Pre-exercise Nutrition

Burke, L. M. Preparation for competition. In: Clinical Sports Nutrition (2nd ed.), edited by L. Burke and V. Deakin. Sydney: McGraw-Hill, 2000, p. 341-368.

Burke, L. M., J. A. Hawley, E. J. Schabort, A. St Clair Gibson, I. Mujika, and T. D. Noakes. Carbohydrate loading failed to improve 100-km cycling performance in a placebo-controlled trial. Journal of Applied Physiology 88: 1284-1290, 2000.

Burke, L. M., A. Claassen, J. A. Hawley, and T. D. Noakes. Carbohydrate intake during prolonged cycling minimizes effect of glycemic index of preexercise meal. Journal of Applied Physiology 85: 2220-2226, 1998.

Palmer, G. S., M. C. Clancy, J. A. Hawley, I. M. Rodger, L. M. Burke, and T. D. Noakes. Carbohydrate ingestion immediately before exercise does not improve 20 km time trial performance in well trained cyclists. International Journal of Sports Medicine 19: 415-418, 1998.

Burke, L. Pre-event meals: high or Low glycemic index foods? Sportscience News May-Jun 1998.
http://www.sportsci.org/news/compeat/glycemic.html

Burke, L. Carbohydrate depletion - is it for you? Sportscience News Jan-Feb 1998.
http://www.sportsci.org/news/compeat/deplete.html

Burke, L. M., and R. S. Read. A study of carbohydrate loading techniques used by marathon runners. Canadian Journal of Sport Science 12: 6-10, 1987.

Burke, L. M. Preparation for competition. In: Clinical Sports Nutrition (2nd ed.), edited by L. Burke and V. Deakin. Sydney: McGraw-Hill, 2000, p. 341-368.

The outcomes of pre-event nutrition strategies range from psychological well-being and confidence to optimal fluid and fuel status. The importance of these strategies will depend on the range and severity of physiological challenges that are likely to limit performance in the athlete's individual event. This may be determined by characteristics of the event itself, as well as the degree to which the athlete has been able to recover since their last workout or competition event. Nutrition strategies may include increased CHO intake during the day(s) prior to the event, as well as the extended fuelling-up known as CHO loading, which has been shown to enhance endurance and the performance of prolonged exercise events. The pre-event meal also provides an opportunity to refuel muscle and liver glycogen stores. There is some concern that pre-exercise CHO feedings may increase CHO utilisation during exercise, but the intake of substantial amounts of CHO can offset the increased rate of substrate use. The choice of low-GI CHO-rich foods in the pre-event menu may also sustain the delivery of CHO during exercise, however this does not provide a guaranteed performance advantage, especially when additional CHO is consumed during the event. Pre-event preparation should also consider fluid balance, with strategies to rehydrate from previous dehydration associated with exercise or weight-making activities, as well as the potential for hyperhydration in preparation for events in which a large fluid deficit is unavoidable. A variety of eating practices can be chosen by the athlete to meet their competition preparation goals. These need to consider the practical aspects of nutrition such as gastrointestinal comfort, the athlete's likes and dislikes, and food availability. Above all, the athlete should experiment with their pre-event nutrition practices to find and fine-tune strategies that are successful. These may be individual to the athlete and their specific event. Pre-event nutrition practices should be undertaken as part of an integrated competition nutrition plan. Ideally, an athlete should combat these challenges of competition by undertaking a systematic plan of nutrition strategies before, during and even in the recovery after an event.

Further details on Clinical Sports Nutrition can be found in the Publications section of our site.

We evaluated the effect of carbohydrate (CHO) loading on cycling performance that was designed to be similar to the demands of competitive road racing. Seven well-trained cyclists performed two 100-km time trials (TTs) on separate occasions, 3 days after either a CHO-loading (9 g CHO. kg body mass(-1). day(-1)) or placebo-controlled moderate-CHO diet (6 g CHO. kg body mass(-1). day(-1)). A CHO breakfast (2 g CHO/kg body mass) was consumed 2 h before each TT, and a CHO drink (1 g CHO. kg(.)body mass(-1). h(-1)) was consumed during the TTs to optimize CHO availability. The 100-km TT was interspersed with four 4-km and five 1-km sprints. CHO loading significantly increased muscle glycogen concentrations (572 +/- 107 vs. 485 +/- 128 mmol/kg dry wt for CHO loading and placebo, respectively; P < 0.05). Total muscle glycogen utilization did not differ between trials, nor did time to complete the TTs (147.5 +/- 10.0 and 149.1 +/- 11.0 min; P = 0.4) or the mean power output during the TTs (259 +/- 40 and 253 +/- 40 W, P = 0.4). This placebo-controlled study shows that CHO loading did not improve performance of a 100-km cycling TT during which CHO was consumed. By preventing any fall in blood glucose concentration, CHO ingestion during exercise may offset any detrimental effects on performance of lower preexercise muscle and liver glycogen concentrations. Alternatively, part of the reported benefit of CHO loading on subsequent athletic performance could have resulted from a placebo effect.

