The science of hydration and refueling for netball

How much do netball players sweat?

We collected information on fluid intake practices on 22 players from the Australian Institute of Sport netball team during several training sessions and matches, during both winter and summer.  Although there was a clear difference in the weather between seasons, the sessions were carried out in an indoor stadium that helped to reduce the differences in playing conditions. The results of our observations are summarised in the Tables below.

Fluid characteristics during on-court training sessions 

Fluid characteristics during games 

We found that sweat rates were greater during games than training sessions, which matches the observation that time spent at high work intensities is greater during competition.  We also found that the change in body mass over an exercise session was greater during summer than winter.  Although there were differences between individual players, the fluid deficits observed among netball players were typically mild.  On about two-thirds of the occasions during summer, players kept their body weight loss to less than 1%. During winter sessions, more than 80% of observations involved a change in body mass of less than 1%.  Although we recommended that each netball player find a comfortable fluid intake plan that suits their rates of sweat loss, we noted that a typical fluid intake for high level netball players during active training sessions and games might be ~ 600-800 ml per hour.  On this basis, the coach or team manager would need to ensure that 20 litres of fluid are available on court for a 2 hour training session or match for a squad of 10-12 players. (Broad et al. 1996).

How does hydration and refueling affect netball?

Several studies involving prolonged intermittent exercise protocols or “stop-start” sports (e.g. tennis, soccer and cricket) show that dehydration and inadequate fuel cause fatigue over the course of the exercise session.  By contrast, when subjects consume fluid and carbohydrate during the session, this fatigue is reduced.  Benefits include better maintenance of activity patterns (greater distances covered at higher speeds in the later parts of a game) and better maintenance of skill and concentration.  These studies need to be conducted on the specific outcomes of a netball game.  The duration and intensity of a single match of netball may not be sufficiently challenging to cause nutritional fatigue in all players.  This may need to be judged for each individual.  Tournament play is likely to involve the greatest risk of nutritional fatigue since players may experience difficulty in fully rehydrating and refueling between games.  However, some studies show that players may not fully rehydrate between practice sessions during intensive training periods. Fatigue will occur earlier if fluid balance and fuel stores are not ideal at the start of a new match or practice.  

Fluid Guidelines for Netball Players

Monitoring hydration status

Monitoring body weight changes over a selection of training and game scenarios will provide a quick check of how well your fluid practices track your sweat losses in a variety of exercise scenarios.  You should weigh yourself in minimal clothing before the session. After the session, you should towel yourself dry and weigh again in the same clothes. It is assumed that the difference in weight is predominantly due to changes in fluid balance.  If you are also able to keep track of how much you drink and eat (in grams) during the session, and any weight changes due to toilet stops during the session, this will allow you to estimate your total sweat losses:

Sweat loss (ml)  = weight change over the session (g) + weight of fluid/food consumed (g) – weight change due to a toilet stop (g)

Information collected first thing in the morning can provide a netball player with an indication of day-to-day hydration practices, and specific hydration status on the morning of a training session or match. It is useful to track morning body weight from day to day, by weighing yourself after waking up and going to the toilet.  A sudden loss of > 0.5 kg may be an indication of a fluid deficit from the previous day(s) fluid intake practices.  Of course, other conditions that affect body weight need to be taken into account (clothing, using the same set of reliable scales, emptying bladder/bowel on waking, sudden reduction in food intake, or a general weight loss program).  When these factors are kept constant, a sudden substantial change in weight usually indicates a fluid deficit.
Some netball players have access to monitoring the characteristics of their first urine sample of the day – for example, the Specific Gravity of their urine (USG). A morning USG reading > 1.020 confirms other evidence of a fluid deficit and suggests that fluid practices of the previous day(s) have fallen behind fluid needs.

