Caryn Zinn Senior Lecturer Auckland University of Technology, New Zealand Registered Dietitian/Sports Nutritionist.

caryn.zinn@aut.ac.nz21It is well known that the maintenance of fluid in the body is critical to optimal exercise performance. However, despite this knowledge athletes are often inadequately hydrated, both during and outside of exercise times. During training sessions and games, athletes rarely drink enough fluid to replace sweat losses. Coined 'voluntary dehydration', there seems to be a number of factors involved which prevents athletes from optimally replacing fluid losses. There does exist a number of physiological explanations for 'voluntary dehydration'.

The desire to drink develops initially from the small loss in blood volume as a result of sweating. When water moistens the mouth, a signal is relayed to the brain telling the body to switch off the thirst button. Unfortunately the thirst desire is often switched off before the body's fluids have been completely restored. In addition to this, when fluid travels from the mouth to the stomach, this movement triggers the same signals to the brain and drinking stops before the body's fluid levels are restored to normal.

Another explanation for why athletes don't drink enough is that they do not like the 'sloshing' of a lot of fluid in their stomach while exercising. This often compromises optimal fluid intake and results in dehydration and consequent reduced performance.

So what do you, as a coach, need to do to get the best performance from your rugby players? Below are some tips as to how you can go about increasing fluid intakes of your players.

EDUCATE EDUCATE EDUCATE!!!

1. Explain to your players why fluid is vital for optimum performance.

2. Encourage your players to drink 8-10 glasses of fluid per day outside of their exercise times in order to keep well hydrated.

3. Prior to exercise (training session or a game): Encourage players to drink 1-2 cups of fluid10-15 minutes before the start of a session. This fluid will help replace the first beads of sweat lost.

4. Insist that all players carry waterbottles to training and games (if they are not provided). Weigh players before and after training. Weight lost during a session is almost entirely fluid loss. Use this to work out the fluid needs, and hence a drinking regimen, of each player for during and after exercise sessions. 1kg weight lost = 1 litre fluid lost.

5. Encourage players to drink early on during training sessions and then at regular intervals. During games, make use of breaks in play to provide players with either water or a sports drink. A good guideline is 150-200ml every 15-20 minutes (a standard sporting type drink bottle is 750ml). However, this is merely a guide and it must be acknowledged that each athlete has a different sweat rate and consequently a unique fluid requirement.

6. To prevent 'voluntary dehydration', ensure that players consume the correct amount that they need and that they do not stop drinking when they no longer feel thirsty.

7. Encourage players to make use of palatable, cold beverages to promote optimal drinking (eg.  Powerade, Replace or a similar sportsdrink).

8. Recovery (post match or training): Encourage players to rehydrate as quickly as possible. If the amount of fluid lost during the session is known, replace 1.5 times this amount to account for additional sweating and urine losses. Remember that both fluid and carbohydrate are now both nutritional priorities for optimal recovery. A sportsdrink helps to replace both of these nutrients. Remember that one 750ml sport drink will supply 50g carbohydrate. This amount of carbohydrate and fluid is therefore probably not sufficient on its own.

9. Below is a table of 'fluid' and 'non-fluid' examples. What is meant by non-fluid is that these beverages contain substances which further increase the risk of dehydration (caffeine, alcohol). These 'non-fluid' beverages are to be avoided when trying to replace fluid stores as they are diuretic in nature.

REMINDERS