Diet-induced metabolic acidosis and the performance of high intensity exercise in man

Summary The influence of four isolated periods of dietary manipulation upon high intensity exercise capacity was investigated in six healthy male subjects. Subjects consumed their normal (N) diet (45±2% carbohydrate (CHO), 41±3% fat, 14±3% protein) for four days after which they exercised to voluntary exhaustion at a workload equivalent to 100% . Three further four-day periods of dietary manipulation took place; these were assigned in a randomised manner and each was followed by a high intensity exercise test. The dietary treatments were: a low CHO (3±1%), high fat (71±5%), high protein (26±3%) diet (HFHP); a high CHO (73±2%), low fat (12±2%), normal protein (15±1%) diet (HCLF); and a normal CHO (47±3%), low fat (27±2%), high protein (26±2%) diet (LFHP). Acid-base status and blood lactate concentration were measured on arterialised-venous blood at rest prior to dietary manipulation on each day of the different diets, immediately prior to exercise and at 2, 4, 6, 10 and 15 min post-exercise. Other metabolite concentrations were measured in the blood samples obtained prior to dietary manipulation and immediately prior to exercise. Exercise time to exhaustion after the HFHP diet (179±63 s) was shorter when compared with the N (210±65 s; p<0.01) and HCLF (219±69 s; p<0.05) diets. Exercise time after the LFHP diet (188±63 s) was also reduced when compared with the HCLF diet (p<0.05) but not significantly when compared with the N diet. Immediately prior to exercise after the HFHP diet plasma pH, bicarbonate, blood PCO₂ and base excess levels were lower when compared with the N diet (p<0.05, p<0.001, p<0.001, p<0.001 respectively), the HCLF diet (p<0.05, p<0.001, p<0.01, p<0.001 respectively) and the LFHP diet (p<0.05, p<0.01, p<0.05, p<0.001 respectively). Levels of plasma bicarbonate and blood base excess were also lower after the LFHP diet when compared with the N (p<0.05) and HCLF (p<0.01, p<0.001 respectively) diets. Immediately prior to exercise, plasma free fatty acids (FFA; p<0.001, p<0.01, p<0.05), blood 3-hydroxybutyrate (3-OHB; p<0.05, p<0.05, p<0.05) and plasma urea (p<0.001, p<0.001, p<0.05) were all higher after the HFHP diet when compared with the N, the HCLF and the LFHP diets respectively; plasma total protein was higher when compared with the N diet (p<0.05). The results of the present experiment suggest that dietary composition influences acid-base balance by affecting the plasma buffer base and circulating non-volatile weak acids and by doing so may influence the time taken to reach exhaustion during high intensity exercise.     

