Search PubMed⌕ Search

Biomedical subjects

F Brouns

Publications and source records attributed to F Brouns.

At least 55 records · Page 3Linked to original sources

Effect of caffeinated drinks on substrate metabolism, caffeine excretion, and performance.

The effect of addition of different dosages of caffeine (Caf) to a carbohydrate-electrolyte solution (CES) on metabolism, Caf excretion, and performance was examined. Subjects (n = 15) ingested 8 ml/kg of water placebo (Pla-W), 7% CES (Pla-CES), or 7% CES with 150, 225, and 320 mg/l Caf (CES-150, CES-225, and CES-320, respectively) during a warm-up protocol (20 min) and 3 ml/kg at one-third and two-thirds of a 1-h time trial. Performance was improved with Caf supplementation: 62.5 +/- 1.3, 61.5 +/- 1.1, 60.4 +/- 1.0, 58.9 +/- 1.0, and 58.9 +/- 1.2 min for Pla-W, Pla-CES, CES-150, CES-225, and CES-320, respectively. The postexercise urinary Caf concentration (range 1.3-2.5 microg/ml) was dose dependent and always far below the doping level of the International Olympic Committee (12 microg/ml) in all subjects. Sweat Caf excretion during exercise exceeded postexercise early-void urinary Caf excretion. Caffeinated CES did not enhance free fatty acid availability, ruling out the fact that performance improvement resulted from enhanced fat oxidation. It is concluded that addition of relatively low amounts of Caf to CES improves performance and that postexercise urinary Caf concentration remained low.

Adult↗

Strategies to enhance fat utilisation during exercise.

Compared with the limited capacity of the human body to store carbohydrate (CHO), endogenous fat depots are large and represent a vast source of fuel for exercise. However, fatty acid (FA) oxidation is limited, especially during intense exercise, and CHO remains the major fuel for oxidative metabolism. In the search for strategies to improve athletic performance, recent interest has focused on several nutritional procedures which may theoretically promote FA oxidation, attenuate the rate of muscle glycogen depletion and improve exercise capacity. In some individuals the ingestion of caffeine improves endurance capacity, but L-carnitine supplementation has no effect on either rates of FA oxidation, muscle glycogen utilisation or performance. Likewise, the ingestion of small amounts of medium-chain triglyceride (MCT) has no major effect on either fat metabolism or exercise performance. On the other hand, in endurance-trained individuals, substrate utilisation during submaximal [60% of peak oxygen uptake (VO2peak)] exercise can be altered substantially by the ingestion of a high fat (60 to 70% of energy intake), low CHO (15 to 20% of energy intake) diet for 7 to 10 days. Adaptation to such a diet, however, does not appear to alter the rate of working muscle glycogen utilisation during prolonged, moderate intensity exercise, nor consistently improve performance. At present, there is insufficient scientific evidence to recommend that athletes either ingest fat, in the form of MCTs, during exercise, or "fat-adapt" in the weeks prior to a major endurance event to improve athletic performance.

Caffeine↗

Carbohydrate-electrolyte feedings improve 1 h time trial cycling performance.

Carbohydrate-electrolyte (CE) feedings have been shown to improve endurance performance at moderate intensities (60-75% VO2max) and or more than 2 h duration. The effects of CE feedings during high intensity exercise (i.e. > or = 80% VO2 max) of shorter duration (approximately 1 h) are less clear. Therefore the purpose of the present study was to investigate the effect of the ingestion of a 7.6% CE solution during exercise on time trial cycling performance of approximately 1 h. This type of performance testing has been shown to be more reproducible (coefficient of variation 3.35%) than the traditional exercise test to exhaustion. On two occasions and in random order nineteen endurance trained cyclists completed an exercise test requiring the accomplishment of a set amount of work as fast as possible (time trial) under strictly standardized conditions. As the start and during the trials they drank in total 14 ml/kg of either a 7.6% CE solution or artificially flavored and colored water (placebo). Time to complete the set amount of work was significantly reduced and thus performance was significantly increase (p < 0.001) with the CE drink by 2.3%. Time to complete the set amount of work was 58.74 +/- 0.52 min with CE and 60.15 +/- 0.65 min with placebo (p < 0.001). Average workload during the time trials was 297.5 +/- 1.4W and 291.0 +/- 10.3 W, respectively. Subjects exercised at 76.4 +/- 0.7% of their maximal work rate (Wmax) with CE and at 74.8% Wmax with placebo (p < 0.001). It was concluded tht also in relative short term (1h) high intensity (75% Wmax) cycling exercise ingestion of a carbohydrate-electrolyte solution compared to placebo improves performance.

