by Janel Willette and Steve Pyle
Staying hydrated while participating in endurance sports is pivotal
to your success. When your body is continuously losing fluid through
perspiration (cooling), and breathing (respiration/evaporation),
keeping sufficiently hydrated is critical to maintain a steady state
of performance. Sprint distance events of an hour or less in cool
or rainy conditions are the only exception to the rule.
A physiologist performed a study quantifying the need for hydration
in short events raced in moderate temperatures. He found that for
events of one hour or less, with temperatures below 20 degrees Centigrade
(68F), there was no performance drop-off if the athlete drank nothing
during the event. This assumed the athlete was well hydrated prior
to the event. He found that the energy used to absorb the fluid
was more detrimental than beneficial at sprint distances. Not enough
fluid could be lost in that time, at that temperature, to cause
a performance drop off.
But, for longer events in warmer weather fluid consumption is absolutely
necessary to avoid performance drop-off—or worse. Sweating
keeps our body temperature within a safe working range. And all
types of metabolic and cellular functions depend on maintaining
a certain fluid level within our bodies. Fluid levels determine
the viscosity of our blood as well. When we lose too much water
our blood becomes thick and cannot be pumped as easily. Our hearts
strain to do the necessary work.
As you do aerobic work, your muscles produce a tremendous amount
of heat as they generate energy, and your body temperature surges
upward. The heat produced by your muscles is then transferred to
your blood as it moves through your muscles, and your blood carries
the heat to your skin. Meanwhile, your sweat glands have shifted
into high gear and soaked your skin with sweat. As sweat evaporates
from the surface of your body, your body heat dissipates with it.
As a result, you stay cool...to a point.
When you exercise in the heat, some of the water that normally
courses through your bloodstream is shunted to the surface of your
skin through your sweat glands. As a result, your blood volume begins
to drop and your heart strains to pump your blood as its viscosity
increases dramatically. The blood vessels leading into your skin
constrict to prevent large drops in blood pressure as well. Once
the blood flow to your skin diminishes, the blast of heat produced
by your hard-working muscles can't be transported to the surface
of your skin and your body temperature begins to climb. Simple as
it sounds, drinking water will halt this chain reaction, keeping
you cool and moving efficiently. The best way to ensure that this
occurs is to drink adequately before, during, and after your workouts.
The amount of liquid we can absorb per unit of time can potentially
limit our performance in the heat during long efforts. Pure water
is absorbed fastest, but we also need calories to maintain a prolonged
effort over long distances. Water with a dissolved sugar solution
is absorbed into our system more slowly than pure water, so the
stronger the solution, the slower it's absorbed.
That's the dilemma. How to get the most possible water into our
system over time and still take in some calories as well. You should
know that food such as energy bars mix with the water in our stomachs
creating a very sweet solution, thus also slowing water absorption.
Another consideration is that the more intense the effort, the less
we're able to absorb any solution quickly. Clearly, a balance is
Experimentation in training is the key to learning what hydration
limitations you'll have to work with in races. Try different sports
drinks at different levels of dilution to find what works best for
you. Instead of finishing that run and guzzling down fluid, take
in sufficient amounts during your workouts. Consistent hydration
during training will help your body get used to the process of absorbing
fluid during the intensity of competition.
The following tips will reduce the summer heat's potentially negative
effect on your running:
- Put no limit on your water intake during the day. In most cases,
don't worry about taking in fluids during runs lasting 45 minutes
- During longer workouts, drink ~10-14 ounces of fluid immediately
before you head out the door to run and then ~3 to 4 ounces every
10 minutes thereafter. If you get stomach cramps or feel pressure
on the left side of your belly initially, slowly increase your
hydration to adapt to increasing levels.
- Monitor how you feel. If you have trouble maintaining your
regular pace, slow down a bit. And if you become light-headed,
slow down and walk for a while. If you experience chills, stop
immediately, and find a shady place to sit down. You must allow
your body to cool. Even though you're having chills, you're not
cold. Your cooling system is about to shut-down and we don't want
this to happen.
- Know yourself. Some people have more difficulty dealing with
the heat than others do. If you're one of them, it doesn't mean
you're a wimp or faint of heart; it simply means that you must
train smart. Take it easy during the hot weather, especially if
you've had trouble dealing with heat in the past. Once you become
heat stressed, you are psychologically susceptible to it for the
rest of your life.
- Run at sunrise or sunset. By running in the morning you avoid
hot sunlight but usually face more humidity. By running in the
afternoon you avoid high humidity but must brave the sun. Experiment
to find out what works best for you. Try to avoid training from
11:30 a.m. to 4:00 p.m. when you must battle maximum humidity
and the heat.
- Go out of your way to stay as cool as possible. Wear light
loose clothing and opt for tree-lined streets or shaded trails.
It's nothing to brag about when you finish a race or workout totally
depleted and dehydrated. When your blood gets thick due to dehydration
it's impossible for your heart to maintain the same level of work
as it would under optimal conditions. If the blood won't flow -
you can't go.