Effect of acute mild hypoxia during exercise on plasma free and sulphoconjugated catecholamines

Catecholamine (CA) response to hypoxic exercise has been investigated during severe hypoxia. However, altitude training is commonly performed during mild hypoxia at submaximal exercise intensities. In the present study we tested whether submaximal exercise during mild hypoxia compared to normoxia leads to a greater increase of plasma concentrations of CA and whether plasma concentration of catecholamine sulphates change in parallel with the CA response. A group of 14 subjects [maximal oxygen uptake, 62.6 (SD 5.2) ml · min^–1 · kg^–1 body mass] performed two cycle ergometer tests of 1-h duration at the same absolute exercise intensities [191 (SD 6) W] during normoxia (NORM) and mild hypoxia (HYP) followed by 30 min of recovery during normoxia. Mean plasma concentrations of noradrenaline ([NA]), adrenaline ([A]), and noradrenaline sulphate ([NA-S]) were elevated (P < 0.01) after HYP and NORM compared with mean resting values and were higher after HYP [20.9 (SEM 3.1), 2.2 (SEM 0.24), 8.12 (SEM 1.5) nmol · 1^–1, respectively] than after NORM [(13.7 (SEM 0.9), 1.5 (SEM 0.14), 6.8 (SEM 0.7) nmol · 1^–1, respectively P < 0.01]. The higher plasma [NA-S] after HYP (P < 0.05) were still measurable after 30 min of recovery. From our study it was concluded that exercise at the same absolute submaximal exercise intensity during mild hypoxia increased plasma CA to a higher extent than during normoxia. Plasma [NA-S] response paralleled the plasma [NA] response at the end of exercise but, in contrast to plasma [NA], remained elevated until 30 min after exercise.     

Influence of moderate cold exposure on blood lactate during incremental exercise

Summary This study examined the effect of exposure of the whole body to moderate cold on blood lactate produced during incremental exercise. Nine subjects were tested in a climatic chamber, the room temperature being controlled either at 30°C or at 10°C. The protocol consisted of exercise increasing in intensity in 35 W increments every 3 min until exhaustion. Oxygen consumption (VO₂) was measured during the last minute of each exercise intensity. Blood samples were collected at rest and at exhaustion for the measurement of blood glucose, free fatty acid (FFA), noradrenaline (NA) and adrenaline (A) concentrations and, during the last 15 s of each exercise intensity, for the determination of blood lactate concentration [la^–]_b. TheVO₂ was identical under both environments. At 10°C, as compared to 30°C, the lactate anaerobic threshold (Th_{an, la} ^–) occurred at an exercise intensity 15 W higher and [Th_{an, la} ^–]_b was lower for submaximal intensities above the Th_{an, la} ^– Regardless of ambient temperature, glycaemia, A and NA concentrations were higher at exhaustion while FFA was unchanged. At exhaustion the NA concentration was greater at 10°C [15.60 (SEM 3.15) nmol·l^–1] than at 30°C [8.64 (SEM 2.37) nmol·l^–1]. We concluded that exposure to moderate cold influences the blood lactate produced during incremental exercise. These results suggested that vasoconstriction was partly responsible for the lower [la^–]_b observed for submaximal high intensities during severe cold exposure.     

Psychomotor performance during prolonged exercise above and below the blood lactate threshold

Previous investigations from this laboratory have demonstrated that during graded exercise with exercise intensities increasing every 3 min until exhaustion the multiple choice reaction time (RT) decreased until the intensity exceeded the lactate threshold (LT) by approximately 25%, and then rapidly increased. The aim of this study was to follow up changes in RT during prolonged exercise at constant intensities above and below LT and to relate these changes to changes in venous blood lactate [La⁻]_b, and plasma catecholamine [CA]_pl concentration responses to the exercise. For this purpose eight young soccer players exercised for 20-min on a cycle ergometer at 10% above LT, and nine exercised for 60 min at an intensity 30% below LT. During both tests RT, heart rate (HR), as well as [La⁻]_b, and [CA]_pl were measured. Above LT, RT decreased from the 5th min until the end of exercise, whilst HR, [La⁻]_b, and [CA]_pl increased progressively. Significant inverse correlations were ascertained between RT and plasma adrenaline (r = − 0.651) and noradrenaline concentrations (r = − 0.678). During exercise below LT, RT decreased up to approximately 40 min, then it reached a nadir, and stabilized at this level. This was accompanied by only small changes in [La⁻]_b and [CA]_pl. The present findings would indicate that young athletes are able to maintain for a relatively long time, or even increase, their psychomotor performance during endurance exercise both below and above the LT. Accepted: 23 June 1997     

