Understanding Nutrition
Chapter 14
Fitness: Physical Activity, Nutrients,
and Body Adaptation
By
A. Fellah, Ph.D.
Physical Activity and Fitness
Is this person physically fit? You can’t tell by looking. Fitness
involves more than muscles. It includes a person’s ability to
sustain physical activity over time.
Fitness
 Fitness is the characteristics that enable the body to perform
physical activity.
 The ability to meet routine physical demands with enough
reserve energy to rise to a physical challenge.
 The body’s ability to withstand stress of all kinds.
 Sedentary: physically inactive (setting down a lot).
 Fosters the development of several chronic diseases.
 Body composition: the proportions of muscle, bone, fat, and
other tissue that make up a person’s total body weight.
Benefits of Fitness
 Activities that promote fitness are themselves enjoyable:
 Restful sleep. Rest and sleep occur naturally after periods of
physical activity. During rest, the body repairs injuries, disposes
of wastes, and builds new physical structures.
 Nutritional health. Physical activity spends energy and thus
allows people to eat more food.
 Optimal body composition. A balanced program of physical
activity limits body fat and maintains lean tissue.
 Optimal bone density. Weight-bearing physical activity builds
bone strength and protects against osteoporosis.
 Resistance to colds and other infectious diseases. Fitness
enhances immunity.
Reducing Risks of Certain Diseases
Benefits of regular physical activity.
Benefits of Fitness
 Low risks of some types of cancers. Lifelong physical activity
may help to protect against colon cancer, and breast cancer.
 Strong circulation and lung function. challenges the heart and
lungs slows the aging of the circulatory system.
 Low risk of cardiovascular disease. lowers blood pressure,
slows resting pulse rate, and lowers blood cholesterol, thus
reducing the risks of heart attack and strokes.
 Low risk of type 2 diabetes. normalizes glucose tolerance,
especially via the secretion of insulin.
 Reduced risk of gallbladder disease in women. reduces
women's risk of gallbladder disease-perhaps by facilitating
weight control and lowering blood lipid levels.
Benefits of Fitness
 Low incidence and severity of anxiety and depression. Active
people deal with better with psychological stress.
 Strong self-image. The sense of achievement that comes from
meeting physical challenges promotes self-confidence.
 Long life and high quality of life in the later years. Active people
have a lower mortality rate than sedentary people.
 As a person becomes physically fit, the health of the entire
body improves.
Checking Heart Rate
To find out if you’re exercising at the right level, take your
pulse during a break or right after you finish exercising.
Components of Fitness
 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 contract repeatedly
without becoming exhausted.
 Cardiorespiratory endurance: the ability to perform dynamic
exercise of moderate-to-high intensity for prolonged periods.
 Conditioning: the physical effect of training; improved flexibility,
strength, and endurance.
 Training: practicing an activity regularly, which leads to
conditioning. (Training is what you do; conditioning is what you
get.)
Components of Fitness
 Progressive overload principle: the training principle that a
body system, in order to improve, must be worked at
frequencies, durations, or intensities that gradually increase
physical demands.
 Frequency: the number of occurrences per unit of time (for
example, the number of activity sessions per week).
 Intensity: the degree of exertion while exercising (the amount
of weight lifted or the speed of running).
 Duration: length of time (the time spent in each activity
session).
People’s bodies are
shaped by the
