Pre-Exercise Carbohydrate Meal and Endurance ...

Nutrition

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Pre-Exercise Carbohydrate Meal and Endurance Running Capacity when Carbohydrates are Ingested During Exercise C. Chryssanthopoulos, C. Williams Department of Physical Education. Sports Science and Recreation Management, LoughboroughUniversity. Loughborough. England

C. Chryssanthopoulos, C. Williams. Pre-Exercise Carbohydrate Meal and Endurance Running Capacity when Carbohydrates are Ingested During Exercise. Int. 1. Sports Med.. Vol. 18, pp. 543 - 548,1997.

This study examined whether combining a pre-exerctse carbohydrate meal with the ingestion of a carbohydrate-electrolyte solution during exercise is better in improving endurance running capacity than a carbohydrate-electrolyte solution alone. Ten men completed three treadmill runs at 70%~0,max t o exhaustion. They consumed 1.) a carbohydrate meal three hours before exercise and a carbohydrate-electrolyte solution during exercise (M + C), or 2.) a llquid placebo three hours before exercise and the carbohydrate-electrolyte solution during exercise (P+ C), or 3.) a placebo three hours before exercise and placebo during exercise (P+ P). When the meal was consumed (M + C) serum insulin concentrations were higher at the start of exercise, and carbohydrate oxidation rates were higher during the first 60min of exercise compared with the values found i n the P + C and P + P trials (p ~0.01).Exercise time was longer i n the M + C (147.4 f 9.6 rnin) compared with the P + C (125.3 7 min) ( p < 0.01). Also, exercise time was longer in M + C and P + C compared with the P + P (115.1 f 7.6 min) (p < 0.01 and p < 0.05 respectively). These results indicate that the combination of a pre-exercise carbohydrate meal and a carbohydrate-electrolyte solution further improves endurance running capacity than the carbohydrate-electrolyte solution alone.

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Key words: Pre-exercise meal. carbohydrate-electrolyte solution, running capacity

(1). However, pre-exercise feeding elevates serum insulin concentration before exercise (1.5.29). accelerates carbohydrate oxidation (1,7,14,15,27,29). and depresses the blood born FFA concentration (1,5,7,29). Collectively, all these metabolic perturbations may not be the most favourable to the endurance athlete, since they may accelerate the use of the limited muscle glycogen stores (5,22).

Ingesting carbohydrates during exercise delays the onset o f fatigue i n cycling (4.6,8.29), as well as in running (16.20.2426). Also. the ingestion o f carbohydrates during exercise does not alter the carbohydrate oxidation rates, at least during the first hour of exercise (4.6.8.24-26). and spares muscle glycogen stores during running (23,24). Therefore, the aim of the present study was to examine whether the ingestion of carbohydrates before and during exercise would improve endurance running capacity to a greater extent than simply ingesting carbohydrates during exercise. Methods

Subjects Ten male reaeational/club level runners volunteered to take part i n this study. Their age, height, body weight. \io,rnax, and maximum heart rate were 34.9 ? 2.5 years, 174.5 2.9 cm, 72.4 r 3.6 kg, 58.6 f 1.9m l x k g x min-I. and 186 2 4 b x min-I respectively (mean 2 SE). Nine subjects completed all three trials, and one completed only two trials. All subjects were fully jnformed about the nature o f the experiments and what was required of them before giving formal consent. The study had the approval o f the Ethical Advisory Committee o f Loughborough University.

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Introduction Consuming a carbohydrate meal 3-4 hours before prolonged exercise improves cycling performance (21.29) and running capacity (1) compared to an overnight fast. Furthermore, the combination of a pre-exercise meal and a carbohydrate-electrolyte solution during exercise improves endurance running capacity to a greater extent than a pre-exercise meal alone

Int. 1. Sports Med.18 (1997) 543-548 O GeorgThieme Verlag Stuttgart .New York

Preliminary measurements After subjects became familiar w i t h treadmill running and experimental procedures, they performed two preliminary tests: a) a 16-rnin incremental submaximal running test to determine the relationship between running speed and oxygen uptake, and b) an uphill treadmill running test to determine each subject's maximum oxygen uptake.

C.Chryssonthopoulos. C. Williams

Int.]. Sports Med. 18 (1997)

All preliminary tests were conducted according to the procedures previously described (28). Subjects also undertook a 60 min treadmill run at 70%~ 0 , m a x ,about one week before the first experimental trial in order to become fully familiarised with the drinking pattern and the measurements used during the main trails. Nutritional status Subjects were required to record training and to weigh their food intake during the two days prior to the first trial, and to replicate these in the next two trials. The dietary information obtained was then analyzed (18).There were no significant differences between the three trials in the average daily energy intake, or composition in terms of carbohydrate, fat, or protein consumed during the two days prior to each trial. Subjects were also required to avoid training the day before each main trial. Experimental design Each subject was required to run to fatigue at 70%irOzmaxona motorised level treadmill (Quinton, Seattle, USA) on three different occasions separated by one week. On the first occasion a high carbohydrate meal was eaten three hours before exercise, and during exercise a carbohydrate-electrolyte solution was ingested ( M + C). On the second and third trials 10 ml x k g 1 BW of a liquid placebo were ingested three hours before exercise (P + C and P+ P). During exercise, in the second trial subjects ingested a carbohydrate-electrolyte solution (P+C), whereas in the third trial a liquid placebo was administered ( P + P). The order of the three trials was random. Since solid food was used before exercise a double blind design was impossible. In order to make the desjgn single blind subjects were told that the purpose of the experiment was to compare solid and liquid carbohydrate food in different combinations and concentrations before and/or duringexercise and that during the three trials they ingested the same amount of carbohydrate by adjusting the concentration of the ljquid parts (i.e. liquid placebo. or orange juice) of the meals. After a 12-hour overnight fast subjects arrived at the laboratory at 8 : 00 a.m. Duplicate 20 p1 capillary blood samples were taken from the thumb of a pre-warmed hand after they had been sitting quietly for 15 min. Following this, subjects ingested either the liquid placebo (P +C and P+ P), or the high carbohydrate meal (M +C). During the 3-hour postprandial period subjects remained in the laboratory reading and writing, or were involved with low intensity physical activities (e.g. attending lectures, doing office work etc.) outside the laboratory. These activities were very similar in all experimental trials. Before the initiation of exercise, each subject's nude body weight was recorded. Thereafter. subjects were seated and a venous blood sample was taken from an antecubital vein as well as another capillary blood sample from a pre-warmed hand. Subjects warmed up for 5 rnin on the treadmill at 60% W,max. Following this. the speed of the treadmill was increased to 70%m 2 m a x and the subjects continued running until exhaustion. They were encouraged to run as long as possible. However, when they were unable to maintain their prescribed running speed, and in order to ensure that fatigue had occurred, the speed was reduced to 60%~ 0 , m a xfor 2 min. Thereafter.