The effects of diet on muscle pH and metabolism during high intensity exercise

Summary Five healthy male subjects exercised for 3 min at a workload equivalent to 100% on two separate occasions. Each exercise test was performed on an electrically braked cycle ergometer after a four-day period of dietary manipulation. During each of these periods subjects consumed either a low carbohydrate (3±0%, mean ±SD), high fat (73±2%), high protein (24±3%) diet (FP) or a high carbohydrate (82±1%), low fat (8±1%), low protein (10±1%) diet (CHO). The diets were isoenergetic and were assigned in a randomised manner. Muscle biopsy samples (Vastus lateralis) were taken at rest prior to dietary manipulation, immediately prior to exercise and immediately post-exercise for measurement of pH, glycogen, glucose 6-phosphate, fructose 1,6-diphosphate, triose phosphates, lactate and glutamine content. Blood acid-base status and selected metabolites were measured in arterialised venous samples at rest prior to dietary manipulation, immediately prior to exercise and at pre-determined intervals during the post-exercise period. There was no differences between the two treatments in blood acid-base status at rest prior to dietary manipulation; immediately prior to exercise plasma pH (p<0.01), blood (p<0.01), plasma bicarbonate (p<0.001) and blood base-excess (p<0.001) values were all lower on the FP treatment. There were no major differences in blood acid-base variables between the two diets during the post-exercise period. Compared with the CHO diet, the FP diet resulted in plasma alanine (p<0.05), blood lactate (p<0.05), and plasma glutamine (p<0.01) levels being lower immediately prior to exercise; plasma free fatty acids (FFA; p<0.05), glycerol (p<0.01), urea (p<0.001) and blood 3-hydroxybutyrate (3-OHB; p<0.01) levels were all higher. After the FP diet blood alanine, lactate and plasma glutamine levels were lower for the whole or the majority of the post-exercise period, while the concentrations of plasma FFA, glycerol, urea and blood 3-OHB and glucose were higher. There was no difference between the diets in pre-exercise glucose and insulin levels and post-exercise insulin levels. There was no difference in muscle pH between the two diets immediately prior to exercise; the decline in muscle pH was 104% greater during exercise on the FP diet resulting in a significant difference in post-exercise pH (p=0.05). The FP diet resulted in 23% decline in muscle glutamine levels, resulting in lower levels (p<0.05) immediately prior to exercise. Exercise had no influence on muscle glutamine levels after the FP diet but produced a 17% decline on the CHO diet. Muscle glycogen content increased by 23% on the CHO diet, but was unchanged after the FP diet. This resulted in levels being significantly different prior to exercise (p<0.05). The decline in muscle glycogen content during exercise was 50% greater on the CHO diet. There were no differences when comparing the two dietary treatments in any of the pre-exercise glycolytic intermediates measured. Immediately post-exercise glucose 6-phosphate levels were 22% higher and fructose 1,6-diphosphate levels were 130% lower on the FP diet. There were no differences between the two diets in muscle triose phosphate or lactate levels at any point of the study. The present study demonstrates that a FP diet can induce metabolic acidosis and may reduce pre-exercise muscle buffering capacity, which may then influence subsequent exercise performance. However, this appears not to influence the efflux of H⁺ from muscle during and after high intensity exercise.     

The effect of high-intensity exercise on the respiratory capacity of sceletal muscle

The effect of high-intensity exercise on the respiratory capacity of skeletal muscle was studied in horses which ran five 600-m bouts on a track with 2 min of rest between exercise bouts, or once to fatigue on a treadmill at an intensity that elicited the maximal oxygen uptake. Venous blood and biopsy samples of the middle gluteal muscle were collected at rest, after each exercise bout, and 30 and 60 min post-exercise. Blood samples were analyzed for lactate concentration and pH and muscle samples for metabolites, pH, and respiratory capacity. Venous blood and muscle pH declined to 6.91±0.02 and 6.57±0.02, respectively, after the fifth track run and to 6.98±0.02 and 6.71±0.07, respectively, after treadmill running. Muscle metabolite changes were consistent with the metabolic response to high-intensity exercise. Muscle respiratory capacity declined >20% (P<0.05) after a single exercise bout and was 45% of the control value after the fifth track run. Tissue respiration was depressed 60 min post-exercise but was normal 24 h later. These observations suggest that high-intensity exercise impairs the respiratory capacity of the working muscle. Although this occurred in parallel with reductions in pH, other factors could be responsible for this response.     

Glucose ingestion before and during exercise does not enhance performance of daily repeated endurance exercise

