An Analysis of Carbohydrate Ingestion as an Ergogenic Aid

For information purposes only. Exercise at your own risk

by Huw Williams
From all areas of sport and exercise, there are many factors that contribute to a successful overall performance. According to Williams (1994), ‘physical performance is mainly a function of an individual’s size, shape, sex, and age’. Although these factors stated by Williams play a large part in the overall performance of an athlete, success in sport at a performance level depends on more important aspects. The use and ingestion of carbohydrates through a multitude of mediums is an area which has received a lot of interest due to its apparent effects on performance. According to Nassis et al (1998), ‘it has been found that if muscle levels of glycogen are not replenished and kept at a high level, then this can lower endurance capacity, power, and strength’. These findings were echoed by Tsintzas et al (1996) who stated that ‘the ingestion of a carbohydrate during or after moderate exercise has been shown to delay the inset of fatigue’.

Athletes of all competitive levels speak about embracing the ideal of sport, success through hard work, or simply doing the best that you physically can. However, this ideal does not match the current reality of sport at a performance level. With the genetics endowed aside, athletes are turning to more extrinsic methods to enhance their performance, such as found in the form of ergogenic aids. With the current high levels of media interest being given to the area of performance enhancement techniques, athletes are searching for ergogenic aids that do not have side effects or illegal properties present. This is where nutritional ergogenic aids including carbohydrate, creatine, and dietary antioxidants have provided promising alternatives.

This paper will look at the relationship between one of these nutritional ergogenic aids, carbohydrate intake, and sporting performance in athletes at an elite level. It will start with the current theory as to what extent carbohydrate affects the performance of an athlete, and the second part of the assignment will examine the current literature published regarding differing amounts of carbohydrate ingested in an athletes diet, and whether these differing amounts result in an enhancement in physical performance. It will examine the different uses of carbohydrates in the days leading up to an event or performance (glycogen supercompensation), and the use of carbohydrates in the hours prior to the event.

The Relationship between Carbohydrate Levels and Performance
In 1991, the International Conference on Foods, Nutrition and Performance recommended that an athlete performing maximally should consume a diet containing 60-70% carbohydrates (Williams & Devlin 1992, cited in Bean 2002). This was also shown by Walberg-Rankin (1995) who stated that ‘carbohydrate consumption as a percentage of total caloric intake for an endurance athlete should be at least 60%’.

The relationship that carbohydrate levels have with exercise performance at all levels is one that has received attention since the 1930’s, where research carried out by Christensen et al (1939) demonstrated that ‘high carbohydrate diets improved endurance performance’. It has been stated by Applegate (1999) that ‘there (Christensen et al) work became the foundation for the dietary regimen that many athletes use today to modify carbohydrate intake prior to, during, and following prolonged endurance exercise’.

During intense exercise, the production of adenosine triphosphate (ATP) is determined by the availability of blood glucose and muscle glycogen. Though it is possible to perform light exercise with low levels of these fuels, depletion results in an inability for the muscles to sustain the contractile tension needed. If carbohydrate levels are low, utilisation of fat and protein can occur in order to generate the required energy, but this is still inadequate when compared to the energy derived from carbohydrates.

Below et al (1995) identified the effects of carbohydrate ingestion on performance during one hour of intense cycling. The study consisted of eight endurance athletes completing four trials while consuming either a large volume (1330 ml) of a 6% carbohydrate solution or a water placebo, or a small volume (200ml) of a 40% maltodexrin solution or a water placebo. The trials were pooled so that the effects of fluid replacement and carbohydrate solutions could be determined. The exercise trials consisted of two phases with phase one requiring the subject to cycle at 80% of their VO2 max for 50 minutes. Phase two consisted of cycling at 10% above the individual subjects lactate threshold for the final ten minutes. The main finding of this study was that the performance of the subjects who ingested the large amount of carbohydrate compared to a large amount of water showed improved performance times. These findings were supported by Nicholas et al (1995), who similarly found that performance during a high-intensity shuttle run test improved in the subjects that ingested the 6% carbohydrate solution compared to the subjects consuming the water placebo. The author stated that ‘the carbohydrate solution had a decreasing effect on the heart rate and ratings of perceived exertion of the subjects’. On concluding the study, the author stated that ‘recreational game players who consumed a 6.9% carbohydrate-electrolyte drink could continue at the same rate for 33% longer’.