Plasma lactate concentration increases as a parabola with delay during ramp exercise

This study presents an elementary model of a system which relates plasma lactate concentration ([La^–]) during ramp exercise to its rate of accumulation (R _c) within its extramuscular distribution space (S). Under the parsimonious assumptions that R _c increases linearly with time (t) with a kinetic delay (), and that the volume of S is constant, it is shown that plasma [La^–] increases as a parabola with the kinetic delay when t increases. This elementary system model describes changes in plasma [La^–] observed in five healthy young subjects during ramp exercise on the cycle ergometer (1 W every 2 s) with great accuracy (r>0.99) with very small residuals (average value less than 0.01 mmol · l^–1), randomly distributed around the fitting curves. The delay between the beginning of exercise and the onset of increase in R _c could be due to the fact that at the corresponding work rates: (1) rate of lactate appearance (R _a), which is equal to the rate of lactate disappearance (R _d), is not modified from rest, since the exercising muscles work in fully aerobic conditions (hypothesis of the anaerobic threshold); or (2) the increase in R _a is associated with a similar increase in R _d. An alternate or complementary hypothesis is that, during ramp exercise, plasma [La^–] could reflect metabolic events within the muscles, with a significant delay.     

Kinetics of heart rate and catecholamines during exercise in humans

Summary To elucidate the role of factors other than the nervous system in heart rate (f _c) control during exercise, the kinetics off _c and plasma catecholamine concentrations were studied in ten heart transplant recipients during and after 10-min cycle ergometer exercise at 50 W. Thef _c did not increase at the beginning of the exercise for about 60 s. Then in the eight subjects who completed the exercise it increased following an exponential kinetic with a mean time constant of 210 (SEM 22) s. The two other subjects were exhausted after 5 and 8 min of exercise during whichf _c increased linearly. At the cessation of the exercise,f _c remained unchanged for about 50 s and then decreased exponentially with a time constant which was unchanged from that at the beginning of exercise. In the group of eight subjects plasma noradrenaline concentration ([NA]) increased after 30 s to a mean value above resting of 547 (SEM 124) pg · ml^–1, showing a tendency to a plateau, while adrenaline concentration ([A]) did not increase significantly. In the two subjects who became exhausted an almost linear increase in [NA] occurred up to about 1,300 pg · ml^–1 coupled with a significant increase in [A]. During recovery an immediate decrease in [NA] was observed towards resting values. The values of thef _c increase above resting levels determined at the time of blood collection were linearly related with [NA] increments both at the beginning and end of exercise with a similar slope, i.e. about 2.5 beats · min^–1 per 100 pg · ml^–1 of [NA] change. These findings would seem to suggest that in the absence of heart innervation the increase inf _c depends on plasma [NA].     

Response of left ventricular diastolic filling to graded exercise relative to the lactate threshold

Summary During incremental exercise, the left ventricular ejection fraction increases up to the intensity of the anaerobic threshold and tends to level off at higher exercise intensities. Since there is a correlation between the response of peak filling rate and ejection fraction to exercise, this study was conducted to determine whether the response of left ventricular diastolic function is similar to the response of systolic function relative to lactate threshold. Twelve healthy men performed two exercise tests on a cycle ergometer. In the first test, lactate threshold and maximal power output were determined. In the second exercise test, gated radionuclide ventriculography was performed at rest, at the lactate threshold intensity, and at peak exercise to measure ejection fraction and peak filling rate. Ejection fraction increased significantly from rest [mean (SD): 62 (5)%] to lactate threshold [76 (7) %] and did not change significantly from lactate threshold to peak exercise [77 (7)%]. Likewise, peak filling rate (normalized for stroke counts) increased from resting [6.1 (0.9)V _s · s^–1] to lactate threshold [9.4 (1.8)V _s · s^–1] and did not change significantly from lactate threshold to peak exercise [9.6 (2.9)V _s · s^–1]. There was no correlation between the change in peak filling rate and the change in ejection fraction from rest to lactate threshold. Thus, during incremental exercise, left ventricular diastolic function responds qualitatively similar to systolic function.     

