Download chapter10 Physical Activity

© 2006 Thomson-Wadsworth

Nutrition and physical activity are interactive
◦ Each influences the other
◦ Demands all three energy-yielding nutrients

Physical activity benefits the body’s nutrition
by helping to regulate the use of fuels
◦ Pushing toward lean body composition
◦ Increasing the daily caloric allowance
 With more calories come more nutrients

Improvement is not only possible but an
inevitable consequence of becoming more
active
◦ As you improve your physical fitness, you not only
feel better and stronger, but you look better
◦ Physically fit people walk with confidence and
purpose
 Posture and self-image improve along with physical
fitness

Training
◦ Regular practice of an activity
◦ Physical adaptations of the body with improvement
in
 Flexibility, strength, or endurance

Fitness depends on
◦ Physical activity
 Bodily movement produced by muscle contractions
that substantially increase energy expenditure
◦ Exercise
 Planned, structured, and repetitive bodily movement
that promotes or maintains physical fitness
◦ More restful sleep
 During rest, the body repairs injuries, disposes of wastes,
and builds new physical structures
◦ Better nutritional health
 Physical activity expends energy and thus allows people
to eat more food
 Active people can consume more nutrients and be less
likely to develop nutrient deficiencies
◦ Enhanced resistance to colds and infections
◦ Stronger circulation and lung function
◦
Improved body composition
 A balanced program of physical activity limits body fat
and increases or maintains lean tissue
◦
Improves bone density
 Weight-bearing physical activity builds bone strength
and protects against osteoporosis
◦
Lower risk of some kinds of cancer
 Lifelong physical activity may help to protect against
colon cancer, breast cancer, and some other cancers
◦
Lower risks of cardiovascular disease
 Physical activity lowers BP, slows resting pulse rate,
lowers total cholesterol, and raises HDL cholesterol
 Some research suggests that physical activity may also
be of benefit by reducing intra-abdominal fat stores
◦ Lower risks of type 2 diabetes
 Physical activity normalizes glucose tolerance
 Regular physical activity reduces the risk of developing
type 2 diabetes and benefits those who already have
the condition
◦ Reduced risk of gallbladder disease (women)
◦ Lower incidence and severity of anxiety and
depression
◦ Stronger self-image
◦ Longer life and higher quality of life

The American College of Sports medicine
(ACSM) and the Dietary Guidelines for
Americans, 2005
◦ Specify that people need to spend an accumulated
minimum of 30 minutes in some sort of physical
activity on most days of each week
◦ The DRI committee recommends at least 60
minutes of moderately intense activity

Flexibility
◦ The capacity of the joints to move through a full range
of motion
◦ The ability to bend and recover without injury

Muscle strength
◦ The ability of muscles to work against resistance

Muscle endurance
◦ The ability of a muscle to contact repeatedly within a
given time without becoming exhausted

Cardiorespiratory endurance
◦ The ability to perform large-muscle dynamic exercise of
moderate-to-high intensity for prolonged periods

A person who practices physical activity adapts
by becoming better able to perform it after each
session
◦ With more flexibility, more strength, and more
endurance
© 2006 Thomson-Wadsworth

How Do My Muscles become Physically Fit?
◦ Overload
 An extra physical demand placed on the body
 An increase in the frequency, duration, or intensity
◦ Hypertrophy
 An increase in size in response to use
 Muscle cells and tissues respond to an overload of
physical activity by gaining strength and size
◦ If not called on to perform, muscle cells dwindle
and weaken; they atrophy

How Does Weight Training Benefit Health and
Fitness?
◦ Weight training/ Resistance Training
 The use of free weights or weight machines to provide
resistance for developing muscle strength and endurance
 A person’s own body weight may also be used to provide
resistance as when a person does push-ups, pull-ups, or
sit-ups
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Helps to prevent and manage several chronic
diseases and enhances psychological well-being
Weight training promotes strong muscles in the
back and abdomen (less back injury)

Helps prevent the decline in physical mobility
that often accompanies aging
 Older adults gain muscle strength
 Improve muscle endurance
◦ Enables them to walk significantly longer before
exhaustion

Can help to maximize & maintain bone mass
◦ Even in women past menopause, a one-year
program of weight training improves bone density
◦ The more weight lifted, the greater the
improvement
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Can emphasize either muscle strength of
muscle endurance
◦ To emphasize muscle strength
 Combine high resistance with a low number of
repetitions
◦ To emphasize muscle endurance
 Combine less resistance with more repetitions

