Cracking the Code on Hydration

Acclimating your body to hot weather reduces your electrolyte losses.

For most cyclists, competing in events under 90 minutes does not cause many problems for hydration, electrolyte supplementation and fueling. Water or a mostly-carbohydrate sports drink work well for both fueling and hydration. In most cases, cyclists do not need to supplement with electrolytes for sessions under 90 minutes long, but there are some athletes?who lose above normal amounts of electrolytes while sweating that will benefit from supplementation during short sessions.?

Sweat Rate and Electrolyte Losses

If you are attempting to delay the onset of dehydration during exercise, the first step is to determine your personal sweat rate in various situations.

Given the same fitness level and environmental conditions, your sweat rate will vary depending on your cycling situation. If you are sitting in the peloton and conserving energy, your hourly sweat rate will be lower than if you are in a three-person breakaway fighting for a podium position.

Because the average speed you produce on a bicycle is not always an accurate reflection of your actual work effort, you can consider linking your sweat rates to your work effort in terms of heart rates produced or average power output.

Cycling situation aside, your fitness and heat acclimatization affects your sweat rate and the contents of your sweat. See the table below.

Electrolyte Contents of Sweat and the Affects of Fitness and Heat Acclimitization


Sweat of unacclimatized, unfit subject

Sweat of fit but unacclimatized subject

Sweat of fit and acclimatized subject

Sodium (Na+)




Potassium (K+)




Magnesium (Mg+)




Chloride (Cl-)




* All values in grams per liter.
* Table adapted from Table 4.2 Electrolyte Contents of Sweat and Blood and the Affects of Fitness and Heat Acclimitization, "Fourth Edition, Lore of Running", Tim Noakes M.D., pp. 214

The major affects of acclimatization to heat can be accomplished in 10 to 14 days. As you can see from the table, if you are unfit and not acclimated to the heat you will lose almost twice the sodium, twice the potassium and one-and-a-half times the chloride in your sweat compared to when you are fit and acclimated.

The bottom line: Fitness and acclimatization reduces your electrolyte losses.

Electrolyte Replacement

It is much easier to determine your sweat losses during exercise than it is to determine your electrolyte losses.

Do you need to take electrolyte tablets or are the electrolytes in your energy drink enough?

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