By Christopher Langdon
The effects of hypohydration, the state resulting from dehydration, have been widely documented in literature and throughout an athlete’s life. Hypohydration, as defined by RJ Maughan in a recent article, is the “impact of mild dehydration on wellness and on exercise performance”and is a “1-2% decrease in body weight due to waterloss” . However, one may not know exactly why hypohydration effects performance nor to what degree if any, it has in impairing our performances.
The body is made up of almost 60% water, and there is 5-10% water
renewed in the body each day,
water turn-over rate. The body is much less able
to deal with fluid restriction than deal with food-restriction. The performance
of prolonged exercise, particularly in warm environments, can result in major loss
of body water, with potential for adverse effects on performance. Some athletes could lose upwards of
10-12L of sweat loss in one athletic event or training bout. There body removes water from a variety of ways, including:
- urine (~1400ml)
- feces (200ml)
- insensible losses from the lungs (400ml)
- loss through the skin (500ml).
Water deficit of only a few percent will impair physical performance: a
slightly larger loss will bring symptoms of tiredness, headache and general
malaise.”
Effects of
hypohydration on wellness
As mentioned in the aforementioned article, severe dehydration can be clearly detrimental to health and is associated
with compromised cardiovascular function, renal impairment, weakness and lassitude,
and a number of diffuse symptoms, including a headache and nausea. In the same article a study was done where 15 subjects underwent a 37-hour fluid
restriction followed by normal fluid intake for a period of 37 hours. In both sessions the fluid retention group and normal fluid group, were given a questionnaire at time
periods
Effects of
dehydration on exercise performance
Most of us athletes have heard our coaches say to drink when
we are thirsty, or give us set times to have water breaks. I am saying that you
need to drink before the onset of the thirst reflex from the body. The article “Impact
of mild dehydration on wellness and on exercise performance” that I have been
reviewing reports that subjects do not report the thirst reflex until they have
lost 2% of body mass via water. Meaning, when one is thirsty it is too late and
one’s athletic ability is being impaired!
The Science
When one is exercising the body cools through the
evaporation of sweat off of the skin. With the combination of the sweat and
breathing one is losing water from their body. This water comes from the intra
and extra-cellular fluid as well as from the cellular plasma volume. When a
cell goes from a euhydrated (normal) cell to a hypohydrated (dehydrated) state
there is a decrease in work capacity of the cell. Meaning it can no longer
function properly or as efficiently as before. Couple this with the fact that
when one is hypohydrated there may be a restriction of blood flow, this means
that the blood will divert to the muscles that are working to supply them with
nutrients. Thus meaning there is less blood flow to the skin and less ability
to cool the core body temperature. When the body “overheats” it is coming out
of homeostasis and negative performance is a result. The article stated that a
reduction of 2% of body mass, hypohydration, had modest restrictions in
performance.