Another study carried out by Nicholas et al (1999) examined the effects of ingesting a carbohydrate sports drink, or placebo, on muscle glycogen utilisation during high intensity intermittent running. According to Nicholas et al (1999) ‘this test was sport specific, and aimed at imitating the exercise rates of a football match’. The subjects undertook six bouts of exercise, each lasting fifteen minutes in duration and consisted of maximal sprinting interspersed with less intense periods of walking and running. The solution consumed by half the group contained 6.9% carbohydrate, and the remainder of the group consumed a water placebo. The results of the study highlighted that the ingestion of a carbohydrate drink resulted in a 22% reduction in the amount of muscle glycogen utilised compared to the ingestion of the water placebo. I feel that the reduction of muscle glycogen shown in the above study may be one of the factors that resulted in the performance increase found in the previously shown study by Nicholas et al (1995). However, Nassis et al (1998) found that ingesting a solution containing 6.9% carbohydrate, does not delay the onset of fatigue during repeated bouts of sub-maximal intermittent high intensity running. During this study, the 9 subjects undertook a treadmill protocol on two occasions interspersed by 10 days. This consisted of three phases, with phase 1 lasting for 60 minutes at 80% VO2 max, phase 2 from 60 – 100 minutes at 85% of VO2 max, and phase 3 lasted from 100 minutes to exhaustion, and required the subject to run at 90% VO2 max. On each occasion, the subjects either consumed the placebo or the carbohydrate solution immediately before the run, and at 20 minute intervals thereafter. It seems that this test differs from others in the intensity of exercise that is being requested of the subjects, and that the concentration of carbohydrate in the solutions that part of the group were consuming were not enough to provide a difference in performance.

The author reported that ‘performance times were not significantly different between the two trials, and no difference was found in the total carbohydrate oxidation rates between trials’. One difference was shown in the levels of blood glucose recorded in the two trial groups, with the author stating that ‘blood glucose concentration was higher in the carbohydrate-electrolyte trial, but only after 40 minutes’. As the author has found no significant difference in performance, future research using this high intensity of exercise should use greater concentration of carbohydrates in the solutions. The results have also shown that there was an increased amount of blood glucose after 40 minutes, and thereafter it decreased to normal amounts. This again highlights that the subjects may not be ingesting enough carbohydrates to adequately undertake the required intensity levels. To conclude his findings, the author stated that ‘the fatigue that occurred after nearly two hours of intermittent exercise was a consequence of a reduction in muscle glycogen concentration and an inadequate rate of phosphocreatine resynthesis’. These results were supported by those of Bosch et al (1996), who stated that ‘fatigue was a result of critically low muscle glycogen content, irrespective of whether a carbohydrate drink was ingested or not. They found that carbohydrate ingestion did not slow the rates of glycogen utilisation by the working muscles until muscle glycogen content fell below 70 mmol kg.

Carbohydrate Ingestion Techniques
Currently, there are a number of techniques that have been adopted regarding the usage of carbohydrates. There is research supporting, and dismissing the differing use of carbohydrates throughout the days leading to an event.

This next section will address the usage of carbohydrates by athletes in the days leading up to an exercise performance. It will look at the use of carbohydrates days before, hours before, and immediately prior to performance, and the subsequent research carried out on their effectiveness as a nutritional ergogenic aid.

Glycogen Supercompensation
The process by which glycogen concentration is raised to levels two or three times greater than normal is called glycogen supercompensation. This process results from a program of exercise followed by a high carbohydrate diet. In previous studies, this process has been known as ‘carbohydrate loading’, and the process at which this technique is used covers the days prior to an event or competition. Three or four days prior to competition, the athlete exercises to near exhaustion. For some sports, the procedure also includes interval sprinting to deplete the type IIb and type IIa fibres of glycogen. The remaining days to competition were then spent on a reduced training volume, and a high carbohydrate diet of around 60 – 70%. Through reading a plethora of research on the use of glycogen supercompensation, there seems to be a question over the advisability of depleting the glycogen stores and then replenishing them to higher than normal levels. This questioning of this technique regards the athlete’s knowledge of the type of carbohydrates that they should consume. This replenishment of the glycogen stores requires complex carbohydrates to be consumed, and if the athlete is not aware of the different carbohydrate types, then a large amount of sugar based products will be consumed. On this issue, Brooks et al (1996) stated ‘refined sugar products and alcohol are not complex carbohydrates and are not recommended’.

Although the high carbohydrate diet is one that has had many researchers stating its effectiveness in training for endurance and high intense exercise, there seems to be several issues that have arose regarding its usage.

The previously stated research has shown the advantages of a high carbohydrate diet for athletes undertaking a number of different sports, but taking on a high level of glycogen can also hamper performance in some sports.

