Fluid Loss During Exercise

Ever wondered how much fluid you should be drinking when working out?  To know that, you need measure your sweat rate.  How?  Weigh yourself before and after exercising and get the difference. 1 kilo of lost weight approximates 1 liter of lost sweat.

Here is how I measured my fluid loss:

Weight before exercising

Weight after exercising
1)  I weigh myself before exercising - 68.5kg.

2)  Exercised for 30 minutes in a stationary bike averaging about 180watts of intensity.  After exercising, this is my weight - 67.6kg.  Almost 1 kilo lost in just 30 minutes of sweating!

I doubt it if I lost any fat in my body (I wish).  All that I lost is body fluid through sweat.  Since 1 liter of water weighs approximately 1 Kilogram, it means I have lost  900ml all in 30 minutes of exercise!

This explains why I have always cramped in very long durations of exercising like playing Tennis or Mountain Biking.  When I do this for more than 2 hours, I almost always cramp due to dehydration, losing electrolytes in my body through sweat.

What I learned from all this is for every hour of exercising - I'll need 2 liters of fluid to hydrate.  For a 2 hour mountain bike ride, I'll need to 4 liters of fluid (I'll even sweat heavier carrying 4 kilos of fluid up the mountains).

Your sweat rate might be different so it might be worth a time to measure yours if you are having problems with hydration. For proper hydration, you should start drinking even before you start exercising, during and after.  Make sure your drink has electrolytes - sodium, potassium, magnesium and calcium.  There are several sports drinks in the market that can supply your need but a good natural option is coconut water because it packs far more electrolytes and nutrients than most sports drinks you see in the market.