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Fundamentals of
Exercise for Nutrition
Module 4.5
Fuel Utilization During Exercise
• The chemical reactions that use these substances to make
energy are called metabolism.
• Two interrelated energy-producing systems:
– Aerobic: requiring oxygen.
– Anaerobic: not requiring oxygen
• Inefficient; generates lactic acid that can be converted into
an energy substrate.
• The energy used by cells is called ATP. ATP production is
synthesized primarily from carbohydrate and fat
• As the intensity of the exercise increases, the percent of
carbohydrates used to produce ATP increases
• Nutrition supplies the fuel (carbohydrate, fat and protein) and
the essential structural components of enzymes (cofactors)
needed to drive chemical reactions to generate ATP through 3
predominant energy pathways:
– Glycolysis
– The citric acid cycle (Kreb Cycle)
– The electron transport chain.
ATP energy production through glycolysis, the citric acid
cycle, and the electron transport chain
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Fuels for Exercise
Glucose
1. Glycolysis Pyruvate to Acetyl CoA •
•
aerobic – pyruvate (pyruvic acid)
anaerobic process (no oxygen) lactic acid
2. Citric Acid Cycle (Krebs Cycle) – aerobic
 oxaloacetate
3. Electron Transport Chain- aerobic
Major Players
1.NADH, FADH- electron transporters (via hydrogen ions)
2.Acetyl CoA- used to convey carbon atoms to citric acid
cycle to be oxidized in energy production
3.ATP-provides the energy to for cell operations
Glycolysis
http://classes.midlandstech.edu/carterp/Courses/bio225/chap05/05-12_Glycolysis-2_1.jpg
Citric Acid Cycle – Kreb Cycle – TCA Cycle
Oxaloacetate
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Carbohydrates
• Carbohydrate as fuel supports high intensity exercise
• Carbohydrate intake can occur prior, during and after exercise
• Carbohydrate are limited in the body
– Blood Glucose - Constantly used by RBC and CNS
– Liver Glycogen (1/3 is stored) - Used to maintain blood glucose
– Muscle Glycogen (2/3rd is stored)
• Amount of exercise and dietary carbohydrate intake
determines the amount
• Used to produce ATP in the muscle during exercise
– Diet and exercise influence glycogen stores in the muscle
• During exercise, the body supplies glucose to the muscles from the
stores of glycogen in the liver and in the muscles
– First 20 minutes 1/5 of total glycogen used
– After first 20 minutes, body shifts to FAT
– At some point glycogen will be depleted. At this point person
can experience “hitting the wall” = overwhelming fatigue.
Carbo-Loading
• Carbohydrate loading is only effective for endurance events
lasting longer than 90 minutes, such as marathons, triathlons, etc.
• During intense, continuous endurance exercise, muscles will
become depleted of glycogen after about 90 minutes. Carbohydrate
loading is meant to store extra glycogen that your muscles can tap
into once the normal stores are used up.
• Combination of reduced training prior to event and increased
carbohydrate intake. Various methods.
The Effect of Exercise Intensity on Fuel Use
Fats
• AT REST burn mostly fat & some CHO
• When you exercise, the fat your muscles burn comes from
the fatty deposits all over the body.
• Desirable body weight may store 25 to 30 pounds of body
fat; 1 pound of carbohydrate.
• Consume low-fat foods prior to exercise and a low-fat (2025% of Calories) diet in general
• Beta-Oxidation -- oxidizes fatty acids to acetyl CoA.
• Acetyl CoA to TCA (Krebs Cycle) materials for ATP
Acetyl CoA - moves carbon atoms into energy pathway.
NADH, FADH -electron carriers
Proteins
• Amount of protein used depends on intensity / duration of
exercise
• Protein
g/kg/day
• RDA for adults
0.8
• Endurance athletes 1.2-1.6
• Resistance Training 1.6-1.7
• To become an energy source, proteins must first be degraded
into amino acids. Nitrogen (NH2) component is removed then:
• The carbon skeletons of the amino acids are
■ converted to acetyl CoA which enters
the Krebs cycle
■ converted into pyruvate
■ others can be converted into
oxaloacetate
Fluid Needs and Exercise
• Replenishing fluid lost during exercise accomplished by
drinking fluid before, during, and after exercise; decreases
risk of heat-related injury
– Heat cramps, heat exhaustion, heat stroke
• Sports drinks designed to enhance the body’s use of
carbohydrate and water.
– Should contain 4%-8% carbohydrates
• The carbohydrate in a sports beverage serves 3 purposes
during exercise:
1. Becomes an energy source
2. Helps maintain blood glucose
3. Helps increase the rate of water absorption from the
small intestine, helping maintain plasma volume
Thermal Regulation and
Hydration
• The ability to keep the body cooled during exercise
is key to exercise capacity and avoiding injury.
• A lot of heat is generated in the body due to the
inefficiencies of energy transfer to make ATP.
• SWEATING creates the evaporative cooling system employed
during exercise to keep the core body temperature in a functional
range.
• The core body temperature rises during exercise
• If the core body temperature >104oF, exercise capacity diminishes
and risk of thermal injury increases
• Fluid, salt, and other components are lost in sweat during exercise
– about a liter of fluid per hour of exercise, and 2.6 grams of salt
per liter
• Salt (NaCl) is 40% sodium, ½ t salt replaces the sodium lost in
1 hour of vigorous exercise.
Body Temperature Regulation
RADIATION –bodies usually warmer than
objects around them. Heat transferred from
body's surface to objects “NEARBY” that are
COOLER. NO DIRECT CONTACT!!
– If environmental temperature is higher
than body temperature, cannot lose heat
by radiation!!
– