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Dehydration and hyperthermia both, if sufficiently severe, will impair exercise performance. Dehydration can also impair performance of tasks requiring cognition and skill. Body temperature may exceed 40 °C in competitive games played in hot weather, but limited data are available. Football played in the heat, therefore, poses a challenge, and effects on some aspects of performance become apparent as environmental temperature increases above about 12-15 °C. Prior acclimatization will reduce the impact of high environmental temperatures but provides limited protection when humidity is also high. Ingestion of fluids is effective in limiting the detrimental effects on performance: drinks with added carbohydrate and electrolytes are generally more effective than plain water and drinks may be more effective if taken cold than if taken at ambient temperature. Pre-exercise lowering of body temperature may aid some aspects of performance, but the efficacy has not been demonstrated in football., (© 2010 John Wiley & Sons A/S.)

During a football match played in warm (34.3 ± 0.6 °C), humid (64 ± 2% rh) conditions, 22 male players had their pre-match hydration status, body mass change, sweat loss and drinking behavior assessed. Pre-match urine specific gravity (1.012 ± 0.006) suggested that all but three players commenced the match euhydrated. Players lost 3.1 ± 0.6 L of sweat and 45 ± 9 mmol of sodium during the 90-min match and replaced 55 ± 19% of their sweat losses and hence by the end of the game were 2.2 ± 0.9% lighter. The water volume consumed during the game was highly variable (1653 ± 487 mL; 741-2387 mL) but there was a stronger relationship between the estimated pre-game hydration status and water volume consumed, than between sweat rate and water volume consumed. In a second match, with the same players 2 weeks later in 34.4 ± 0.6 °C, 65 ± 3% rh, 11 players had a sports drink available to them before and during the match in addition to water. Total drink volume consumed during the match was the same, but approximately half the volume was consumed as sports drink. The results indicate that substantial sweat water and electrolyte losses can occur during match play in hot conditions and a substantial water and sodium deficit can occur in many players even when water or sports drink is freely available., (© 2010 John Wiley & Sons A/S.)

Heat stress may contribute to decreased match performance when football is played in extreme heat. This study evaluated activity patterns and thermal responses of players during soccer matches played in different environmental conditions. Non-acclimatized soccer players (n=11, 20±2 years) played two matches in conditions of moderate heat (MH) and high heat (HH) index. Core temperature (T(c) ) and physical performance were measured using a telemetric sensor and a global positioning system, respectively. The average ambient temperature and relative humidity were MH 34±1 °C and 38±2%; HH 36±0 °C and 61±1%. Peak T(c) in the MH match was 39.1±0.4 °C and in the HH match it was 39.6±0.3 °C. The total distance covered in the first and second halves was 4386±367 and 4227±292 m for the MH match and 4301±487 and 3761±358 m for the HH match. Players covered more distance (P<0.001) in the first half of the HH match than in the second half. In football matches played at high environmental temperature and humidity, the physical performance of the players may decrease due to high thermal stress., (© 2010 John Wiley & Sons A/S.)

Physical training and competition in football markedly increase the need for macro- and micronutrient intake. This requirement can generally be met by dietary management without the need for dietary supplements. In fact, the efficacy of most supplements available on the market is unproven. In addition, players must be cautious of inadequate product labelling and supplement impurities that may cause a positive drug test. Nonetheless, a number of dietary supplements may beneficially affect football performance. A high endurance capacity is a prerequisite for optimal match performance, particularly if extra time is played. In this context, the potential of low-dose caffeine ingestion (2 - 5 mg . kg body mass(-1)) to enhance endurance performance is well established. However, in the case of football, care must be taken not to overdose because visual information processing might be impaired. Scoring and preventing goals as a rule requires production of high power output. Dietary creatine supplementation (loading dose: 15 - 20 g . day(-1), 4 - 5 days; maintenance dose: 2 - 5 g g . day(-1)) has been found to increase muscle power output, especially during intermittent sprint exercises. Furthermore, creatine intake can augment muscle adaptations to resistance training. Team success and performance also depend on player availability, and thus injury prevention and health maintenance. Glucosamine or chondroitin may be useful in the treatment of joint pain and osteoarthritis, but there is no evidence to support the view that the administration of these supplements will be preventative. Ephedra-containing weight-loss cocktails should certainly be avoided due to reported adverse health effects and positive doping outcomes. Finally, the efficacy of antioxidant or vitamin C intake in excess of the normal recommended dietary dose is equivocal. Responses to dietary supplements can vary substantially between individuals, and therefore the ingestion of any supplement must be assessed in training before being used in competition. It is recommended that dietary supplements are only used based on the advice of a qualified sports nutrition professional.

