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ReHydration and Exercise

We don't all sweat the same amount during the same exercise.. Crucially, the concentration of sodium in our sweat varies considerably from person to person.. therefore we all have personalised hydration requirements. For the more serious athlete, hydration (of the correct electrolytes) can mean the difference between achieving their goals and not.

Personalised Sweating!

The average person loses about 950mg of sodium per litre of sweat, but the range is from 200mg/l to 2000mg/l.

The amount of sodium you lose is determined by:

- diet

- acclimatisation to heat

- severe dehydration

- your genetics! (which stabilizes after infancy)

Why is loss of sodium (in sweat) relevant?

Sweat contains sodium as well as significantly smaller amounts of potassium, calcium & magnesium. Sodium is critical for maintaining your blood volume, because sweat is drawn from blood plasma. This causes strain on your cardiovascular system, making it harder to pump blood to your working muscles and to your skin to cool down your body.

How To Personalise Your Hydration?

1.For Serious Athletes - Do a sweat test (see below) or...

"It takes less than half an hour, electrodes are used to diffuse a drug called pilocarpine into a patch of skin about the size of a quarter on a person’s forearm. The pilocarpine stimulates intense sweating in that area, and this sweat can be collected and run through a device that measures its electrical conductivity, and thus determines its salt content." Excert from "Innovation in Hydration: Sweat testing is next level of sports hydration" written by Tom Taylor, 28 April 2016 in Sports Illustrated (

2. For medium-serious athletes: Measure your sweat rate as demonstrated by Precision Hydration's Andy Blow:

3. For recreational athletes - Estimate!

You may be a "Saltier Sweater" if at least 3-4 of the following apply:

a) White, salty marks on clothing after exercise

b) your sweat tastes very salty and/or stings your eyes/cuts/grazes

c) you feel faint or suffer head rushes when standing up quickly after exercise

d) you often feel terrible after exercising in the heat

e) you suffer from muscle cramp during/after long periods of sweating

f) you crave salty foods during and after exercise

What to Drink?

"A good guideline to use when preparing for an outdoor workout, whether it's walking, running, biking, or tennis, is to drink about two cups of fluid two hours before the activity. That helps make sure you are well-hydrated before you ever go outdoors.

Then, during the activity, try to drink 4-6 ounces every 15-20 minutes to keep your muscles well-hydrated. If you are planning an hour-long walk or gym workout, fill a water bottle with about 16 ounces (2 cups) and take it with you.

After exercise drink what you have lost. ideally, weigh yourself before you start exercising and again when you are finished. For each pound of water weight you lose, drink 20 ounces of fluid."

"If your activity lasts an hour or more, either fruit juice diluted with water or a sports drink will provide carbohydrates for energy plus minerals to replace lost electrolytes (sodium, potassium, magnesium) in your sweat."

If you are a "Saltier Sweater" (determined by the questions above) or you do an activity for 1hr+ ..."Sports drinks like Gatorade, Powerade, and All Sport can give you a needed energy boost during your activity. They are designed to rapidly replace fluids and to increase the sugar (glucose) circulating in your blood. Read the label to determine which sports drink that is best for you. Ideally, it will provide around 14 grams of carbohydrates, 28 mg of potassium, and 100 mg of sodium per 8-ounce serving. The drink's carbohydrates should come from glucose, sucrose, and/or fructose -- all of which are easily and quickly absorbed."

ref article: Drink Up for Sports and Fitness The best beverages to help you stay hydrated By Kathleen M. Zelman, MPH, RD, LD

Ref,, Fitness Matters Magazine Issue 6, Autumn 2018


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