Adult↗

Exercise performance, red blood cell deformability, and lipid peroxidation: effects of fish oil and vitamin E.

Previous studies have indicated that fish oil supplementation increases red blood cell (RBC) deformability, which may improve exercise performance. Exercise alone, or in combination with an increase in fatty acid unsaturation, however, may enhance lipid peroxidation. Effects of a bicycle time trial of approximately 1 h on RBC characteristics and lipid peroxidation were, therefore, studied in 24 trained cyclists. After 3 wk of fish oil supplementation (6 g/day), without or with vitamin E (300 IU/day), trial performance, RBC characteristics, and lipid peroxidation were measured again. RBC deformability appeared to decrease during endurance exercise. After correction for hemoconcentration, plasma total tocopherol concentrations decreased by 0.77 micromol/l (P = 0. 012) or 2.9% and carotenoid concentrations by 0.08 micromol/l (P = 0. 0008) or 4.5%. Endurance exercise did not affect the lag time and rate of in vitro oxidation of low-density lipoproteins (LDLs), but the maximum amount of conjugated dienes formed decreased by 2.1 +/- 1.0 micromol/mmol LDL cholesterol (P = 0.042) or 1.2%. Fish oil supplementation with and without vitamin E did not affect RBC characteristics or exercise performance. Both supplements decreased the rate of LDL oxidation, and fish oil supplementation with vitamin E delayed oxidation. The amount of dienes, however, was not affected. The supplements also did not change effects of exercise. We conclude that the changes observed during endurance exercise may indicate increased oxidative stress, but further research is necessary to confirm this. Fish oil supplementation does not improve endurance performance, but it also does not cause or augment changes in antioxidant levels or LDL oxidation during exercise.

Adult↗

Effects of carbohydrate (CHO) and fat supplementation on CHO metabolism during prolonged exercise.

The aim of the study was to examine carbohydrate (CHO) utilization in subjects receiving CHO or CHO + medium-chain triglycerides (MCT) supplements during 180 minutes of exercise at 50% maximal aerobic work rate ([Wmax] 57% maximal oxygen consumption [VO2max]). In a double-blind crossover design, nine trained athletes cycled four times. Subjects received a bolus of 4 mL x kg(-1) at the start and 2 mL x kg(-1) every 20 minutes during exercise of either a 150-g x L(-1) CHO solution (CHO trial), an equicaloric 70 energy% (en%) CHO-30 en% MCT suspension containing 29 g MCT (CHO + MCT trial), or a 150-g x L(-1) CHO (high-CHO [HCHO]) solution plus 20 g MCT (HCHO + MCT trial). A fourth trial consisted of a 13C-background control trial (CON). The four trials were randomized. Before and after the exercise bout, muscle biopsies were taken from the quadriceps muscle and muscle glycogen levels were determined. During exercise, breath samples were collected for estimation of exogenous and endogenous CHO oxidation. No significant differences were detected in glycogen breakdown among the trials (277 +/- 14 mmol x kg dry weight(-1) CHO, 249 +/- 20 CHO + MCT, and 240 +/- 18 HCHO + MCT) or in the respiratory exchange ratio during exercise. Mean exogenous CHO oxidation rates during the final hour of exercise were 0.79, 0.63, and 0.73 g x min(-1), respectively. No differences were observed between the trials regarding exogenous or endogenous CHO oxidation. Plasma free fatty acid (FFA) concentrations were elevated during exercise to a level of approximately 500 micromol x L(-1) and were comparable in all trials, whereas plasma ketone concentrations significantly increased after MCT ingestion as compared with the CHO trial. It is concluded that 29 g MCT co-ingested with CHO during 180 minutes of exercise does not influence CHO utilization or glycogen breakdown.

Adult↗

A new validated endurance performance test.

