Carbohydrate-containing sports drinks can improve athletic work capacity during high-intensity and/or prolonged workouts and can also upgrade immune function following such training. However, anecdotal reports have indicated that carbohydrate-containing-including sports drinks may be linked with a very undesirable form of sports injury â€“ an irritated gastrointestinal tract, with associated diarrhoea and abdominal discomfort. Are sports drinks really worse than plain water in this regard, and, if so, are some sports drinks more irritating than others?
To find out, researchers at the Gatorade Sports Science Institute in Barrington, Illinois recently asked 36 adult and adolescent athletes (18 males and 18 females) to complete four 12-minute 'quarters' of circuit training which included sprints, lateral hops, shuttle runs, and vertical jumps, with short recovery periods between each quarter ('Gastrointestinal Distress During High-Intensity Intermittent Training: Effect of Fluids Containing Carbohydrate (CHO)', Journal of the National Strength and Conditioning Association, Vol. 16(4), Abstracts from the 2002 NSCA Conference, p. 9, 2002). The basic idea was to simulate the kind of high-intensity training carried out by athletes in sports such as football, rugby, hockey, and lacrosse. The 36 subjects were tested three times on separate days in a random-order, double-blind trial of three beverages containing either 0%, 6%, or 8% carbohydrate (the 0% drink was plain water). The athletes used just one of the beverages per 48-minute workout and ingested 4.5 ml of the chosen drink per kilogram of body weight after the second quarter (ie, after 24 minutes) and 1.5 ml per kilogram after the first and third 12-minute quarters (after 12 and 36 minutes of training). Since mean body mass of the athletes was 70 kilos, this meant that about 100 ml of beverage were consumed after the first and third quarters, while 315 ml were poured down at half-time.
As it turned out, ratings of gastrointestinal distress tended to increase over the course of the training session, regardless of the type of drink utilised (water, 6% carb solution, or 8% carb concoction). Thus, the use of water instead of a carbohydrate drink did not necessarily decrease the risk of tummy troubles. However, after the third and fourth quarters gastrointestinal upset was greatest for the 8% sports drink, compared with 6% carbs or water. In addition, ratings for stomach disturbance were largest after the third quarter for the 8% sports drink. There was no statistically significant difference between the 6% solution and plain H2O.
The Illinois researchers reasonably concluded that stomach and intestinal distress tend to increase during high-intensity training and that the magnitude of this increase is greatest with 8% carbohydrate sports drinks, compared with 6% drinks and water. This is an important finding, since gut distress can decrease motivation, hurt performance, and even keep athletes off the playing field completely. The results are consistent with previous research which has found that 8% beverages empty from the stomach more slowly than either water or sports drinks with a lower concentration of carbohydrate. It is believed that stomach fullness is directly related to gastrointestinal discomfort levels during intense sporting activity. Thus, athletes in high-power, high-intensity sports which involve repeated sprints intermixed with nearly continuous motion may want to consider favourably the utilisation of sports drinks with moderate carb concentrations of about 6% or so during both their training sessions and competitions. Such drinks are generally well tolerated, and they can definitely enhance performance.