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versión On-line ISSN 1980-0037
Rev. bras. cineantropom. desempenho hum. vol.14 no.3 Florianópolis 2012
Evaluation of hydration status following soccer matches of different categories
Avaliação de parâmetros de hidratação após jogos de futebol de diferentes categorias
Daniel Barbosa CoelhoI; Emerson Rodrigues PereiraI; Elisa Couto GomesI; Leonardo CoelhoI,II; Danusa Dias SoaresI; Emerson Silami-GarciaI
IFederal University of Minas Gerais. Center for Sports Excellence. School of Physical Education, Physiotherapy and Occupational Therapy. Belo Horizonte, MG. Brazil
IIFederal Center for Technological Education of Minas Gerais. Timoteo, MG, Brazil
The purpose of this study was to evaluate the hydration status and thermoregulatory responses, during official soccer matches, of soccer players in different categories. The participants of the under-15 (U-15, n=36) and of the under-17 category (U-17, n=14) were placed into different groups according to the amount of time spent in the field: Main group; Partial group; Intermediate group; Control group. The thermoregulatory responses and hydration status were measured. The Main group and the Partial group presented significantly higher water intake, weight loss and sweat rate compared with the Intermediate and Control group (p< 0.05). The under-17 players of the Main group had a larger weight difference pre and post match compared with the under-15 players of the same group (p< 0.05). It was concluded that an official soccer match altered significantly the hydration status of the players, and it was related with the time spent in the match.
Key words: Body water; Dehydration; Environment; Sports.
Objetivo do presente estudo foi avaliar o padrão de hidratação e respostas termorregulatórias de jogadores de futebol de diferentes categorias ao longo de um jogo oficial. Participaram desse estudo jogadores de futebol das categorias sub-15 (N 36) e sub-17 anos (N 14). Os jogadores foram divididos em grupos de acordo com o tempo de atuação em nos jogos: grupo principal, o grupo parcial, grupo intermediário grupo controle. As respostas termorregulatórias decorrentes dos jogos e o estatus de hidratação foram determinados e comparados entre os grupos apresentados. Os grupos principal e parcial apresentaram maiores valores de consumo de água, perda de peso e taxa de sudorese em comparação aos grupos intermediário e controle (p< 0,05). A diferença de peso pré e pós-jogo entre as categorias foi maior nos atletas da categoria sub17 em comparação com os atletas sub 15 no mesmo grupo (p< 0,05). Conclui-se que um jogo de futebol foi capaz de alterar de forma significativa os parâmetros de hidratação dos jogadores de futebol tendo relação direta com o tempo de atuação em campo.
Palavras-chave: Água corporal; Ambiente; Desidratação; Esporte.
During a soccer match, players can run distances of approximately 10 to 13 km at intensities near their anaerobic threshold, at an average around 85% maximum heart rate (%HRmax) and 75% of maximum oxygen consumption (%VO2max)1. This is equivalent to a total energy expenditure of approximately 1700 kcal, with a range of 6.5 to 16.9 kcal.min-1 2. Most of this energy is transformed into heat, with a consequential increase in body temperature, sweat rate and need for fluid ingestion3.
When physical activity is performed in the heat, the combination of high sweat rate with inadequate fluid replacement or carbohydrate drinks can increase the risk of hyperthermia. During a soccer match, the players only have access to fluid when there are interruptions during the game, at half-time, or at the end of the match. According to Saltmarsh4 this can limit the players' fluid intake; thus, affecting their hydration status. As a consequence, there are thermoregulatory and cardiovascular alterations which can lead to deterioration in players' performance5-9.
There are various studies analysing players' hydration and soccer, be it during training sessions9, friendly matches6,10-12, with amateur players13 or in low level divisions12. Nevertheless, there has not been to date a study that comprises different high level category players during official matches in a hot environment with an ad libitum hydration strategy. Therefore, the aim of the present study was to evaluate the hydration status and thermoregulatory responses of soccer players of different categories during official matches.
Thirty six male soccer players of the under-15 (U-15) category (mean ± SD = 14.2 ± 0.8 years; 176.1 ± 6.5 cm; 64.5 ± 7.6 kg; 15.7 ± 2.6% body fat; 54.2 ± 3.0 VO2max) and fourteen male players of the under-17 (U-17) category (mean ± SD = 16.2 ± 1.2 years; 181.4 ± 7.6 cm; 71.5 ± 7.1 kg; 10.7 ± 2.3% body fat; 52.7 ± 1.9 VO2max) took part in this study. Both teams were in the first division of the Brazilian soccer series. The participants signed an informed consent form and ethical approval by Ethics Committee in Research of the Federal University of Minas Gerais (ETIC-1291/2010). For inclusion in the study, the athlete should be registered with the Brazilian Football Confederation (CBF) and fit to play. The injured players throughout the game were excluded from the study.
