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Cracking the Code
on Hydration
Acclimating your
body to hot weather reduces your electrolyte losses.
By
Gale Bernhardt
For Active.com
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 |
|
Electrolyte |
Sweat of
unacclimatized, unfit subject |
Sweat of
fit but unacclimatized subject |
Sweat of
fit and acclimatized subject |
|
Sodium (Na+) |
3.5 |
2.6 |
1.8 |
|
Potassium
(K+) |
0.2 |
0.15 |
0.1 |
|
Magnesium
(Mg+) |
0.1 |
0.1 |
0.1 |
|
Chloride (Cl-) |
1.4 |
1.1 |
0.9 |
* 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?
Unfortunately,
there is no easy and universal answer to that question. According to
Noakes, it is "the amount of sodium and potassium in the body that
determines the water balance, not the other way around." Therefore, your
electrolyte balance affects your hydration balance.
A good place to
begin is to consume a sports drink containing electrolytes when training
or racing for durations over two hours. If you believe, based on the
salt mine on your clothing and helmet straps, that you lose a lot of
electrolytes in your sweat consider supplementing with electrolyte
tablets.
Begin with the low
end of the manufacturer's recommended dosage AND the recommended fluid
intake. Be very wary of water cooler or message board recommendations to
pop a handful of electrolyte tablets because "top racer Ricky or Renee"
does.
Remember: your
body likes balance. Consuming too much water and no electrolytes during
extended exercise is not good and can cause hyponatremia. Consuming too
many electrolytes with too little fluid is not good and can cause your
body to retain fluid rather than releasing it for cooling purposes.
Fluid
Replacement
The average sweat
rate is between 0.8 to 1.4 liters (roughly 27.4 to 47.3 ounces) per hour
during exercise. The average fluid absorption rates range from 0.8 to
1.2 liters per hour (27.4 to 40.6 ounces). Unfortunately, while the
sweat-rate range and the fluid absorption ranges are close, some
athletes sweat at higher rates per hour than their fluid absorption
rate.
Do you have to
replace every drop of sweat you lose during exercise? The rule of thumb
is that you should neither gain weight during exercise (consuming more
fluid than you lose) nor lose excessive weight. Excessive weight loss is
considered to be more than 2 percent of your body weight.
If you lose up to
2 percent of your body weight, performance is affected less if you are
performing in a cool environment than if you are performing in a hot
environment. Weight losses above 2 percent of your body weight should be
avoided.
Gastric
Emptying
Sloshing. It's a
horrible feeling. Sloshing occurs when you are consuming fluids--and
perhaps solids--but rather than moving to your intestines the mix just
sits in your stomach. Sloshing is worse for runners and mountain bikers
than road cyclists, but roadies get it too.
Eventually,
sloshing is followed by slowed-to-a-snail's pace performance, barfing or
both.
You can increase
the rate of gastric emptying by:
-
Keeping a
small fluid volume in your stomach by consuming fluids every 15 to
20 minutes rather than attempting to consume larger quantities of
fluid at 60-minute or more intervals.
-
Keeping fat,
protein and carbohydrate concentrations low. How much protein and
fat you can tolerate depends on your exercise pace and individual
tolerance level.
-
Remaining
hydrated. Dehydration decreases gastric emptying.
-
Keeping
exercise intensity low. Intensity above 75 percent of maximum
decreases the emptying rate.
You can increase
intestinal fluid absorption by:
-
Using a
low-to-moderate level of glucose plus sodium.
-
Using a
low-to-moderate level of sodium.
What Should You Do?
All of this
information can seem overwhelming. To begin cracking your hydration
code:
-
Determine your
sweat rate in various environmental and racing conditions.
-
Once you know
your sweat rates, hydrate at rates appropriate to each situation.
Your sweat and hydration rates are not constant and will need
conscious modification given your fitness, the environment and your
pace.
-
Hydrate so
that you keep your body weight loss to less than 2 percent during
training and racing sessions.
-
Avoid
over-hydrating and weight gain during exercise sessions.
Most importantly,
know that you have a range of optimal fluid replacement and what is
optimum for you may or may not work for the athlete standing next to
you. |