The extensive use of performance tests in diet intervention studies mirrors the importance of such a measurement. Although many different endurance performance tests have been used in the past, the majority of these different protocols has never been validated. In this study reproducibility of three different endurance performance tests was evaluated. Thirty well-trained subjects were matched on age, weight, and Wmax and divided into three subgroups. Each group of subjects performed one of three exercise protocols: protocol (A) consisted of cycling at 75% Wmax until exhaustion. In (B) subjects received a preload of 45 min 70% Wmax and then performed as much work as possible in 15 min. (C) consisted of a time trial, in which subjects had to complete a preset amount of work as fast as possible. Each subject performed one of the trials six times. Coefficient of variation (CV) was calculated for each protocol. CV(A) was 26.6%, CV(B) 3.49%, and CV(C) 3.35%. It was concluded that reproducibility of a test at 75% Wmax until exhaustion is poor and these tests are not reliable. Time trial protocols may result in better performance evaluation.

Adolescent↗

Effect of endogenous carbohydrate availability on oral medium-chain triglyceride oxidation during prolonged exercise.

The present study examined the medium-chain triglyceride (MCT) oxidation rate of oral carbohydrate (CHO) + MCT supplements after a glycogen-depletion trial [low glycogen (LG)] and in the glycogen-loaded state [normal-to-high glycogen (HG)]. Eight elite athletes cycled four times 90 min at 50% maximal workload (57% maximal O2 uptake). In two trials, they followed a LG protocol to achieve low-glycogen stores in the leg muscles the evening before the experiment, and in two trials they followed a HG protocol. Subjects received a bolus of 4 ml/kg at the start and 2 ml/kg every 20 min during exercise of either a 15% CHO (long-chain glucose polymer) solution or an equicaloric CHO + MCT suspension. Exogenous MCT oxidation was measured by adding a [1,1,1-13C]trioctanoate tracer to the MCT oil and measuring 13CO2 production in the breath. The results show that 85% of MCT ingested was oxidized in LG and 69% in HG during the 60- to 90-min period. There was no statistically significant difference in MCT utilization between LG and HG. Peak oxidation rates were 0.15 and 0.13 g/min, respectively. MCT contributed 7.6% (LG) and 6.5% (HG) to total energy expenditure during the 60- to 90-min period. Total fatty acid oxidation was significantly elevated in the LG trial but was not influenced by MCT ingestion. Concomitantly, CHO oxidation was reduced in LG but no effect of MCT was observed. We conclude that 1) the contribution of MCT to total energy expenditure was small and 2) strenuous exercise the day before the experiment, followed by a low CHO intake and leading to a low CHO availability, substantially increased total fat oxidation but did not significantly increase MCT oxidation.

Adult↗

Chronic oral lactate supplementation does not affect lactate disappearance from blood after exercise.

This study tested the hypothesis that a 3-week oral lactate supplementation affects postexercise blood lactate disappearance in untrained male subjects. Fifteen men were randomly assigned to either a lactate supplementation (n = 8) or a placebo (n = 7) treatment. During the treatment period they drank an oral lactate or a maltodextrin (placebo) supplement twice a day. The lactate drink contained 10 g of lactate as calcium, sodium, and potassium salts. Blood lactate concentrations were studied before, during, and immediately after three exercise tests, both pre- and posttreatment. Peak lactate values for placebo (PL) or lactate (L) treatment groups during different tests were as follows: Test 1 PL, 13.49 +/- 3.71; L, 13.70 +/- 1.90; Test 2 PL, 12.64 +/- 2.32; L, 12.00 +/- 2.23; Test 3 PL, 12.29 +/- 2.92; L, 11.35 +/- 1.38 and were reached 3 min postexercise. The decrease in blood lactate during the long (30- to 45-min) recovery periods amounted to / 10 mmol/L. Blood lactate changes were highly reproducible. However, a 3-week oral lactate supplementation did not result in differences in lactate disappearance. This study does not support the hypothesis that regular oral lactate intake at rest enhances the removal of lactate during and following exercise, that is, not with the given lactate load and supplementation period.

Administration, Oral↗

Metabolic availability of medium-chain triglycerides coingested with carbohydrates during prolonged exercise.

