Carbohydrate can play an important role in preparation for competition. Carbohydrate intake in the days before competition mainly replenishes muscle glyco-gen stores, whereas carbohydrate intake in the hours before competition optimizes liver glycogen stores. Because carbohydrate intake in the days before competition has distinctly different effects than carbohydrate intake immediately before competition, these issues will be discussed separately.
Scandinavian researchers discovered that muscle glycogen could be supercompensated by changes in diet and exercise (Bergstrom et al. 1967b). In a series of studies, they developed a so-called supercompensation protocol, which resulted in extremely high muscle glycogen concentrations. This diet and exercise regimen started with a glycogen-depleting exercise bout (see figure 6.5). The exercise was then followed by 3 days of a high-protein, high-fat diet. Another exhausting exercise bout was performed on day 4, after which the subjects were placed on a high-carbohydrate diet for 3 days. Another group of subjects followed the same exercise protocol, but their diets were in reverse order. This study revealed that the subjects who received the high-protein, high-fat, low-carbohydrate diet first followed by the high-carbohydrate diet had higher rates of muscle glycogen resynthesis. The authors therefore concluded that a period of carbohydrate deprivation further stimulated glycogen resynthesis when carbohydrates were given after exercise.
The regimen that was proposed is generally referred to as the classical supercompensation protocol (see figure 6.5). Several top athletes have used it successfully, including the legendary British runner Ron Hill. In fact, nowadays many marathon runners use this method to optimize their performance. Although the supercompensation protocol has been effective in increasing muscle glycogen to very high concentrations, it also has several important (potential) disadvantages of which athletes should be aware:
- Hypoglycemia during the low-carbohydrate period
- Practical problems (difficulty in preparing extreme diets)
- Gastrointestinal problems (especially on the low-carbohydrate diet)
- Poor recovery when no carbohydrate is ingested
- Tenseness during a week without training
- Increased risk of injury
- Mood disturbances (lethargy and irritability) during the low-carbohydrate period
The main problem may be the incidence of gastrointestinal problems when using this regimen. Diarrhea has often been reported on the days when the high-protein, high-fat diet is consumed. During the first 3 days, athletes may also experience hypoglycemia, and they may not recover well from the exhausting exercise bout when no carbohydrate is ingested. Also, the fact that athletes cannot train in the week before an event is not ideal, because the worst punishment for most athletes seems to be asking them to avoid training. These factors may also have an effect on mental preparation for an event.
Because of the numerous disadvantages of the classical supercompensation protocol, studies have focused on a more moderate supercompensation protocol that would achieve similar results. Sherman et al. (1981) studied three types of muscle glycogen supercompensation regimens in runners. The subjects slowly reduced their training over a 6-day period from 90 minutes of running at 75% of V.O2max to complete rest on the last day. During each taper, they ingested one of the following three diets:
- A mixed diet with 50% carbohydrate
- A low-carbohydrate diet (25% carbohydrate) for the first 3 days followed by 3 days of a high-carbohydrate diet (70%) (classical supercompensation protocol)
- A mixed diet for the first 3 days (50% carbohydrate) followed by 3 days of a high-carbohydrate diet (70%) (moderate supercompensation protocol)
The classical protocol resulted in very high muscle glycogen stores (211 mmol/kg w.w.), confirming the results of earlier studies. But the moderate approach produced similar muscle glycogen levels (204 mmol/kg w.w.). Therefore, a normal training taper in conjunction with a moderate-carbohydrate to high-carbohydrate diet proved just as effective as the classical supercompensation protocol. A slightly modified and commonly applied strategy of the moderate supercompensation protocol is depicted in figure 6.5b. Because it does not have the disadvantages of the classical protocol, the moderate supercompensation protocol is the preferred regimen.
More recently, various glycogen-loading protocols have been used successfully. In one study endurance-trained athletes performed very high-intensity exercise for only 2 min (cycling for 150 s at 130% of V.O2max followed by 30 s of all-out cycling) and then consumed a very high-carbohydrate diet (Fairchild et al. 2002). This protocol resulted in very high muscle glycogen concentrations 24 hours later (198 mmol/kg w.w.). Clearly, an exhausting bout of exercise is not necessary to achieve very high (supercompensated) glycogen stores (Bussau et al. 2002). Finally, note that after glycogen stores are high they will stay high for several days if limited exercise is performed.
Early reports suggested that women have reduced ability to synthesize glycogen (Tarnopolsky et al. 1995), but this view has changed because the research findings may have been a result of the smaller amount of carbohydrate that the female subjects ingested in that study. When men and women consume a comparable amount of carbohydrate (expressed in grams per kilogram of fat-free mass, FFM), no differences in glycogen loading are observed (McLay et al. 2007; Tarnopolsky et al. 1997). In addition, it has been suggested that glycogen loading might be affected by menstrual cycle phase, but a study found no differences in the ability to synthesize glycogen in different phases of the menstrual cycle (McLay et al. 2007).
Carbohydrate loading, or increased carbohydrate stores, increases time to exhaustion (endurance capacity) on average by about 20% and reduces the time required to complete a set task (time trial, endurance performance) by 2% to 3% (Hawley et al. 1997). But the available studies seem to suggest that the duration of exercise has to be at least 90 minutes before performance benefits occur. Carbohydrate loading seems to have no effect on sprint performance and high-intensity exercise up to about 30 minutes compared with normal diets (~50% carbohydrate). This finding is expected, because at these high intensities glycogen depletion is probably not the performance-limiting factor. But several days on a very low-carbohydrate diet (<10%) after a prolonged cycle ride to exhaustion has been shown to impair endurance capacity at 100% of V.O2max (Maughan et al. 1997).
Carbohydrate loading has also been reported to improve performance in team sports involving high-intensity intermittent exercise and skills, such as soccer and hockey (Balsom et al. 1999), although this result has not always been confirmed. A study was performed in elite Swedish soccer players who played two matches separated by 3 days (Saltin 1973). One group consumed a high-carbohydrate diet, and the other group consumed a normal diet between the matches. Before the second match, muscle glycogen concentrations were 50% lower in the group that consumed the control diet. At halftime (after 45 minutes), muscle glycogen was virtually depleted in this group, whereas the high-carbohydrate group still had some glycogen left (see table 6.2). This glycogen status was related to the distance covered during the match, which was significantly lower with the control diet and low muscle glycogen concentrations. The players also spent less time sprinting and thus were believed to have impaired running performance.
So several strategies can optimize muscle glycogen, and these do not necessarily involve a complicated approach. The approach is similar for men and women. In essence, carbohydrate intake should be very high in the days before the event and muscle activity should be limited.
Figure 6.5 (a) The classical supercompensation protocols consisting of a glycogen-depleting exercise
bout followed by 3 days of a high-protein, high-fat diet, another exhausting exercise bout on day 4,
followed by a 3-day high-carbohydrate diet. (b) A more moderate protocol was later suggested to be
almost as effective.