Lactate uptake by forearm skeletal muscles during repeated periods of short-term intense leg exercise in humans

We investigated the role of the forearm skeletal muscles in the removal of lactate during repeated periods of short-term intensive leg exercise, i.e. a force-velocity (FV) test known to induce a marked accumulation of lactate in the blood. The leg FV test was performed by seven untrained male subjects. Arterial and venous blood samples for determination of arterial ([la^–]_a) and venous ([la^–]_v) plasma lactate concentrations were concomitantly taken at rest before the test, during the FV test at the end of each period of intensive exercise just before the 5-min between-sprint recovery period, and after the completion of the test at 2, 4, 6, 8, 10, 15, and 20 min of the final recovery. The arteriovenous difference in concentration for plasma lactate ([la^–]_a–v) was determined for each blood sample. During the test, [la^–]_a and [la^–]_v increased significantly (P < 0.001;P < 0.001) with significantly higher values for [la^–]_a (P < 0.001). At the onset of the test, [la^–]_a–v became positive and increased up to a braking force of 6 kg, correlating significantly with [la^–]_a (r = 0.61,P < 0.001) with power (r = 0.58,P < 0.001) during the test. At the end of the test, [la^–]_a, [la^–]_v and [la^–]_a–v decreased (P < 0.001;P < 0.001;P < 0.001 respectively) but were still higher than the basal values after 20-min of passive recovery. In conclusion, forearm skeletal muscles would seem to have been involved in the removal of lactate from the blood during the leg FV test, with an increase in lactate uptake proportional to the increase in plasma lactate concentration and power.     

Blood glucose responses in humans mirror lactate responses for individual anaerobic threshold and for lactate minimum in track tests

The equilibrium point between blood lactate production and removal (La^? _min) and the individual anaerobic threshold (IAT) protocols have been used to evaluate exercise. During progressive exercise, blood lactate [La^?]_b, catecholamine and cortisol concentrations, show exponential increases at upper anaerobic threshold intensities. Since these hormones enhance blood glucose concentrations [Glc]_b, this study investigated the [Glc] and [La^?]_b responses during incremental tests and the possibility of considering the individual glucose threshold (IGT) and glucose minimum (Glc_min) in addition to IAT and La^? _min in evaluating exercise. A group of 15 male endurance runners ran in four tests on the track 3000?m run (v _3km); IAT and IGT – 8?×?800?m runs at velocities between 84% and 102% of v _3km; La^? _min and Glc_min– after lactic acidosis induced by a 500-m sprint, the subjects ran 6?×?800?m at intensities between 87% and 97% of v _3km; endurance test (ET) – 30?min at the velocity of IAT. Capillary blood (25?μl) was collected for [La^?]_b and [Glc]_b measurements. The IAT and IGT were determined by [La^?]_b and [Glc]_b kinetics during the second test. The La^? _min and Glc_min were determined considering the lowest [La^?] and [Glc]_b during the third test. No differences were observed (P??1; r?=?0.096; P?? _min [285 (SD 21)] and Glc_min [287 (SD 20) m.?·?min^?1 r?=?0.77; P??]_b reached 5.0? (SD 1.1) and 5.3 (SD 1.0) mmol?·?l^?1 at 20 and 30?min, respectively (P?>?0.05). We concluded that for these subjects it was possible to evaluate the aerobic capacity by IGT and Glc_min as well as by IAT and La^? _min.     