The present study examined the metabolic response to medium-chain triglycerides (MCTs) ingestion with or without carbohydrates (CHOs). Eight well-trained athletes cycled 4 x 180 min at 50% maximal work rate (57% maximal O2 consumption). Subjects drank a bolus of 4 ml/kg at the start and 2 ml/kg every 20 min during exercise of either a 15% (214 g) CHO solution (CHO trial), an equicaloric 149 g CHO-29 g MCT suspension (CHO+MCT trial), 214 g CHO [high CHO (HCHO)]-29 g MCT suspension (HCHO+MCT trial) or 29 g MCT solution (MCT trial). Exogenous MCT oxidation was measured by adding a [1,1,1-13C]trioctanoate tracer to the MCT oil. 13CO2 enrichment of breath samples were measured every 15 min. During the second hour (60- to 120-min period), the amount of MCT oxidized was 72% of the amount ingested during the CHO+MCT trial, whereas during the MCT trial only 33% was oxidized. The rate of MCT oxidation increased more rapidly during the HCHO+MCT and CHO+MCT trials compared with the MCT trial, yet in all three cases the oxidation rate stabilized at 0.12 g/min during 120-180 min of exercise. It is concluded that more MCTs are oxidized when ingested in combination with CHOs. Data do confirm the hypothesis that oral MCTs might serve as an energy source in addition to glucose during exercise because the metabolic availability of MCTs was high during the last hour of exercise, with oxidation rates being approximately 70% of the ingestion rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

Breath 13CO2 background enrichment during exercise: diet-related differences between Europe and America.

A traditional North American diet contains a high percentage of carbohydrates (CHO) derived from C4 plants (maize, sugar cane), whereas a European diet contains primarily CHO derived from C3 plants (potato, sugar beet). The natural 13C enrichment of the first type of CHO is higher than that of the latter type. 13CO2 production from orally ingested C4 plant-derived CHO can, therefore, be used to quantify oxidation rates of orally ingested CHO at rest and during exercise. Recently it has been shown that oxidation rates assessed this way in North Americans should be corrected for an increase in breath background 13CO2 during exercise. We hypothesized that the indicated difference in metabolic origin of CHO would imply that no such correction is required for subjects on a European diet. We therefore studied changes from rest in breath 13CO2 enrichment in Dutch volunteers during cycle ergometry at 65% maximal work load (experiment 1, 2h, 6 subjects) and 70% maximal oxygen uptake (experiment 2, 90 min, 8 subjects) while ingesting water (experiments 1 and 2) and potato starch-derived glucose (experiment 2). Experiment 1 was done before and after careful instruction of the subjects to refrain from nutrient sources potentially containing CHO of C4 metabolic origin. No significant changes from rest 13CO2 enrichment were observed in tests with water and potato-derived glucose ingestion in subjects who excluded CHO of C4 metabolic origin from their diet.

Adipose Tissue↗

Exogenous carbohydrate oxidation from different carbohydrate sources during exercise.

The exogenous carbohydrate (CHO) oxidation of naturally enriched [13C]CHO sources with different solubilities was studied during cycling exercise (150 min, 60% maximum work output). Moreover, the effect of adding a 13C tracer with different physical properties than the tracee on exogenous CHO oxidation was investigated. Test solutions (28.5 ml/kg body wt) were water for control of 13C background, 15% soluble partially hydrolyzed corn starch (SOL), 15% insoluble corn starch (In-SOL), and 15% InSOL with [13C6]glucose as tracer. Both the mean and peak exogenous oxidation rates were significantly greater (P < 0.05) in the SOL trial than in the InSOL trial (mean oxidation rate, 0.84 +/- 0.21 and 0.50 +/- 0.15 g/min, respectively; peak oxidation rate, 1.10 +/- 0.18 and 0.81 +/- 0.25 g/min, respectively). The amount of the ingested CHO that was oxidized was significantly higher (P < 0.05) in the SOL trial (126 +/- 31 g) than in the InSOL trial (75 +/- 25 g). When we added an extrinsic tracer ([13C]glucose), the apparent mean and peak oxidation rates of the trial with InSOL and [13C6]glucose were significantly (P < 0.05) higher (0.91 +/- 0.30 and 1.23 +/- 0.41, respectively) than the InSOL values. These results 1) indicate that the addition of the soluble [13C]glucose tracer to an insoluble starch tracee leads to overestimation of the exogenous CHO oxidation rates and 2) suggest that soluble CHO is oxidized at a higher rate during exercise than isocaloric insoluble CHO.

