The influence of carbohydrate-electrolyte ingestion on metabolism and soccer skill performance during and following prolonged intermittent exercise
Although soccer is one of the more researched intermittent team sports, there is a surprisingly modest amount of information available on the effects of fatigue on skill performance. The main reasons for this are due to the problems of overcoming the barriers of controlling the many variables in the field and a lack of reliable and valid skill tests. The Loughborough Intermittent Shuttle running Test (LIST) is a recently developed exercise protocol which closely simulates the demands of multiple-sprint sports such as soccer in a controlled environment. Furthermore, the Loughborough Soccer Passing Test (LSPT) and Loughborough Soccer Shooting Test (LSST) were developed (and modified further as part of this thesis, Chapters 5 and 6) and found to be reliable and valid indicators of soccer skill. Therefore, one of the main aims of this thesis was to investigate the influence of 90 min of the LIST on soccer skill performance. Early researchers (e. g. Karlsson, 1969 and Saltin, 1973) reported the -benefits of maintaining a high muscle glycogen content on soccer performance and more recent investigators looked at the effect of providing carbohydrate (CHO) during exercise on work rate and soccer skill. However, many of these experiments were completed in the field setting and used poor tests of skill. Therefore, the primary aim of these series of experiments was to determine the influence of ingesting a carbohydrate-electrolyte (CHO-E) solution during the LIST on soccer skill performance. There was an 8% deterioration in LSPT performance following 90 min of intermittent high-intensity running, even with fluid ingestion (p<0.05). Furthermore, the ingestion of a CHO-E solution during exercise showed tendencies for better maintenance of skill performance towards the end of exercise. Moreover, CHO-E supplementation better maintained sprint performance and a higher relative exercise intensity during exercise (p<0.05). This is crucial in soccer perfon-nance, as players who are unable to sprint to get to the ball will be unable to perform the necessary skill. From the results of Chapters 5 and 6 it was found that the modified passing (LSPT) and goal-shooting (LSST) tests were valid and reliable tests of soccer skill. Moreover, they were found to be more repeatable when higher calibre players performed the tests. As in previous studies there was a speed-accuracy trade-off' in LSST performance i. e. subjects increased the time taken to complete each shot sequence and reduced the shot speed to maintain shooting accuracy post-LIST. There was a trend for CHO-E ingestion to maintain a better shot speed and time taken for each sequence. The ingestion of CHOE also reduced the perception of effort (p<0.05) and led to more positive feelings of affective valence during the last 30 min of the LIST. Therefore, based on these findings, it was concluded that the ingestion of CHO-E solutions over water alone should be encouraged to soccer players because of the tendency to better maintain soccer skill and the associated physiological, biochemical and psychological benefits during such exercise.