CYCLING PERFORMANCE TIPS
Last updated: 2/15/2012
Overhydration With Exercise
Failure to rehydrate with exercise is a frequently
unrecognized factor in poor performance with endurance events, particularly
with hot and humid conditions. It can also be an issue at
and should be kept in mind while exercising
on fitness equipment at home or at
With the frequent emphasis on "staying hydrates", the pendulum on fluid replacement
requirements has swung to the opposite extreme where overcompensation,
drinking excessive amounts of electrolyte free water (read
sodium or salt here), has occasionally led to an even more serious and life
condition - dilutional hyponatremia (low blood sodium concentration). This is
supported by a recent study which found that overhydration with hyponatremia
was a far more frequent finding in runners who had collapsed than dehydration.
Prior to 1990, the problem of dilutional hyponatremia
was aggravated by the false assumption that sodium chloride losses
during prolonged exercise were minimal and posed less of a threat to health
and athletic performance than overall dehydration. As a result, many coaches
emphasized fluid replacement of any type, including pure water alone.
All endurance athletes need to understand the basic physiology of water and
electrolyte balance with exercise and "thread the needle" so to
speak, replacing both the fluids as well as electrolytes lost during an event.
Sweat contains 15 - 50 meq Na per liter (about 1 gram), and you can lose
from 2 to 4 liters (1 liter =~ 1 quart =~ 2
pounds of body weight) of sweat per hour while exercising. Thus with prolonged
exercise, salt losses can be significant (up to 4 grams)and easily outstrip
normal compensatory physiologic mechanisms
(see also handling heat).
The magnitude of the problem of hyponatremia was emphasized by a study of 64
finishers of the 1984 Hawaiian Ironman triathlon. It demonstrated an abnormally
low serum sodium concentration in 29%. As overhydration or "water intoxication" with a
low blood sodium concentration can be accompanied by nausea, fatigue, confusion,
and even seizures, it was common enough to be more of a factor in poor performance than
As a rule, hyponatremia occurs in events of five hours or more, and in high-heat
and humidity conditions, sodium depletion can occur in as little as 2 hours.
Interestingly hyponatremia may be a more significant problem in slower athletes who:
Beginners especially, who spend longer than average on the course, need to be
particularly sensitive to this condition, especially if they over drink
salt-poor fluids - which describes many sports drinks.
- may experience less nausea and thus drink more,
- cover the event distance over a longer time interval and thus have
the opportunity to take in greater amounts of fluid.
There are several scenarios to consider in the development of hyponatremia
with prolonged exercise.
What is an adequate strategy to properly hydrate?
First, fluid intake of 500 ml/hr is a good goal for the majority of
athletes during prolonged exercise. Heavier athletes, extreme levels of exercise
(prolonged periods at high % of VO@max), and severe environmental conditions may
require higher rates. With this approach, dilutional hyponatremia is usually limited to
episodes of endurance exercise lasting more than 5 to 7 hours where it
can be identified by post exercise WEIGHT GAIN from the extra
fluid ingested over that lost in the urine or sweat. The athlete:
- Sodium losses in sweat are moderate and total body sodium content is
near normal but replacement of fluid losses with a LARGE volume of sodium free
water dilutes out the blood sodium concentration. (The most likely today as
so many athletes, sensitized to fluid replacement, overcompensate in their drinking.)
- Both sweat water volume and sweat sodium losses are large. Water, but not
sodium losses are replaced by electrolyte poor snacks or commercial
drinks. Again, any water ingested dilutes out the blood sodium concentration.
In this scenario total body sodium content is diminished. (More common in
undertrained individuals or those competing in unusually hot and humid conditions.)
- An inappropriate release of the hormone vasopressin with exercise leads to a
decreased urine volume but, unaware of this, the athlete continues water replacement
at normal rates. Total body sodium concentration is normal, total body water content is
above normal or baseline. (Felt to be uncommon alone, but may play some role in
combination with either of the first two scenarios.)
For endurance athletes (especially those exercising under high heat and
humidity conditions), it is reasonable to plan an intake of one gram
(1,000 milligrams) of sodium per liter (quart) of fluid loss. (1,000 mg is about
one-half teaspoon of salt.) It is preferable to eat salty foods or drinks
rather than taking salt tablets to avoid overcompensation on the electrolyte side.
- should not assume that he or she can drink unlimited amounts of water
fluid during exercise expecting that the excess will be lost either in sweat
or through the kidneys.
- should realistically attempt to estimate his or her OWN real sweat and urine
losses and replace them accordingly.
- should use a scale during training rides or during the event itself to answer
the question as to whether water loss and replacement have been balanced correctly.
Athletes who have suffered from hyponatremia (with symptoms
including seizures), have continued to compete after modifying their fluid intake
(based on the above principles) and have gone on to complete subsequent
endurance events without problems.
Peripheral edema (swelling of the ankles and feet) will occasionally occur with long
distance cycling. As peripheral edema is uncommon with hyponatremia (excess
electrolyte free water
replacement) other causes such as:
- excess salt replacement
- venous or lymphatic obstruction from positioning on the bicycle
Although mild edema is common in women, it is recommended that recurrent
problems of more than a minor nature be evaluated by a family practitioner or
internist as it might be the first indication of a kidney or heart problem.
Assuming a negative examination, there are 2 treatments to consider - support
stockings or a mild diuretic. Although the latter
has few side effects for the casual cyclist, ongoing treatment should be
monitored by a physician.
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