number 3660/80-3, CAPES, Brazil