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Fluid and Electrolyte Balance in Elite Gaelic Football Players   Back Bookmark and Share
M Newell,J Newell,S Grant
Ir Med J. 2008 Sep;101(8):236-9.

M Newell, J Newell, S Grant
Institute of Biomedical and Life Sciences, University of Glasgow, Scotland

The aim of this study was to investigate fluid and electrolyte balance in elite Gaelic Football players (n=20) during a typical training session in a warm environment (16 to 18°C, 82-88% humidity). Pre-training urine samples were used to determine hydration status. Sweat sodium concentration was collected from four body site locations using absorbent patches. The mean sweat rate per hour was 1.39 l·h-1 and mean body mass loss was 1.1%. Mean sweat sodium concentrations were 35 mmol·l-1 (range 19-52 mmol·l-1). On average, players did not drink enough fluid to match their sweat rates (p<0.001) and this fluid deficit was not related to pre-training hydration status (p= 0.67). A single hydration strategy based on published guidelines may not be suitable for an entire team due to variations in individual sweat rates. Maximising player performance could be better achieved by accurate quantification of individual fluid and electrolyte losses.


Sweating has an important role in body thermoregulation during exercise and is influenced by the duration and intensity of exercise, fitness levels, environmental conditions, acclimatisation, body mass, and choice of clothing.1 However, extensive body water and electrolyte losses from prolific and repeated sweating reduce the capacity of the temperature regulatory and circulatory systems, depleting cells of fluids and electrolytes and can result in a threat to health and performance.2 It is generally accepted that the human body can tolerate dehydration levels of between 1 and 2% body mass particularly in endurance activities in ambient temperatures of 20-21°C lasting less than 60 minutes. However, dehydration of 2% body mass in events lasting longer than 60 minutes in warmer temperatures 31-32°C may increase the risk of fatigue including loss of performance, increased risk of injury, and other neuromotor problems.3,4,5

A recent study of American football players found that players who suffer muscle cramps in training and competition had greater sweat losses and a higher sweat sodium content than players matched for fitness who did not suffer from muscle cramps.6 Although difficult to link exercise-induced muscle cramps with electrolyte disturbances directly, a recent study on Gaelic Football injuries reported that more injuries occurred in the final quarter of training and games than at any other time, and may suggest a possible link between dehydration and injury.7 The aim of this study was to investigate fluid and electrolyte losses in a group of elite Gaelic Football players training in a warm environment. Assessment of fluid and electrolyte losses during training would provide coaches and players with information on the possible hydration needs during and after training.

Gaelic Football players (n=20) were recruited from a Senior Inter- County (elite) team. The elite team was representative of the population of players competing at the highest level of Gaelic Football, whose training intensity and match schedule were typical of elite teams competing at this level.7 All players were male aged between 18 and 36 years. Subjects, who were deemed to have any adverse medical condition, were not recruited. Ethics approval for the study was obtained from the ethics committees of Glasgow University and the National University of Ireland Galway. Data on environmental conditions were acquired from the local meteorological office.

Players were monitored during a typical training session on a warm and humid evening in June, the air temperature ranged from 16 to 18°C, and humidity ranged from 82 to 88%. This was the third training session of that particular week and players had a day’s rest before the session. Training consisted of a dynamic warm-up (including repetitive sprints and stretching) followed by a variety of intensive game drills (defending and tackling), a series of small-sided conditioned games, culminating in a final cool down. The training session was deemed by the coach to be of typical duration and intensity for the players. The total duration of the training session was 80 minutes and all players followed the same programme.

Before the training session
Each player was assigned a study code and given three personalised water bottles. Each bottle contained 1litre of tap water and were placed in crates on the ground beside the training area. Players were then instructed to provide urine samples (to ascertain pre-training hydration status) and these were assessed for urine specific gravity using a handheld clinical refractrometer (Spartan, Tokyo, Japan). Players were then weighed to nearest 0.1 kg (in dry pants) using calibrated weighing scales (Seca 770, Hamburg, Germany); the mass of the individual drinks bottles were also recorded using scales (Soenhle Magnum 802U Digital Food Scale, Switzerland). Absorbent sweat patches (3M Tegaderm +Pad, 3m Healthcare, MN, USA) were used to measure the electrolyte loss in sweat. Patches were applied at four different anatomical sites (Table 1) on the right hand side of the body. Each anatomical site was cleaned with deionized water and dried with a clean electrolyte-free gauze swab prior to the attachment of absorbent patches.8

During the training session
Players were instructed to only drink from their own bottle and not to spit out any water. Any urine voided during the training session was collected and the volume recorded. Sweat patches were removed after twenty minutes (to prevent saturation) and placed in individual sealed sterile universal containers (Sarstedt, Wexford, Ireland).

