Faculty of Physical Therapy, University of Valladolid. Campus de Soria, Soria, Spain; se. Soccer is a complex team sport and success in this discipline depends on different factors such as physical fitness, player technique and team tactics, among others. In the last few years, several studies have described the impact of caffeine intake on soccer physical performance, but the results of these investigations have not been properly reviewed and summarized. The main objective of this review was to evaluate critically the effectiveness of a moderate dose of caffeine on soccer physical performance. The search included studies with a cross-over and randomized experimental design in which the intake of caffeine either from caffeinated drinks or pills was compared to an identical placebo situation.
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Contemporary elite soccer features increased physical demands during match-play, as well as a larger number of matches per season. Now more than ever, aspects related to performance optimization are highly regarded by both players and soccer coaches.
Here, nutrition takes a special role as most elite teams try to provide an adequate diet to guarantee maximum performance while ensuring a faster recovery from matches and training exertions. It is currently known that manipulation and periodization of macronutrients, as well as sound hydration practices, have the potential to interfere with training adaptation and recovery. A careful monitoring of micronutrient status is also relevant to prevent undue fatigue and immune impairment secondary to a deficiency status.
Furthermore, the sensible use of evidence-based dietary supplements may also play a role in soccer performance optimization. In this sense, several nutritional recommendations have been issued. The physical demands of elite match-play have been increasing within the past few decades [ 2 , 3 ].
The number of matches per season has also increased, with elite clubs frequently playing over 60 competitive matches over a season [ 4 ]. Periods of fixture congestion i. Achieving the highest performance during training and competition, improving and accelerating recovery, achieving and maintaining an optimal body weight and physical condition, and minimizing the risk of injury and illness are key issues in contemporary elite soccer.
Different fields of scientific knowledge have addressed all these issues, including the field of nutrition [ 9 , 10 , 11 , 12 , 13 ], where specific recommendations have been developed for soccer players. As the physiological demands of soccer are challenging and vary greatly depending on the nature of training, playing schedules and intensity of play, sound dietary practices should be followed [ 13 , 14 ]. This review gathers the most relevant and up-to-date nutritional recommendations for elite male soccer, covering from macro and micronutrients to hydration and selected supplements.
For this review, databases PubMed and Scopus were used and searches were performed up to December Manuscripts were individually selected for their relevance but no specific scientific approach was used in their selection. References of retrieved articles were used whenever they were considered relevant. Additionally, the books Soccer Science [ 15 ], Clinical Sports Nutrition [ 16 ] and Science and Soccer: developing elite performance [ 17 ] were used as complements.
Soccer is an intermittent team-based sport. Here, elite players perform low-intensity movements e. During a soccer match, fatigue may occur temporarily after short, intense periods during both halves and progressively towards the end of each half [ 21 ].
The total distance and high-intensity activities have been found to decrease following the most demanding 5-min periods during a match and at the end of the second half compared with the first half [ 20 ]. However, the distance run at high intensities can remain constant throughout the second half, due to pacing strategies [ 22 ], whereby players perform fewer actions at low or moderate intensities to spare their efforts [ 23 ].
Finally, jumping, sprinting and intermittent exercise performance, when evaluated after a match, seems to be significantly lower, compared to baseline values [ 24 , 25 , 26 ].
Collectively, these findings suggest that, at an elite level of play, players experience fatigue towards the end of the match and temporarily following intense bursts.
Regarding positional differences, a significantly greater total distance covered during elite soccer match play has been shown in central midfielders and wide midfielders both about 12 to 13 km , whereas central defenders have been consistently shown to complete the least total distance about 10 km or less.
Accordingly, central defenders also cover the shortest distance at high intensity and combined high-intensity running and sprinting [ 27 , 28 ]. Regarding sprint activities, wide midfielders and attackers are those who cover the greatest distance during match-play [ 2 ]. Mean recovery time between high intensity actions has also shown positional differences, with central defenders generally having more time to recover than others, as opposed to wide defenders [ 29 ].
In summary, soccer is characterized by the execution of anaerobic actions that are performed against a backdrop of aerobic energy supply. Nevertheless, and although high-intensity actions make up for a relatively low percentage of the match, these actions cannot be underestimated as they can reveal critical to the outcome of a competition [ 30 ].
Athletes who are involved in team sports such as soccer, covering significant distances during a match, are generally aided by a lighter and leaner physique [ 31 , 32 ].
A lean body, with a greater muscle-to-fat ratio, is often advantageous in sports where speed is involved [ 33 ], as the storage component of body fat may act as a dead weight to be lifted against gravity during jumping and sprinting e.
