Download Chapter 10 Nutrients, Physical Activity, and the Body`s Responses

Chapter 10
Nutrients, Physical Activity, and the Body’s Responses
Nutrition & fitness have a two-way relationship
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Optimal nutrition contributes to athletic performance &
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Conversely, regular exercises contribute to a person’s ability to use & store nutrients
optimally
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Together, the two are indispensable to a high quality of life
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Fitness, like good nutrition, is an essential component of good health
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Nutrition and physical activity are interactive
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Each influences the other
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The working body demands all three energy-yielding nutrients
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The body also needs protein and a host of supporting nutrients to build lean tissue
Physical activity benefits the body’s nutrition by helping to regulate the use of fuels
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Pushing the body composition toward the lean
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Increasing the daily caloric allowance
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Improvement is not only possible but an inevitable consequence of becoming more active
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As you improve your physical fitness, you not only feel better and stronger, but you look
better
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Physically fit people walk with confidence and purpose
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With more calories come more nutrients and other beneficial constituents of
foods
Posture and self-image improve along with physical fitness
If you are already fit
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You move with ease and balance
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You have endurance
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Your energy lasts for hours
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You are strong and meet daily physical challenges without strain
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You are prepared to meet mental and emotional challenges
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Physical fitness supports mental and emotional energy and resilience
The more active you are the more fit you are likely to be
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Fitness builds slowly and so activity should increase
gradually
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For beginners, consistency is very important
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Establish a regular pattern of physical activity first
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Plan to increase that amount over time
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View your exercise time as a lifelong commitment
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FIT
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F= Frequency
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I= Intensity
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T= Time
Fitness
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Fitness depends on a certain minimum amount of
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Physical activity
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Bodily movement produced by muscle contractions that substantially increase
energy expenditure
Exercise
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Planned, structured, and repetitive bodily movement that promotes or
maintains physical fitness
Benefits of Fitness
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People who regularly engage in just moderate physical activity live longer on average
than those who are physically inactive
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25% of adults in the U.S. are completely inactive
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A sedentary lifestyle ranks with smoking and obesity as a risk factor for
developing cardiovascular disease, some forms of cancer, stroke, diabetes, and
hypertension
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Every year ≈$24 billion is spent on health-care costs attributed to physical inactivity in the U.S.
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Compared with unfit people, physically fit people enjoy
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More restful sleep
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During rest, the body repairs injuries, disposes of wastes generated during
activity, and builds new physical structures
Better nutritional health
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Physical activity expends energy and thus allows people to eat more food
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If they choose wisely, active people will consume more nutrients and be less
likely to develop nutrient deficiencies
Benefits of Physical Activity Include
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Increase self-confidence
More energy
Less stress & anxiety
Improved sleep
Enhanced immunity
Lower risk of heart disease
Lower risk of certain cancer
Stronger bones
Lower risk of diabetes
Lower risk of high blood pressure
Improve quality of life
Increase independence in life’s later years
Benefits of Fitness
• Our bodies need Regular & Moderate Exercise that gets our
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Heart beat faster
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Muscle work harder
• Physiologically speaking, overall fitness is a balance between different body systems
The Essentials of Fitness
• Three things are needed for Physical activity
– Oxygen
– Water
– Source of Energy
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The body’s ability to meet physical demands, composed of four components:
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Flexibility
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Strength
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Muscle endurance &
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Cardiovascular Endurance
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
Cardiovascular 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
Physical activity need not be strenuous to achieve health benefits
– The institute of medicine recommends that we spend a total of at least 60 minutes on
most day of the week engaged in any one of numerous forms of physical activities (see
page 317)
– These 60 minutes can be accumulated in relatively brief session in period as short as 8
to 10 minutes
– Total amount of activity is more important than the manner in which it is carried out
How Do My Muscles become Physically Fit?
– Overload
• An extra physical demand placed on the body
• An increase in the frequency, duration, or intensity of an activity
• A principle of training is that for a body system to improve, it must be worked at
frequencies, durations, or intensities that increase by increments
– 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
• A response called hypertrophy
– If not called on to perform, muscle cells dwindle and weaken; they atrophy
– A variety of physical activities produces the best overall fitness
– People need to work different muscle groups from day to day
– For balanced fitness
– Stretching enhances flexibility
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– Weight training develops muscle strength and endurance
– Aerobic activity improves cardiorespiratory endurance
Aerobic
– Requiring oxygen
– Aerobic activity strengthens the heart and lungs by requiring them to work harder than
normal to deliver oxygen to the tissues
Anaerobic Metabolism
Anaerobic Exercise (without Oxygen)
– When the muscles exertion becomes greater enough that their energy demand
outstrips the oxygen supply, they must also rely on Anaerobic metabolism for energy.
