Eur J Appl Physiol (1982) 48:297-302 European Journal of

Applied Physiology and Occupational Physiology

Springer-Verlag 1982

Muscle Glycogen and Diet in Elite Soccer Players

Ira Jacobs, Nils Westlin, Jan Karlsson, Margareta Rasmusson, and Bob Houghton

Laboratory for Human Performance, Dept. of Clinical Physiology, Karolinska Hospital, S-10401 Stockholm, Sweden Dept. of Orthopaedic Surgery, Maim6 General Hospital, Maim6, Sweden

Summary. The top players in an elite soccer team volunteered as subjects in a study to determine intramuscular glycogen concentrations after a regular season match, and whether optimal glycogen levels could be re-attained prior to the team's next match. Fifteen players were biopsied in the M. vastus lateralis following a regular season game (Day I). Of these, eight were biopsied 24 h later in the evening of a free day during which no training session was held (Day II), and again 24 h later after a very light training session (Day III). Muscle glycogen concentrations for the eight players averaged (+ SD) 45.9 + 7.9, 68.9 + 2.7, and 72.8 + 8.3 mmol glucose units x kg -1 wet muscle weight on Day I, Day II, and Day III respectively. Dietary records were analysed during a week of peak season competition and training. The average daily total energy consumption and total quantity of carbohydrates consumed were less than what is normally consumed by athletes in similar sports. The inability of the players to maintain even normal, resting levels of muscle glycogen is probably related to their dietary practices.

Key words: Glycogen - Muscle fiber types - Soccer - Diet

Introduction

The importance of intramuscular glycogen levels to exercise performance both in laboratory and field conditions has been repeatedly demonstrated (Karlsson and Saltin 1971). The fraction of energy derived from glycogen stores depends to a large extent on relative exercise intensity in addition to factors such as diet, training status, environmental conditions, etc. (for review see Costill and Miller

* Supported in part by grants from the Jfirnhardtska Fund and the Swedish Football Associa- tion

Offprint requests to: I. Jacobs, Dr. Med. Sci., Dept. of Clinical Physiology, Karolinska Hospital (address see above)

0301-5548/82/0048/0297/$ 01.20

298 I. Jacobs et al.

1980). The relatively high exercise intensity and long dura t ion of m a n y compet i t ive t eam sports suggest that muscle glycogen levels would be of re levance to pe r fo rmance in such sports. Surprisingly few studies have examined glycogen utilization during actual league game situations (Green et al. 1978; Zap iec and Taylor 1979). Based on data ob ta ined during an exhibit ion soccer game, Saltin (1973) descr ibed how glycogen levels and player pe r fo rmance covary. N o study could be found which describes the changes in in t ramuscular g lycogen levels during consecut ive days in elite soccer players. Thus the purpose of the present s tudy was to de te rmine int ramuscular glycogen levels following an actual league game in national-cal ibre soccer players, in addit ion to the extent of reple t ion during the following 2 days. The study was not in tended to be exper imenta l in nature , since the subjects were professional soccer players and not part icularly enthusiastic about any type of manipula t ion of their environ- ment . H o w e v e r , descriptive data are presented.

Methods

The subjects studied were 15 players from Malm6 F.F. soccer team - one of Sweden's top, national league teams at the time of the study. These players were part of one of Europe's best soccer clubs during the previous season, as demonstrated by their being placed second in the European Cup, 1979. Their mean (range) age, height and weight were 23.6 (20-30) years, 178.5 (168-194) cm, and 73.5 (68-92) kg, respectively.

The M. vastus lateralis in each player was sampled by percutaneous needle biopsy. Muscle fiber type frequency and the relative muscle area occupied by each fiber type were determined with histochemical methods described previously (Jacobs 1981).

Eight players agreed to have biopsies taken on 3 consecutive days during the peak season. The first biopsy (Day I) was taken immediately following a crucial regular season game which greatly affected league standings. After consultation with the coaching staff, it was decided not to obtain pre-game biopsies in order to avoid the possibility of the procedure affecting player performance during this important game. All eight players played the entire game. The second biopsy (Day II) was taken in the evening, approximately 3 h after dinner, on the day after the match. Players were free during this day with no training sessions. The third biopsy (Day III) was taken on the following day immediately after a light training session in the late afternoon consisting of stretching exercises and calisthenics. Each muscle sample was divided into two parts. One part was used for serial section staining of both myofibrillar ATPase and periodic acid-Schiff (PAS) (Pearse 1961) for qualitative estimation of the location of glycogen depletion and/or repletion (Gollnick et al. 1973), while the second part was used for biochemical determination of total glycogen content (Karlsson 1971).