Effect of the intensity of training on catecholamine responses to supramaximal exercise in endurance-trained men

In this study we investigated whether plasma catecholamine responses to the Wingate test are affected by the intensity of training in endurance-trained subjects. To do this we compared plasma adrenaline (A) and noradrenaline (NA) concentrations in response to a Wingate test in three different groups: specialist middle-distance runners (MDR) in 800-m and 1,500-m races, specialist long-distance runners (LDR) 5,000-m and 10,000-m races, and untrained subjects (UT). The maximal power (W _max) and the mean power (W) were determined from the Wingate test. Blood lactate (La), plasma A and NA concentrations were analysed at rest (La₀, A₀ and NA₀), immediately at the end of the exercise (A_max and NA_max) and after 5 min recovery (La_max, A₅ and NA₅). The ratio A_max/NA_max was considered as an index of the adrenal medulla responsiveness to the sympathetic nervous activity. At the end of the test, W _max and W were similar in the three groups but La_max was significantly greater in MDR compared to LDR and UT [15.2 (2.2) mmol l^–1, 11.7 (3.1) mmol l^–1, 11.6 (1.6) mmol l^–1, respectively, for MDR, LDR and UT; mean (SD)]. Concerning the plasma catecholamine concentrations in response to exercise, MDR and LDR A_max values [3.73 (1.53) nmol l^–1, 3.47 (0.74) nmol l^–1, respectively, for MDR and LDR] were significantly greater than those of UT [1.48 (0.32) nmol l^–1] who also exhibited the lowest NA_max values [11.09 (6.58) nmol l^–1] compared to MDR and LDR [20.43 (3.51) nmol l^–1; 15.85 (4.88) nmol l^–1, respectively, for MDR and LDR]. However, no significant differences were observed between the two trained groups either for A_max or NA_max. These results suggest that long-term endurance training can enhance plasma catecholamine concentrations in response to supramaximal exercise. However, as there were no significant differences between MDR and LDR A_max and NA_max values, the effect of the intensity of training remains to be clarified.     

Heart rate deflection related to lactate performance curve and plasma catecholamine response during incremental cycle ergometer exercise

The correlation between the behaviour of the heart rate/work performance (f _c W) curve and blood lactate ([la]_b) and plasma adrenaline/noradrenaline concentrations ([A]/[NA]) during incremental cycle ergometer exercise was investigated. A group of 21 male sports students was divided into two groups: group I, with a clear deflection of thef _c W curve; group II, without or with an inverse deflection of thef _c W curve. The aerobic threshold (Th_aer) and the lactate turn point (LTP) were defined. Between Th_aer and maximal work performance (f _c W _max) the behaviour of thef _c W curve as well as the behaviour of [la^–]_b and [A]. [NA] were described mathematically. Thef _c, systolic blood pressure (BP_S),W, [la^–]_b, [A] and [NA] at rest, Th_aer, LTP,f _c W _max, after 3 and 6 min of recovery (Re₃/Re₆) were calculated. A significant difference between the two groups could only be detected forf _c at LTP, Re₃ and Re₆ (P < 0.05). No significant, correlation could be found between individualf _c W-behaviour and individual time course of [la^–]_b, [A] and [NA]. However, a significant correlation was visible between [la^–/W-behaviour and individual catecholamine response. These results and the fact that the different flattening at the top of thef _c W curve was related to diminished stress-dependent myocardial function led us to the conclusion that it is possible that sympathetic drive is not directly involved in mechanisms of regulation between load dependentf _c and myocardial function. In addition, individualf _c W behaviour was independent of BP_S andW _max, or individual conditions of energy supply.     

Perceived exertion and blood lactate concentration during graded treadmill running

The purpose of this study was to investigate the influences of treadmill gradients on the rating of perceived exertion (RPE) at two fixed blood lactate concentrations ( [La^–]_b). Ten subjects performed three different incremental treadmill protocols by running either uphill (concentrically-biased), downhill (eccentrically-biased), or on the flat (non-biased). Individual data of each protocol were interpolated to reflect [La^–]_b corresponding to 2.0 and 4.0 mmol·l^–1. At 2.0 mmol·l^–1 [La^– _b, RPE and treadmill speed during downhill running were greater than during level running which was greater than during uphill running (p < 0.05) . Also, the downhill heart rate (HR) was greater than the uphill HR, and downhill minute ventilation ( ) was greater than the level . Treadmill speed was the only measure at 4.0 mmol·l^–1 [La^–]_b to differ between gradients. There was a moderate correlation of RPE with HR at both [La^–]_b (r = 0.73 at 2.0 mmol·l^–1;r = 0.48 at 4.0 mmol·l^–1) while treadmill speed was moderately correlated with RPE only at 2.0 mmol·l^–1 [La^–]_b (r = 0.70). The results of this study demonstrated that the degree of eccentric-bias during running exercise is an influence of perceived exertion at a moderate but not at a high exercise intensity.     