Competition drinking strategies for players

• Sweat rates and fluid needs vary according to your playing style, playing conditions and the weather.  You should have a fluid intake plan based on your individual needs, rather than a “one size fits all” approach for all players in the team.  Monitoring body weight changes over a selection of exercise sessions will provide you with a quick check of how well your fluid practices track your sweat losses in a variety of match scenarios.
• The general advice for fluid intake during exercise is to try to drink to replace most of your sweat losses, at least to the level that is practical and comfortable.  Typically, athletes are advised to try to keep fluid deficits to less than 2% of body weight.
• Warm-up, formal breaks, injury time and bench time provide opportunities to drink fluid during a match. With a good plan you should be able to use these occasions to maintain your hydration over the match.
• In some conditions, some players will not be able to drink at a rate that replaces all sweat losses incurred during the game; however you should drink at a rate that is comfortable and keeps pace with sweat losses as well as possible.
• Your fluid intake plan should not require you to drink excessive amounts of fluid, so that a substantial weight gain occurs over the match. Over-consumption of fluids can lead to gastrointestinal discomfort.  If carried out to extremes, it can also cause a medical problem called hyponatremia, where blood sodium concentrations fall to a dangerous level.
• Having your own drink bottle avoids the hygiene problems associated with sharing drinking vessels. It also allows you to keep track of how much you have consumed over the match.
• Sports drinks provide opportunities for intake of fuel as well as fluid during matches.  Research shows that carbohydrate intake may enhance performance during matches by increasing endurance and delaying the onset of fatigue.  It may also assist in helping to maintain concentration.  In comparison to water, sports drinks may help you to perform for longer and at higher intensity for the duration of the match, and to maintain skills and decision-making capability at an optimum level. 
• The maintenance of carbohydrate stores over the length of a tournament is also important.  Using sports drinks during a game and in recovery will assist in the maintenance of glycogen stores so that optimum energy levels are available at the finals end of the tournament.

Training drinking strategies for players

• Training sessions often provide the most practical opportunity to undertake monitoring of your typical sweat losses in different netball activities.  Monitoring changes in body weight over the session, adjusted for toilet breaks and intake of food and drinks, can provide a picture of your sweat losses, success in replacing fluid during the session and the remaining fluid deficit at the end of the session.  This information can help you to develop a fluid intake plan for training and matches, and to monitor the results from time to time.
• Make use of scheduled breaks in team and individual training sessions to achieve your fluid intake plan.
• Take a drink bottle and have a fluid intake plan for all training sessions, regardless of the weather or perceived need to drink.  Even in cool weather or an indoor environment, it is possible that sweat losses can be substantial.
• You should generally avoid drinking at a rate that exceeds your sweat losses, leading to a gain in body mass over a training session.  Of course, this might not be a problem if fluid intake helps to overturn a fluid deficit carried into the session. However, over-consumption of fluids can lead to gastrointestinal discomfort.  If carried out to extremes, it can also cause a medical problem called hyponatremia, where blood sodium concentrations fall to a dangerous level.
• Sports drinks provide opportunities for intake of fuel as well as fluid during training.  This may help to sustain skills and work output right to the end of lengthy sessions.
• When you are training more than once in a day, you will need a careful fluid intake plan for each session, and for full rehydration between sessions.

Issues for team management/coaches

• A professional approach is to have a “team drinking plan” that incorporates the range in needs of all players, rather than relying on “good luck” practices of individual players or “one size fits all” for the team.
• It is good to encourage individual or team “fluid monitoring” activities. Monitoring changes in body weight and fluid intake over training sessions and matches will provide each player with a feel for their typical sweat losses in different situations.  It will also provide each player with some feedback of how well their present practices meet their needs.  Players who continually fail to hydrate appropriately during training or matches should be referred for specific advice.
• There should be an adequate supply of fluids available to players, especially when matches are played at a remote location away from a water supply, or in countries where the local water supply is unsuitable for consumption.  Calculations should be made to supply a volume of fluid that is adequate to cover the needs of each player.
• Best practice is to provide team supplies of sports drink and water in insulated drink coolers.  This ensures that players have access to suitable and palatable drinks, but also provides an education message that hydration practices are important.
• Provision of separate drink bottles to each player provides further opportunity and education regarding fluid intake during the match.
• Issues of drink availability (provision of coolers and bottles) are also important in the training situation.  The coach should schedule regular drink breaks into the training program according to the likely fluid needs of the players.  This may need to be adjusted according to the weather and the intensity of training. Players should receive encouragement and education messages about suitable hydration practices during training sessions at each break.

References
Broad, E. M., Burke, L. M., Cox, G. R., Heeley, P. and Riley, M. Body weight changes and voluntary fluid intakes during training and competition sessions in team sports. Int J Sport Nutr 1996; 6: 307-320.

Written by AIS Sports Nutrition, last updated December 2009. © Australian Sports Commission.