Summary The effect of glucose (Glc) ingestion before and during daily, repeated, prolonged exercise on metabolism and performance was tested. Seven young, healthy males performed cycling exercise in two series, with 1 month interval. Each exercise series consisted of 1 h/day on 3 successive days. On the 3rd day, exercise was continued until exhaustion. The intensity was 73.4 (7.7) % [mean (SD)] of maximal oxygen uptake ( ). Glucose (Glc) or placebo (P) drink was ingested 15 min before the start, and at 15 and 45 min of each daily exercise. The total amount of Glc ingested was 43.1 (4.2) g. During exercise, blood Glc concentrations were significantly higher (P<0.05) when Glc was ingested than when P was ingested [Glc 5.14 (0.32) and P 4.12 (4.17) mmol · 1^–1 at exhaustion]. However, Glc ingestion did not improve performance time to exhaustion [Glc 92.05 (29.55) and P 98.07 (27.33) min]. Free fatty acid concentrations were significantly lower when Glc was ingested than when P was ingested [Glc 0.63 (0.21) and P 1.39 (0.46) mmol · l^–1 at exhaustion]. There were no significant differences in exercise heart rate, , respiratory exchange ratio, blood lactate concentrations or rating of perceived exertion between the conditions nor were there any significant differences in these parameters on different days of exercise. It seems that ingestion of small amounts of Glc does not increase the metabolism of carbohydrate or improve the performance of intensive endurance exercise of poorly trained subjects, even when the exercise is repeated daily.     

Dietary composition and acid-base status: limiting factors in the performance of maximal exercise in man?

Summary Seven healthy male subjects exercised to exhaustion at a workload equivalent to 100% of their maximal oxygen uptake ( ) on 3 separate occasions. Each high intensity exercise test was performed on an electrically braked cycle ergometer; the first took place after a normal diet (46±8% carbohydrate (CHO), 41±7% fat and 13±3% protein); the second after 3 days of a low CHO diet (7±3% CHO, 64±5% fat and 29±4% protein) and the third after 3 days of a high CHO diet (76±6% CHO, 14±5% fat and 10±2% protein). Acid-base status and selected metabolites were measured on arterialised venous blood at rest prior to exercise and during the post-exercise period. Plasma urea concentration and urine total acidity were measured on each day of the experiment. Exercise time to exhaustion was longer after the normal (p<0.05) and high (p<0.01) CHO diets compared with the low CHO diet. Pre-exercise plasma bicarbonate concentration and blood were higher after the high CHO diet when compared with the normal (p=0.05, p<0.05 respectively) and low CHO conditions (p<0.05, p<0.05 respectively). Pre-exercise bicarbonate was also higher after the normal CHO diet when compared with the low CHO diet (p<0.05). Mean dietary acid intake for each 3 day period of dietary variation and plasma urea immediately prior to exercise were lower after the high CHO diet when compared to both normal (p<0.01, p<0.01) and low (p<0.01, p<0.001) CHO diets. They were also lower (p<0.01, p<0.01) after the normal when compared with the low CHO diet. Urine total acidity was higher after the low CHO diet when compared with both the normal (p<0.01) and high CHO (p<0.01) diets and near significance was found (p<0.06) when comparing the normal and high CHO diets. The present exsuggests that dietary variation alone can significantly affect the acid-base balance of the blood and may thereby influence endurance time during high intensity exercise.     

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.     

The effects of a glycogen loading regimen on acid-base status and blood lactate concentration before and after a fixed period of high intensity exercise in man

Summary Six healthy male subjects exercised after an overnight fast for a fixed 3 min period at a workload equivalent to 100% of their maximal oxygen uptake ( ) on 3 separate occasions. The first test took place after subjects had consumed a mixed diet (43±3% carbohydrate (CHO), 41±5% fat and 16±3% protein) for 3 days, and was followed 2 h later by prolonged cycling to exhaustion at 77±3% to deplete muscle glycogen stores. Following this, subjects consumed a low CHO diet (4±1% CHO, 63±5% fat and 33±6% protein) for the remainder of the day and for the subsequent 2 days; on the morning of the next day a second high intensity test took place. Finally subjects followed a 3 day high CHO diet (73±7% CHO, 17±6% fat and 10±1% protein) before their last test. Acid-base status and selected metabolites were measured on arterialised-venous blood at rest prior to exercise and at intervals for 15 min following exercise. Prior to exercise, plasma pH and blood lactate concentration were higher (p<0.05) after the high CHO diet when compared with the low CHO diet. Pre-exercise plasma bicarbonate, blood PCO₂ and blood base excess were all higher after the high (p<0.001,p<0.01,p<0.01 respectively) and normal (p<0.05,p<0.05,p<0.05 respectively) CHO diets when compared with the low CHO diet. During the post-exercise period there were no differences in plasma pH or blood base excess between the three experimental situations; plasma bicarbonate was higher (p<0.05) at 2 min post-exercise after the high CHO diet when compared with the low CHO diet; blood PCO₂ was higher throughout the post-exercise period after the high CHO diet when compared with the low CHO diet and at 2 min post-exercise was higher after the normal CHO diet than after the low CHO diet (p<0.5). The post-exercise blood lactate concentration after the high CHO diet was at all times higher than the corresponding values recorded after the normal CHO diet and until 15 min post-exercise was significantly higher than the values recorded after the low CHO diet. The present experiment further substantiates the view that a pattern of dietary and exercise manipulation can significantly influence the acid-base status of the blood and by doing so may influence high intensity exercise performance.     