Blood ammonia and lactate concentrations during endurance exercise of differing intensities

Summary The purpose of this study was to examine the changes of blood ammonia concentration ([NH₃]_b) during endurance exercise of differing intensities on the cycle ergometer and to compare [NH₃]_b to the changes observed in the simultaneously monitored blood lactate acid concentrations ([la^–]_b) measurements. A group of 16 endurance-trained athletes participated in the first part of the study and performed exercise of 30 min duration in a randomized order at intensities of 85%, 95%, 100% and 105% of their individual anaerobic threshold (Th_an,ind; E85–E105) which had been determined beforehand by a cycle exercise test with stepwise increments in intensity. In the second part, 18 average endurance-trained sports students underwent exhausting intensive endurance exercise (IEE) with an intensity of 95% of Th_an,ind. An extensive endurance exercise (EEE) of the same duration at 85% of the Than,ind was carried out 2 days later. The [NH₃]_b increased constantly with increasing duration of all exercise. However, [la^–]_b only increased during exercise with intensities above the Th_an,ind (E105). The increase of [NH₃]_b was higher with higher exercise intensities. At IEE, [NH₃]_b was significantly higher from the 30th min than at EEE, whereas [la^–]_b increased from the 5th min. In conclusion, [la^–]_b responded more sensitively to the intensity of exercise than [NH₃]_b, but it is conceivable that in the future measurements of [NH₃]_b could be used to advise on the duration of endurance training. At present, however, the lack of experience and lack of appropriate values still hinders the systematic use of [NH₃]_b measurements in the physiological monitoring of sports training.     

Sustained noradrenaline sulphate response in long-distance runners and untrained subjects up to 2 h after exhausting exercise

Summary We investigated the response of plasma and platelet free catecholamine ([CA]) and sulphated catecholamine ([CA-S]) concentrations after an incremental treadmill test to exhaustion and during recovery. In triathletes (n = 9) plasma and platelet [CA] and [CA-S] were measured before, immediately after and 0.5 and 24 h after exercise. In long-distance runners (n = 9) and in controls (n = 10) plasma [CA] and [CA-S] were determined 2 h instead of 24 h after exercise. Platelet [CA] and [CA-S] remained unchanged throughout the study. Plasma [CA] increased after exercise in all groups (P<0.05) and returned to pre-exercise values within 0.5 h of recovery. Plasma sulphoconjugated noradrenaline concentration ([NA-S]) was elevated after exercise in the triathletes, long-distance runners and in controls [9.96 (SEM 0.84) nmol·1^–1, 11.8 (SEM 1.19) nmol·1^–1, 9.53 (SEM 1.10) nmol·l^–1, respectively;P<0.05] compared with resting values [7.13 (SEM 1.04) nmol·l^–1, 6.19 (SEM 0.56) nmol·l^–1, 6.76 (SEM 0.67) nmol·1^–1, respectively] and remained elevated after 0.5 h of recovery [9.94 (SEM1.14) nmol·l^–1, 10.96 (SEM 0.80) nmol·l^–1, 8.95 (SEM 0.99) nmol·l^–1, respectively;P<0.05]. In the long-distance runners and controls plasma [NA-S] remained elevated during 2 h of recovery [9.96 (SEM 0.76) nmol·l^–1, 9.03 (SEM 0.88) nmol·l^–1, respectively]. These results would indicate that plasma [NA-S] increases after sympathetic nervous system activation by an exhausting incremental exercise test and remain elevated up to 2 h after exercise.     