A few weeks earlier, during a part of the season similar in game frequency and training intensity to the experimental period, a diet diary was recorded by each player for a week according to the detailed instructions of a certified dietician and nutritionist. From this diary, the total average daily energy consumption as well as the proportion of fat, protein and carbohydrates were determined.

Results

Values for the variables associated with the de terminat ion of the muscle fiber type composi t ion are descr ibed in Table 1. The f requency of type II (fast twitch, FT) muscle fibers (% FT) predomina tes in these subjects and this is more

Glycogen and Soccer

Table 1. Muscle fiber characteristics of 15 elite soccer players

299

Mean SD Range

Number of fibers counted % fast twitch % fast twitch area FT mean fiber area 0*m 2) ST mean fiber area (gm 2) FT/ST mean fiber area

356 187 110-688 59.8 10.6 40.8-79.1 65.6 10.6 49.1-86.7 6976 1198 5338-9128 5486 850 4295-6625 1.28 0.22 1.03-1.72

Table 2. Glycogen concentrations in the M. vastus lateralis of soccer players immediately following a league soccer match (Day I), one day later (Day II), and two days later (Day III)

Day I Day II Day III

Mean 46 69 73 SD 8 3 8 Range 35-63 64-71 61-85

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Glycogen after match (mmol xkg-1)

Fig. L The relationship of glycogen concentrations in the M. vastus lateralis after a regular league soccer match to the absolute increase in glycogen concentrations over the following 24 h during which time the subjects engaged in no exercise

300 I. Jacobs et al.

Table 3. Nutritional profile of elite soccer players as compared to recommended optimal nutritional status for athletes. Values are expresssed as means (SD)

Daily Protein Protein Fat Fat Carbo- Carbo- energy (%) (g) (%) (g) hydrate hydrate consump- (%) (g) tion (k J) b

Soccer players 20,700 13.6 170 29.2 217 47.0 596 (4,713) (1.6) (27) (8.4) (36) (3.3) (127)

Recommended a 24,697 10-15 145-220 25-30 164-197 55-60 811-885

a Values adapted from reference [10] b 1 kJ = 0,239 kcal

pronounced when the relative area occupied by the FT fibers is considered (59.8% FT and 65.6% FT area).

The changes in muscle glycogen levels during the 3 consecutive days of the study are described in Table 2. Glycogen levels after the soccer game were 63% of the mean values observed for the same players in their glycogen "filled" condition (i.e., Day II and/or Day III). No significant difference was evident between glycogen concentrations observed on Day II and Day III.

The increase in glycogen levels from after the game on Day I until the evening of the free Day II, was significantly related to the extent of glycogen depletion during the game (Fig. 1). Thus, the lower the absolute glycogen concentration on Day I, the greater was the increase in glycogen 24 h later (r = -0.95, p < 0.01). Evaluation of the PAS staining intensity suggested that both the ST and the FT muscle fibers were approximately equally depleted of glycogen on Day I. Player position was not related to glycogen levels after the match. No difference between fiber types was evident with regard to the speed of refilling the glycogen depots.

Analysis of the diet diaries showed a low mean, daily energy consumption for elite athletes during the peak season (Table 3). The relative proportion of energy intake consisting of fats, proteins or carbohydrates was not significantly related to absolute glycogen concentrations on any of the experimental days, nor to the increase in glycogen levels from Day I to Day II or Day III.

Discussion

The main finding of the present study was the low glycogen levels observed in the leg musculature following a regular national league soccer match. Of at least equal importance was the observation that during a 2-day period following the match, glycogen levels increased by only 27 mmol x kg -1 wet weight. Thus, 48h following a difficult match the mean glycogen concentration was 72.8 mmol x kg -1 - a value lower than that usually observed for sedentary subjects (Costill and Miller 1980; Piehl 1974) and certainly lower than the optimal value desired for elite athletes at the peak of the season.