Influence of sodium bicarbonate ingestion on plasma ammonia accumulation during incremental exercise in man

Summary This investigation evaluated the influence of metabolic alkalosis on plasma ammonia (NH₃) accumulation during incremental exercise. On two occasions separated by at least 6 days, six healthy men cycled at 70, 80, and 90%g of maximum oxygen consumption ( ) for 5 min; each exercise period was followed by 5 min of seated recovery. Exercise was then performed at 100% until exhaustion. Beginning 3 h prior to exercise, subjects ingested 3.6 mmol · kg body mass^– NaHCO₃ (test, T) or 3.0 mmol · kg body mass^–1 CaCO₃ (placebo, P) (both equivalent to 0.3 g · kg^–1) over a 2-h period. Trials were performed after an overnight fast and the order of treatments was randomized. Arterialized venous blood samples for the determination of acid-base status, blood lactate and plasma NH₃ concentrations were obtained at rest before treatment, 15 s prior to each exercise bout (Pre 70%, Pre 80%, Pre 90%, and Pre 100%), and at 0, 5 (5Post), and 10 (10'Post) min after exhaustion. Additional samples for blood lactate and plasma NH₃ determination were obtained immediately after each exercise bout (Post 70%, Post 80%, Post 90%) and at 15 min after exercise (15Post). Time to exhaustion at 100% of was not significantly different between treatments [mean (SE): 173 (42) s and 184 (44) s for T and P respectively]. A significant treatment effect was observed for plasma pH with values being significantly higher on T than on P Pre 70% [7.461 (0.007) vs 7.398 (0.008)], Pre 90% [7.410 (0.010) vs 7.340 (0.016)], and 10'Post [7.317 (0.032) vs 7.242 (0.036)]. The change in plasma pH was significantly greater following the 90%g bout (Pre 100% Pre 90%) for T [–0.09 (0.02)] than for P [–0.06 (0.01)]. Blood base excess and plasma bicarbonate concentrations were significantly higher for T than P before each exercise bout but not at the point of exhaustion. During recovery, base excess was higher for T than P at 5Post and 10Post while the bicarbonate concentration was higher for T than P at 10Post. A significant treatment effect was observed for the blood lactate concentration with T on the average being higher than P [7.0 (1.0) and 6.3 (1.1) mmol · l^–1 for T and P averaged across the 12 sampling times]. Plasma NH₃ accumulation was not different between treatments at any point in time. In addition, no differences were observed between treatments in blood alanine accumulation. The results suggest that under the conditions of the present investigation metabolic alkalosis does not influence plasma NH₃ accumulation or endurance capacity during intense incremental exercise.     