activities they
perform.
Warming Up and Cooling Down
It’s always a good idea to S–T–R–E–T–C–H before exercise.
Conditioning by Training
 Warm-up: 5 to 10 minutes of light activity, such as easy
jogging or cycling, prior to a workout to prepare the body for
more vigorous activity.
 Cool-down: 5 to 10 minutes of light activity, such as walking or
stretching, following a vigorous workout to return the body's
core gradually to near-normal temperature.
 Moderate exercise: activity that can be sustained comfortably
for 60 minutes or so.
 Hypertrophy: of muscles, growing larger; an increase in size in
response to use.
 Atrophy: of muscles, becoming smaller; a decrease in size
because of disuse, undernutrition, or wasting diseases.
Percentage of Adults Who Exercise
The percentage of adults aged 18 and over who engaged
in physical activity five or more times per week in 1990.
Conditioning by Training
 Weight training (also called 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 abdominal
crunches.
Americans and Exercise
The proportion of people aged six and older who engage in
no leisure-time physical activity.
Cardiorespiratory Endurance
 VCLmax: the maximum rate of oxygen consumption by an
individual at sea level.
 Cardiorespiratory conditioning: improvements in heart and
lung function and increased blood volume, brought about
by aerobic training.
 Cardiac output: the volume of blood discharged by the
heart each minute; determined by multiplying the stroke
volume by the heart rate.
 The stroke volume is the amount of oxygenated blood the
heart ejects toward the tissues at each beat.
 Cardiac output (volume/minute) = stroke volume
(volume/beat) x heart rate (beats/minute).
Physical Activity Guidelines
Delivery of O2 by Heart and
Lungs to the Muscles
 The more fit a muscle is, the more oxygen it draws from the
blood.
 This oxygen comes from the lungs, so the person with more fit
muscles extracts oxygen from inhaled air more efficiently than a
person with less fit muscles.
 The cardiovascular system responds to increased demand for
oxygen by building up its capacity to deliver oxygen.
 Researchers can measure cardiovascular fitness by measuring
the amount of oxygen a person consumes per minute while
working out. This measure of fitness is called VO2 max.
Delivery
of O2 by
Heart and
Lungs to
the
Muscles
Determining VO2 Max
This man is running on a treadmill.
His nose is plugged, so he must
breathe through a tube in his mouth.
The tube is attached to an apparatus
that measures the total amount of air
breathed in and out, and the
difference between the amount of
oxygen inhaled and exhaled.
Every few minutes the slope or speed
of the treadmill is increased, making
the exercise more intense.
The amount of oxygen he utilizes at
the point when his exercise intensity
can go no higher is considered
“maximal oxygen consumption,” or
VO2 max.
Energy Systems, Fuels, and Nutrients
to Support Activity
 ATP: in the muscle, ATP provides the chemical driving force
for contraction. When ATP is split, its energy is released and
muscle cells channel some of the energy into mechanical
movement.
 CP, creatine phosphate: a high-energy compound in muscle
cells that acts as a reservoir of energy that can maintain a
steady supply of ATP, CP provides the energy for short bursts
of activity.
 During rest:
ATP + creatine → CP
 During activity: CP → ATP + creatine
Glucose Use during Physical Activity
 Diet Affects Glycogen Storage and Use:
 The body constantly uses and replenishes its glycogen.
 To fill glycogen stores, eat plenty of carbohydrate-rich food.
 Intensity of Activity Affects Glycogen Use:
 Intense activity: exercises at a rate that exceeds the capacity
of the heart and lungs to supply oxygen to the muscle.
• The glucose is the source of energy (anaerobic activity).

