Fluids

Part 1 of 2

Without a doubt, consuming adequate fluids will improve your sense of energy, alertness, and exercise performance. Indeed, one can spend both money and time looking for the perfect sports drink or hydration system. One of the best (and cheapest) performance enhancing products is—you guessed it—water, but there are times when water may simply not be enough.

Literature supports the notion that total body water averages 60 per cent (ranging from 45- 75 per cent) of total body weight depending upon the body composition. Fat-free mass (muscle, bone, blood, other fluids) is approximately 70-80 per cent water and is the primary reason for this rather large variation. Maintaining normal hydration is important for normal body functions, which includes thermoregulation (maintaining your core body temperature) during exercise.

During exercise the degree of sweating is dependent on a variety of factors. Duration and intensity of exercise, environmental conditions, and type of clothing all play a significant role in sweat rate and its fluid and electrolyte losses. Additionally, body weight, genetic predisposition, acclimatization, and metabolic efficiency will also influence sweat rates. Temperate environments where body temperature does not rise significantly can result in far less sweat rates than hot or hot/humid environments where body temperature increases are not dissipated through normal sweating and environmental cooling with evaporation from the surface of the skin.

The prevention of excessive fluid loss (more than two per cent total body weight loss) and electrolyte imbalance is the goal of hydration during exercise. A loss of body weight greater than two per cent during an exercise session is directly related to physiologic strain measured through core temperature, heart rate and perceived exertion. Two per cent of body weight for someone weighing 60 kilograms (132 pounds.) would be 1.2 kilograms (2.6 pounds).

With losses this great, a decline in performance is inevitable. The greater the total body water deficit, the greater the physiologic strain which can include the following acting in concert: increased core temperature, increased cardiovascular strain, increased glycogen utilization, altered metabolic function and perhaps central nervous system function. A greater than 2 per cent body weight degrades aerobic exercise and cognitive function in temperate to hot environments but less so in cooler environments. In fact, the body can tolerate greater body weight losses (3-5 per cent) from sweat with less detrimental effect on aerobic performance in cooler conditions.

The two simplest markers that aid an individual in determining their hydration status are weight and urine output. Although these have significant limitations, there are accessible “field” evaluations that all athletes can use. Weighing in naked before and after an exercise session and taking into consideration any fluids consumed during the exercise session can both be a fairly direct measure of how much an athlete sweats during a particular type of exercise under the particular environment of the day. The loss of one kilogram of weight is the equivalent of one litre water. If an athlete is lighter by one kilograms, drank 500 millilitres fluid during exercise, their fluid losses in that workout are one litre + 500 millilitres = 1.5 litres. The ideal situation is that you measure your sweat rate in different environmental conditions. What happens at the gym where the environment is climate controlled? What happens at 10 °C, 20 °C or 30 °C outside while you run and play at your exercise? Knowing specifically, how much sweat you lose under different conditions and calculating based on an hourly rate, is a very effective way to predict how much you need to drink during, and after, exercise to re-hydrate. Re-hydration recommendations are that you drink 150 per cent of your losses within a short time after exercise, doing a urine check at about four hours to see if your urine is pale in color. If you are still producing dark urine, you haven’t caught up yet, so drink some more.