The storage of glycogen results in a retention of water which can prove detrimental to performance. According to Brooks et al (1996), ‘storage of each gram of glycogen requires almost 3 grams of water, each gram of glycogen in effect adds 4 grams body weight’. In some sports such as gymnastics and sprinting, no extra carbohydrate stores would be beneficial, but the extra weight that they may carry due to pre-loading with glycogen may affect the performance in a negative way. This extra water from the resulting glycogen storage may be beneficial to athletes who compete in sports where the risk of dehydration is an issue. This factor could explain the results found by Burke et al (2000), who stated that ‘carbohydrate loading has also been associated with increased exercise performance in the heat; a condition where carbohydrate availability is not usually thought to limit exercise performance’. Another issue was highlighted by Lambert et al (1997) regarding the 2 day period of carbohydrate starving that is part of the glycogen loading process.

According to Brooks et al (1996), ‘this period when proteins and fats were consumed results in a heightened glycogen super-compensation effect’. However, Lambert et al (1997) stated that ‘it has never been convincingly demonstrated that adding such a carbohydrate starving period is beneficial’. On this issue, Hargreaves et al (2004) stated that ‘carbohydrate starvation after exhausting exercise is a form of malnutrition and has often been reported to produce serious side effects’. Also, Sherman et al (1981) found that ‘the carbohydrate starvation period is unlikely to improve either muscle glycogen storage or running performance’. Due to these findings, Hargreaves et al (2004) concluded that ‘inducing a period of muscle wasting, depression, and lethargy immediately prior to competition is no longer thought to be the best way to prepare an athlete psychologically or physiologically’.

The effectiveness of glycogen super compensation, and its comparison to other carbohydrate related techniques, is an area that has received mixed responses since it was adopted by sportsman and athletes across a multitude of sporting events.

According to current research, the process of ingesting a high carbohydrate diet in the days leading up to an event can give a multitude of benefits to the athlete. Regarding one of the said benefits, Fairchild et al (2002) stated that ‘it has even been suggested that trained athletes can greatly increase their muscle glycogen stores in less than 24hrs by performing only 3 min of supramaximal exercise and then consuming a high carbohydrate diet’. The importance of raising the muscle glycogen levels directly relates to an athletes performance. On the basis of results gathered from isotope tracer studies, and ones from arteriovenous difference measurements of blood glucose across working limbs and muscle biopsies, Brook et al (1996) stated it has been estimated that muscle glycogen contributes three to five times as much fuel as does blood glucose during prolonged submaximal exercise’. However, it has been suggested by Hargreaves et al (2004) that ‘females may have a reduced ability to increase muscle glycogen during a period of dietary carbohydrate loading’. This conclusion was not supported by Walker et al (2000), who stated that ‘other studies have not observed reduced muscle glycogen storage in females’. The author concludes their study by stating ‘thus, with adequate energy and carbohydrate intake, female athletes benefit from carbohydrate loading as much as male athletes’. This is not to say that blood glucose is a lesser used fuel of the two as they both have different uses during exercise. The body needs to have a high level of blood glucose also, but this will be discussed more in reference to the pre-match meal.

According to Hargreaves et al (2004), ‘carbohydrate loading does not appear to further increase exercise performance when carbohydrate availability is maintained high with a pre-exercise carbohydrate meal and carbohydrate ingestion during exercise’.

Carbohydrate Ingestion 3 – 4 Hours Prior to Performance
In the hours prior to a performance, ingestion of a carbohydrate rich meal is becoming the norm among athletes. The pre-event meal, and its contents, is an area that has been identified as a performance altering factor. According to Coyle et al (1985), ‘ingestion of a carbohydrate rich meal 3-4 hours before exercise has been shown to increase muscle glycogen, and enhance exercise performance’. This increase in performance may be attributed to the subsequent increase of the muscle glycogen stores, but it could also be attributed to other factors. The glycogen levels in the liver will be decreased due to the overnight fasting, and an ingestion of carbohydrate will increase these stores. On this issue, Casey et al (2000) stated ‘ingestion of carbohydrate may increase these reserves, and together with any ongoing absorption of the ingested carbohydrate, to the maintenance of blood glucose concentrations and improved performance during subsequent exercise’.