– Anaerobic pathway can only burn carbohydrate for fuel, it draws heavily on your
limited stores of carbohydrates
– Thanks to anaerobic metabolism, you can dash out of the way of an oncoming car .
Unfortunately, this system is extremely inefficient
0nly 5% of Carbohydrate’s energy-producing potential is harness by this pathway.
It produces Lactic acid – partly broken down portion of glucose.
When lactic acid build up in muscles it causes burning pain and leads to muscle exhaustion if it is
not drained away.
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
Neither the Aerobic nor Anaerobic pathways functions exclusively to supply energy.
Work together, complementing and supporting each other.
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The Carbohydrate is absolutely essential for exercise.
Without it, your muscles cannot perform.
When you exercise AEROBICALLY, muscles burn fat and extract energy from glucose more
efficiently in the presence of Oxygen, thereby conserving your body’s limited stores of glucose.
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Glucose use during physical activity depends on the duration of the activity
– As well as on its intensity
Energy for Exercise
Thus, you want to exercise at an intensity that allows your heart and lungs to keep pace
with the oxygen needs of your working muscles
For total fitness, an exercise program should incorporate
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Aerobic Activity
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Strength Training &
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Stretching
It makes sense to give muscles a rest
– It takes a day or two to replenish muscle fuel supplies and to repair wear and tear
incurred through physical activity
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Periodic rest gives muscle time to adapt to an activity
• During rest, muscles build more of the equipment required to perform the
activity that preceded the rest
The term Fitness is not restricted to the seasoned athletes you need:
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Reasonable weight
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Enough flexibility
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Muscle strength
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Muscle endurance &
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Cardiovascular Endurance
To meet everyday demands, plus some to spare
Physical Conditioning:
Planned program of exercise directed toward improving the function of a particular body system
Placing physical demand on your body & forcing it to do more
This principle applies equally to all aspects of fitness It is called OVERLOADING
Strength
Is the ability of the muscles to work against resistance
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Muscles
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Tendons
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Ligaments &
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Connective tissues
Become stronger
Prevent energy
Benefit continues to a very old age
Flexibility
A flexible body can move as it was designed to move & will bend rather than tear or break in
response to sudden stress
Flexibility depends on the condition & interrelationship of:
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Bones
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Ligaments
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Muscles &
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Tendons
Flexibility tends to decrease with age but improves response to stretching
Cardiovascular Conditioning
Increase total blood volume so that the blood carry more O2
– Heart muscles become stronger & larger, so each beat pumps more blood
– Lung muscles become stronger & larger & breathing becomes more efficient
– Circulation through arteries vein improve & the blood pressure falls
Muscles through out the body become firmer
How Does Cardiovascular Training Benefit the Heart?
– Blood HDL increases
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Effective activities elevate the heart rate, are sustained for longer than 20 minutes,
and use more of the large-muscle groups of the body
• swimming, cross-country skiing, rowing, fast walking, jogging, fast bicycling,
soccer, hockey, basketball, in-line skating, lacrosse, rugby
To make these gains you must elevate your heart beat
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This elevated heart beat is called
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Target heart rate
– That must be considerably faster than resting rate but not so fast as to strain it
To achieve this goal you must work up to the point of which you can exercise aerobically for at
least 20 minutes or more.