The Official Soccer Matches
Two official matches corresponding to the third round of the state championship were analysed. The first one was an U-15 game that took place from 2 to 4pm. Soccer players from both teams took part in this study. The other game was an U-17 one that took place after the previously-mentioned game at the same stadium, from 4:30 6:30pm. From this match, only the home-team players took part in this study. Therefore, a total of 3 soccer teams were tested on the whole.
Both soccer matches took place on an official sized field. The U-15 match allowed for 5 player substitutions and was composed of two 35 min halves with a 15 min break. The U-17 match had two halves of 40 min each, also with a 15 min interval and the same number of substitutions. Apart from these changes, the matches were played according to the rules set by the International Federation of Association Football (FIFA) for these categories.
Experimental group composition
Within each team, the players were placed into different groups according to the amount of time spent in the field. Main group (MAIN) played between 51 min - 80 min; Partial group (PAR) played 31 min - 50 min; Intermediate group (INT) played 10 min - 30 min; Control group (CON) players that remained on the bench throughout the entire match and didn't played.
Pre and Post Matches Procedures
Body composition of the players was determined with skin folds measurement and players' VO2max was tested with the Yoyo Endurance Test specific for soccer and intermittent sports players14. This test was applied at the beginning of the tournament. Immediately before and after the matches, urine sample was collected from each player. Urine specific gravity was measured by placing a small sample (0.05 mL) on a refractometer (503 Nippon Optical Works®, Japan), and urine osmolality was analysed using an osmometer (5004 MicroOsmette™, Precision Systems Inc., USA). The samples were measured in duplicate.
The players were weighed before (Wb) and after (Wa) the match (Filizola® scale - MF 100, Brazil), while wearing just their shorts and football socks - these were also weighed and their values were subtracted from the total weight. Weight loss was calculated as Wb Wa. Sweat rate (mL·min-1) was calculated using the following equation: Wb - (Wa - Water intake) / total activity time15. In this case, the activity time considered here were 70min (U-15) and 80min (U-17). We used the total time of play for the calculation of sweat rate because the sampling occurred before the game and only at the end of the game, even the player acted less time. This was because the researchers could only make measurements at these times. This fact can be considered a limitation of the study.
The players' tympanic temperature was measured (infrared thermometer, G-TECH, IR1DB1, USA), as well as their skin temperature (infrared thermometer, FLUKE®, USA) through the use the following equation16: (0.43 chest temperature ºC) X (0.25 arm temperature ºC) X (0.32 thigh temperature ºC). Mean body temperature was calculated according to Consolazio et al.17 body temperature = (0.67 Core temperature ºC) + (0.33 skin temperature ºC). Only the players from the MAIN group had their body temperature analysed. This was due to the fact that the temperatures could only be measured at the start and end of the game; thus, if a player left before the match finished, his temperature would have decreased if measured at the end of the match.
The official players' heart rates (Polar® Team System®, Finland) were monitored during the warm-up and during the match. Data are presented as absolute values in beats per minute (bpm) and percentage of maximum heart rate (HRmax). Each player's HRmax was defined as the highest HR measured during the analysed match or during other games that were routinely monitored by the soccer team's Physiology Department. The purpose of HR monitoring was to present data of effort intensity from the match.
Each player had his own bottle being allowed to drink ad libitum. The amount ingested was then measured. Players were instructed to not wet their heads with their water nor throw it away. During previous training sessions and friendly matches, they had the opportunity to familiarize themselves with this procedure.
Dry temperature (DT), humid temperature (HT) and wet globe bulb temperature (WGBT) were measured (RS214, WIBGET®, USA) and relative humidity (RH) was calculated. These measures were made every 5 min throughout both matches (1st and 2nd match). Mean temperatures and RH were compared between each half time of the matches (1st and 2nd half)
Differences between pre and post match variables were analyzed using paired student t test. The ANOVA two-way test was used to analyze difference between the groups and categories (Sigma Stat 2.0.15 statistical software). When a significant F value was found, the post-hoc of Tukey was used. All measures compared show a normal distribution. Statistical significance was accepted at p< 0.05.
No difference in the volume of water intake was observed between categories. However, there was a difference between the groups (Table 1, Figure 1A). Players of the MAIN and PAR groups ingested significantly more water compared with both the INT and CON groups (p< 0.05). In addition, the players from the INT group ingested significantly more water compared with the CON group (p< 0.05).
