UltraFit Magazine - Issue 114, Page 36

by Paul Taylor

Replenishment of Glycogen Stores Following Exercise

In the first part of this series on Carbohydrate as a Performance Aid in Team Sports, we discussed the general need for participants of team sports to maximise the availability of carbohydrate (CHO) during games. As was pointed out in Part 1, the opportunities for replenishing CHO stores during a game are few and limited to official breaks in play (half-time and in some sports, quarter time). Therefore, it makes perfect sense to go into a game with maximum stores of CHO. This process starts not with the pre-game meal, but with feeding that takes place after the last training bout.

From examining the scientific research, it is obvious that the benefits of CHO loading protocols for endurance exercise are well documented. Burke & Deakin (2002) found that CHO-loading protocol postpones fatigue in steady-rate exercise by 20% and improves performance (two very different things that are often confused) over a set distance/workload by two to three per cent. However, the frequency of training and playing prevents participants of competitive team sports from undertaking the more extreme CHO loading practices adopted by endurance runners and cyclists who compete less often. A daily intake of 65-70% of calories from CHOs should ensure adequate daily restoration of glycogen stores during peak season (Costill et al, 1981). When this is compared with the 47% CHO intake reported in elite soccer players (Jacobs et al, 1982), the need for nutritional advice becomes obvious.

If routine consumption of 65-70% calories from CHO is not attainable, players should at least try to achieve this on the day preceding a game. It would appear that for events of 60-90minutes, 24 hours rest and a CHO intake of 7-10g/kg-body mass (bm), in the absence of muscle damage, is adequate for normalising glycogen stores (Burke & Deakin, 2002). A high CHO diet (8.8g/kg bm) restored endurance capacity in sixteen male runners, whereas an isocaloric (same amount of total calories) diet without additional CHO (5.8g/kg bm) did not (Fallowfield and Williams, 1993). Lambert & Goedecke (2003) recommend a minimum CHO intake of 6g/kg body mass/day in order to delay fatigue in subsequent exercise.

These results agree with more recent, soccer specific studies (most of the funding involves research into soccer, although the ramifications can be applied to all similar team sports) into the effects of CHO intake on intermittent running capacity. The first experiment, which was very well put together, used the Loughborough Intermittent Shuttle Test (Nicholas et al, 1997) and a randomised, crossover design. Subjects performed the test after consuming their normal diet, then repeated it 22 hours later after following either a diet that contained 10g/kg bw of CHO (CHO group), or an isocaloric diet comprising their normal diet, supplemented with extra fat and protein (CON group). They found that intermittent running capacity was not matched following CON diet, but it actually improved when the CHO diet was consumed and that these differences were statistically significant. Importantly, what also transpired from this study was that ad libidum intakes of CHO (when the athletes consumed as much or as little as they felt like) fell well below that required to optimise replenishment of glycogen stores - this backs up the need for athletes to seek professional help.

Rockwell et al (2003) studied the effects of 24 hour diet on performance of intermittent exercise (repeated 60 second cycling sprints). High CHO (85%, CHO, 10-15% Protein, 5% Fat) diets or low CHO diets (5-10% CHO, 15-20% Protein, 65-75% Fat) were prescribed by a dietician, and energy was matched to previously compiled 24 hour intakes. A crossover design was used to eliminate any bias. Baseline muscle glycogen levels and time to fatigue were significantly higher following high CHO diet.

In a laboratory study, Balsom et al (1999) examined the effects or high versus low CHO diets (for 48 hours) on muscle glycogen levels and performance of repeated six second bouts of high intensity intermittent (30 second intervals), short (10 minutes) and prolonged (30 minutes) exercise on a cycle ergometer. They found that glycogen levels and work done were significantly lower in both trials, following the low CHO diet. Validity of the results was improved by the employment of a crossover design (a better design) and have been supported by Bangsbo et al (1992), who reported improved performance of intermittent running by soccer players following a high CHO diet (65% calories) measured against a low CHO (39% calories) diet. Further evidence is presented from a field study by Balsom et al (1999b) into the effects of a high (65%) CHO versus a low (30%) CHO diet on workrates during a 90 minute four-a-side game of soccer. Movement analysis revealed that the players performed significantly (33%) more work after the high CHO diet.

