Bibliothek

Notizen: Deterium (2H) accumulation in the circulation was determined in 10 subjects after they ingested 7 ml · kg−1 of a dilute glucose-electrolyte solution that contained 10 g of 2H2O and was hot (50°C) on one occasion and cold (4°C) on another. In addition, 7 subjects repeated their first trial on a third occasion. Subjects fasted overnight and remained seated at rest during the experiment Blood 2H concentration was significantly greater at 5 min after ingestion of the hot as compared with the cold treatment and at 60 min for the cold as compared with the hot treatment The rate of blood 2H accumulation was not different when the same solution was ingested on different days. The results indicate that the rate of 2H accumulation is: 1) similar for hot and cold solutions and 2) reproducible when the same solution is ingested on different days. This implies that the rate at which dilute glucose-electrolyte solutions are made available to the body is not much influenced by the temperature at which they are ingested.

Notizen: Summary The effect of a pattern of exercise and dietary modifications, which was designed to produce alterations in the muscle glycogen content, on the capacity to perform anaerobic exercise was investigated. Six young male subjects worked to exhaustion on a bicycle ergometer at a supramaximal work load equivalent to 104±5% of $$\dot V$$ O2 max after a normal diet, after a carbohydrate (CHO)-free diet following prolonged exhausting exersise, and after a high-CHO diet. This regimen has previously been shown to cause changes in the glycogen content of the working muscle. Mean work time for subjects on the first test was 4.87±1.07 min (mean ± SD). After the low-CHO diet, the time for which work could be maintained was reduced to 3.32±0.93 min, whereas administration of the high-CHO diet resulted in an increase to 6.65±1.39 min. The resting blood lactate concentration was lower than normal following the low-CHO diet and higher than normal following the high-CHO diet. Post exercise blood lactate concentrations reached a peak between 2 and 6 min after exhaustion and again were lower (8.60±1.58 mmol/l) after the low-CHO diet and higher (12.86±1.42 mmol/l) after the high-CHO diet than after performing the same intensity of work to exhaustion on a normal diet (11.66±1.16 mmol/l). The rate of lactate accumulation appeared to be approximately the same during exercise under all three dietary conditions. If this is the case, it suggests that the alterations in endurance capacity do not result from changes in the rate of anaerobic glycolytic energy production, but possibly from a change in the total capacity of the system.

Notizen: Summary The influence of variations in muscle fibre composition on isometric endurance capacity was measured in 23 young healthy untrained male volunteers. After determination of the maximum voluntary force of contraction (MVC), subjects sustained to fatigue contractions at forces of 80%, 50% and 20% of MVC with a 5-min rest between each. A needle biopsy was obtained from m. vastus lateralis and used for histochemical determination of fibre composition based on myosin ATP-ase activity, and fibre are a based on succinate dehydrogenase (SDH) activity. Endurance times were 21±9 s (mean±SD) at 80% of MVC, 56±17 s at 50% of MVC and 203±89 s at 20% of MVC. A wide range of muscle fibre compositions was observed with Type I fibres accounting for 48.0±10.5% of the total, corresponding to 45.0±11.5% of the total muscle area. Muscle fibre composition, whether expressed as the proportions of the different fibre types present, or as the fraction of total muscle cross-sectional area occupied by each fibre type was not correlated with isometric endurance capacity at any of the three forces studied. Endurance time was also unrelated to MVC. In contrast to the results of previous studies where trained subjects were used, or where different muscle groups were compared, these results suggest that isometric endurance is not influenced by muscle fibre composition.

Notizen: Summary Six men were studied during exercise to exhaustion on a cycle ergometer at 73% of $$\dot V_{O_{2max} } $$ following ingestion of glycerol, glucose or placebo. Five of the subjects exercised for longer on the glucose trial compared to the placebo trial (p〈0.1; 108.8 vs 95.9 min). Exercise time to exhaustion on the glucose trial was longer (p〈0.01) than on the glycerol trial (86.0 min). No difference in performance was found between the glycerol and placebo trials. The ingestion of glucose (lg · kg−1 body weight) 45 min before exercise produced a 50% rise in blood glucose and a 3-fold rise in plasma insulin at zero min of exercise. Total carbohydrate oxidation was increased by 26% compared to placebo and none of the subjects exhibited a fall in blood glucose below 4 mmol · l−1 during the exercise. The ingestion of glycerol (lg · kg−1 body weight) 45 min before exercise produced a 340-fold increase in blood glycerol concentration at zero min of exercise, but did not affect resting blood glucose or plasma insulin levels; blood glucose levels were up to 14% higher (p〈0.05) in the later stages of exercise and at exhaustion compared to the placebo or glucose trials. Both glycerol and glucose feedings lowered the magnitude of the rise in plasma FFA during exercise compared to placebo. Levels of blood lactate and alanine during exercise were not different on the 3 dietary treatments. These data contrast with previous reports that have indicated glucose feeding pre-exercise produces hypoglycaemia during strenuous submaximal exercise and reduces endurance performance. It appears that man cannot use glycerol as a gluconeogenic substrate rapidly enough to serve as a major energy source during this type of exercise.