Enhances performance in other sports
◦ Swimmers can develop a more efficient stroke
◦ Tennis players can develop a more powerful serve
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How Does Cardiorespiratory Training Benefit
the Heart?
◦ Blood HDL increases
◦ Effective activities elevate the heart rate, are
sustained for longer than 20 minutes, and use more
of the large-muscle groups of the body
◦ Pulse rate falls
◦ The muscles that inflate and deflate the lungs
gain in strength and endurance
 Breathing becomes more efficient
◦ Blood moves easily through the blood vessels

Fuels that support body activity are
◦ Glucose
 From carbohydrate
◦ Fatty acids
 From fat
◦ To a small extent, amino acids
 From protein
◦ The body uses different mixtures of fuels
depending on the intensity and duration of its
activities and depending on its own prior training

During rest
◦ Little more than half of energy from fatty acids
 Most of the rest from glucose
 A little from amino acids

During physical activity
◦ The body adjusts its fuel mix to use the stored glucose
of muscle glycogen
◦ In the early minutes of activity, glycogen provides the
majority of energy the muscles use to go into action
 As the activity continues, messenger molecules, including
epinephrine, flow into the bloodstream to signal the liver
and fat cells to liberate their stored nutrients
 Primarily glucose and fatty acids

As activity continues
◦ Glucose from the liver’s stored glycogen and dietary
glucose absorbed from the digestive tract also
become important sources of fuel for muscle
activity

The body constantly uses and replenishes its
glycogen
◦ The more carbohydrate a person eats
 The more glycogen muscles store (up to a point)
 The longer the stores will last to support physical
activity

A classic report compared fuel use during
activity by three groups of runners, each on a
different diet
◦ The high-carbohydrate diet enables the athletes to
work longer before exhaustion

The body’s glycogen stores are much more
limited than its fat stores
◦ Glycogen can easily support everyday activities but
is limited to less than 2,000 calories of energy
 How long a person’s glycogen will last while exercising
depends on both diet and intensity of the activity
◦ Fat stores can usually provide more than 70,000
calories and fuel hours of activity without running
out
 Not requiring oxygen
 Requires strength but does not work the heart & lungs

Intense activity uses glycogen quickly
◦ Muscles must begin to rely more heavily on glucose
 Which can be partially broken down by anaerobic
metabolism

Anaerobic Use of Glucose
◦ Glucose can yield energy quickly
◦ Anaerobic breakdown of glycogen yields energy to
muscle tissue when energy demands outstrip the
body’s ability to provide energy aerobically
 Lavish spending of the muscles’ glycogen stores

Lactic acid
◦ A compound produced during the breakdown of
glucose during anaerobic metabolism

During intense activity, anaerobic breakdown
of glucose produces lactic acid
◦ When production of lactic acid exceeds the ability of
muscles to use it, they release it, and it travels in
the blood to the liver
 Liver enzymes convert the lactic acid back into glucose
 Glucose can then return to the muscles to fuel
additional activity

Moderate physical activity uses glycogen
slowly
◦ The individual breathes easily and the heart beats
at a faster pace than at rest but steadily
◦ The activity is aerobic

During aerobic metabolism muscles extract
their energy from both glucose and fatty
acids
◦ By depending partly on fatty acids, moderate
activity conserves glycogen stores
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At low intensities, lactic acid is readily cleared
from the blood by the liver
At higher intensities, lactic acid accumulates
When the rate of lactic acid production exceeds
the rate of clearance, intense activity can be
maintained for only one to three minutes
Lactic acid was long blamed for a type of muscle
fatigue
◦ Evidence disputes this idea
◦ Muscles produce lactic acid during a type of fatigue
◦ But the lactic acid does not cause the fatigue

Glucose use during physical activity depends
on the duration of the activity
◦ As well as on its intensity
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In the first 10 minutes or so of activity
◦ The active muscles rely almost entirely on their own
stores of glycogen
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Within the first 20 minutes or so of moderate
activity
◦ A person uses up about one-fifth of the available
glycogen
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As the muscles devour their own glycogen, they
increase their uptake of blood glucose
dramatically
◦ During moderate activity, blood glucose declines slightly
 Reflecting its use by the muscles