Adult↗

Oxidation rates of orally ingested carbohydrates during prolonged exercise in men.

Six male volunteers exercised on a cycle ergometer at 65% of maximal work load for 120 min on six occasions while ingesting water (W) only, four doses of maltodextrin (M) [0.92, 1.85, 2.77, and 3.70 g/kg body wt (4, 8, 12, and 16% M, respectively)], and sucrose (S) [1.85 g/kg body wt (8% S)]. Drinks were given during warm-up (8 ml/kg body wt) and each 15 min during exercise (2 ml/kg body wt). M and S were of high 13C natural abundance. Total carbohydrate (CHO) and fat oxidations were calculated from the nonprotein respiratory exchange ratio. M and S increased total CHO oxidation compared with W; no difference was observed between CHO solutions. Total CHO oxidation decreased continuously with time and more rapidly after W than after M or S. Fat oxidation increased continuously in all treatments. Oxidation rates of ingested CHO were 52 +/- 19, 76 +/- 12, 86 +/- 10, and 91 +/- 9 g/2 h for 4, 8, 12, and 16% M, respectively. The oxidation rate of S was 81 +/- 10 g/2 h (not different from 8% M), which indicated that the glucose polymer had no advantage over S. Oxidation rates of M and S increased to a plateau after 90-120 min of exercise. For all solutions except 4% M, the plateau oxidation rate was close to 1.0 g/min. Differences between 8, 12, and 16% M and 8% S were minimal such that ingestion of 8% M or S may well have had an optimal ergogenic effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

Effects of electrolytes in carbohydrate beverages on gastric emptying and secretion.

Two experiments were done at rest to examine gastric residue and secretion volume and electrolyte composition after ingestion of beverages of varying composition. In the first experiment the effects of two different sport drinks, one isotonic (7% carbohydrate, primarily sucrose) (I) and one hypertonic (18% carbohydrate, primarily maltodextrin) (H), and a control beverage (0.08 g.l-1 aspartame in water) (C) on titratable acid, pH, osmolality, gastric emptying and secretion volume, and Na+, K+, and Cl- content were measured. In a second experiment five solutions were tested all containing 150 g.l-1 maltodextrin, with 28 meq.l-1 Na+ (low Na), 140 meq.l-1 Na+(high Na), 28 meq.l-1 K+(K), or 140 meq.l-1 Na+ and 28 meq.l-1 K+(high NaK). Beverages H and C, and distilled water (W) were also tested. Samples were taken via a nasogastric tube. A dye dilution technique for serial sampling was employed to determine beverage and secretion volumes. After receiving a bolus of 8 ml.kg-1 body weight, samples of gastric residue were taken at 0, 10, 20, 30, 40, 60, and 80 min. Gastric secretion of Na+, K+, and Cl- was fairly constant despite large differences in beverage composition. Changes in gastric residue pH, titratable acid, osmolality, and electrolyte composition reflected the increasing proportion of the residue that was from gastric secretions. The effects of varying concentrations of Na+ and K+ (in a 150 g.l-1 maltodextrin solution) on gastric emptying were not significant. The high carbohydrate concentration and/or the large volume ingested may have overridden any effect of sodium or potassium. No differences were observed between W and C. Secretion was decreased in these two solutions versus all the others. Although nonsignificant, there was a trend for greater secretion in H versus the other carbohydrate containing solutions in experiment 2. This may be a result of the higher pH maintained after ingestion of this beverage.

Adolescent↗

Is the gut an athletic organ? Digestion, absorption and exercise.

