// Sodium replacement during training

Gauging your client's level of dehydration during training will allow you to effectively plan for fluid replacement and make the most of every session, says Emilie Isles.

What exactly is dehydration and at what point should a trainer be concerned by it? Like a car’s engine, the body becomes hot during exercise. Some of this heat is produced by the muscles as they contract, while heat may also be absorbed from the environment. The body has its own radiator system to prevent it from becoming too hot. Acting as the body’s main cooling mechanism, the evaporation of sweat from the skin absorbs heat from the body and helps to maintain body temperature within an acceptable range.

Of course, the side-effect of sweating is to lose fluid and electrolytes from body stores. When exercise continues in the face of a building fluid deficit, particularly in a hot environment, it becomes more challenging for the body to maintain its activity regulation. Body temperature and heart rate will elevate to higher levels than when fully hydrated, and most clients will perceive the exercise as being harder to do – feeling more fatigued and possibly not being able to gain the most benefit from a session. This explains why we encourage fluid intake during exercise; to keep overall fluid losses to a modest level. There is no need for clients to drink more than they sweat; in fact, it is dangerous to drink excessive amounts of fluid (see page 51), so it is good to have an idea of clients’ typical sweat rates during exercise, so you can develop a fluid plan that ‘paces itself’ just below their likely fluid losses.

There is a considerable degree of variation among individuals in terms of both sweat rate (amount of sweat produced during a training session) and sweat composition (what else is in the sweat apart from fluid). Characteristics that affect sweat include:

  • The intensity of the exercise.
  • Fitness level of the client/athlete.
  • Environmental conditions (and whether acclimatisation has taken place).
  • Body size and gender (males have been shown to sweat more than females).
  • Clothing worn.
  • Cooling strategies that may be in use.

Before you can begin to provide a plan for fluid replacement you need to be able to estimate fluid losses. An estimate of sweat loss during exercise can be obtained by weighing clients both before and after exercise, with weight change reflecting total fluid loss. When assessing fluid loss during an exercise session you need to consider the following sequence of measurements:

  • Client to empty bladder prior to exercise session.
  • Weigh clients in minimal clothing and bare feet prior to exercise session.
  • Measure client’s full drink bottle.
  • Client to towel dry and empty bladder before weighing at the completion of the session to remove excess sweat.
  • Measure drink bottle at the end with whatever fluid remains (if your client wishes to refill during the session then simply repeat the process of drink bottle weighing).
  • Note the weight change in kg at the end of the session. This approximates the change in fluid status over the session. For example, 1kg in weight change equals 1 litre of fluid change.
  • Add the amount of total fluid consumed during their session to their recorded weight change during the session to estimate overall sweat losses. A client who loses 1kg during a session in which they drank 500 ml has a total sweat production of 1.5L

Following the above guide (also available to print or download as an amended A4 resource from www.fitnessnetwork.com.au/gymbag) will allow you to provide your clients with an estimate of their fluid losses during a session. As this information is specific to that particular session, it would be wise to record any extra details that you have available to you such as temperature, humidity, air conditions, breeze (fans or wind) and clothes worn. Of course, the overall body fluid deficit may not be the same as the fluid lost over the session.  Sometimes clients can start the session already dehydrated (in which case, their total fluid deficit is greater than you have estimated), or they may have over-hydrated in preparation for training (in which case, their actual fluid deficit is less than your estimates). These factors can be taken into account when you plan how much the client should drink during the session to stay within reasonable touch of their overall hydration levels.

A range of major electrolytes are lost via sweat during physical activity, with sodium depleting by the greatest amount. Drinking a fluid containing sodium during and after exercise can help to enhance overall fluid balance in several ways. First, it reduces the loss of thirst that accompanies fluid intake, helping people to feel like drinking more. Second, sodium replacement helps to retain fluid that is consumed, particularly after exercise, by reducing the amount that is lost in urine production. Some athletes who experience very high salt losses via sweat may directly benefit from higher amounts of salt replacement during exercise. There is renewed interest in whether some types of exercise-related cramps might be associated with large sodium losses. When you are observing sweat characteristics of your clients, it may be beneficial to watch out for dried salt on the skin or clothing after the session as a rough guide to whether your client is a ‘salty sweater’. If you have serious concerns about the amount of sodium a client might be losing, or you have a client who presents with regular cramping that seems unrelated to their level of conditioning or fitness, you should consider referring them to an Accredited Sports Dietitian who can investigate further and can also arrange testing of sweat sodium concentration.