A person who exercises moderately for longer
than 20 minutes begins to use less glucose and
more fat for fuel
◦ Still, glucose use continues
 If the activity goes on long enough and at a high enough
intensity, muscle and liver glycogen stores will run out
almost completely
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Glycogen depletion generally occurs after
about two hours of vigorous exercise
◦ Physical activity can occur for a short time
thereafter only because the liver produces some
glucose from available lactic acid and certain amino
acids
 This minimum amount of glucose may briefly forestall
exhaustion
 But when hypoglycemia accompanies glycogen depletion,
it brings nervous system function almost to a halt

Maintaining Blood Glucose for Activity
◦ Eat a high-carbohydrate diet regularly
◦ Take glucose (usually in sports drinks) periodically
during endurance activities
◦ Eat carbohydrate-rich foods after performance
◦ Train the muscles to maximize glycogen stores
 Carbohydrate loading
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Glucose During Activity
◦ Glucose ingested before and during exhausting
endurance activities makes its way from the
digestive tract to the working muscles
 Augmenting dwindling internal glucose supplies from
the muscle and liver glycogen stores
 Especially during games which last for hours and
demand repeated bursts of intense activity, athletes
benefit from carbohydrate-containing drinks taken
during the activity

Before concluding that sugar might be
good for your own performance,
consider first whether you engage in
endurance activity
◦ Do you run, swim, bike, or ski
nonstop at a rapid pace for more
than 45 minutes at a time, or do you
compete in games lasting for hours?
◦ If not, the sugar picture changes
 For an everyday activity lasting less than
60 minutes, sugar probably won’t help (or
harm) performance

Even in athletes, extra carbohydrate does not
benefit those who engage in sports in which
fatigue is unrelated to blood glucose
◦
◦
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100-meter sprinting
Baseball
Casual basketball
Weight lifting
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Carbohydrate Loading
◦ A regimen of moderate exercise, followed by eating
a high-carbohydrate diet
◦ Glycogen stored beyond their normal capacity
 Can nearly double muscle glycogen concentration
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Carbohydrate Loading
◦ Glycogen storage occurs slowly in the plan
presented in Table 10-2
◦ Athletes must alter their training in the days just
before the event

Quick method of carbohydrate loading that
has produced promising preliminary results
• Eat a high-carbohydrate diet after a short but very
intense bout of exercise
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Can benefit an athlete who must keep going
for 90 minutes or longer
Shorter durations- a regular high-carb diet
In a hot climate, extra glycogen confers an
additional advantage
• As glycogen breaks down, it releases water
• Which helps to meet the athlete’s fluid needs

Glucose After Activity
◦ Eating high-carbohydrate foods after physical
activity also enlarges glycogen stores
 Train normally, and then, within 2 hours after physical
activity, consume a high-carbohydrate meal
 This method accelerates the rate of glycogen storage
by 300% for a while
 This is especially important to athletes who train hard
more than one time a day
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For athletes who don’t feel like eating right
after exercise, high-carbohydrate energy
drinks are available
◦ Fruit-flavored commercial beverages used to
restore muscle glycogen after exercise or as a
pregame beverage

For athletes wishing to maximize muscle
glycogen synthesis after strenuous training,
eating foods with a high glycemic index
may restore muscle glycogen most rapidly
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Muscles that deplete their glycogen stores
through work adapt to store greater amounts
of glycogen to support that work
Trained muscles burn more fat, and at higher
intensities, than untrained muscles
◦ So they require less glucose to perform the same
amount of work
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People with diabetes
◦ Who must take insulin or insulin-eliciting drugs
 Sometimes find that as their muscles adapt to physical
activity, they ca reduce their daily drug dose
◦ Physical activity may also improve type 2 diabetes
by helping the body lose excess fat

Factors that affect glucose use during
physical activity
◦ Carbohydrate intake
◦ Intensity and duration of the activity
◦ Degree of training

When endurance athletes “fat load” by
consuming high-fat, low-carbohydrate diets
for one to three days…
◦ Performance is impaired because their small
glycogen stores are depleted quickly

Endurance athletes who adhere to a high-fat,
low-carbohydrate diet for more than a
week…
◦ Adapt by relying more on fat to fuel activity
◦ Even with fat adaptation performance benefits have
not been consistently shown

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High-fat diets carry risks of heart disease
Fat restriction is not recommended either
◦ <20% of total energy intake may fail to consume
adequate energy and nutrients
◦ Consume 20%-30% of their energy from fat