After the training session
At the end of the exercise session, the drinks bottles were collected. Players were towel dried and their post exercise body mass recorded along with the mass of their individual water bottles. The amount of fluid consumed during training was calculated by subtracting the mass of the drinks bottle at the end of training from the mass of the bottle at the start of training. Total sweat loss was calculated using the formula: Total Sweat Loss = (pre exercise body mass – post exercise body mass + fluid intake– urine volume). Similarly the total amount of fluid consumed during training was used to calculate drink volume consumed per hour. The urine specific gravity readings and percentage change in body mass were compared against published indexes of hydration status (Table 2) from the American College of Sports Medicine’s Position on Exercise and Fluid Replacement.4

Prior to analysis, the volume of sweat collected in each patch was determined gravimetrically (Precisa, Zurick, Switzerland) by subtracting the mass of a new unused patch and universal from the weight of the universal containing the absorbent patch and sweat. Individual samples were diluted with deionized water and thoroughly mixed using a vortex.9 The sodium concentration was analysed using a flame spectrometer (Corning 410c, Corning Ltd., Essex, UK).

Statistical Analysis
A Chi-square test was used to compare the proportion of pretraining hydrated and dehydrated players (based on urine specific gravity readings). An Analysis of Covariance model was fitted to the data to compare mean fluid loss across the team while adjusting for initial pre-training hydration status. The adequacy of the model was checked using suitable residual plots while the assumed additive effect of the covariate was tested by including an interaction term to allow for separate slopes. A Bonferroni adjusted one sample-t-test was used to compare the mean fluid balance for the team against a hypothesised value of zero where each test was performed at the 0.05/2 significance level. The adjustment was made in order to maintain a global Type 1 error rate of 0.05 across the two comparisons. The likely mean fluid balance for the population of interest was estimated using (Bonferroni adjusted) 97.5% Confidence Intervals for a mean.

The majority of elite players (n=15) were well hydrated (usg<1.010) prior to exercise activity (Table 3), however three players displayed signs of minimal dehydration (usg 1.010 – 1.020) and two players showed significant levels of dehydration (usg 1.021-1.030).4 Mean body mass loss over the duration of the training session was 0.8kg with values ranging from 0.5 to 2kg. Using percentage body mass loss as a measure of post training dehydration, the values recorded ranged from +0.5% to -2.4% (mean 1.1%). The majority (n=12) of elite players were classified as being minimally dehydrated post training (-1 to -3% body mass change). Total sweat losses ranged from 0.85 l to 3.15 l (mean 1.86 l), while the amount of fluid consumed by players (rounded to the nearest 5ml) during training, ranged from 300ml to 2000ml with a mean of 1034ml. Comparing the sweat rate per hour to the amount of fluid consumed per hour, there is a mean fluid balance of –0.62 l·h-1 with values ranging from +0.37 to –1.5 l·h-1. Only 56% of sweat volume was replaced during training with values ranging from 23% to 133%.

There was significant evidence (p<0.01) of evidence to indicate that fluid deficit was simply related to pretraining hydration status (p= 0.67).

Figure 1 Relationship Between Pre-Training
Hydration Level (measured by urine specific
gravity) and Post-Training Hydration Balance.

Fluid deficit across the team (Fig. 1). Based on the ANCOVA model, there was no Fluid deficit was significant across the team (p<0.01), even for players classified as being well hydrated at the start of training.

Virtually all points lie below the line of equality and there is strong evidence, that the mean fluid deficit is not zero (p<0.001). An estimate of the likely mean fluid deficit for the Elite ‘population’ is between 319ml and 881ml.

With the exception of 5 players, all points lie below the line of equality indicating an imbalance between the volume of fluid consumed during exercise and the corresponding volume lost through sweat.