The use of alcohol is often intimately associated with sport, and the association is particularly strong in football. As well as providing a source of energy, alcohol (ethanol) has metabolic, cardiovascular, thermoregulatory, and neuromuscular actions that may affect exercise performance. Its actions on the central nervous system, however, result in decrements in skill and behavioural changes that may have adverse effects on performance. There is also evidence of dose-dependent decrements in aerobic capacity. Although the mechanisms are not well understood, the aftermath of alcohol use (hangover) may also adversely affect performance for many hours after intoxication. Alcohol intoxication may adversely affect the player's dietary choices by displacing carbohydrate from the diet at a time when restoration of glycogen stores should be a priority.

Sweat rate and sweat composition vary extensively between individuals, and quantification of these losses has a role to play in the individualisation of a hydration strategy to optimise training and competitive performance. Data were collected from 26 male professional football (soccer) players during one 90 min pre-season training session. This was the 2nd training session of the day, carried out between 19.30 and 21.00 h when the mean +/- SD environment was 32 +/- 3 degrees C, 20 +/- 5 %rh and WBGT 22 +/- 2 degrees C. Training consisted of interval running and 6-a-side games during which the average heart rate was 136 +/- 7 bpm with a maximum rate of 178 +/- 7 bpm (n = 19). Before and after training all players were weighed nude. During training all players had free access to sports drinks (Gatorade) and mineral water (Solan de Cabras). All drink bottles were weighed before and after training. Players were instructed to drink only from their own bottles and not to spit out any drink. No player urinated during the training session. Sweat was collected by patches from the chest, arm, back, and thigh of a subgroup of 7 players. These remained in place for the first 15 - 30 min of the training session, and sweat was analysed for sodium (Na (+)) and potassium (K (+)) concentration. Body mass loss was 1.23 +/- 0.50 kg (ranging from 0.50 to 2.55 kg), equivalent to dehydration of 1.59 +/- 0.61 % of pre-training body mass. The sweat volume lost was 2193 +/- 365 ml (1672 to 3138 ml), but only 972 +/- 335 ml (239 to 1724 ml) of fluid was consumed. 45 +/- 16 % of the sweat volume loss was replaced, but this ranged from 9 % to 73 %. The Na (+) concentration of the subgroup's sweat was 30.2 +/- 18.8 mmol/l (15.5 to 66.3 mmol/l) and Na (+) losses averaged 67 +/- 37 mmol (26 to 129 mmol). The K (+) concentration of the sweat was 3.58 +/- 0.56 mmol/l (2.96 to 4.50 mmol/l) and K (+) losses averaged 8 +/- 2 mmol (5 to 12 mmol). The drinking employed by these players meant that only 23 +/- 21 % of the sweat Na (+) losses were replaced: This ranged from replacing virtually none (when water was the only drink) to replacing 62 % when the sports drink was consumed. These elite soccer players did not drink sufficient volume to replace their sweat loss. This, however, is in accord with data in the literature from other levels of soccer players and athletes in other events. These measurements allow for an individualisation of the club's hydration strategy.