As fuel for activity, body fat stores are more
important than fat in the diet
◦ Fat stores can fuel hours of activity
◦ Body fat is (theoretically) an unlimited source of
energy
 Even the lean bodies of runners carry enough fat to
fuel several marathons
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Early in activity, muscles begin to draw on
fatty acids from two sources
◦ Fats stored within the working muscles
◦ Fats from fat deposits such as fat under the skin

Intensity and Duration Affect Fat Use
◦ The intensity of physical activity affects the
percentage of energy contributed by fat
 Fat can be broken down for energy only by aerobic
metabolism
 When the intensity of activity becomes so great that
energy demands surpass the ability to provide energy
aerobically, the body cannot burn more fat
 Instead, it burns more glucose
◦ The duration of activity matters to fat use
 At the start of activity, the blood fatty acid concentration
falls
 After about 20 minutes of activity, the blood fatty acid
concentration rises above normal resting concentrations
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Degree of Training Affects Fat Use
◦ Training stimulates muscles to develop more fatburning enzymes
 Aerobically trained muscles burn fat more readily than
untrained muscles
 With aerobic training, the heart and lungs become stronger
and better able to deliver oxygen to the muscles during
high-intensity activities
 This improved oxygen supply enables the muscles to burn
more fat
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Intense, prolonged activity may increase your
basal metabolic rate (BMR)
Athletes in training, whether endurance
athletes or power athletes, expend huge
amounts of energy each day while practicing
◦ The harder an athlete works, the more energy the
athlete spends
◦ The greater the intensity and the longer the duration of the
activity, the longer the metabolic rate remains elevated
◦ The more muscle is developed the more metabolically
active
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Protein for Building Muscle Tissue
◦ In the hours of rest that follow physical activity
 Muscles speed up their rate of protein synthesis
 They build more of the proteins they need to perform the
activity
 Eating protein, together with carbohydrate, enhances
protein synthesis
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Dietary protein provides the needed amino
acids for the synthesis of new muscle protein
Protein for Fuel
 Protein contributes about 10% of the total fuel used
 Both during activity and during rest

Diet Affects Protein Use during Activity
 A carbohydrate-rich diet spares protein from being used
as fuel
 Some amino acids can be converted into glucose when
needed
 If your diet is low in carbohydrate, much more protein will be
used in place of glucose

Intensity and Duration Affect Protein Use
◦ Endurance athletes may deplete glycogen and use
protein for energy

Anaerobic strength training does not use
more protein for energy
◦ Does demand more protein to build muscles

The protein needs of both endurance and
strength athletes are higher than those of
sedentary people
◦ But not as high as the protein intakes many athletes
consume

Degree of Training Affects Protein Use
◦ Particularly in strength athletes, the higher the
degree of training, the less protein a person uses
during an activity at a given intensity

Most athletes need more protein than do
sedentary people
◦ Average protein intakes in the U.S. are high enough
to cover those needs
◦ Athletes in training should attend to protein needs
but should back up the protein with ample
carbohydrate
 Otherwise, they will burn off as fuel the very protein
they wish to retain as muscle

The DRI committee does not recommend high
protein intakes for athletes
 ADA & Dietitians of Canada recommend protein
intakes slightly more than 0.8 g/kg of body weight

Athletes who eat a balanced, highcarbohydrate diet consume enough protein
◦ No special foods, protein shakes, or supplements

Many vitamins and minerals assist in
releasing energy from fuels and transporting
oxygen
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
Vitamin C is needed for the formation of the
protein collagen
◦ The foundation material of bones and the cartilage
that forms the linings of joints and other connective
tissues
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Folate and vitamin B12 help build red blood
cells
Calcium and magnesium help make muscles
contract
© 2006 Thomson-Wadsworth
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In general, people who eat well-balanced
meals do not need vitamin or mineral
supplements
◦ Vitamin E and iron do merit special attention
 Vitamin E is addressed because so many athletes take
supplements of it
 Iron is discussed because some female athletes may be
unaware that they need supplements

Vitamin E is a potent fat-soluble
antioxidant
◦ Defends cells membranes against oxidative
damage

Some athletes take megadoses of vitamin E
in hopes of preventing such oxidative
damage to muscles
◦ Supplementation with vitamin E does seem to
protect against exercise-induced oxidative stress,
◦ There is little evidence that vitamin E
supplements can improve performance

Physically active young women, especially
those who engage in endurance activities, are
prone to iron deficiency
 Iron losses in sweat may contribute to deficiency
 The muscles’ high demands for iron to make the ironcontaining molecules of aerobic respiration
 Habitually low intakes of iron-rich foods, high iron
losses through menstruation, and extra demands can
contribute to iron deficiency in young female athletes