The mean sweat sodium concentration (based on a four site average) was 35 mmol·l-1 (range 19 to 52 mmol·l-1). This equates to a total sodium loss (calculated by multiplying mean sweat sodium concentration with mean sweat loss) of 65 mmol (range 35 to 96 mmol) (Table 1). There is a suggestion of player-toplayer variability with regard to sweat sodium concentration from each of the different collection sites, but no evidence of within player variability (p=0.811). The relationship between pre-training body mass and sweat sodium concentration was not significant for all players (p=0.984).

Figure 2 Sweat rate and fluid consumption per

The mean sweat rate per hour of 1.39 l.h-1 for elite Gaelic Football players is similar to results published for elite players from other codes similar to Gaelic Football. Mean sweat rates for Australian Rules Footballers of 1.4 l h-1 and 1.8 l h-1 have been reported, when they trained in a temperate (12-15°C) and warm (27°C) environments. Published sweat rates for professional soccer players during training range from 1.13 l h-1 in a cool environment (5°C), 1.2 l h-1 in warm conditions (25°C), to 1.46 l h-1 in hot conditions (32°C).8,9,10

The mean volume of fluid intake by elite players (1034ml) is similar to the value published (972ml) for professional soccer players9 training in temperatures of 32±3°C. With the exception of four players, who did not have fluid deficit, the majority of players had a fluid deficit ranging from 375 to 1500ml. On average, players replaced 56% of sweat loss. These values are in accordance with previous research, which showed that even with unlimited access to plain water, athletes typically only replace around 50% of the water required.11

It is suggested that if an athlete begins exercise in a reasonably euhydrated state (usg <1.010) and continues to exercise at moderate levels of intensity for less than an hour in cool (5 to 10°C) or temperate conditions (21-22°C), there is no clear physiological need to consume additional fluid so long as body mass dehydration is within the 2%.3 The majority of players in this study were suitably hydrated prior to the commencement of training (mean usg 1.009), and although the mean % body mass loss (1.12%) is within the recommended levels of tolerable dehydration (<2%) there is however, wide variety across the team. Three players had measured levels of hypohydration of (2.3%, 2.3%, and 2.4% decrease in body mass). Conversely, assuming that drinking does not influence sweating response, if no fluid had been consumed the mean % body mass loss of players would have been 2.3% although some players would have had % body mass losses in the region of 3.5%, highlighting that the fluid intake strategies in general, were successful in reducing the potential adverse effect of sweat loss.

The mean sweat sodium concentration (35 mmol·l-1) for players in this study, is in accordance with published values2,3 for sweat sodium concentration (average 35 mmol·l-1, range 10-70 mmol·l-1). The results correspond to published data for professional soccer players10 (30.2 ±18.8 mmol·l-1) training in slightly warmer (32°C) conditions.

The highest mean concentration for sweat sodium concentration was found in the thigh (38 mmol·l-1). This contradicts the published literature as other studies have reported highest values in the chest and back.8,9 However, it was observed in the study that four players wore insulative shorts under their regular shorts and may suggest a possible link between the insulative shorts and a (hypothesised) corresponding localised increase in thigh temperature and subsequent increase in sweat rate. If these players are not included in the pooled data, the highest sodium concentrations are found in the chest and back in accordance with other published studies documenting sweat and electrolyte losses.

The mean volume of total sodium loss was 65 mmol (range from 35 to 96 mmol). It is suggested that players with high sweat sodium loss, may benefit from consuming drinks with a higher sodium concentration (40-80 mmol·l-1) post-exercise, especially during intensive periods of training and games with little recovery time between exercise bouts as typically occurs during the summer months of the Gaelic Football season. It is inappropriate to advocate that all players would improve their performance by increasing their fluid intake. However, sweat losses for some players, even in relatively cool environments may be considerable and large enough to result in dehydration levels greater than 2% body mass. A single hydration strategy based on published guidelines is unlikely to be suitable for an entire team, due to variations in individual sweat rates. Knowledge of individual hydration requirements and specific advice on post-exercise electrolyte restoration should be considered as a possible contributory factor for performance enhancement during training and games.4,8,9 It is suggested that Gaelic Football teams should conduct routine urine tests to determine pre and post, training, and match hydration status, and sweat electrolyte assessments to determine sweat sodium concentration.


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Author's Correspondence
M Newell Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland
The author wishes to acknowledge the support of the Gaelic Football teams that participated in this study, Prof Ron Maughan, and Dr Susan Shirreffs, (Loughborough Univ) Lucozade Sport and 3M Ireland for their assistance with this study.
Other References
No References
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