In turn, this affects energy expenditure [ 34 ] and is inversely related to aerobic capacity, power-to-weight ratio, and thermoregulation [ 35 ]. Nevertheless, the body fat levels of team sport players are not as low as those typically found in endurance athletes such as runners and cyclists [ 32 ]. Some investigations explored the association between body composition namely body fat or adiposity and physical performance in soccer [ 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 ].
Brocherie and collaborators [ 41 ] found that the sum of six skinfolds associated with adipose mass index was largely correlated with speed decrements in a repeated-sprint ability RSA test in a group of 16 players from senior male Qatar national team. Furthermore, Silvestre and collaborators [ 44 ] showed that reduced body fat levels were associated with improved sprint performance and jump height in a sample of 27 male collegiate soccer players at the beginning of the season.
When discussing their research in power testing, Nikolaidis and collaborators [ 42 ] found a positive correlation between body fat with mean and m sprint times of a RSA test, in 36 male semi-professional Greek soccer players. More recently, a similar trend was seen [ 43 ] where the body fat level of adult soccer players from third and fourth Greek national divisions positively correlated to m sprint times. Together, these data seem to support an association between body fat levels and sprint performance i.
Currently, there are no defined optimal overall body composition values for soccer players [ 45 ], although several investigations have reported on the body composition of professional adult male players [ 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 ].
Normative data regarding the sum of eight skinfolds through the standardized ISAK protocol is scarce. Hencken and White [ 49 ] evaluated the sum of skinfolds of 24 professional soccer players from an English Premier League club and reported a range between Positional differences were reported in some studies, with the main difference being goalkeepers evidencing higher body fat values compared to field players [ 47 , 53 , 55 , 56 ].
However, this is not always the case [ 54 , 57 ]. Very limited information is available on seasonal differences in body composition changes among playing positions [ 52 ] but in a recent study [ 57 ] the players of a professional soccer team were evaluated at multiple times across the season and the changes found were similar for all playing positions. The authors concluded that players undergo changes in their fat mass, fat-free soft tissue mass and mineral mass across the season, irrespective of the playing position.
Seasonal trends reflect an increase in body fat levels during the offseason, which are then reduced during the preseason, when training volume is highest [ 53 , 57 ]. Another study also found that body composition of elite soccer players changed throughout the competitive season.
Specifically, fat mass decreased from the start of preseason to the start of the competitive season. Nevertheless, by the end of the competitive season, it had returned to start of preseason values. Fat-free mass significantly increased from start of preseason until the start of the season and these changes were maintained over the entire competitive season [ 58 ]. Thus, it may be useful for practitioners to provide individualized target zones for players.
For a detailed comparison between each of these methods, the reader is referred to the review by Ackland et al. For an elite soccer player, it is very important to provide adequate energy to meet the challenges of high-intensity, intermittent exercise. Several studies have estimated and measured total energy expenditure in soccer players using doubly labeled water, heart rate, video match analysis and activity record monitoring [ 60 , 61 , 62 ].
Mean energy expenditure above rest for a match has been estimated to be approximately Kcal [ 62 ], whereas to kcal per day were estimated for daily training [ 60 ]. More recently, Anderson et al reported that mean energy expenditure of elite soccer players was approximately 3, kcal during a seven-day period including five training days and two matches [ 63 ].
However, besides the impact of individual factors i. The use of heart rate monitors and GPS systems might be useful as they can provide some estimation of individual energy expenditures based on algorithms during training, but accuracy can vary greatly among systems, and values should be interpreted with caution [ 13 ]. In another study, from Bettonviel et al. These two investigations also showed evidence of energy intake periodization, that is, players adjusted their intake according to the different training and match demands [ 63 , 65 ].
Players must therefore balance overall energy intake per training and competition demands as well as individual body composition goals, while reaching key macronutrient targets, as discussed below. In this section, we review the most up-to-date nutritional strategies to promote optimal performance in soccer, covering macronutrients and hydration, micronutrients and supplementation. Carbohydrates CHO are considered of vital importance in sports in general and in soccer in particular, as muscle glycogen is the predominant substrate for energy production during a match.
After this type of effort, nearly half of vastus lateralis muscle fibers have been classified as empty or near empty in relation to their glycogen content [ 26 ]. As such, glycogen depletion is commonly cited as a contributing factor for the progressive fatigue observed towards the end of a match [ 6 , 66 ]. The following position is summarized in Table 1. Recommended intakes for selected macronutrients in different situations includes hydration. General nutritional recommendations for peak performance promote strategies to achieve optimal muscle glycogen concentrations through means of high CHO availability.