Hyperoxia during recovery from consecutive anaerobic exercises in the sickle cell trait

The sickle cell trait (HbAS) does not affect anaerobic exercise performance. However, lower blood lactate concentrations ([La^–]) are consistently found during repeated anaerobic exercise in HbAS, and could be related to type of recovery. To study this, on three different occasions 17 HbAS and 17 matched control athletes (HbAA) underwent a series of three maximal cycle exercise tests of approximately 2-min duration, separated by 10-min recovery periods of rest, breathing either room air (P) or 100% oxygen (H) , or of light pedaling (A). In all tests, work performed, heart rate, blood hematocrit, and [La^–] were measured. Despite similar evolution of performance in each series of three anaerobic exercises, significantly lower [La^–] were consistently found in HbAS in P and A, compared to HbAA (P < 0.0001). However, in H, similar [La^–] was found in HbAS and HbAA. Higher mean heart rates were consistently measured in HbAS at exhaustion, and during the first 4 min of recovery, these differences being unrelated to type of recovery. We conclude that type of recovery does not influence subsequent performance in HbAS or HbAA. We speculate that improved regional oxygen availability in exercising muscle is associated with marked modification of lactate kinetics in highly trained HbAS, but not in similarly fit HbAA athletes.     

Muscle buffer capacity and aerobic fitness are associated with repeated-sprint ability in women

In addition to a high aerobic fitness, the ability to buffer hydrogen ions (H⁺) may also be important for repeated-sprint ability (RSA). We therefore investigated the relationship between muscle buffer capacity (m_{in vivo} and m_{in vitro}) and RSA. Thirty-four untrained females [mean (SD): age 19 (1) years, maximum oxygen uptake (O_2peak) 42.3 (7.1) ml·kg^–1·min^–1] completed a graded exercise test (GXT), followed by a RSA cycle test (five 6-s sprints, every 30 s). Capillary blood was sampled during the GXT and before and after the RSA test to determine blood pH (pH_b) and lactate concentration ([La^–]_b). Muscle biopsies were taken before (n=34) and after (n=23) the RSA test to determine muscle lactate concentration ([La^–]_i), hydrogen ion concentration ([H⁺]_i) pH_i, m_{in vivo} and m_{in vitro}. There were significant correlations between work decrement (%) and m_{in vivo} (r=–0.72, P<0.05), O_2peak (r=–0.62, P<0.05), lactate threshold (LT) (r=–0.56, P<0.05) and changes in [H⁺]_i (r=0.41, P<0.05). There were however, no significant correlations between work decrement and m_{in vitro}, or changes in [La^–]_i, or [La^–]_b. There were also no significant correlations between total work (J·kg^–1) during the RSA test and m_{in vitro}, m_{in vivo}, or changes in [La^–]_i, pH_i, [La^–]_b, or pH_b. There were significant correlations between total work (J·kg^–1) and both O_2peak (r=0.60, P<0.05) and LT(r=0.54, P<0.05). These results support previous research, identifying a relationship between RSA and aerobic fitness. This study is the first to identify a relationship between m_{in vivo} and RSA. This suggests that the ability to buffer H⁺ may be important for maintaining performance during brief, repeated sprints.     

Relationship between plasma potassium and ventilation during successive periods of exercise in men

Summary During and after two successive incremental cycle ergometer tests (tests A and B), plasma potassium concentration ([K⁺]_p), plasma pH (pH_p), plasma partial pressure of carbon dioxide, blood lactate concentration ([Lac^–]_b) and ventilation (V_E) were measured. While there was a good correlation between the increase in [K⁺]_p and V_E or pH_p, respectively, in test A, in test B a close correlation was found only between the increase in V_E and [K⁺]_p (r>0.9 for nearly all single cases; r was 0.84 and 0.89 for all (pooled) cases in tests A and B, respectively; the correlation coefficients between changes in pH_p and V_E in tests A and B were r=0.74 and r=0.28, respectively, and r=0.89 and r=0.10 between the changes in [Lac^–]_b and V_E in tests A and B). The close relationship for individuals between V_E and [K⁺]_p in tests A and B supported the hypothesis that the extracellular increase in [K⁺] may contribute to the ventilatory drive during exercise. The comparison of the results of tests A and B further indicated that the relationship between pH_p and V_E was dependent on the experimental design, and that pH_p and V_E changes are unlikely to be cause and effect.The study was carried out in the Centre of Physiology, Department of Sports- and Exercise Physiology, Medical School, W-3000 Hannover, Federal Republic of Germany     