As a rule of thumb
– The average resting plus rate for adult is around 70 beats per minute
– Can be higher or lower
– Active people may have resting plus rates of 50 or even lower
Estimate Your Maximum Heart Rate (MHR)
Subtract your age from 220. This provide an estimate of the MHR
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Should never exercise at this rate
Determine your Target Heart Rate range
Multiply MHR by 55 & 90 % to find your upper & lower limits
Example
Age 25
MHR: 220-25= 195
Range: 0.55x195=107
0.90x195=176
Fluids and Temperature Regulation in Physical Activity
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
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
Sweat cools the body
– In hot, humid weather, sweat may fail to evaporate because the surrounding air is
already laden with water
• Little cooling takes place and body heat builds up
• In such conditions, athletes must take precautions to avoid heat stroke
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An especially dangerous accumulation of body heat with accompanying
loss of body fluid
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
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
Water
The best drink for most active bodies is plain cool water
– Water rapidly leaves the digestive tract to enter the tissues
– Water cools the body from the inside out
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
Sports drinks offer fluids to help you offset the loss of fluids during physical activity
– Plain water can do this
For athletes who exercise intensely for 45 minutes or more
– Sports drinks provide an advantage over water
Fitness water does not provide glucose and electrolytes
– Some active people may prefer its light flavor to plain water
Carbonated beverages are not a good choice for meeting an athlete’s fluid needs
– Although they are composed largely of water
– The air bubbles from the carbonation make a person feel full quickly
• So may limit fluid intake
Beverages that contain alcohol are inappropriate as fluid replacements
– Alcohol is a diuretic
– It promotes the excretion of
• Water
• Vitamins such as thiamin, riboflavin, and folate
• Minerals such as calcium, magnesium, and potassium
Fuel For Exercise
Energy producing pathway requires oxygen & two fuels
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Glucose
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Fat
Glucose, mainly provided by the muscles & some by the
Liver
Fatty acids, also, come mainly from fat inside the muscles but partly from adipose tissues
During rest
• The body derives a little more than half of its energy from fatty acids
• Most of the rest from glucose
A little from amino acids
For Physical activity the body uses different mixtures of fuels depending on the intensity and
duration of its activities and depending on its own prior training
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
Longer the exercise lasts or the more intense it is, the more glucose a person uses
– Jogging & brisk walking, in which the body can meet the oxygen demand body use
glycogen more conservatively
– For 1st 20 minutes or so, body uses glycogen rapidly
– If exercise continues beyond 20 minutes glycogen use slows down & body begins to
rely more on fat
People who run out of muscle glycogen “hit the wall”
– They must slow down their pace because muscle glycogen is no longer available
– Liver can release small amount of glucose to briefly delay body shutdown
– When blood glucose dip too low, the nervous system function comes almost to a halt
Another factor that influences glycogen use during exercise is:
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How trained the person is
– Untrained muscles quickly & easily extract energy from glucose
– Trained muscles adapt & pack their cells with more fat-burning enzymes
The amount of glycogen present in the muscles before exercise also influence glycogen use
A classic report compared fuel use during activity by three groups of runners, each on a
different diet
– For several days before testing, one of the groups ate a normal mixed diet; a second
group ate a high-carbohydrate diet; the third group ate a high-fat diet
– The high-carbohydrate diet enables the athletes to work longer before exhaustion
Activity Intensity, Glucose Use, and Glycogen Stores
• 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
Activity Duration
Affects Glucose Use
• In the first 10 minutes or so of activity
– The active muscles rely almost entirely on their own stores of glycogen
• Within the first 20 minutes or so of moderate activity
– A person uses up about one-fifth of the available glycogen
• 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
• 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
• 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
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Especially during games which last for hours and demand repeated bursts of
intense activity, athletes benefit from carbohydrate-containing drinks taken
during the activity
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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
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Even in athletes, extra carbohydrate does not benefit those who engage in sports in which
fatigue is unrelated to blood glucose
– 100-meter sprinting
– Baseball
– Casual basketball
– Weight lifting
Carbohydrate Loading
– A regimen of moderate exercise, followed by eating a high-carbohydrate diet
– Enables muscles to temporarily store glycogen beyond their normal capacity
• Can nearly double muscle glycogen concentration
– A.k.a. glycogen loading or glycogen supercompression
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Extra glycogen gained through carbohydrate-loading can benefit an athlete who must keep
going for 90 minutes or longer
Those who exercise for shorter times simply need a regular high-carbohydrate 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
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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 highcarbohydrate 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
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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
To Burn More Fat
during Activity, Should Athletes Eat More Fat?