Digestion is a process which takes place in resting conditions. Exercise is characterised by a shift in blood flow away from the gastrointestinal (GI) tract towards the active muscle and the lungs. Changes in nervous activity, in circulating hormones, peptides and metabolic end products lead to changes in GI motility, blood flow, absorption and secretion. In exhausting endurance events, 30 to 50% of participants may suffer from 1 or more GI symptoms, which have often been interpreted as being a result of maldigestion, malabsorption, changes in small intestinal transit, and improper food and fluid intake. Results of field and laboratory studies show that pre-exercise ingestion of foods rich in dietary fibre, fat and protein, as well as strongly hypertonic drinks, may cause upper GI symptoms such as stomach ache, vomiting and reflux or heartburn. There is no evidence that the ingestion of nonhypertonic drinks during exercise induces GI distress and diarrhoea. In contrast, dehydration because of insufficient fluid replacement has been shown to increase the frequency of GI symptoms. Lower GI symptoms, such as intestinal cramps, diarrhoea--sometimes bloody--and urge to defecate seem to be more related to changes in gut motility and tone, as well as a secretion. These symptoms are to a large extent induced by the degree of decrease in GI blood flow and the secretion of secretory substances such as vasoactive intestinal peptide, secretin and peptide-histidine-methionine. Intensive exercise causes considerable reflux, delays small intestinal transit, reduces absorption and tends to increase colonic transit. The latter may reduce whole gut transit time. The gut is not an athletic organ in the sense that it adapts to increased exercise-induced physiological stress. However, adequate training leads to a less dramatic decrease of GI blood flow at submaximal exercise intensities and is important in the prevention of GI symptoms.

Diarrhea↗

Physiological changes and gastro-intestinal symptoms as a result of ultra-endurance running.

One hundred and seventy-two competitors of the Swiss Alpine Marathon, Davos, Switzerland, 1988, volunteered for this research project. Of these volunteers 170 (158 men, 12 women) finished the race (99%). The race length was 67 km with an altitude difference of 1,900 m between the highest and lowest points. Mean age was 39 (SEM 0.8) years. Average finishing times were 8 h 18 min (men) and 8 h 56 min (women). Loss of body mass averaged 3.4% body mass [mean 3.3 (SEM 0.2)%; 4.0 (SEM 0.4)%; men and women, respectively]. Blood samples from a subgroup of 89 subjects (6 women and 83 men) were taken prior to and immediately after completion of the race. Changes in haemoglobin (9.3 mmol.l-1 pre-race, 9.7 mmol.l-1 post-race) and packed cell volume (0.44 pre, 0.48 post-race) were in line with the moderate level of dehydration displayed by changes in body mass. Mean plasma volume decreased by 8.3%. No significant changes in plasma osmolality, sodium, or chloride were observed but plasma potassium did increase by 5% (4.2 mmol.l-1 pre-race, 4.4 mmol.l-1 post-race). Mean fluid consumption was 3290 (SEM 103) ml. Forty-three percent of all subjects, and 33% of those who gave blood samples, complained of gastro-intestinal (GI) distress during the race. No direct relationship was found between the quantity or quality of beverage consumed and the prevalence of GI symptoms.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

Exogenous carbohydrate oxidation from maltose and glucose ingested during prolonged exercise.

Intestinal perfusion studies have shown that glucose absorption from maltose occurs faster than from isocaloric glucose. To determine whether ingested maltose might be a superior source of carbohydrate (CHO) for endurance athletes, we compared the rates of gastric emptying, absorption and oxidation of 15 g.100 ml-1 solutions of maltose and glucose. Six endurance-trained cyclists drank 1200 ml of either U-14C maltose or U-14C glucose as a 400-ml loading bolus immediately before exercise, and as 8 x 100-ml drinks at 10-min intervals during a 90-min ride at 70% of maximal oxygen consumption. The rates of gastric emptying [maltose 690 (SD 119) ml.90 min-1; glucose 655 (SD 93) ml.90 min-1], the appearance of U-14C label in the plasma, and the peak rates of exogenous CHO oxidation [maltose 1.0 (SD 0.09) g.min-1; glucose 0.9 (SD 0.09) g.min-1] were not significantly different. Further, the 51 (SD 8) g of maltose and the 49 (SD 9) g of glucose oxidised during exercise were similar. Each accounted for approximately 20% of the total CHO oxidised during the 90 min of exercise. Since only half of the CHO delivered to the intestine was oxidised in the 90-min ride (maltose 49%; glucose 50%), we conclude that neither the rate of gastric emptying, nor digestion limited the rate of ingested CHO utilisation during the early stages of exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