Ingestion of a Glucose Syrup Drink during Long Distance Canoeing

The use of a drink containing glucose syrup and mineral salts has been compared with a placebo in a group of eight long-distance canoeists under simulated race conditions. The findings suggest that maintenance of blood glucose above fasting level during severe exercise prevents both a deterioration of performance and prolonged post-exercise exhaustion. There was no evidence to suggest that the benefits were psychological in nature. Introduction In severe exercise the requirement for respiratory fuel increases (Down, 1968; Saltin and Hermansen, 1967, and Thomas, 1970) (1, 2, 3) and adipose tissue triglyceride is mobilized to provide an alternative fuel to glucose, when levels of the latter are low, as shown by the rise in blood glycerol and plasma free fatty acids (F.F.A.). The increase in concentration of F.F.A. results in an increased rate of ketone body formation; during exercise these are utilized as fuel and therefore do not accumulate, but, on cessation of work, ketone bodies tend to accumulate and continue at an elevated level, causing the condition of "post-exercise ketosis" (Johnson, Walton, Krebs and Williamson, 1969) (4). When glucose is made available during exercise, fat mobilization is greatly reduced (Havel, Naimark and Borchgrevink, 1963 and Carlson, Havel, Ekelund and Holmgren, 1963) (5, 6) whilst pre-exercise glucose ingestion results in a rise in the respiratory quotient indicating a preference for glucose as a metabolic fuel (Issekutz, Berkhead and Rodahl, 1963) (7). Thomas (3) has stated that, to some extent, performance is governed by the ability of the performer to avoid or delay hypoglycaemia, a view supported by Bannister (8) who listed hypoglycaemia among the chief dangers of marathon racing. For many years sportsmen have used glucose supplements, often in the form of dextrose monohydrate tablets, but whilst these may be convenient, many have found that they present problems of nausea, and particularly during an event, a neurosympathetic inhibition of salivation. To overcome these, a logical development is a drink in which the carbohydrate used is glucose syrup, a partial hydrolysate of starch (Wood, 1970) (9). Glucose syrup has the advantage of being much less sweet than table-sugar or dextrose, and the absence of cloying sweetness, when compared in isocaloric concentration, assists palatability and acceptance, allowing it to be used freely. Recently, a glucose syrup drink for sportsmen has been formulated containing 46% w/v glucose syrup, with added mineral salts to replace salt losses caused by sweating, 250 ml of the drink providing 355 kilo-calories. Glucose syrup is speedily absorbed (Bennett and Dodds, 1925; Dodds, Fairweather, Miller and Rose, 1959) (10, 11) and utilized (Butterfield, Sargent and Whichelow, 1964) (12) when taken orally. The rate of absorption from isolated rat intestine has been studied by Chain and his co-workers (Chain, Mansford and Pocchiari, 1960) (13) who found that both glucose syrup and dextrose were absorbed about twice as fast as sucrose and fructose and that the non-dextrose constituents of glucose syrup were absorbed without prior breakdown to dextrose. The initial testing of this drink was performed in the laboratory and gymnasium using a cycle ergometer (Brooke, Davies and Green, 1972) (14) and a treadmill (Green and Thomas, 1972) (15). Both series of trials were designed to simulate competitive events and extremely encouraging results were obtained, but it seemed possible that field trials might provide better motivation. The first sport studied was canoeing, where weather and water conditions had to be taken into account. Methods Ten canoeists (9 male, 1 female) aged 17 to 38 years were tested on two occasions; they were divided into two groups for each test, one group receiving the glucose syrup drink (Treatment T1) and the second, (Treatment T2), a placebo which was identical in all respects but without carbohydrate (less than 1 kcal per 250 ml). The products were presented to the participants in plain bottles to prevent identification. On the second occasion those subjects who had used the glucose syrup drink for the first test were given placebo and vice versa. The trials were carried out between 10.00 and 14.00 hours on warm, dry days and consisted of five laps of approximately 2.5 miles each; both the air temperature and the level of the river were similar on each day. group.bmj.com on October 27, 2017 Published by http://bjsm.bmj.com/ Downloaded from