• 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
• High-fat diets carry risks of heart disease
– Physical activity offers some protection against cardiovascular disease
• Even athletes can suffer heart attacks and strokes
– Most nutrition experts agree that the potential for adverse health effects from
prolonged high-fat diets makes them an unwise choice for athletes
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A diet that overly restricts fat is not recommended either
– Athletes who restrict fat below 20% of total energy intake may fail to consume
adequate energy and nutrients
– Sports nutrition experts recommend that endurance athletes consume 20%-30% of their
energy from fat
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As fuel for activity, body fat stores are more important than fat in the diet
– Fat stores can fuel hours of activity without running out
– 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
• Areas with the most fat to spare donate the greatest amounts of fatty acids to
the blood
– Although they may not be the areas that one might choose to lose fat
from
– This is why “spot reducing” does not work
Muscles do not own the fat that surrounds them
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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
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Degree of Training Affects Fat Use
– Training stimulates muscles to develop more fat-burning 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 also increase your basal metabolic rate (BMR)
Using Protein and Amino Acids to Build Muscles and Fuel Activity
Athletes use protein to build and maintain muscle and other lean tissue structures
– And, to a small extent, to fuel activity
• The body handles protein differently during activity than during rest
• 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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Whenever the body rebuilds a part of itself, it must tear down old structures to make way for
the new ones
– Physical activity, with just a slight overload, calls into action both the proteindismantling and protein-synthesizing equipment of individual muscle cells that work
together to remodel muscles
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Dietary protein provides the needed amino acids for the synthesis of new muscle protein
– However, the true director of
synthesis of muscle protein is
physical activity
– Repeated activity signals the
muscle cells’ genetic material
to begin producing more of the
proteins needed to perform the
work at hand
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After muscle cells have made all the decisions about which proteins to build and when, protein
nutrition comes into play
– During muscle-building phases of training, a weight lifter might add between 0.25 ounce
and 1 ounce of protein to existing muscle mass each day
– This extra protein comes from ordinary food
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The DRI committee does not recommend greater-than-normal protein intakes for athletes
– Other authorities do
• A joint position paper by the American Dietetic Association and the Dietitians of
Canada recommend protein intakes somewhat higher than the 0.8 gram of
protein per kilogram of body weight recommended for sedentary people
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Athletes who eat a balanced, high-carbohydrate diet that provides enough total energy also
consume enough protein
– They do not need special foods, protein shakes, or supplements
Vitamin and Minerals - Keys to Performance
Many vitamins and minerals assist in releasing energy from fuels and transporting oxygen
Nutrient supplements do not enhance the performance of well-nourished athletes or active
people
• Deficiencies of vitamins and minerals do impede performance
• Regular, strenuous physical activity increases the demand for energy
• Athletes and active people who eat enough nutrient-dense foods to meet energy needs also
meet their vitamin and mineral needs
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Taking vitamin or mineral supplements just before competition will not enhance performance
– Most vitamins and minerals function as small parts of larger working units
– After entering the blood, they have to wait for the cells to combine them with their
appropriate other parts so they can do their work
• This takes hours or days
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If you want to excel physically
– Apply the most accurate nutrition knowledge with dedication to rigorous training
– A diet that provides ample fluid and consists of a variety of nutrient-dense foods in
quantities to meet energy needs will enhance athletic performance and overall health
Controversy: Ergogenic Aids: Breakthroughs, Gimmicks,
• Store shelves and the Internet abound with ergoenic aids
– Each striving to appeal to performance-conscious people
– Protein powders, amino acid supplements, caffeine pills, steroid replacers, “muscle
builders,” vitamins, and more
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In light of the evidence, this section concludes what most people already know
– Consistent training and sound nutrition serve an athlete better than any pill, powder, or
supplement
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Amino Acid Supplements
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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
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Carnitine
– A nonessential nutrient
• 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 scientific studies, carnitine supplementation for 7 to 14 days neither raised
muscle carnitine concentrations nor influenced fat or carbohydrate oxidation
Nore do such supplements enhance exercise performance
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Chromium Picolinate
– Chromium is an essential trace mineral involved in carbohydrate and lipid metabolism
– The great majority of studies show no effects of chromium picolinate on body fatness,
lean body mass, strength, or fatigue
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Eating extra protein will not stimulate muscle growth
– Muscle growth is stimulated by physically demanding activity
– Not by excess protein
Purified protein preparations contain none of the other nutrients needed to support the
building of muscle protein
– An entire array of nutrients from food is required
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Hormone Preparations
– These substances are clearly damaging to the body
– Don’t consider using these products