Showing papers by "Michael Gleeson published in 1988"

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

Abstract: Five healthy male subjects exercised for 3 min at a workload equivalent to 100% $$\dot V_{{\text{O}}_{{\text{2 max}}} } $$ 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 $$P_{{\text{CO}}_{\text{2}} } $$ (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.

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

Abstract: 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% VO2max. 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 less than 0.01) and HCLF (219 +/- 69 s; p less than 0.05) diets.(ABSTRACT TRUNCATED AT 250 WORDS)

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

Abstract: 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;\(\dot V_{O_{2\max } }\) = 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\(\dot V_{O_{2\max } }\) 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<001) Pre-exercise blood bicarbonate (HCO3−) concentration,\(P_{CO_2 }\) and base excess (BE) were lower after F compared with ND (p<005) Prior to exercise, circulating concentrations of free fatty acids (FFA), gb-hydroxybutyrate (B-HB) and glycerol were higher after F compared with ND (p<001) 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<001) than on ND; blood lactate concentration was significantly lower for the whole of the post-exercise period after F compared with ND (p<001) 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.

Abstract: 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 (VO2max) 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% VO2max 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 arterialized-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 less than 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 less than 0.001, p less than 0.01, p less than 0.01 respectively) and normal (p less than 0.05, p less than 0.05, p less than 0.05 respectively) CHO diets when compared with the low CHO diet.(ABSTRACT TRUNCATED AT 250 WORDS)