Weight loss, sweat rate and HR
It was only possible to analyse the weight loss between categories of players from the MAIN group due to the reduced number of measurements taken from the other groups. Players of the U-17 category presented a significantly higher weight loss when compared with the players from the younger category (p< 0.05) (Figure 2). When the athletes were grouped together, according to the time of action on game and not considering their categories, the weight loss were higher in the MAIN comparing to the INT group (p< 0.05) (Table 1, Figure 1B). The same pattern could be seen when the dehydration on percentage was analysed (Table 1, Figure 1C).
The HR of the players recorded during the matches were; Main group 172 ± 8.6 bpm, PAR group 175 ± 6.3 bpm, INT group 174 ± 7.5 bpm and CON group 78 ± 10.3 bpm. There were no differences between categories or the groups of soccer players who played. The CON group present lower HR than another group (P< 0.05).
Urine osmolality and specific gravity
No difference for urine osmolality was found either between categories, groups or when pre and post match samples were compared. As for urine specific gravity, there was a significant increase at the post-match time-point compared with the pre-match time point (p< 0.05) for the MAIN and PAR groups (Table 2).
Body temperature and environmental conditions
Body temperature was only measured from the players in the MAIN groups (n=24) of both categories. No difference was observed between the pre and post match values for either category. In addition, there was no difference between the categories (table 3).
The environmental conditions for both matches are presented in Table 3.
The main finding of the paper was the increase in water intake and sweat rate with the higher time spent in field during soccer matches (figure 1). Players of the MAIN and PAR groups ingested higher volumes of water compared with the other groups. This result was expected because these players spent more time playing. Nevertheless, there was no significant difference in this variable between the MAIN and PAR groups, even though the last group spent less time in field. This result can be explained by the accessibility of the athletes to hydration stations4,18. The athletes of the PAR group could have ingested more water during the first half of the match, before entering the match, or after they were substituted in the second half because they had easy access to their water bottles.
Krustrup et al.6 observed an average water intake of 0.69 L in a friendly match. The present study found higher values: 1.39 ± 0.06 L and 1.69 ± 0.34 L for the MAIN and PAR groups respectively. This difference can be due to the higher intensity of the matches analysed. In addition, the volume of water ingested and sweat rate were higher in the groups that played during a longer period of time.
In the present study, a weight loss of 0.49 ± 0.12 kg (MAIN group) was observed. These results were lower than those reported by Guerra et al.11 when evaluating the carbohydrate supplementation in an experimental group and in a control group. The latter presented a mean weight loss of 1.75 ± 0.47 kg, but they did not have access to water during the match, only at half-time. Shirreffs et al.9 also reported lower values of weight loss (1.23 ± 0.50 kg) in a study analysing 26 professional soccer players during a 90 min training session in a warm and dry environment (30ºC, RH 20%). Considering that the presented study evaluated a training session and not a competitive game, lack of motivation could have hindered the performance of the players, as shown by Antonacci et al.19. Thus, we expected a greater response to weight loss in this study, unlike what was found. Maughan et al.18 reported a higher weight loss (0.84 ± 0.52 kg) compared with the present study. Although the authors used a similar methodology, as well as professional soccer players, the environmental conditions were very different: temperatures between 6 and 8º C, RH between 50 and 60%.
Al-Haazza et al.13 compared the dehydration percentage between children and young soccer players and reported that the groups presented a loss of 2.35% and 3.62% of their body weight respectively. Similar to this study, the authors found a relationship between parameters of hydration and time of performance of athletes. The dehydration percentages in the present study were smaller than values compared with the ones presented by Al-Haazza et al.13. It is important, however, to take into account that the effort intensity presented as HR (172 ± 8.6 bpm and 87.2 ± 2.6 %HRmax) during the matches of the present study were similar, not only compared with that reported by Al-Haazza et al.13, but also compared with those of other studies evaluating competitive situations reporting average values of 165 bpm or 85%HRmax 20,21.
Shephard8 reports that soccer players can lose between 3.5 and 4 L of sweat during a match in a warm environment. This might represent a 5% decrease in body weight which can decrease performance. According to Murray7, physical activity performance is negatively influenced by dehydration above 3% of body weight. The present study showed lowers values than present by Murray7. Casa et al.5 suggest that body weight loss ≥ 2% can be associated to a decrease in performance. Nevertheless, it is important to point out that fatigue during exercise can be explained by a combination of factors, such as metabolic, cardiovascular and respiratory factors, and not dehydration alone6; 22.