Effect of acute sodium bicarbonate ingestion on excess C02 output during incremental exercise

Summary The effect of bicarbonate ingestion on total excess volume of CO₂ Output (CO₂ excess), due to bicaronate buffering of lactic acid in exercise, was studied in eight healthy male volunteers during incremental exercise on a cycle ergometer performed after ingestion (0.3 g · kg^–1 body mass) of CaCO₃ (control) and NaHCO₃ (alkalosis). The resting arterialized venous blood pH (P<0.05) and bicarbonate concentration ([HCO₃ ^–]_b;P<0.01) were significantly higher in acute metabolic alkalosis [AMA; pH, 7.44 (SD 0.03); [HCO₃ ^–]_b; 29.4 (SD 1.5) mmol·1^-1] than in the control [pH, 7.39 (SD 0.03); [HCO₃ ^–]_b, 25.5 (SD 1.0) mmol·1^–1]. The blood lactate concentrations ([la^–]_b) during exercise below the anaerobic threshold (AT) were not affected by AMA, while significantly higher [la^–]_b at exhaustion [12.29 (SD 1.87) vs 9.57 (SD 2.14) mmol·1^–1,P < 0.05] and at 3 min after exercise [14.41 (SD 1.75) vs 12.26 (SD 1.40) mmol · l^–1,P < 0.05] were found in AMA compared with the control. The CO₂ excess increased significantly from the control [3177 (SD 506) ml] to AMA [3897 (SD 381) ml;P < 0.05]. The CO₂ excess per body mass was found to be significantly correlated with both the increase of [la^–]_b from rest to 3 min after exercise ( [la^–]_b;r=0.926,P < 0.001) and with the decrease of [HCO₃ ^–]_b from rest to 3 min after exercise ( [HCO₃ ^–]_b;_r=0.872,P<0.001), indicating that CO₂ excess per body mass increased linearly with both [la^– _b and [HCO₃ ^–]_b. As a consequence, CO₂ excess per body mass per unit increase of [la^–]_b (CO₂ excess·mass^–1· [la^–]_b) was similar for the two conditions. The present results would suggest that the relationship between CO₂ excess and blood lactate accumulation was unaffected by acute metabolic alkalosis, because the relative contribution of bicarbonate buffering of lactic acid was the same as in the control.     

The effects of buffer ingestion on metabolic factors related to distance running performance

We examined the effects of sodium bicarbonate (BIC) and sodium citrate (CIT) ingestion on distance running performance. Seven male runners [mean = 61.7 (SEM 1.7) ml · kg^–1 · min^–1] performed three 30-min treadmill runs at the lactate threshold (LT) each followed by a run to exhaustion at 110% of LT. The runs were double-blind and randomly assigned from BIC (0.3 g · kg body mass^–1), CIT (0.5 g · kg body mass^–1) and placebo (PLC, wheat flour, 0.5 g · kg body mass^–1). Venous blood samples were collected at 5, 15 and 25 min during the run and immediately post-exhaustion (POST-EX) and analysed for pH, and the concentrations of lactate ([1a^–]_b) and bicarbonate ([HCO₃ ^– ]). Performance was measured as running time to exhaustion at 110% of LT (TIME-EX). The pH was significantly higher (P 0.05) for the BIC and CIT trials during exercise, but not POST-EX compared to PLC. The [1a^–]_b was significantly higher (P 0.05) for the CIT trial compared to PLC during exercise, and for both CIT and BIC compared to PLC at POST-EX. Blood [HCO₃ ^–] was significantly higher (P 0.05) during exercise for BIC compared to PLC. TIME-EX was not significantly different among treatments: BIC 287 (SEM 47.4) s; CIT 172.8 (SEM 29.7) s; and PLC 222.3 (SEM 39.7) s. Despite the fact that buffer ingestion produced favourable metabolic conditions during 30 min of high intensity steady-state exercise, a significant improvement in the subsequent maximal exercise run to exhaustion did not occur.     