Although the evidence of benefits from ingesting a pre-match meal containing high levels of carbohydrate has been found to be equivocal, other studies have observed no benefit to exercise performance from a high carbohydrate meal 4 hours before exercise. On this issue, Okano et al (1996) stated ‘despite plasma glucose and insulin concentrations returning to basal levels, ingestion of carbohydrate in the hours before exercise often results in a transient fall in glucose with the onset of exercise, increased carbohydrate oxidation, and a blunting of free fatty acid mobilisation’. These metabolic perturbations can persist for up to 6 hours after the ingestion of carbohydrate, but according to Montain et al (1991), it is not detrimental to their performance as ‘increased carbohydrate availability will compensate for the greater carbohydrate utilisation’. Similar results stating the apparent lack of benefits found were recorded by Wee et al (1999), who stated that ‘no differences in exercise performance have been observed after ingestion of meals that produced marked differences in plasma glucose and insulin concentrations’.

From reading through the plethora of research on the area of carbohydrate ingestion in the hours leading up to a performance, it seems that the majority of the studies that have found positive benefits from high carbohydrate intake 3 – 4 hours before exercise, have also found positive results when carbohydrate is ingested during the exercise. On this issue, Williams et al (1997) stated that ‘the effects of a high carbohydrate meal 3-4 hours before exercise on subsequent performance may be equivalent to those observed with carbohydrate ingestion during exercise’. This view was supported by Wright et al (1991), who stated that ‘the combination of a pre-exercise carbohydrate meal and carbohydrate ingestion during exercise may further enhance exercise performance’.

Carbohydrate Ingestion 30 – 60 Minutes Prior to Performance The largest and most researched area of carbohydrate use in the days leading up to performance is the minutes just prior to the performance or event. This is a chance for an athlete to ingest carbohydrates, normally in the form of a drink or gel, at the last possible minute to hopefully gain an advantage over their opponent. However, we have seen the potential benefits from either loading up on carbohydrates in the days leading up to the performance, or by taking in a carbohydrate loaded pre-event meal, but by taking in carbohydrates so close to the event, can this be as beneficial as the other ingestion techniques?

According to Hargreaves et al (2003), ‘the ingestion of carbohydrate in the hour before exercise results in a large increase in plasma glucose and insulin concentrations’. This is a desired outcome for the athlete, but this increase close to a performance can result in a negative effect. Hargreaves et al (2003) continued stating ‘with the onset of exercise, however, there is a rapid fall in blood glucose concentration as a consequence of the combined stimulatory effects of hyperinsulinaemia and contractile activity on muscle glucose uptake and inhibition of the exercise-induced rise in liver glucose output’. By ingesting a large amount of carbohydrate pre-performance, fat oxidation is also decreased during the following exercise. This is due to the lower plasma FFA availability, but also as a result of inhibition of lipid oxidation within muscle (Coyle et al 1997). In longer performance events, the reduction in fat oxidation could be detrimental to performance, so different techniques have been adopted to combat this loss. One technique is the ingestion of triglycerides prior to performance in an attempt to raise the FFA levels that inhibit the fat oxidation. A problem found relating to this ingestion is the affect that it has on glycogen levels. On this issue, Horowitz et al (2000) stated that ‘co-ingestion of medium-chain triglycerides with carbohydrate, as a strategy to increase plasma FFA, has no effect on muscle glycogen use during subsequent exercise’. As these are consequences of hyperglycaemia and hyperinsulinaemia, the interest in strategies that minimise these effects has also increased. Such techniques include fructose intake to replace glucose, due to its different glycaemic index, differing carbohydrate amounts, and the introduction of a warm-up in the pre-exercise schedule. These techniques are aimed at controlling or delaying the onset of hyperglycaemia and hyperinsulinaemia that can occur from adopting the pre-performance feeding of carbohydrates.
Conclusion
The evidence that benefits occur from ingesting carbohydrates at specific times during a training regime, or match situation, is equivocal. The published results from many research projects have shown these benefits in a number of different sporting situations. The controversy, and differing opinions on the subject arise in the question of when this ingestion should take place. It seems that the process of loading up on carbohydrate in the days leading up to a performance is a successful method of increasing the muscle glycogen stores to a higher than normal level, with studies showing increases in a number of different areas of the performance. However, this process has also proven to have potentially negative affects on performance due to its water retenting side effect. Along with the ingestion of a carbohydrate rich meal on the day of the event, and in the minutes prior to a performance, the use of carbohydrate loading is met with differing success depending on the sport that is being undertaken. I feel that as a popular ergogenic aid that is currently being adopted by athletes, the effects that are come from the different ingestion techniques have been shown to benefit the athlete in a number of ways. However, this excess ingestion is a technique that is not ideal for some sports where body mass is an issue.