the speed was returned to the prescribed speed and the subjects were encouraged to continue for as long as possible. One minute expired air samples and duplicate 2 0 ~ capillary 1 samples were collected at 10min and 20min into exercise and every 20 min thereafter. Expired air and capillary blood samples were also collected at the last minute of the run. Also. each subject's rate of perceived exertion (RPE) was obtained using the Borg's scale. Furthermore, two additional scales were used, one to monitor the subject's abdominal discomfort (AD) and the other was used to assess their sensation of gut fullness (CF). Both scales ranged from 0 (AD: "Completely comfortable"; GF: "Empty") up to 10 (AD: "Unbearable pain": GF: "Bloated"). Heart rate was monitored throughout exercise by short-range telemetry (Polar Electro Sports Tester PE 3000). Wet sponges were available for the subjects to use ad libitum throughout each of the runs, Immediately after subjects stopped exercise, a further venous sample was taken while they were seated: thereafter subjects dried themselves, and postexercise nude body weight was recorded. All trials were conducted under similar laboratory conditions: temperatures: M + C: 19.8 0.8 "C, P + C: 20.3 0.6 "C, and P + P: 20.1 ? 0.8 "C; relative humidity: M + C: 59.6 r 2.8 %. P + C: 53.3 r 2.4%,and P+ P: 51.9 &2.3%(mean +SE;n.s.).

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Carbohydrate feedings Three hours before each run subjects consumed either 10 m x kg-' BW of a liquid placebo (dilute sugar free orange juice; less than I kcal per 700 ml undiluted) (P+C. and P + P trials), or the high carbohydrate meal (M + C) (2.5 g carbohydrates per kg BW). The pre-exercise meal (M + C) consisted of white bread, jam, cornflakes, sugar, skimmed milk and orange juice which amounted to 86%of energy intake from carbohydrate, 11% from protein and less than 3%from fat. About 88%of the carbohydrate included in the meal was obtained from food classified as having a high glycaemic index. whereas the rest was obtained from food with moderate and low glycaemic index (11). During exercise in the M + C and P + C trials an isotonic lemon and lime carbohydrate-electrolyte solution was ingested, whereas in the P + P trial equivalent amount of a liquid placebo (dilute sugar free lemon and lime juice) was given. The carbohydrate-electrolyte solution was a commercially available sports drink (Lucozade Sport) which contained 6.9%carbohydrate (dextrose, maltodextrin and glucose syrup) and four electrolytes (24 mmol x I- sodium. 2.5 mmol x I-' potassium. 1.2 mmol x I- calcium, and 0.8 mmol x 1- magnesium). Immediately prior to the start of exercise subjects ingested 5 ml x k g BW of the carbohydrate solution ( M + C and P + C trials) or equivalent amount of placebo (P+ P), and 2 ml x kg-' BW of the assigned fluid every 20min thereafter. The total amount of carbohydrate ingested in the M+C trial was 259 k 13.8 g (181 ? 9 g as meal and 78 6 g during exercise), whereas in the P + C trial was 70? 4 g.

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Analyses The method of collection and analysis of expired air samples was the same as previousfy described (28). Venous blood samples were collected into lithium heparin and serum tubes. Blood glucose, blood lactate, haemoglobin, haematocrit, percentage changes in plasma volume, plasma FFA, and plasma

Pre-Exercise Carbohydrate Meal and Endurance Running Capacity

Int.]. Sports Med. 18 (1997)

glycerol, were measured as previously described (28). Serum sodium and potassium were anaIysed by flame photometry (Coming 435 flame photometer). Serum samples were also stored at - 70°C and analysed a t a later date for serum insulin radioimmunoassay; Coat-A-Count Insulin. DPC kit) using a gamma counter (Packard. Cobra 5000). Statistical analyses A two-way analysis of variance (ANOVA) for repeated meas-

ures on two factors (treatment by time) was used to compare cardiovascular changes, blood glucose. and blood lactate responses between trials. The remaining responses were examined using a two tailed Student's t-test for dependent samples. When significant differences were revealed using the ANOVA, a Tukey post hoc test was performed. The accepted level of significance was set at p < 0,05. Data are reported as mean f SE.

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Respiratory exchange ratio (RER) during the M + C, P + C. and

P + P trials (mean f SE; n = 9) pc0.01 fromP+Cand P t P ; "

Results

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