Effects of acute carbohydrate supplementation during sessions of high-intensity intermittent exercise

Abs tract The present study evaluated the acute effects of carbohydrate supplementation on heart rate (HR), rate of perceived exertion (RPE), metabolic and hormonal responses during and after sessions of high-intensity intermittent running exercise. Fifteen endurance runners (26 ± 5 years, 64.5 ± 4.9 kg) performed two sessions of intermittent exercise under carbohydrate (CHO) and placebo (PLA) ingestion. The sessions consisted of 12 × 800 m separated by intervals of 1 min 30 s at a mean velocity corresponding to the previously performed 3-km time trial. Both the CHO and PLA sessions were concluded within ∼28 min. Blood glucose was significantly elevated in both sessions (123.9 ± 13.2 mg dl⁻¹ on CHO and 147.2 ± 16.3 mg dl⁻¹ on PLA) and mean blood lactate was significantly higher in the CHO (11.4 ± 4.9 mmol l⁻¹) than in the PLA condition (8.4 ± 5.1 mmol l⁻¹) (P < 0.05). The metabolic stress induced by the exercise model used was confirmed by the elevated HR (∼182 bpm) and RPE (∼18 on the 15-point Borg scale) for both conditions. No significant differences in plasma insulin, cortisol or free fatty acids were observed during exercise between the two trials. During the recovery period, free fatty acid and insulin concentrations were significantly lower in the CHO trial. Supplementation with CHO resulted in higher lactate associated with lipolytic suppression, but did not attenuate the cortisol, RPE or HR responses.     

Energy metabolism and regulatory hormones in women and men during endurance exercise

Summary Gender differences in the changes substrates of carbohydrate and lipid metabolism as well as in adrenaline, noradrenaline, growth hormone, insulin and cortisol were investigated in 24 women and 24 men during exhaustive endurance exercise. Training history and current performance capacity were taken into consideration in the design of the study. Since previous papers present conflicting results the purpose of the present study was to obtain further information regarding possible gender differences in lipid metabolism and its regulation by hormones. Non-endurancetrained women and men each ran 10 km on a treadmill at an intensity of 75% of ; endurance-trained women and men ran 14 and 17 km, respectively, at an intensity of 80% of . Blood glucose levels in non-endurance-trained women were higher when compared to non-endurance-trained men. This might be explained by increased mobilization of free fatty acids from intramuscular fat depots during energy production in non-specifically trained women. In contrast, no substantial gender differences in endurancetrained persons were seen in lipid metabolism. The changes in substrates of lipid metabolism confirm the higher lipolytic activity and greater utilization of free fatty acids in endurance-trained persons. During endurance exercise, changes in adrenaline, noradrenaline, growth hormone, insulin and cortisol were not substantially affected by the sex of the subjects. This study does not present any conclusive results that endurance-trained persons show gender differences in lipid metabolism and major regulatory hormones. Supported by the Bundesinstitut für Sportwissenschaft K?ln, FRG     

Pulmonary gas exchange does not worsen during repeat exercise in women

The purposes were to determine (1) if repeat exercise worsens pulmonary gas exchange in women, and, (2) if the level of pulmonary edema obtained in these same women is related to the gas exchange impairment during exercise. Fourteen women (27 +/- 4 yrs; maximal oxygen uptake = 3.12 +/- 0.42 L/min) with minimal arterial PO2 (PaO2) ranging from 76 to 104 mmHg with a maximal alveolar-arterial PO2 difference (AaDO2) ranging from 7 to 35 mmHg performed three bouts of near-maximal exercise on a cycle ergometer (236 +/- 27 W) for 5 min each with 10 min of rest between sets. Cardiorespiratory parameters and oxygenation were measured at rest, throughout exercise and recovery. Chest radiographs were obtained before and 30 min after the interval training session (see Respir Physiol Neurobiol, 153 (2006) 181-190). Repeat exercise did not affect pulmonary gas exchange between sets 1 and 3 (change in PaO2 = 3 +/- 2 mmHg; change in AaDO2 = 1 +/- 2 mmHg P > 0.05). Arterial PCO2 decreased by 4 +/- 2 mmHg (P < 0.05) between sets 1 and 2, which did not reduce further in set 3. The level of PaO2 or AaDO2 was not related to the change in edema score or the post-exercise edema score (P > 0.05). In conclusion, pulmonary gas exchange is not worsened in women during interval training despite the mild edema triggered by exercise.     

