Proper Fueling Prevents
Fatigue During Long Workouts By Nancy Clark, MS, RD -
Nancy Clark's Sports Nutrition Guidebook
"I'm at the gym from 5:30 to 7:00 pm and
feel exhausted by the end of my workout. What can I do to prevent fatigue?"
"I'm training for a marathon ... I dread
the long runs. I'm dragging after 12 miles. Any suggestions for how to boost my
"I'm whipped by the end of my
after-school soccer practices ..."
Sound familiar? Preventing fatigue is the
No. 1 concern of active people who exercise for more than an hour.
This article can help you enjoy high energy
and enhanced stamina during long, hard exercise sessions. (For shorter exercise
sessions, a pre-exercise snack and some water should fuel you well.)
To prevent fatigue during extensive exercise
that lasts for more than 60 to 90 minutes, you have two nutrition goals:
1. To prevent dehydration
2. To prevent your blood sugar from
The following tips can help you reach those
Sweat and dehydration
When you exercise hard, you sweat. Sweating
is the body's way of dissipating heat and maintaining a constant internal
temperature (98.6°F).During hard exercise, your muscles can generate 20
times more heat than when you are at rest.
You dissipate this heat by sweating. As the
sweat evaporates, it cools the skin. This in turn cools the blood, which cools
the inner body. If you did not sweat, you could cook yourself to death.
A body temperature higher than 106°F
damages the cells. At 107.6°F, cell protein coagulates (like egg whites do
when they cook), and the cell dies. This is one serious reason why you
shouldn't push yourself beyond your limits in very hot weather.
When you sweat for more than an hour, you
lose significant amounts of water from your blood. The remaining blood becomes
more concentrated and has, for example, an abnormally high sodium level. This
triggers the thirst mechanism and increases your desire to drink.
To quench your thirst, you have to replace
the water losses and bring the blood back to its normal concentration.
Unfortunately for athletes, this thirst
mechanism can be an unreliable signal to drink. Hence, you should plan to drink
before you are thirsty. By the time your brain signals thirst, you may have
lost 1 percent of your body weight, the equivalent of 1.5 pounds (24 ounces) of
sweat for a 150-pound person.
This 1 percent loss corresponds with the
need for your heart to beat an additional three to five times per minute. This
contributes to early fatigue.
Thirst sensations change with age and older
people, even athletes, become less sensitive to thirst. For example,
56-year-old hikers became progressively dehydrated during 10 days of strenuous
hill walking. The younger, 24-year-old hikers remained adequately hydrated.
This means older people, in particular, should carefully monitor their fluid
Light-colored urine, in significant volume,
is a sign of adequate hydration.
Most athletes voluntarily replace less than
half of sweat losses; thirst can be blunted by exercise or overridden by the
mind. To be safe, always drink enough to quench your thirst, plus a little
If you know how much you sweat, you can then
replace those losses according to a plan. To learn your sweat rate (and fluid
targets), weigh yourself naked before and after a workout. For every pound (16
ounces) you lose, you should strive to replace 13 to 16 ounces (80 to 100
percent of that loss) while exercising.
This requires training your gut to handle
this volume. Do not drink more water if your stomach is already sloshing;
enough is enough!
You might find it helpful to figure out how
many gulps of water equate to 16 ounces, and even set an alarm wristwatch to
remind you to drink on schedule. You'll also need to plan on having the right
quantity of enjoyable fluids readily available. Do not be in such a rush to
start your workout that you fail to bring with you the sports drinks and fluids
that will enhance your efforts.
Carbohydrates and blood sugar
As Ive mentioned above, you can
significantly increase your stamina by consuming a pre-exercise snack that
provides fuel for the first hour of the workout and by drinking adequate fluids
The third trick to enhancing endurance is to
consume carbs after an hour of exercise. Depending on your body size and
ability to tolerate fuel while you work out, you'll want to target 100 to 250
calories of carbohydrates per hour of endurance exercise.
The larger you are, the more calories you
need. For example, if you weigh 180 pounds, you should target about 250
calories per hour, such as 8 ounces of a sports drink every 15 minutes, or a
250-calorie energy bar plus water.
During a moderate to hard endurance workout,
carbohydrates supply about 50 percent of the energy. As you deplete
carbohydrates from muscle glycogen stores, you increasingly rely on the carbs
(sugar) in your blood for energy. By consuming carbohydrates such as sports
drinks, bananas, or energy bars during exercise, you can both fuel your muscles
as well as maintain a normal blood sugar level.
Because your brain relies on the sugar in
your blood for energy, keeping your brain fed helps you think clearly,
concentrate well, and remain focused. So much of performance depends on mental
stamina; maintaining a normal blood sugar level is essential to optimize your
workouts and boost your stamina.
Your body doesn't care if you ingest solid
or liquid carbohydrates both are equally effective forms of fuel.
You just have to learn which sports snacks settle best for your body
gels, gummy bears, dried figs, animal crackers, defizzed cola, whatever.
Despite popular belief, sugar can be a
positive snack during exercise and is unlikely to cause you to "crash"
(experience hypoglycemia). That's because sugar feedings during exercise result
in only small increases in both insulin and blood glucose. Yet, too much sugar
or food taken at once can slow the rate at which fluids leave the stomach.
Hence, "more" is not always better.
Because consuming 100 to 250 calories per
hour of exercise (after the first hour) may be far more than you are used to
taking in during exercise, you need to practice fueling while exercising to
figure out what foods and fluids settle best.
You'll learn through trial and error which
snacks help prevent fatigue, boost performance and contribute to enjoyment of
your long, hard workouts.
Copyright: Nancy Clark, MS, RD
Nancy Clark, MS, RD, nutritionist at
SportsMedicine Associates (617-739-2003) in Brookline MA.
Nancy Clark's Sports Nutrition Guidebook