It’s a simple rule, we exercise, we sweat, we replenish. Isn’t it ironic then that some of the most important things we know we have to do often get overlooked!? Some might argue that they don’t sweat when they train, but you don’t have to be overtly wet in order to have lost fluid. We also lose fluid through perspiration such as when we breathe known as insensible losses. Insensible losses are difficult to gauge making it difficult to know the amount of fluid we lose via this route, but the Australian Institute of Sport (AIS) explain that we can lose approx 500-650ml per day from breathing alone! On top of this, we also stand (or sit, as the case might be) to lose approx 100ml per day through our faeces!
As the days get warmer, our urge to get out in the sun rises, meaning our demand for fluid increases proportionately. Be sure to consume at least 30-35ml of fluid per kg body weight (e.g. water, squash, tea/coffee) per day to meet your fluid requirements when performing general daily activity, and more still if you are exercising. If you are performing physical activity, or you notice that you are sweating a lot you may need an isotonic beverage which enhances the absorption of fluid into your body, delivers carbs for energy as well as some key electrolytes such as sodium and potassium lost through sweating.
The average person excretes approx 1000-1500ml of urine when resting, accounting for well over half of our fluid loss a day. This amount can rise by at least 500ml through sweating and insensible losses. During intense physical activity, you can quite feasibly lose 1 litre of fluid an hour, and depending on exercise intensity and ambient air temperature, this value can increase to more than 3 litres!
Australian Institute of Sport, (2009). Effective hydration strategies for sweat loss. Retrieved 2nd May, 2013, from http://www.ausport.gov.au/ais/nutrition/factsheets/hydration/how_much_do_athletes_sweat
Adapted from: Rehrer, N. J., and L. M. Burke, (1996). Sweat losses during various sports. Australian Journal of Nutrition and Dietetics. 53(4): S13-S16.