There are few data in the published literature on sweat loss and drinking behaviour in athletes training in a cool environment. Sweat loss and fluid intake were measured in 17 first-team members of an elite soccer team training for 90 min in a cool (5 degrees C, 81% relative humidity) environment. Sweat loss was assessed from the change in body mass after correction for the volume of fluid consumed. Sweat electrolyte content was measured from absorbent patches applied at four skin sites. Mean (+/- s) sweat loss during training was 1.69+/-0.45 l (range 1.06-2.65 l). Mean fluid intake during training was 423+/-215 ml (44-951 ml). There was no apparent relationship between the amount of sweat lost and the volume of fluid consumed during training (r2 = 0.013, P = 0.665). Mean sweat sodium concentration was 42.5+/-13.0 mmol l(-1) and mean sweat potassium concentration was 4.2+/-1.0 mmol x l(-1). Total salt (NaCl) loss during training was 4.3+/-1.8 g. The sweat loss data are similar to those recorded in elite players undergoing a similar training session in warm environments, but the volume of fluid ingested is less.

Purpose: To investigate the effect on gastric emptying of intermittent exercise at varying intensities such as occurs during a soccer match., Methods: We compared the emptying rate of a carbohydrate-electrolyte (CE) drink during two 15-min periods of a competitive 5-a-side indoor soccer match separated by 10 min and during two 15-min periods of low-intensity walking exercise. Seven healthy male subjects, all of whom regularly played soccer, completed the study. Exercise intensity on each trial was calculated from heart rate recordings. Subjects ingested 500 mL of the CE drink immediately before starting each exercise period. Before and after completing each 15-min exercise period, the gastric contents were aspirated and the volume recorded. Ambient room temperature ranged from 16-22 degrees C and humidity ranged from 57-72% on both trials., Results: Mean +/- SD heart rate was higher during the Soccer trial than during the Walking trial at all time points. Exercise intensity was calculated to be 54 +/- 23% and 63 +/- 20% VO2max, respectively, for the first and second periods of exercise on the Soccer trial and 13 +/- 9% and 12 +/- 11% VO2max, respectively, for the first and second periods of exercise on the Walking trial. During the first 15-min period of exercise, a greater (median (range)) volume of the CE drink was emptied from the stomach on the Walking trial (247 mL (102-361 mL)) than on the Soccer trial (84 mL (17-230 mL); P = 0.022). In the second exercise period, however, gastric emptying rates were not different (P = 0.16) between the Walking trial (247 mL (104-363 mL)) and Soccer trial (148 mL (17-293 mL))., Conclusion: As indicated by heart rate, the overall exercise intensity of an indoor soccer match appears to be moderate. The pattern of activity during a match is intermittent with periods of low level activity punctuated by short bursts of high-intensity sprinting. The present study demonstrates that the intensity of activity during this type of exercise is sufficient to slow gastric emptying.

Objective: To examine the dietary habits of professional soccer players at two Scottish Premier League clubs during the competitive season., Methods: A study of the dietary intake of 51 professional soccer players with two different clubs was carried out by the seven day weighed intake method., Results: Physical characteristics of the two groups of players were similar, with only small differences in age and body mass but no difference in height and body fat. Mean (SD) daily energy intake for club A was 11.0 (2.6) MJ, and for club B 12.8 (2.2) MJ. The higher energy intake at club B was largely accounted for by a higher (P < 0.005) fat intake (118 v 93 g d-1): there was no difference in the absolute amounts of protein, carbohydrate, or alcohol consumed. When expressed as a fraction of total energy intake, mean protein intake was higher (P < 0.05) and fat intake lower (P < 0.01) at club A., Conclusions: The mean energy intake of these players was not high compared with athletes in endurance sports. Fractional contribution of the macronutrients to total energy intake was broadly similar to that of the general population.

Soccer is an endurance sport that consists of moderate activity levels interspersed with intermittent high-intensity bursts, leading to high rates of metabolic heat production. Even when the weather is cold, significant sweat loss will occur, leading to a degree of dehydration which impairs exercise performance. Fluid intake before and during the game will provide water to reduce the degree of dehydration and can also supply carbohydrate to supplement the body's limited carbohydrate stores. Dilute carbohydrate-electrolyte drinks are most effective for rehydration. The optimum formulation will vary between individuals and will also depend on climatic conditions. Players should be encouraged to experiment with fluid intake during training to identify the type of drink and the amount and frequency of drinks that best meet their needs.