The relation of ventilation to metabolic rate during moderate exercise in man

Summary To characterize more precisely the relationship between ventilation (V _E) and CO₂ output (VCO₂) during incremental exercise, 35 healthy males were studied at rest and during upright cycle ergometry, with the work rate incremented every 4 min up to each subject's anaerobic threshold ( _an). Twenty-one subjects had arterial blood sampled at rest and in the steady state at each work rate to determine the relationship between physiological dead space ventilation (V _D) and VCO₂. At these work rates arterial PCO₂ was regulated at the resting, control value. V _E (BTPS) was linearly related to VCO₂ from rest to _an with a slope of 24.6. However, the regression had a significant positive intercept of 3.2 L·min^–1. This causes the ventilatory equivalent for CO₂ (i.e., V _E/VCO₂) to decrease with increasing work rates. V _D also increased linearly with increasing VCO₂. However, this was consequent to increased breathing frequency as V _D remained constant. Thus, the observed fall in V _E/VCO₂ with increasing work rates is due to the positive intercept but the inherent relationship between V _E and VCO₂, reflected by the linear regression slope, remains unchanged from rest through moderate exercise.This investigation was supported by National Institutes of Health Grant HL-11907     

急性代谢性酸中毒时CSFpCO2在CSF酸碱调节中的作用

本文旨在探讨急性代酸时ＣＳＦｐＣＯ＿２在ＣＳＦ酸碱调节中的作用及其机制。４组急性代酸犬模型均由静脉内输入０．２ＮＨＣｌ产生，血浆［ＨＣＯ＿３－］ｌｈ内下降到１２±２ｍｍｏｌ／Ｌ，实验持续６ｈ。Ⅰ组控制ＰａＣＯ＿２常，６ｈ时ＣＳＦ［ＨＣＯ＿３－］下降了１．１ｍｍｏｌ／Ｌ；Ⅱ组自然呼吸，ＣＳＦｐＣＯ＿２伴随ＰａＣＯ＿２下降，６ｈ时ＣＳＦ［ＨＣＯ＿３－］下降了６．５ｍｍｏｌ／Ｌ；Ⅲ组机械通气，ＰａＣＯ＿２和ＣＳＦｐＣＯ２均迅速下降，６ｈ时ＣＳＦ［ＨＣＯ＿３－］下降了８．２ｍｍｏｌ／Ｌ；Ⅳ组控制ＰａＣＯ＿２正常，脑室注入乙酰唑胺，６ｈ时ＣＳＦ［ＨＣＯ＿３－］下降了１１．４ｍｍｏｌ／Ｌ。结果说明急性代酸时．ＣＳＦ［ＨＣＯ＿３－］取决于ＣＳＦｐＣＯ＿２。ＣＳＦＨＣＯ＿３－主要来源于ＣＮＳＣＯ＿２的水化作用，与ＣＡ活性显著相关。     

An acute oral dose of caffeine does not alter glucose kinetics during prolonged dynamic exercise in trained endurance athletes

This study investigated the possible influence of oral caffeine administration on endogenous glucose production and energy substrate metabolism during prolonged endurance exercise. Twelve trained endurance athletes [seven male, five female; peak oxygen consumption ( ) = 65.5 ml·kg^–1·min^–1] performed 60 min of cycle ergometry at 65% twice, once after oral caffeine administration (6 mg·kg^–1) (CAF) and once following consumption of a placebo (PLA). CAF and PLA were administered in a randomized double-blind manner 75 min prior to exercise. Plasma glucose kinetics were determined with a primed-continuous infusion of [6,6-²H]glucose. No differences in oxygen consumption ( ), and carbon dioxide production ( ) were observed between CAF and PLA, at rest or during exercise. Blood glucose concentrations were similar between the two conditions at rest and also during exercise. Exercise did lead to an increase in serum free fatty acid (FFA) concentrations for both conditions; however, no differences were observed between CAF and PLA. Both the plasma glucose rate of appearance ( ) and disappearance ( ) increased at the onset of exercise (P<0.05), but were not affected by CAF, as compared to PLA. CAF did lead to a higher plasma lactate concentration during exercise (P<0.05). It was concluded that an acute oral dose of caffeine does not influence plasma glucose kinetics or energy substrate oxidation during prolonged exercise in trained endurance athletes. However, CAF did lead to elevated plasma lactate concentrations. The exact mechanism of the increase in plasma lactate concentrations remains to be determined. Electronic Publication     