Having said all of this, timing of CHO intake seems important only when total CHO intake is less than optimal. That is, if CHO intakes are adequate over a 24 hour period, then early or regular feeding appears to confer no additional benefits (Burke& Deakin, 2002). If recovery time is limited, however, early feeding after exercise or training is essential, as glycogen resynthesis is reported to occur at twice the rate if CHO is ingested in the first two hours following exercise when compared to the second two hours (Ivy, 1998; Parkin et al, 1997). It should also be noted that when CHO is consumed following exercise there is strong evidence to suggest that high Glycemic Index (GI) foods induce greater muscle glycogen resynthesis (Siu & Wong, 2004; Burke & Deakin, 2002). Therefore it would be prudent for team sports players to consume a large amount of high GI CHO as soon as possible after competition or training, in order to take advantage of the advantageous metabolic factors discussed in the previous article, and maximise glycogen resynthesis.

To summarise, all of these studies strongly suggest that in order to influence performance or the amount of high intensity exercise performed in team sports, a high CHO diet should be consumed both immediately following exercise or competition in order to prepare for training and games. Additionally, a significant amount of training should be avoided on the day before a match, as all team sports involve a significant amount of eccentric exercise, which has a negative impact on glycogen resynthesis that may last for several days (Costill, 1991; ASP, 1999) and thus negatively impact on even the best planned strategies.

In the next issue we will examine the research behind the timing and nutrient composition of pre-game meals.

References:

Asp S Daugaard JR Rohde T Adamo KB Graham T (1999) Muscle glycogen accumulation after a marathon: roles of fiber type and pro- and macroglycogen J Appl Physiol 86 474-8
Balsom PD Gaitanos GC Soderlund K Ekblom B (1999) Highintensity exercise and muscle glycogen availability in humans. Acta Physiol Scand 165(4) 337-45
Balsom PD Wood K Ekblom B (1999b) Carbohdyrate intake and multiple sprint sports: with special reference to football (soccer) Int J sports Med 20(1) 48-52
Bangsbo J Norregaard L Thorsoe F (1992) The effect of carbohdyrate diet on intermittent exercise performance. Int J Sports Med 13(2) 152-7.
Burke L Deakin V Clinical Sports Nutrition McGraw-Hill Book Commpany NSW 2nd Ed 2002
Costill DL Pascoe DD fink WJ Robergs RA Barr SI Pearson D (1991) Impaired muscle glycogen resynthesis after eccentric exercise J Appl Physiol 69 46-50
Fallowfield JL Williams C (1993) Carbohydrate intake and recovery from prolonged exercise Int J Sport Nutr 3 150-64
Ivy JL Lee MC Bronzinick JT Reed MC (1988) Muscle glycogen storage following different amounts of carbohydrate ingestion J Appl Physiol 65 2018-23
Jacobs I Westlin N Karlsson J (1982) Muscle glycogen and elite soccer players Eur J Appl Physiol 48 297-302
Lambert EV Goedecke JH (2003) The role of dietary macronutrients in optimizing endurance performance Curr Sports Med Rep 2(4) 194-201
Nicholas CW Green PA Hawkins RD Williams C (1997) Carbohydrate intake and recovery of intermittent running capacity Int J Sport Nutr 7(4) 251-60
Parkin JAM Carey MF Stojanovska L Febbraio MA (1997) Muscle glycogen storage following prolonged exercise: effect of timing of ingestion of high glycaemic index food Med Sci Sports Exer 29 220-4
Rockwell MS Rankin JW Dixon H (2003) Effects of muscle glycogen on performance of repeated sprints and mechanisms of fatigue Int J Sport Nutr Exer Metab 13(1) 1-14
Siu PM Wong SH (2004) Use of the glycaemic index: effects on feeding patterns and exercise performance J Physiol Anthro App Hum Sci 23(1) 1-6