Vegetarian female athletes are particularly
vulnerable to iron insufficiency
◦ The bioavailability of iron is often poor in plant-based
diets
◦
Vegetarian female athletes
◦ Vegetarian diets are usually rich in vitamin C
◦ To protect against iron deficiency, vegetarian athletes
need to pay close attention to their intake of good
dietary sources of iron (fortified cereals, legumes,
nuts, and seeds)
 And include vitamin C-rich foods with each meal

As long as vegetarian athletes, like all athletes,
consume enough nutrient-dense foods, they
can perform as well as anyone

The body’s need for water far surpasses its need for
any other nutrient
◦ If the body loses too much water, its life-supporting
chemistry is compromised
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The exercising body loses water primarily via sweat
Second to that, breathing costs water, exhaled as
vapor
During physical activity, both routes can be
significant
◦ Dehydration is a real threat
 The first symptom is fatigue
 A water loss of even 1%-2% of body weight can reduce a person’s
capacity to do muscular work
 A person with a water loss of ≈7% is likely to collapse

Even in cold weather, the body still sweats
and needs fluids
◦ The fluids should be warm or at room temperature
to help prevent hypothermia
© 2006 Thomson-Wadsworth

Endurance athletes can lose 2 or more
quarts of fluid in every hour of activity
◦ The digestive system can only absorb about a
quart or so an hour
 The athlete must hydrate before and rehydrate during
and after activity to replace all the lost fluid
◦ In hot weather, the digestive tract ay not be able
to absorb enough water fast enough to keep up
with an athlete’s sweat losses
 Some degree of dehydration becomes inevitable
© 2006 Thomson-Wadsworth
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Athletes who rely on thirst to govern fluid
intake can easily become dehydrated
◦ During activity thirst becomes detectable only after
fluid stores are depleted
◦ Don’t wait to feel thirsty before drinking
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Endurance athletes are an exception
◦ They need more from their fluids than water alone
◦ The first priority for endurance athletes should always
be replacement of fluids
 To prevent life-threatening heat stroke
◦ Endurance athletes need carbohydrate to supplement
their limited glycogen stores

During physical activity, the body loses
electrolytes in sweat
◦ The minerals sodium, potassium, and chloride

The body’s adaptation to physical activity
includes better conservation of these electrolytes
© 2006 Thomson-Wadsworth
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Many different diets can support an athlete’s
performance
◦ Food choices must obey the rules of diet planning
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Nutrient Density
◦ Athletes need a diet composed mostly of nutrientdense foods
 That supply a maximum of vitamin and minerals for
the energy they provide
◦ When athletes eat mostly refined, processed foods
that have suffered nutrient losses and contain
added sugar and fat, their nutrition status suffers
© 2006 Thomson-Wadsworth
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Balance
◦ Athletes must eat for energy
 Their energy needs can be immense
◦ Athletes need full glycogen stores
 Need to strive to prevent heart disease and cancer by
limiting fat
 especially saturated fat
 A diet that is high in carbohydrate (60%-70% of total
calories), moderate in fat (20%-39%), and adequate in
protein (10%-20%) is best for all these purposes
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Ergogenic Aids
◦ Appeal to performance-conscious people
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Protein powders
Amino acid supplements
Caffeine pills
Steroid replacers
“muscle builders”
Vitamins and more
◦ Research findings do not support the claims
◦ Almost anything can be sold under the label of
“dietary supplement” with scant regulation by
authorities
© 2006 Thomson-Wadsworth
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Amino Acid Supplements
◦ Are unnecessary
◦ Healthy athletes eating a well-balanced diet never
need them
◦ In a few cases these supplements have proved
dangerous
 Amino acids complete for carriers
 An overdose of one can limit the availability of some other
needed amino acid
 Can lead to digestive disturbances and excess water
accumulation in the digestive tract
© 2006 Thomson-Wadsworth
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Branched-chain amino acids (BCAA)
◦ Advertised as a source of fuel for the exercising body
◦ Compared to glucose and fatty acids, provide very little
fuel to working muscles
 When they are needed, trained muscles have plenty on hand
◦ No consistent findings exist to indicate a performance
benefit from supplemental BCAA
◦ A diet too low in carbohydrates or energy triggers
activity of an enzyme that breaks down BCAA for energy
 An athlete who consumes adequate carbohydrate and
calories conserves BCAA in the tissues
◦ Large doses of BCAA can raise plasma ammonia
concentrations, causing fatigue
© 2006 Thomson-Wadsworth
◦ Provides mental stimulation
◦ Provides a physical boost during endurance sports
 Athletes performing high-intensity, short-duration
activities derive little or no performance edge