Information about your client’s sweat characteristics and exercise goals will help you to decide on an appropriate fluid plan for each type of exercise session or activity. Suggestions on how much needs to be consumed are summarised below. The choice of drink will depend on issues such as energy balance, fuel needs and the importance of taste. For example, a pleasant tasting drink is likely to encourage greater fluid intake than water alone and may assist a reluctant drinker to increase their fluid intake. While the carbohydrate content of a sports drink may benefit a client who needs fuel support for a prolonged moderate  to high intensity exercise session (>1 hour), the same may not be true of a client who wants to create an energy deficit to lose weight by undertaking a shorter low to moderate intensity session. Drinks with higher sodium levels (e.g. Gatorade Endurance) are more useful for prolonged exercise activities (>3 to 4 hours duration) or salty sweaters. During and after shorter sessions, unless sweat rate and sweat sodium loss indicate otherwise, the sodium (salt) consumed in meals/snacks following training sessions is likely to easily replace overall sodium losses. It is important to be flexible with your recommendations and know the individual goals of each client, as there is no ‘one size fits all’ approach to hydration strategies.

When getting down to the specifics of guiding a client on a hydration management plan, the following advice should help you get started:

  • Encourage clients to turn up to training sessions well hydrated (a two per cent loss of body weight in a poorly hydrated client will give vastly different consequences to a two per cent loss of body weight in a well hydrated client)
    • It might also be beneficial to encourage consumption of fluid at the beginning of the session when plans for the day’s training are being discussed.
  • Aim to replace most of the sweat losses that occur during training, or for the client to drink sufficient fluids to avoid a total deficit of more than two per cent of body weight as fluid during a session (this equates to 2kg for a 100kg person or 1kg for a 50kg person).
  • Ensure fluid is readily available during sessions (drink bottles, fountains, taps)
    • Fluids should be cool and palatable to encourage consumption.
  • Encourage clients to drink to a plan that includes ‘listening’ to thirst as well as using information gained in previous workouts to set a suitable drinking pace (this may mean encouraging a certain volume between sets or over a specific time period)
    • Ensure that drinking opportunities are incorporated into your training sessions.
  • Replace remaining fluid losses in a timely manner following the end of the session. Knowing how much fluid a client loses in a session will help you provide more detailed guidelines on how much fluid to drink with subsequent meals and snacks.
  • Encourage heavy sweaters to include some dietary sources of sodium with their post exercise meal/snack to assist with restoring hydration status (this should be considered in the context of a healthy diet and may require the referral of your patient to a dietitian in your area).
  • Manipulate environmental conditions to reduce sweat losses; e.g. use a fan to facilitate loss of heat from the skin via convection when air flows across the skin, encourage appropriate exercise clothing.

Hydration status should be considered an integral part of achieving client goals. Incorporating discussions about the importance of optimising hydration into your training sessions with clients, as well as giving them some specific, and at times prescriptive, advice in regard to fluid and sodium intake is an excellent way of adding value to your sessions. Consulting other professionals, such as Accredited Sports Dietitians, as well as information available through organisations such as the Australian Institute of Sport and Sports Dietitians Australia will help you to provide the most current information to your clients.

With thanks to Louise Burke of the Australian Institute of Sport for her contribution to this article.


Emilie Isles
As an Accredited Practicing Dietitian and Accredited Sports Dietitian, Emilie has worked in areas ranging from Sydney Children’s Hospital to West Tigers NRL team. She is an active member of Sports Dietitians Australia which, in collaboration with the Australian Institute of Sport and Victorian Institute of Sport, works closely with Gatorade and its new Endurance product. Having contributed to publications such as Body and Soul, Madison and Your Body, Emilie consults with Nutrition Lab in practices throughout Sydney. For more information visit www.nutritionlab.com.au.

• PP 49-51