Summer is here in Queensland and we all know the importantance of correct hydration and fluid replacement while training, racing and during recovery… or do we?
When it comes to animals, I have a background in Emergency Medicine and Critical Care so I appreciate that not all fluids are the same and rehydrating a patient with an inappropriate fluid composition or rate can have deleterious over-hydration effects. Our bodies are comprised approximately 50% (female)-60% (male) water (total body water or TBW) and on a day to day basis we have what are called insensible losses that equate to our daily fluid maintenance rate (for an adult canine this daily maintenance rate is 60mL/kg/day, for an adult human around 35mL/kg/day). If we raise our body temperature this daily maintenance level will increase by a minimum 200mL/day which accounts for our evaporative cooling systems (panting and sweating). When we exercise we lose water and electrolytes as part of our cooling mechanism, to prevent dehydration, we have to match this loss with the intake of an appropriate fluid (water + electrolytes). Standard sports drinks contain 10-25 mmol/L sodium and 3-5 mmol/l potassium.
Estimating Fluid Loss
The best gauge of fluid loss is your body weight, a 1kg loss in bodyweight over a given training period equates to 1000mL fluid + 0g fat, so don’t get too excited with your weight loss as it is crucial that you replace that fluid loss in the hours following your training session.
Dehydration and Performance
Dehydration is a reduction in your total body water (TBW) balance. I say “TBW balance” as the water in your body is divided into compartments that are separated by porous membranes allowing water to shift freely between the compartments guided primarily by the sodium level of each compartment. TBW = 2/3 within body cells (intracellular fluid or “ICF”) and 1/3 outside body cells (extracellular fluid or ‘ECF”). ECF is further divided 2/3 Interstitial (between cells) and 1/3 intravascular (in your blood vessels).
Sodium is an extremely important electrolyte:
The majority fluid shifts within the body are along a sodium gradient (osmotic gradient). The kidneys are designed to retain sodium and maintain body sodium levels at the expense of other electrolytes. A decrease in blood pressure will trigger receptors to retain sodium in the body in an attempt to maintain blood volume and pressure.
If we rehydrate with fluid that has insufficient sodium (and other electrolytes) we run the risk of diluting our body sodium levels and ‘fluid overloading’, I have experienced this once many years ago and suffered an episode of pulmonary oedema (fluid on the lungs) as a result. I hear that fluid overload occurs more commonly in places like the UK during a heat wave when people become obsessed with the consumption of bottled water, the moral being we need more than just water to rehydrate. On the flip side, I have treated more than one canine for sodium overload and subsequent cerebral oedema (water on the brain) following a novel trip to the beach on a hot day with owners that forgot their pet gets thirsty too, the only water the dog can find is salt water and bingo, sodium overload.
In the case of post-exercise rehydration, there is sound evidence that the replacement of electrolyte losses, particularly sodium, must occur before fluid balance is fully restored.
Guidelines for sodium intake during prolonged exercise range from 0.5-0.7 g per litre of fluid (21-30 mmol/l) [American College of Sports Medicine 1996 position statement on fluid replacement in sport, regarding exercise greater than one hour] to 0.25-0.5 g per hour for people susceptible to the risk of hyponatraemia during ultra-endurance events [Doug Hiller, Medical Director, Ironman triathlon].
The typical intake of a standard sports drink (e.g. 700 ml per hour of Gatorade) would provide an hourly sodium replacement of 0.29 g.
As dehydration progresses, there is a gradual reduction in physical and mental performance, an increase in heart rate and body temperature, and an increased perception of how hard the exercise feels, especially when exercising in the heat. Studies show that loss of fluid equal to 2% of body mass is sufficient to cause a detectable decrease in performance (that’s a 1.4 kg loss in a 70 kg athlete) and a loss greater than 2% loss of body weight increases the risk of nausea, vomiting, diarrhoea, and other gastro-intestinal problems during exercise. Dehydration also reduces the rate of fluid absorption from the intestines, making it more difficult to reverse the fluid deficit, so you may end up feeling bloated and sick if you delay fluid replacement.
There is some anecdotal information that whole body or ‘heat” cramps are associated with large sodium losses in susceptible athletes (prolonged or large losses of salty sweat).
SIS (Science in Sport) supplements
Science in Sport know all about refuelling and rehydrating. Photo by Naomi Hansen
With all this information I decided to assess the SIS supplements I am currently using, as I have never actually looked at their ‘nutritional information’
SIS PSP22 Fuel now called GO ENERGY: no electrolytes at all, this powder is designed as a carbohydrate source (energy) to be used in the 2-3 hour interval between breakfast and racing, ensuring your carbohydrate levels are topped up prior to race start. GO ENERGY is great during winter training when the sweat rate is low and we just need to fuel.
SIS GO ELECTROLYTE: 0.2g Sodium, 22mg Calcium, 5mg Magnesium, 60mg Potassium and 146kcal/40g serve in 500mL water with advise is to drink 500mL/45-60 minutes of exercise,
SIS GO BAR: 0.1g Sodium, 138kcal, 4,6g protein1.6g fat/40g bar
SIS GO ISOTONIC GEL: 0.01g Sodium, 86kcal/60mL gel, the beauty of an isotonic gel is that it does not have to be taken with water so I find them very easy to consume as they are not so thick and go great in a squeezy gel bottle
SIS GO HYDRO: 0.3g Sodium, 102mg Calcium, 8.1mg Magnesium, 1.3mg Zinc, 65mg Potassium, 7Kcal per 4g tablet is a great new product designed to pop in your water after racing to help rehydrate
So If I am to consume 1000mL + 1 bar +/- 1 gel for every hour of racing and follow with one hydro tablet in 500mL water post racing I will comfortably meet my sodium requirements during and post racing.
The main problem with nutrition and rehydration during racing is the individual nature of the beast, we are all individuals and our requirements for fluid and electrolytes differ accordingly; if you are a ‘big sweater’ you will have higher than average sodium requirements, if you are a cramper you may have higher magnesium or calcium requirements and if you have a sensitive stomach you have to be super careful about what you select as a supplement. Needless to say water alone is not enough and a nutritional advisor is probably the best person to ask on an individual basis, especially if you find yourself cramping or feeling dehydrated despite following an appropriate hydration regimen. I have tried several different brands of supplements and returned to SIS on several occasions as they have a complete range of easy to eat/drink supplements and an isotonic gel that can be consumed without water. If you haven’t tried any of the SIS gear I would encourage you to try just once and see what you think, they also do a great RECO RECOVERY powder but the recovery story is a whole other world to hydration.