Saturday, 1 December 2012

Fatigue in Soccer

Fatigue can be defined as a decline in performance due to the necessity to continue performing. In soccer it is manifest in a deterioration in work-rate towards the end of a game. Studies which have compared work-rates between first and second halves of matches have provided evidence of the occurrence of fatigue.

   Belgian university players were found to cover on average a distance of 444 m more in the first half than in the second half (Van Gool et al., 1988). Bangsbo et al. (1991) reported that the distance covered in the first half was 5% greater than in the second. This decrement does not necessarily occur in all players. Reilly and Thomas (1976) noted an inverse relation between aerobic fitness (VO2max) and decrements in work-rate. The players with the higher VO2max values, those in midfield and full-back positions, did not exhibit a significant drop in distance covered in the second half. In contrast all the centre-backs and 86% of the strikers had higher figures for the first half, the difference between halves being significant. It does seem that the impact of a high aerobic fitness level is especially evident in the later parts of a match.

  The amount of glycogen stored in the thigh muscles pre-match appears to have an important protective function against fatigue. Swedish club players with low glycogen content in the vastus lateralis muscle were found to cover 25% less overall distance than the other players (Saltin, 1973). A more marked effect was noted for running speed; those with low muscle glycogen stores pre-match covered 50% of the total distance walking and 15% at top speed compared to 27% walking and 24% sprinting for players who started with high muscle glycogen concentrations. Attention to diet and maintaining muscle glycogen stores by not training too severely are recommended in the immediate build-up for competition. These considerations would be most important in deciders where drawn matches are extended into 30 minutes extra time.
  Youth players of a professional club showed positive responses to consuming a maltodextrin solution during training. The subjective assessments of coaches of their players’ performance corroborated the judgments of the players (Miles et al., 1992). Dietary advice given to the senior professionals resulted in an alteration of nutritional support. The distribution of macro-nutrients in the diet of the players also improved (Reilly, 1994b). Manipulation of energy intake by provision of a high carbohydrate diet improved performance in a running test designed to interpret the activity profile of a soccer match (Bangsbo et al., 1992). Whilst goals may be scored at any time during a game, most are scored towards the end of a game.

This is exemplified by data from the Scottish League during an extended period of the 1991–92 season (Figure 5.3). A higher than average scoring rate occurred in the final 10 minutes of play. This cannot be explained simply by a fall in work-rate, as logically this would be balanced out between the two opposing teams. It might be accounted for by the more pronounced deterioration among defenders which gives an advantage to the attackers towards the end of a game. Alternatively it may be linked with ‘mental fatigue’, lapses in concentration as a consequence of sustained physical effort leading to tactical errors that open up goal-scoring chances. The phenomenon may be a factor inherent in the game, play becoming more urgent towards the end despite the fall in physical capabilities. Irrespective of the nature of the phenomenon, a team that is physiologically and tactically prepared to last 90 minutes of intense play is likely to be an effective unit.

   Environmental conditions may also impose a limit on the exercise intensity that can be maintained for the duration of a soccer game or hasten the onset of fatigue during it. Major soccer tournaments, for example the World Cup finals in Spain in 1982, in Italy in 1990 and in the USA in 1994, have been held in hot countries with ambient temperatures above 30 °C. The work-rate is adversely affected when hot conditions are combined with high humidity. Performance is influenced both by the rise in core temperature and dehydration, and sweat production will be ineffective for losing heat when relative humidity is 100%. Cognitive function, akin to the kind of decision making required during match-play, is better maintained during 90 minutes of continuous exercise when water is supplied intermittently to subjects compared to a control condition (Reilly and Lewis, 1985). Adequate hydration pre-exercise and during the intermissions is important when players have to play in the heat. The opportunity to acclimatize to heat prior to competing in tournaments in hot climates is an essential element in the systematic preparation for such events. This may be realized by astute location of training camps, a good physiological adaptation being realized within 10–14 days of the initial exposure in hot weather or regular and frequent exposures to heat in an environmental chamber.

Italian football (soccer) player Elvis Abbruscato

  The major consequences of playing in cold conditions are likely to be associated with liability to injury. This would be pronounced when playing on icy pitches without facilities for underground heating. Muscle performance deteriorates as muscle temperature falls; therefore a good warm-up prior to playing in cold weather and use of appropriate sportswear to maintain warmth and avoid the deterioration in performance synonymous with fatigue would be important. It is also established that injury is more likely to occur in games players if the warm-up routine is inappropriate (Reilly and Stirling, 1993). Therefore, pre-match exercises should engage the muscle groups employed during the game, particularly in executing soccer skills.

   The interactions between environmental variables and soccer performer are covered more extensively elsewhere in this volume. A consensus statement of nutritional needs of the soccer player and guidelines for fluid replacement to offset work-rate deterioration are outlined by Ekblom and Williams (1994).

Science and Soccer
by Thomas Reilly

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