The Sweat Rate Test

It is important to develop an understanding of your sweat rate so that you can develop a thorough understanding of your sweat losses during an event.

The easiest way to measure your sweat rate is to weigh yourself without clothes on before and after exercising for one hour, taking note of the climatic conditions you were exercising in.

Method

• Weigh yourself without clothes on before you head out to train.
• Conduct one hour of training in as similar conditions to race day as possible. intensity, pace and discipline. 
• After one hour, return home, strip down, thoroughly dry your skin and hair, and then weigh yourself again.

Results

Assuming you did not use the toilet or consume any fluids during exercise, your weight loss is your sweat rate.

1kg of weight lost = 1L of fluid lost

If you drank any fluids or used the rest room between the two weight samples, you will need to include both of these estimated weights in your calculations.

• Add any fluids consumed to the amount of weight lost
• Subtract estimated bodily void weight from the total weight lost.

Important Considerations

Weather and climatic conditions strongly influence sweat rates.  For example, on a cooler overcast morning you will loose less sweat volume than on a hot, humid morning.  Therefore, be sure to record the heat, humidity and weather conditions in your sweat test and repeat the test in cool, humid, windy and hot conditions.

Sweat rate also changes with pace and effort increases.  For example, if you monitored your sweat rate for a shorter ½ marathon race pace and then want to step up to a 50 or 100km race that requires a lower effort over a prolonged period of time, you will need to conduct the above tests again to highlight the new effort zone.

Conclusion

Now that you know your sweat rates, you now need to develop an understanding of how much fluid replacement your stomach can tolerate.  For more information on how to rehydrate during events, you may like to read the article Hydration for Endurance Performance

For a comprehensive understanding on sports nutrition & hydration read: Sweat. Think. Go Faster by Darryl Griffiths

See our comprehensive Sports Nutrition range for Trail Runners HERE