Moderate activity: the individual breaths easily, the heart
beats steadily (aerobic activity).
• Energy derived from both glucose and fatty acids.
The effect of diet on physical endurance
A high-carbohydrate diet can triple an athlete’s endurance
Exercise Intensity and Heart Rate
Schematic representation showing the proportionate use of
sources of energy for physical activities of various intensities.
Most activities are fueled by both fat and glucose.
Glucose and Fatty Acids in Their Energy-Releasing Pathways
Glucose as an
aerobic fuel
Recycling of Glucose
Glucose use during physical activity.
Glucose Depletion
 To maximize glucose supply, endurance athlete:

• Eat a high-carbohydrate diet regularly.
• (approximately 8 grams of carbohydrate per kilogram of
body weight or about 70 percent of energy intake)

• Take glucose periodically during activity that lasts for an
hour or more. (usually in sports drinks, diluted fruit juice, or
other beverages).

• Eat carbohydrate-rich foods following activity.
• (approximately 60 grams of carbohydrate)

• Train the muscles to store as much glycogen as possible.
Glycogen Depletion in Cyclists.
Fat Use during Physical Activity
 Duration of Activity Affects Fat Use


When blood fatty acids level fall, the hormone epinephrine
is released and the fat cells begin breaking down stored
triglycerides and librating fatty acids into the blood.
After 20 minutes of activities, the blood fatty acid
concentration surpasses the normal resting level.
 Intensity of Activity:



As intensity increases, fat makes less contribution.
Fat can be broken down for energy only by aerobic
metabolism.
This process requires oxygen.
 Training Affects Fat Use:




To burn more fat , train aerobically.
Training stimulate the muscle cells to make more and
larger mitochondria, the cellular structures that conduct
aerobic metabolism.
To lose weight, increase your physical activity enough to
spend more energy than you consume from foods.
Select an activity and an intensity level that are
challenging, but not overwhelming.
Fat as an
aerobic
fuel
Protein Use during Physical Activity
 Protein Used in Muscle Building:

Synthesis of protein is suppressed during activity and for several hours.

Then it accelerates beyond normal resting levels.


The physical work of muscle cell acts as a signal to its DNA and RNA to
produce proteins needed for that work.
During active muscle –building phases of training, an athlete may add
between ¼ -1 ounce (7-28 g) of body protein to existing muscle mass
each day.
 Protein Used as Fuel:


Muscles speed up their use of amino acids for energy during physical
activity.
Protein contributes at most ~10% of total fuel used.
 Diet Affects Protein Use during Activity;
 To conserve protein, eat a diet adequate in energy and rich
in carbohydrate.
 Intensity and Duration of Activity Affect Protein Use during
Activity
 Intensity and long duration, may deplete glycogen stores.
 Training Affects Protein Use
 The higher the degree of training, the less protein a person
uses.
 Protein Recommendations for Active People
 All athletes in training should attend to protein needs, but
should back up the protein that they wish to retain in muscle.
Vitamins and Minerals to Support Activity
 Supplements:
 Don’t enhance the performance of well-performance.
 Active people who eat enough nutrient-dense foods to meet
energy needs also meets their vitamin & minerals needs.
 Iron:


Physically active young women are prone to iron deficiency.
Physical activity can affect iron status in:
• Iron losses in sweat, destruction of red blood cells, poor
iron absorption, and high demands of muscle myoglobin.
 Sports anemia:
 A transient condition of low hemoglobin in the blood,
associated with the early stages of sports training
Fluids and Electrolytes to Support Activity
 During physical activity, water losses from sweating and
breathing are significant, and dehydration becomes threat.
 First symptom of dehydration is fatigue:
 1-2% water loss of body weight can reduce a person’s
capacity to do the work.
 7% water loss, a person is likely to collapse.
 Hyperthermia: an above-normal body temperature.

Body heat builds up and triggers maximum sweating, bur without sweat
evaporation, little cooling takes place.
 Heat stroke: a dangerous accumulation of body heat with
accompanying loss of body fluid.

Symptoms: headache, nausea, dizziness, clumsiness, stumbling
Active
people
need extra
fluid, even
in cold
weather
Hydration Schedule
Hydration schedule for physical activity.
An Athlete’s Meal Selections: 1 of 4
Breakfast
An Athlete’s Meal Selections: 2 of 4
An Athlete’s Meal Selections: 3 of 4
An Athlete’s Meal Selections: 4 of 4
Summary
 Regular physical activity benefits a person physically,
psychologically and socially and provides many health benefits.
 Flexibility, strength, muscle endurance and cardiorespiratory
endurance are components of fitness.
 Training conditions the human body to be more fit.
 Muscle cells adapt in size and work capacity in response to
demands.
 Cardiovascular conditioning A improves heart and lung
functioning to bring more oxygen to the cells.
 Both strength and endurance activities need to be included in a
balanced fitness program.
Summary
 A mixture of fuels is required for physical activity.
 During intense activity, muscles use glucose primarily.
 Low to moderate activity uses more fat.
 Protein is needed to build and maintain lean body tissue.
 Vitamins and minerals must be provided to support energy
metabolism and tissue building.
 Water helps to distribute the fuels and eliminate waste.
 Water is especially important during training and competition.
Summary
 The most common problems of female athletes include eating
disorders, iron deficiency, amenorrhea and osteoporosis.
 A suggested diet for physically active people must provide
ample fluids, and a variety of nutrient-dense foods in quantities
that meet energy needs.
 A healthful diet surpasses the need for pills and powders to
enhance athletic performance.
 Highlight 14 addresses the issues of supplements as
ergogenic aids.