As readers will know, there has been a lot of scientific evidence to show the advantages of high dietary intakes of carbohydrate, but much of this relates to specific one-off performances of volunteers in a laboratory. Little research has been carried out to assess the performance change of elite team-sport athletes caused by additional carbohydrate. A recent study has done just that, combining the scientific assessment of performance in the laboratory with the intensive training carried out by a national squad of athletes.

Researchers at the University of Memphis in the States worked with 14 female members of the US National Field Hockey Team during an intensive training period lasting seven days. A typical training day consisted of two sessions, each of at least two hours, including competitive drills at match intensity. The athletes were paired for position, training specificity and training volume.

One of each pair (Group CHO) ingested a high- carbohydrate concentrated drink (Exceed High Carbohydrate Source) containing lg.kg-1 of carbohydrate four times a day. This provided approximately 1000 calories of extra energy as carbohydrate per day. The other of the paired athletes (Group P) ingested a flavoured and textured water placebo identical in volume to the true supplement. A battery of physiological tests was administered before and during the training week, as well as a test of psychological status after each individual training bout. The aim of the study was to see whether carbohydrate supplements affected these measures in any way.

And what was the result?
First, dietary intake over the seven days was found to differ between the groups. Hardly surprising, perhaps, but it did show that Group CHO were not subconsciously compensating (ie, eating less) for their increased energy intake due to the supplements. Second, psychological analysis of post-exercise fatigue suggested a possible slight reduction for Group CHO compared to Group P. Third, CHO was found to have improved performance of incremental treadmill exercise time to exhaustion over the training period (+3.2%), whereas Group P declined in this measure of aerobic performance (-2.7%). Some observations did not show any differences, either pre- to post-training period, or between groups, such as maximal strength, maximal power and certain cardiopulmonary measures such as ventilatory threshold.

So it appears that some advantages can be obtained from increasing carbohydrate intake during periods of intense training. Maximum training response can be achieved if carbo intake is high. The reason for this proposed by the researchers was the greater and more rapid replenishment of muscle glycogen stores between training bouts. Glycogen stores have, of course, been shown to be directly related to prolonged endurance exercise and repeated bouts of exercise in controlled laboratory experiments.

The investigators in this study admit that if direct measurement of muscle glycogen had taken place, they could have drawn conclusions more confidently. How, it is difficult, not surprisingly, to persuade elite athletes to allow direct muscle tissue samples to be taken. Nevertheless, the theoretical reasoning for the findings in this study seems sound.

The fact that certain measurements showed no improvement over time may be because of the already highly trained nature of the athletes, the fact that certain body systems were not trained specifically, and a period of recovery from the intense training was not allowed. Any tests of fitness for athletes should be carried out after a couple of days of relatively light training, during which the positive adaptations to training stress can occur.

The conclusion?
The results of the study add to the existing evidence indicating that a high carbohydrate diet can aid training response and resulting performance. It shows (using scientific evidence) that this can apply to elite competitors in a true-to-life training situation. There are obvious implications for all sports, including team sports, where heavy training and/or match schedules are involved. High carbohydrate diets and supplements should not be the preserve of endurance athletes alone.

However, the proviso of allowing two-to-three hours between a meal and the following exercise still holds. There is now growing scientific evidence for the beneficial effects of a high carbo intake in performances of varied intensity and duration, especially when repeated over a lengthy period of time. The simple message is: whatever your sport, carbohydrate is the key. ('Effects of Carbohydrate Supplementation During Intense Training on Dietary Patterns, Psychological Status, and Performance', International Journal of Sport Nutrition, 1995, vol. 5, no 2, pp125-135.)
Alun William