The influence of a respiratory acidosis on the exercise blood lactate response

Summary The purpose of the present study was to examine the influence of a respiratory acidosis on the blood lactate (La) threshold and specific blood La concentrations measured during a progressive incremental exercise test. Seven males performed three step-incremental exercise tests (20 W · min^–1) breathing the following gas mixtures; 21% O₂ balance-nitrogen, and 21% O₂, 4% CO₂ balance-nitrogen or balance-helium. The log-log transformation of La oxygen consumption (VO₂) relationship and a 1 mmol ·1^–1 increase above resting values were used to determine a La threshold. Also, theVO₂ corresponding to a La value of 2 (La2) and 4 (La4) mmol · 1^–1 was determined. Breathing the hypercapnic gas mixtures significantly increased the resting partial pressure of carbon dioxide (PCO₂) from 5.6 kPa (42 mm Hg) to 6.1 kPa (46 mm Hg) and decreased pH from 7.395 to 7.366. During the incremental exercise test,PCO₂ increased significantly to 7.2 kPa (54 mm Hg) and 6.8 kPa (51 mm Hg) for the hypercapnic gas mixtures with nitrogen and helium, respectively, and pH decreased to 7.194 and 7.208. In contrast, bloodPCO₂ decreased to 4.9 kPa (37 mm Hg) at the end of the normocapnic exercise test and pH decreased to 7.291. A blood La threshold determined from a log-log transformation [1.20 (0.28) 1·min^–1] or as an increase of 1 mmol·1^–1[1.84 (0.46) 1·min^–1] was unaffected by the acid-base alterations. Similarly, theVO₂ corresponding to La2 and La4 was not affected by breathing the hypercapnic gas mixtures [2.12 (0.46) 1·min^–1 and 2.81 (0.52) 1·min^–1, respectively]. Blood La values were reduced significantly at maximal exercise while breathing the hypercapnic gas mixtures (5.72±1.34 mmol ·1^–1) compared with the normocapnic test (6.96±1.14 mmol·1^–1). It is concluded that respiratory-induced acid-base manipulations due to the inspiration of 4% CO₂ have a negligible influence on the blood La response during a progressive exercise test at low and moderate power outputs. Lower blood La values are observed at maximal exercise with an induced respiratory acidosis but this negative influence is less than what has been reported for an induced metabolic acidosis.     

The effects of dietary manipulation on blood acid-base status and the performance of high intensity exercise

Summary The effect of a pattern of exercise and dietary modification, which is normally used to alter muscle glycogen content, upon the acid-base status of the blood and the ability to perform high intensity exercise was studied. Eleven healthy male subjects cycled to exhaustion on an electrically braked cycle ergometer at a workload equivalent to 100% of their maximal oxygen uptake ( ) on three separate occasions. The first exercise test took place after a normal diet (46.2±6.7% carbohydrate (CHO)), and was followed by prolonged exercise to exhaustion to deplete muscle glycogen stores. The second test was performed after three days of a low carbohydrate diet (10.1±6.8% CHO) and subsequently after three days of a high CHO diet (65.5±9.8% CHO) the final test took place. Acid-base status and selected metabolites were measured on arterialised venous blood at rest prior to exercise and during the post-exercise period. Exercise time to exhaustion was longer after the normal (p<0.05) and high (p<0.05) CHO dietary phases compared with the low CHO phase. Resting pre-exercise pH was higher after the high CHO diet (p<0.05) compared with the low CHO diet. Pre-exercise bicarbonate, PCO₂ and base excess measurements were higher after the high CHO treatment compared with both the normal (p<0.01,p<0.05,p<0.01 respectively) and low CHO phases (p<0.001,p<0.01,p<0.001 respectively). Daily dietary acid intake, estimated from food composition tables, was higher than normal during the low CHO diet and lower than normal during the high CHO diet. The present investigation suggests that a predetermined regimen of dietary and exercise variation can significantly affect blood acid-base status and may thereby influence high intensity exercise performance.     

