Considerable depletion of intramuscular glycogen stores occurs during soccer games which affects the distance covered by players during the second-half of a match-play (Saltin, 1973). Although it appears that players skills deteriorate with fatigue, it is difficult to quantitatively investigate the skill performance during a soccer game. Additionally, the effects of muscle glycogen depletion and a carbohydrate enriched diet on skill performance such as dribbling and shooting are not known.
The aim of this study was to determine (1) whether an intermittent treadmill exercise similar in distance and intensity to soccer match could impair the skill performance of midfield soccer players, and (2) if a carbohydrate enriched diet could influence the skill performance after the intermittent treadmill exercise.
Six midfield soccer players participated in the study, with mean (+/-SD)age, mass, height and VO2max of 18 +/-1.8 years, 68.72 +/-3.43 kg, 1.75 +/-0.035 m, and 61.97 +/-4.89 ml/kg/min, respectively.
Subjects first completed a treadmill exercise with the objective of reducing the muscle glycogen stores. The treadmill exercise, which mimicked the distance and intensity of a soccer match-play consisted of 11.16 km intermittent running at various speeds and slopes conducted over a 1 hour period. Subjects were then given either a mixed diet (40% carbohydrate, 30% fat and 30% protein) or a carbohydrate enriched diet (80% carbohydrate, 10% fat, and 10% protein) over a 48 hour period.
On completion of the dietary manipulation, a modified Zelenka Functional Performance Test (Zelenka et al., 1967) was administered to subjects. The test, which showed an acceptable reliability with a coefficient of 0.78, consisted of dribbling in and out of cones and shooting at a 1.5 m wide goal, 15.6 m away. The time to continuously complete 5 repeated circuits plus the shooting accuracy were recorded as the skill performance. This was then followed by intermittent treadmill exercise as before. On completion of the treadmill exercise, subjects repeated the skill test. Approximately two weeks after the first test, subjects repeated the protocol under the alternative dietary regime.
Blood samples were obtained pre exercise and after each procedure to determine glucose and lactate concentrations. Heart rate was recorded throughout the experimental protocol using a Polar Sport Tester PE4000. Statistical analysis was carried out with Repeated measures MANOVA.
RESULTS AND DISCUSSION
Results showed that (1) the skill performance was not impaired by the intermittent treadmill exercise (p>0.05); (2) the carbohydrate enriched diet did not increase the ability of the players to shoot or dribble (p>0.05); (3) there was a significant increase in the heart rate during the post treadmill exercise skill test compared with that during the pre treadmill exercise test (p<0.05); and (4) no significant differences in blood glucose and lactate concentrations were found between the tests.
The results suggest that (1) the intermittent treadmill exercise similar in distance and intensity to that of soccer match-play did not affect the ability of the players to execute complex skills of shooting and dribbling; and (2) the 48 hour carbohydrate enriched diet had no significant influence on the skill performance, either pre or post the treadmill exercise.
It is speculated that either (1) muscle glycogen depletion may not impair the ability of the player to execute game skills; (2) an alternative fatigue mechanism such as dehydration or transient lactate accumulation may be a causative factor in the reduction in skill performance; and (3) the treadmill protocol employed failed to induce a significant degree of glycogen depletion large enough to cause a significant fall in skill performance.
Saltin B. (1973). Metabolic fundamentals in exercise. Med. Sci. Sports. 5: 137-146.
Zelenka V., Seliger V. & Ondrej O. (1967). Specific function testing of young football players. J. Sports Med. Phys. Fit. 7: 143-147.