The oxygen uptake-power regression in cyclists and untrained men: implications for the accumulated oxygen deficit

The regression of oxygen uptake (O₂) on power output and the O₂ demand predicted for suprapeak oxygen uptake (O_2peak) exercise (power output = 432 W) were compared in ten male cyclists [C, mean O_2peak = 67.9 (SD 4.2) ml · kg^–1 · min^–1] and nine active, yet untrained men [UT, mean O_2peak = 54.1 (SD 6.5) ml · kg^–1 · min^–1]. The O₂-power regression was determined using a continuous incremental cycle test (CON4), performed twice, which comprised several 4-min exercise periods progressing in intensity from approximately 40%–85% O_2peak. Minute ventilation (_E), heart rate (HR), respiratory exchange ratio (R), blood lactate concentration ([1a^–]_b) and rectal temperature (T _re) were measured at rest and during CON4. The slope of the O₂-power regression was greater (P 0.05) in C [12.4 (SD 0.7) ml · min^–1. W^–1] compared to UT [11.7 (SD 0.4) ml · min^–1 W^–1]; as a result, the O₂ demand (at 432 W) was also higher (P 0.05) in C [5.97 (SD 0.23) l · min^–1] than UT [5.70 (SD 0.15) 1 · min^–1]. ExerciseR and [la^–]_b were lower (P 0.05) in C .in comparison to UT at all power outputs, whereas _E and HR were relatively lower (P 0.05) in C at power outputs approximating 180 W, 220 W and 270 W. Differences in fat metabolism estimated over the first three power outputs accounted for approximately 19% of the difference in O₂-power slopes between the groups and up to 46% of the difference in O₂ at a given intensity. Although the O₂-power regressions were linear for C [r = 0.997 (SD 0.001)] and UT [r = 0.997 (SD 0.001)], the O₂-power slope was higher at power outputs at or above the lactate threshold (13.2 ml · min^–1 · W^–1 than at lower intensities (11.6 ml · min^–1 · W^–1) in C, an effect which was less profound in UT. As a result, the exclusion of O₂ at the highest power outputs completely abolished the difference in O₂-power slopes between C and UT. Thus, the relatively higher O₂ during incremental exercise in C can be almost entirely attributed to the higher O₂ cost of cycling at higher power outputs. In addition, the presence of non-linear responses in O₂ at higher intensities also confirms the invalidity of describing the O₂ response across a wide range of power outputs using a linear function, and challenges the validity of predicting the O₂ demand of more intense exercise by a linear extrapolation of this same function.     

Relationship between plasma ammonia and blood lactate concentrations after maximal treadmill exercise in circumpubertal girls and boys

Summary The purpose of the study was to define a relationship between plasma ammonia [NH₃]_p1 and blood lactate concentrations [1a^–]_b after exercise in children and to find out whether the [NH₃]_p1, determined during laboratory treadmill tests, may be useful as a predictor of the children's sprint running ability. A group of 20 girls and 14 boys trained in athletics or swimming and 8 untrained boys, aged 13.2 to 13.7 years, participated in the study. Their [NH₃]_p1 and [1a^–]_b were measured before and after incremental maximal treadmill exercise. In addition, the subjects' running performance was tested in 30-, 60- and 600- or 1000-m runs under field conditions. The [NH₃]_p1 during the treadmill runs increased by 20.1 (SD 17.3), 24 (SD 16.7) and 10 (SD 4.3) mol·1^–1 in the girls, the trained boys and the untrained boys, respectively. The postexercise [NH₃]_p1 correlated positively with [1a^–]_b (r=0.565 in the girls and 0.812 in the boys) and treadmill speed attained during the test (r=0.489 in the girls and 0.490 in the boys). Significant correlations were also found between [NH₃]_p1 obtained during the treadmill test and the times of 30- and 60-m runs (r= –0.676 and –0.648, respectively) in the boys but not in the girls. A comparison of the present data with those reported previously in adults showed that increases in [NH₃]_p1 during maximal exercise in children would seem to be lower than in adult subjects both in absolute values and in relation to [1a^–]_b. The present data would also suggest that [NH₃]_p1 reflects involvement of anaerobic processes during maximal treadmill exercise in circumpubertal children but it has a small practical value for predictiton of their sprint running ability.