Notizen: Summary The acute effect of running a 42.2 km marathon race on plasma lipoproteins was investigated in 12 female subjects (aged 21 to 41 years). During the race there was a significant increase (P〈0.01) in the concentration of total plasma cholesterol. The mean post-race concentration of high density lipoprotein cholesterol (HDL-C) was 64.0±16.2 (SD) mg 100 ml−1, compared with 52.1±14.0 mg 100 ml−1 before the race, representing a significant increase (P〈0.002). There was no significant difference in the concentration of very low density lipoprotein (VLDL) or low density lipoprotein (LDL) before and after the exercise. The mean concentration of the cholesteryl ester moiety of the HDL increased from 43.7±12.3 to 54.3±15.7 mg 100 ml−1 (P〈0.002), while there was no significant change in the concentration of the unesterified cholesterol, phospholipid, triacylglycerol or protein moieties of the HDL. The relative proportions of apolipoproteins A-I, A-II, C and E remained unchanged during the exercise. The changes in the concentration of each of the lipoprotein fractions observed during the marathon varied considerably between subjects. The individual increases in the concentration of HDL-C ranged from 4.1 to 28.4 mg 100 ml−1, while both increases and decreases in individual concentrations of VLDL and LDL as well as of total plasma cholesterol were observed. These observations suggest that women undergo greater changes in HDL-C concentration than men during acute exercise, while considerable variation between individuals occurs.

Notizen: Summary 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.

Notizen: 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 ( $$\dot VO_{2\max } $$ ) for 5 min; each exercise period was followed by 5 min of seated recovery. Exercise was then performed at 100% $$\dot VO_{2\max } $$ 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 (5′Post), 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 (15′Post). Time to exhaustion at 100% of $$\dot VO_{2\max } $$ 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 5′Post and 10′Post while the bicarbonate concentration was higher for T than P at 10′Post. 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.

Notizen: Abstract This study examined the effect of the sodium content of drinks on the rehydration process after exercise. Six healthy male volunteers were dehydrated by a mean (SEM) of 1.9(0.0) % of body mass by intermittent cycle exercise in a warm (32°C), humid (54% RH) environment. Subjects exercised on four occasions at weekly intervals with each trial beginning in the morning, 3 h after a standard breakfast. Over a 30-min period beginning 30 min after the end of exercise, subjects ingested one of the four test drinks in a volume equivalent to 1.5 times their body mass loss. Drink composition was constant except for the sodium (and matching anion) content. Sodium content of drinks A, B, C and D was 2, 26, 52 and 100 mmol · l−1, respectively. Treatment order was randomised using a four-way crossover incomplete block design. Blood and urine samples were obtained before exercise, immediately before and after the rehydration period and at 0.5, 1.5, 3.5 and 5.5 h after the end of the rehydration period. Data were analysed by parametric or non-parametric statistical tests as appropriate. The volume of fluid consumed was the same on all trials [2045(45) ml]. From the 1.5-h sample onwards, a significant treatment effect on cumulative urine output was apparent, with the volume excreted being inversely related to the sodium content of the drink consumed. By the end of the trial, subjects were in net negative fluid balance on trials A [by 689(124) ml] and B [by 359(87) ml]; on trials C [−2(79) ml] and D [+98(67) ml], subjects were approximately euhydrated. Cumulative urinary sodium output was higher on treatment D than on the other trials after 5.5 h. Plasma volume was lower after exercise than before; on trials B, C and D, plasma volume was higher than the pre-exercise value from 0.5 h after the end of the rehydration period onwards. On trial A, plasma volume was higher than the pre-exercise value at 3.5 and 5.5 h after the end of the rehydration period. At 1.5 h after the end of the rehydration period, the increase in plasma volume was greater on trials C and D than on trial A. These results suggest that the fraction of the ingested fluid that was retained was directly related to the sodium concentration.

Notizen: Summary The acute effects of running a 42.2 km marathon race on the concentration and composition of the plasma lipoproteins were studied in 56 men of varying fitness, training experience, age and physical characteristics. There was no change in the mean concentration of total serum cholesterol, but a 10.9% increase (P〈0.001) in the mean concentrations of high-density lipoprotein cholesterol (HDL-TC), representing an 11.1% increase (P〈0.001) in the cholesteryl ester (CE) and 9.9% increase (P〈0.001) in the unesterified cholesterol (UC) moieties of HDL. The ratio of total serum cholesterol to HDL-TC decreased significantly (P〈0.001) during the exercise. Changes in lipoprotein concentrations during the marathon varied considerably between individual subjects, with a small proportion of subjects exhibiting relatively large increases or decreases in HDL-TC, HDL-CE and HDL-UC. Small sub-populations of runners were identified who showed abnormally large decreases in HDL-UC and abnormally small increases in HDL-CE relative to HDL-UC. A correlation (P〈0.05) was found between the average weekly mileage of training and the increase in HDL-TC, whilst faster runners (finishing time 〈3 h; n=13) had a significantly greater (P〈0.02) increase in HDL-TC than slower runners (〉4 h; n=14). The observed alterations in the lipoproteins are consistent with increased rates of lipolysis of triacylglycerol-rich lipoproteins and of cholesterol esterification during the marathon and suggest that the effect of exercise on the activities of the enzymes that catalyse these processes may vary considerably between different subjects and may be modulated by training and other factors.

Notizen: Summary Seven healthy male subjects exercised to exhaustion at a workload equivalent to 100% of their maximal oxygen uptake ( $$\dot V_{O_{2\max } }$$ ) 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 $${\text{P}}_{{\text{CO}}_{\text{2}} }$$ 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.