Sweat rate was higher in both the MAIN and PAR groups compared with INT and CON groups. Although the MAIN group played longer than the PAR group, no difference between sweat rates was found between them. This might have happened due to higher effort intensity on behalf of the players that spent less time in field. This behaviour was not found in the INT group here players did not present higher sweat rate values compared with the CON group. The CON group was composed of athletes who did just the warm up routine. This step consisted of displacement and intense exercise of short duration. Due to this fact the players in the group CON presented low sweat rates.
Additionally, the similarity between the INT and CON groups could be due to individual variation, sweating during resting condition throughout the game or the low number of players analysed in the CON group.
The sweat rate results, found in the present study for the MAIN (25.58 ± 1.52 mL/min, 1.53 ± 0.09 L/h) and PAR groups (27.17 ± 5.39 mL/min, 1.63 ± 0.32 L/h), represented in mL/min and L/h, are different from the values reported by Reis et al.12: 8.8 ± 6.6 mL/min with a large variation of 1.7 to 28.3 mL/min. These authors, however, evaluated a 60 min training session at a lower temperature (14°C) and RH (70%). Another study23 evaluating two 90 min female soccer training sessions reported sweat rates of 0.49 and 0.44 L/h in environmental conditions of 14.1°C and 71% RH (1st session) and 6.2°C and 74% RH (2nd session). Moreover, McGregor et al.24 presented the following sweat rate results from a soccer specific performance test in environmental conditions of approximately 20° C and RH 57%: 1.4 L/h for the group which ingested liquid throughout the test and 1.2 L/h for the group which ingested no liquids. The sweat rates reported in the present study are higher than those mentioned in the studies above probably because of the competitive situation that was analysed.
The U-17 athletes lost more weight compared to the younger category possibly due to the longer game duration and the unfavourable heat dissipation in the environmental conditions during their match: higher dry temperature. Additionally, the RH was higher during the 1st and 2nd halves of the U-17 match compared with the 1st half of the U-15 match. It has been well established that a combination of elevated temperature and RH results in higher losses of body fluids. Nevertheless, no differences in sweat rate were observed between the categories despite the different environmental conditions, game durations (35 and 40 min) and players' age (U-17 and U-15). Another point that must be considered is the absence of differences among the body temperatures of the athletes.
Besides dehydration percentage, other variables, such as urine specific gravity and osmolality, can be used to verify an individual's hydration status. Harvey et al.25 analysed players' urine specific gravity before and after two soccer matches and showed an increase from 1.012 to 1.020 g/mL. This corroborates the present study that found an increase after the match for both the MAIN and PAR groups. Except for the CON group, classified by the ACSM26 the players started the activity with higher values of considered euhydrated (≤ 1,020 g/mL). However Armstrong et al.27 consider a variation from 1010 to 1030 g/mL, to classify individuals as euhydrated.
Players in this study, even showing no difference in osmolality in relation to pre and post and between both groups could be considered dehydrated because they had values below 700mOsm/kg26. This is in accordance with the study of Maughan et al.18 who investigated a soccer match in a cold environment. Ali et al.10, on the other hand, did show that there is a reduction of urine osmolality after specific training of female soccer players. Taking into account characteristics of soccer matches (i.e intermittent, high intensity, long duration), together with adverse environmental conditions, efficient hydration strategies are important to avoid dehydration during the match.
It has been suggested that blood analysis (plasma volume and osmolality) provide better indication of the hydration status because urine parameters can indicate a false-positive result28. The shifts evaluation in plasma volume and osmolality weren't did. This can be one limitation of the present study.
Field research present difficulties of standardization of data . Researches on sports in competitive situations are difficult to perform due to interference in the routine of athletes. Outdoor team sports like Soccer have great difficulties to be searched. All these aspects can be highlighted as difficulties or limitations of scientific research. Nevertheless, field researches in the sports in real situations have a high ecological validity and applicability in sports training science.
In summary, the present data showed that football matches were capable of altering significantly some parameters hydration status of players taking into consideration the time spent in the field. Better hydration strategies are needed, especially in warm condition, because the ones used during the official matches analysed here were to fulfil hydration needs.
We thank CAPES, CNPq, FAPEMIG and BRAZILIAN MINISTRY OF SPORTS for their financial support.
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Address for Correspondence
Daniel Barbosa Coelho
Federal University of Minas Gerais
School of Physical Education, Physiotherapy and Occupational Therapy
Phisiology Exercise Laboratory
Adress: Av. Antônio Carlos, 6627
CEP: 31270-901 - Belo Horizonte, MG. Brazil
Received: 17 June 2011
Accepted: 03 January 2012