Glycogen and Soccer 301

The glycogen reserve in exercising musculature has been repeatedly shown to be a limiting factor to the ability to continue to exercise at high submaximal exercise intensities (Saltin and Karlsson 1971). Previous studies have reported running speed, glycogen utilization (Saltin 1973), heart rates and blood lactates (Agnevik 1970) for soccer players involved in exhibition matches, and all of these variables indicate that exercise intensity surpasses the minimal threshold for a large contribution of glycogenolysis to energy production.

It should be noted that this study was carried out at the peak of the season, with 1 -2 matches a week in addition to training every non-match day, with one free day per week. The glycogen levels observed on Days II and III are probably a good reflection of the maximal glycogen-loaded state which these players will achieve during this part of the season, since it is doubtful that activity intensity will be lighter than it was during the 48-h period of Days II and III. Costill et al. (1971) and Costill and Miller (1980) have demonstrated that when exercise is performed on consecutive days, the effect on pre-exercise glycogen levels is cumulative, in that exercise is begun on each successive day with a glycogen level lower than the starting level of the previous day. It can probably be assumed that the performance impairments associated with glycogen depletion would occur earlier on each successive day. Saltin (1973) has described a study in which a group of soccer players were glycogen depleted prior to playing an exhibition match. Using film analysis of the game, it was discovered that the glycogen depleted players covered less ground during the match and at a slower average speed than did the control players in that study.

Such impairments are not confined only to the realm of submaximal endurance performance. It has also been recently demonstrated that short time (< i min) maximal intensity exercise performance is also impaired parallel to glycogen depletion and that this impairment may be a function of a reduced anaerobic glycogenolytic flux (Jacobs 1981). Since both endurance and explosive power are integral components of soccer, low intramuscular glycogen levels may directly impair playing performance, particularly during the latter stages of both individual games and the peak season as a whole.

The low glycogen levels observed in the "refilled" state (i.e., Day II or III) may be a result of either insufficient carbohydrate consumption, a lack of sufficient time to allow for refilling of stores (which would again be depleted during the game on the day after Day III), or a combination of these two factors. It has been reported that up to 46 h may be required fully to regain normal pre-exercise concentrations after prolonged exercise (Piehl 1974). However, recent studies have indicated that the type of exercise inducing glycogen depletion may influence the rate of refilling. These findings suggest that the high intensity, intermittent exercise nature of soccer should permit sufficient refilling over 24 h to regain normal values typical of sedentary subjects (MacDougall et al. 1977). Thus the time factor itself is not an acutely limiting factor to refilling in the present study. The second factor described, carbohydrate intake, is thus implicated. Total daily energy intake is, on the average, less than that consumed by other groups of elite, competing athletes of a similar body weight (Fox 1979). The daily quantity of carbohydrates consumed was approximately 30% less than that suggested for athletes competing in similar sports (Fox 1979). Moreover, the

302 I. Jacobs et al.

proportion of the total energy consumed consisting of carbohydrates was less than the value recommended for a normal sedentary population. The optimal proportion of carbohydrates for athletes during their peak season should be higher than this recommended proportion for the sedentary population. The prime cause of the low intramuscular glycogen concentrations observed, even after 48 h of rest and light physical training, probably lies with the players' dietary habits.

Acknowledgements. The authors thank the players and coaches of Malm6 F.F. for their participation, E.-G. Andersson and L. Lindberg for technical assistance. Present address for M. Rasmusson is Kungsornen Limited, Johanneshov, Sweden.

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Costill DL, Bowers R, Granam G, Sparks K (1971) Muscle glycogen utilization during prolonged exercise on successive days. J Appl Physiol 31:834-838

Costill DL, Miller J (1980) Nutrition for endurance sport: carbohydrate and fluid balance. Int J Sports Med 1:2-14

Fox EL (1979) Sports physiology. WB Saunders, Philadelphia, pp 251-252, 261 Gollnick P, Armstrong R, Sembrowich W, Shepherd R, Saltin B (1973) Glycogen depletion patterns

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Accepted January 4, 1982