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We studied the effects of the glycemic index (GI) of preexercise meals on metabolism and performance when carbohydrate (CHO) was ingested throughout exercise. Six well-trained cyclists performed three counterbalanced trials of 2-h cycling at approximately 70% of maximal oxygen uptake, followed by a performance ride of 300 kJ. Meals consumed 2 h before exercise consisted of 2 g CHO/kg body mass of either high-GI potato (HGI trial) or low-GI pasta (LGI trial), or of a low-energy jelly (Con trial). Immediately before and throughout exercise, subjects ingested a 10 g/100 ml [U-14C]glucose solution for a total of 24 ml/kg body mass. Despite differences in preexercise glucose, insulin, and free fatty acids concentrations among trials, both total CHO oxidation for HGI, LGI, and Con trials, respectively, during steady-state exercise [403 +/- 16, 376 +/- 29, and 373 +/- 24 (SE) g/2 h] and oxidation of the ingested CHO (65 +/- 6, 57 +/- 6, and 63 +/- 5 g/2 h) were similar. There was no difference in time to complete the subsequent performance ride (946 +/- 23, 954 +/- 35, and 970 +/- 26 s for HGI, LGI, and Con trials, respectively). When CHO is ingested during exercise in amounts presently recommended by sports nutrition guidelines, preexercise CHO intake has little effect on metabolism or on subsequent performance during prolonged cycling (approximately 2.5 h).

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This study examined the effects of carbohydrate ingestion on 20 km cycle time-trial (TT) performance in 14 well-trained cyclists (11 males, 3 females; peak oxygen uptake [VO2peak] 4.52 +/- 0.60 l/min; values are mean +/- SD). All subjects performed two experimental trials on their own bicycles mounted on an air-braked ergometry system (Kingcycle). Subjects were instructed to maintain the same training and dietary regimens before trials, which were conducted in a random order, 3-7 days apart, and at the same time of day for each subject. On the day of a trial, subjects reported to the laboratory and ingested an 8 ml/kg body mass bolus of either a 6.8 g/100 ml commercial carbohydrate-electrolyte (CHO) beverage (39 +/- 4 g of CHO), or a coloured, flavoured placebo. Ten min after finishing the drink, subjects commenced a 5 min warm-up at 150 W, before commencing the 20 km TT. The average power output (312 +/- 40 vs 311 +/- 38 W) and heart-rate (171 +/- 6 vs 171 +/- 5 beats/min for CHO and placebo, respectively) during the two rides did not differ between treatments. Accordingly, the performance times for the two TT's were the same (27:41 +/- 1:39 min:sec, for both CHO and placebo). We conclude that the ingestion of approximately 40 g of carbohydrate does not improve maximal cycling performance lasting approximately 30 min, and that carbohydrate availability, in the form of circulating blood glucose, does not limit high-intensity exercise of this duration.

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Burke, L. Pre-event meals: high or Low glycemic index foods? Sportscience News May-Jun 1998.

http://www.sportsci.org/news/compeat/glycemic.html

Athletes have been cautioned that eating carbohydrate foods in the hour before exercise may alter exercise metabolism by stimulating insulin production, which in turn increases the rate at which the muscles burn carbohydrate. As a result of this faster rate of carbohydrate oxidation, blood glucose levels may actually fall (a condition known as hypoglycemia) shortly after exercise begins. In most cases this effect is short term, and metabolism corrects itself as exercise continues. The occasional athlete experiences impaired performance, and it has been found in one study. But mostly there are no problems, and in some situations pre-exercise carbohydrate can even improve exercise performance. Nevertheless, the stigma about athletes eating carbohydrate before exercise persists, and many athletes and coaches talk about "rebound hypoglycemia" with fear, even though eating carbohydrate could potentially provide extra fuel during a prolonged training session or race.

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Burke, L. Carbohydrate depletion - is it for you? Sportscience News Jan-Feb 1998.

http://www.sportsci.org/news/compeat/deplete.html

The original carbohydrate loading protocol was probably one of the first modern sports nutrition strategies to receive widespread publicity. It had all the ingredients to make a good story - scientists using special techniques to study a muscle, evidence of performance improvements, and good timing. It hit exercise science journals in the early 70s, then found its way into running magazines during the start of the popular running boom. For both elite and recreational runners, this new carbohydrate loading technique seemed like a perfect prescription to build up muscle glycogen.

Link to full article.

Burke, L. M., and R. S. Read. A study of carbohydrate loading techniques used by marathon runners. Canadian Journal of Sport Science 12: 6-10, 1987.

Carbohydrate loading techniques were studied in a survey of 76 marathon runners. It was found that these runners practised a variety of methods that they believed would achieve carbohydrate loading. Analysis of records of food use showed that the diets actually used by runners did not reach the level of carbohydrate specified in the high carbohydrate phase of the glycogen loading regimens reported in the literature. It is suggested that in a free-living situation, without specific instructions or a knowledge of nutrition and food composition, runners are limited in their ability to achieve the dietary requirements of carbohydrate loading.

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