Adverse effects
◦ Upset stomach, nervousness, irritability, headaches,
dehydration, and diarrhea, diuretic
◦ High doses constrict the arteries and raise blood
pressure above normal
 Making the heart work harder to pump blood
 An effect potentially detrimental to sports performance

Some competitions prohibit >5-6c of coffee
in a two-hour period prior to competition
◦ Athletes are disqualified if urine tests detect more
than this amount
 Often marketed as a “fat burner’
 In the body, does help to transfer fatty acids across the
membrane that encases the cell’s mitochondria
 In studies, carnitine supplementation for 7 to 14 days
did not influenced fat or carbohydrate oxidation
 Nor do such supplements enhance exercise performance

For those concerned about adequate carnitine
◦ Milk and meat products are good sources
◦ Carnitine is nonessential
 The body makes plenty for itself when needed
◦ Essential trace mineral involved in carbohydrate and
lipid metabolism
◦ Studies show no effects of chromium picolinate on
body fatness, lean body mass, strength, or fatigue

Chromium picolinate safety
◦ Allergic reactions
◦ The release of chromium from chromium
picolinate creates molecular free radicals that can
contribute to potentially harmful levels of
oxidative stress in body tissues

Creatine
◦ The outcomes of some studies suggest that creatine
supplementation may enhance performance of highintensity strength activity such as weight lifting or
repeated sprinting
◦ Other studies have found no effect of creatine
supplements on strength performance

Creatine safety
◦ Appropriate long-term studies are lacking
◦ Cramping and gastrointestinal distress seem to occur
with about the same dosages reported to benefit
performance
◦ Short-term supplementation may pose risk to athletes
with kidney disease or other conditions
© 2006 Thomson-Wadsworth
◦ Medical and fitness experts voice concern that
creatine is being taken in huge doses and that
children as young as 9 years old are taking it with
unknown consequences
◦ Creatine levels from foods, even diets high in
creatine-rich foods like red meat, do not approach
the amount athletes take in supplement form
© 2006 Thomson-Wadsworth
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Protein Powders
◦ Whey protein
 Can supply amino acids to the body
 Offers no special benefits beyond those provided by ordinary
milk or yogurt

Extra protein will not stimulate muscle growth
◦ Muscle growth is stimulated by physical activity
◦ Not by excess protein

Purified protein contains none of the other
nutrients needed to support the building muscle
◦ An entire array of nutrients from food is required
© 2006 Thomson-Wadsworth
◦ The testes and adrenal glands in men and the
adrenal glands in women make anabolic steroid
hormones naturally
◦ Often taken without any medical supervision or
testing
◦ Synthetic versions of these natural hormones
produce accelerated muscle bulking in response to
physical activity in both men and women
 Injections of these “fake” hormones produce muscle
size and strength far beyond that attainable by training
alone
 At the price of great risks to health
 “steroid rage”

Steroid Alternative Supplements
◦ “andro” (androstenedione) or DHEA or a number of
herbal preparations
 Claims made for these substances - that they reduce
fat, build muscle, slow aging, and other miracles - are
unsupported by research
 These substances are converted to active hormones by
body tissues
 Users incur many of the same serious risks as for
steroid drugs
 People respond unpredictably
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Herbal or even insect sterols hawked as
“natural” substitutes for steroid drugs are
useless in sports
◦ The body cannot convert them into human steroids
 Nor do they stimulate the body’s own steroid
production
◦ These products may contain toxins
 “natural” does not mean “harmless”
© 2006 Thomson-Wadsworth
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Human Growth Hormone (HGH)

Athletes in power sports are most likely to
experiment with HGH
◦ Can induce huge body size
◦ Is less readily detected in drug tests than steroids
◦ Believing the injectable hormone will provide the
benefits of anabolic steroids without the dangerous side
effects
◦ Alternatively, they may take growth hormone
“stimulators” such as the amino acids ornithine and
arginine
◦ HGH causes the disease acromegaly
◦ The amino acids ornithine and arginine do not stimulate
growth hormone release
© 2006 Thomson-Wadsworth