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Fluid Replacement

It has always seemed strange that football in financial terms, the most professional of sports is perhaps the least professional in terms of the approach of individual players to training and other aspects of preparation. Football clubs, as employers and investors in the players, have also been slow to take advantage of the opportunities to maximise the return on their expenditure. Nutrition has generally been low on the priority list, if it has featured at all.

Nutrition

Every club expects the players to train, but it hardly seems worthwhile insisting on this if the opportunities offered by good nutrition are neglected. One of the key areas where nutrition can have a direct impact on performance is in the area of hydration. There is good evidence that players who become dehydrated are more susceptible to the negative effects of fatigue, including loss of performance and increased risk of injury. There is also growing evidence that excessive sweat losses, especially high salt losses, can be a factor in some of the muscle cramps that affect players in training and competition.

Recently, however, a number of clubs have recognised that hydration is important and that no single strategy suits all players in all environments. This has led to an assessment of individual needs so that a personal drinking strategy can be put in place. This practice appears to have gained ground in American football, where pre-season training typically takes place in extreme heat and involves two sessions per day. In recent years, a number of high-profile fatalities, including that of Korey Stringer in the NFL, have raised the awareness of what can happen when things go seriously wrong. Several of the top English football clubs now have monitoring strategies in place.

Zero-cost analysis

At its simplest level, weighing of players before and after training gives an indication of their level of dehydration and risk of heat illness. This takes account of both the amount of sweat lost and the amount of fluid drunk and gives the net balance. There will be a small amount of weight loss due to the fuels used to produce energy (mostly carbohydrate, with a bit of fat), but this amount is relatively small. There will also be water loss from the lungs and loss through the skin. Broadly speaking, a weight loss of 1kg represents a net loss of 1L of body fluid.

A slightly better measure is obtained if the player is weighed before and after training or competition (nude and dry on both occasions) and his (or her) drinks bottle is also weighed before and after, assuming that all players drink from their own bottles and that anything that is taken from the bottle is swallowed and not spilled/poured over the head/spat out. If the decrease in weight of the drinks bottle is added to the decrease in weight of the player, we get the actual sweat loss. We also get a measure of the player's drinking behaviour.

All of this is easy to do, and all it requires is a set of kitchen scales to weigh the drinks bottles, a reliable set of scales to weigh the players, and a bit of organisation. The cost is effectively nil -just a bit of time and effort on the part of one of the backroom staff. There is one more measure that can be usefully added, but this needs rather more specialised apparatus and is thus likely to be the preserve of the top clubs only: the measurement of salt losses in sweat.

Identifying salty sweaters

There are many ways to measure salt losses in sweat. The one that is most convenient in practice is to use gauze swabs covered with an adhesive plastic film: typically, four are applied at different sites before exercise begins and left in place for an hour or so. After they are removed, the amount of sweat and the amount of salt in the patch can be measured, allowing the 'salty sweaters' to be identified.

We have made these measurements on the first team squads at a number of Europe's top teams, typically testing about 20-30 players at each club. They results have been consistent between clubs when the training sessions have been similar, but the variability between individual players has been striking. Key findings in a typical 90-minute training session are as follows:

  1. Average sweat loss is typically about 2L, but this can vary from about 1L to over 3L, even though all the players are doing the same training in the same conditions and are wearing the same amount of clothing.
  2. Average fluid intake is typically about 800-1,000ml, but this can vary from about 250ml to over 2L.
  3. There is no relationship between the amount of sweat a player loses and the amount he drinks.
  4. The sweat salt content varies greatly: the better acclimatised players have lower sweat content, but again there is a large individual difference. Sweat salt (sodium chloride) losses can reach almost l0g in a single training session in some players, and this during twice-a-day training. Others lose only small amounts - 2g or less in the same training session.
  5. When training takes place in the cold, sweat losses may be almost as high as when training in the heat, but players drink far less and so end up just as dehydrated - or even more so.

These findings may appear simplistic and predictable - apart from the last one, which is not intuitively obvious - but they give the training staff of a club that is serious about maximising its human assets a chance to prescribe fluid according to the player's needs. The aim should be not to drink too much, as some players do, but to drink enough to limit weight loss to no more than 1-2% of the pre-exercise weight.

There is also a suspicion - and I should stress it is no more than a suspicion at present - that players with a very high sweat salt content are more prone to cramp and that this risk can be reduced by salt supplements.

These simple steps can make a difference between being able to score that vital goal in the last minute and being a virtual spectator. It is only surprising that it has taken the world of professional football so long to realise this.


References

  1. MAUGHAN, R. (2004) It used to be oranges in the centre circle... now it is a personal hydration strategy. Peak Performance, 196, p. 6-7

Article Reference

The information on this page is adapted from Maughan (2004)[1] with the kind permission of Electric Word plc.

Page Reference

If you quote information from this page in your work then the reference for this page is:

  • MACKENZIE, B. (2005) Fluid Replacement [WWW] Available from: https://www.brianmac.co.uk/football/hydration.htm [Accessed

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