The effects of training on the metabolic and respiratory profile of high-intensity cycle ergometer exercise

Summary The tolerable work duration (t) for high-intensity cycling is well described as a hyperbolic function of power (W):W=(W'·t ⁻¹)+W _a , whereW _a is the upper limit for sustainable power (lying between maximumW and the threshold for sustained blood [lactate] increase,Θ _lac), andW' is a constant which defines the amount of work which can be performed >W _a . As training increases the tolerable duration of high-intensity cycling, we explored whether this reflected an alteration ofW _a ,W' or both. Before and after a 7-week regimen of intense interval cycle-training by healthy males, we estimated (^)Θ _lac and determined maximum O₂ uptake ;W _a ;W'; and the temporal profiles of pulmonary gas exchange, blood gas, acid-base and metabolic response to constant-load cycling at and aboveW _a . Although training increased (24%), (15%) andW _a (15%),W' was unaffected. For exercise atW _a , a steady state was attained for , [lactate] and pH both pre- and post-training, despite blood [norepinephrine] and [epinephrine] ([NE], [E]) and rectal temperature continuing to rise. For exercise >W _a , there was a progressive increase in (resulting in at fatigue), [lactate], [NE], [E] and rectal temperature, and a progressive decrease for pH. We conclude that the increased endurance capacity for high-intensity exercise following training reflects an increasedW asymptote of theW−t relationship with no effect on its curvature; consequently, there is no appreciable change in the amount of work which can be performed aboveW _a . Furthermore, regardless of training status,W _a represents the upper power limit at which , blood [lactate] and blood pH can eventually be stabilized. Exercise >W _a , in contrast, is characterized by a steadily increasing and blood [lactate], a falling blood pH and consequently, imminent fatigue. Supported in part by a UCLA Graduate Division Doctoral Research Award     

The effect of sodium bicarbonate and sodium citrate ingestion on anaerobic power during intermittent exercise

Summary The effect of sodium bicarbonate and sodium citrate ingestion on cycling performance in three 30 s Wingate Anaerobic Tests separated by 6 min recovery periods has been studied using 6 male subjects. Subjects ingested either sodium bicarbonate (B), sodium bicarbonate plus sodium citrate (BC), sodium citrate (C) or sodium chloride (P) 2.5 h prior to exercise in a dose of 0.3 g kg⁻¹ body weight. Pre-exercise blood pH was 7.44±0.06, 7.42±0.05, 7.41±0.05 and 7.38±0.04 in the C, BC, B and P conditions respectively. Mean and peak power output were significantly reduced by successive Wingate tests but not significantly affected by the treatments. Performance in the second and third tests was highest following C, BC and B ingestion. The total work done in the 3 tests was 103%, 102% and 101% of that achieved in the P condition after C, BC and B ingestion respectively. The increased alkali reserve recorded subsequent to bicarbonate and citrate treatment reduced mean post-exercise acidosis, although pH was significantly higher only in the C condition (p<0.05) compared to P after each exercise bout. No significant differences in plasma lactate concentration were recorded at any time. Citrate ingestion appears to be most effective in elevating blood pH and [HCO₃ ⁻], and in enhancing performance in short-term intermittent exercise. This study demonstrates that alkali ingestion results in significant shifts in the acid-base balance of the blood and has a small, but non-significant, effect on anaerobic power and capacity as measured in a series of 3 Wingate Anaerobic Tests.