However, recent research has provided new insights into the interactions of exercise with low CHO availability, whereby the acute and chronic adaptive responses to training or recovery are enhanced in an environment of low exogenous and endogenous CHO stores, since consistently high levels of muscle glycogen seem to attenuate training adaptations [ 75 ]. Anderson and colleagues [ 6 ] quantified the daily training and accumulative weekly load reflective of both training and match play in professional soccer players during a one, two and three match per week schedule and found evidences of training periodization.
Specifically, results showed that training load was progressively reduced in the three days prior to match day one match per week ; that daily training load and periodization was similar in a one and two match per week schedule although total accumulative distance was higher in a two-match week ; and that daily training total distance was lower in a three-match week although accumulative weekly distance was highest and more time was spent in high speed zones. As such, these authors suggested that CHO intake should also be periodized according to training periodization, suggesting high CHO availability on the day before match, on the day of the match and on the day after match on both one match and two match per week schedule, and a reduced CHO availability on the other days.
Given the extreme frequency of match play on a three match per week schedule, these researchers do not advise adopting a low CHO availability in these conditions.
Given the relevance of muscle carbohydrate content for exercise performance, every feeding opportunity may matter for achieving the highest values. Researchers found that pre-match muscle glycogen concentrations following the high CHO diet were significantly higher than following the low CHO diet.
Most importantly, players performed significantly more high-intensity exercise in the match played following the high CHO diet, without any observed differences on the evaluated technical variables. Regarding the pre-event meal, a study [ 78 ] evaluated the effects of ingesting a CHO meal 2.
The last meal should ideally take place 3—4 h before match and include easy-to-digest foods. The meals 4 h before the start of competition main meals, e. Within 60 min before the match, usually until warm-up, light snacks containing high CHO 25—30 g may further increase the availability of CHO before match, thus sparing liver glycogen. However, there are still some concerns about reactive hypoglycemia due to increases in insulin production when CHO are consumed within the last hour prior to exercise [ 82 ].
Although it is reasonable to consider that higher pre-exercise insulin concentrations may affect exercise performance by glycemic disposal at the start of the exercise, studies have shown that this does not seem to compromise exercise performance [ 83 ].
To this respect, we believe that the precise timing and quantity of feeding within 1 h prior to match should be based on individual preference. It is also important to ensure that the pre-event meal is composed of familiar foods to avoid gastrointestinal issues that many athletes experience before big events. Nervousness and unfamiliar food can sometimes lead to stomach cramps, nausea and diarrhea. Keeping meal choices simple and familiar may be the most important concept for successful pre-event fuelling.
Another strategy used in endurance sports to maximize muscle glucose content before an exercise event is glycogen supercompensation. This can be interesting in isolated events, occurring from time to time, but its effects are less known in intermittent high-intensity sports like soccer, where maximum performance is needed frequently, often more than once a week.
McInerney and colleagues [ 84 ] tested six trained athletes on three exercise trials, with each exercise bout separated by 48 h. After each exercise session, subjects were fed a high-CHO meal and monitored during the subsequent 3 h of recovery. Before and immediately upon completion of each of these three exercise bouts, a muscle biopsy was taken. As a result of this protocol, researchers found that well-trained men cannot repeatedly supercompensate muscle glycogen content after a glycogen-depleting exercise and two days of a high-CHO diet, suggesting that the mechanisms responsible for glycogen accumulation are attenuated as a consequence of successive days of glycogen-depleting exercise.
Furthermore, exercise performance was similar on days three and five despite the lack of glycogen accumulation on day five. Therefore, the intake of extremely high doses of CHO i. The benefits of ingesting CHO during endurance exercise are well established, and general recommendations for sports where exercise duration ranges from 1 to 2. Nicholas and colleagues [ 86 ] undertook a study in which they provided soccer players with either a 6.
Contemporary elite soccer features increased physical demands during match-play, as well as a larger number of matches per season. Now more than ever, aspects related to performance optimization are highly regarded by both players and soccer coaches. Here, nutrition takes a special role as most elite teams try to provide an adequate diet to guarantee maximum performance while ensuring a faster recovery from matches and training exertions. It is currently known that manipulation and periodization of macronutrients, as well as sound hydration practices, have the potential to interfere with training adaptation and recovery.
Nutrition and Supplementation in Soccer
With better dope testing methods and hence the possibilities of detection and life ban from the sport, athletes and coaches are looking for legitimate ways to improve performance and hasten recovery. The various ways by which performance can be improved are known as Ergogenic Aids. The Code provides five international standards on:. The Prohibited List is published on the 1st of October and becomes effective from the 1st of January. Some substances are banned in competition only, others are banned at all times, and some may be banned in specific sports.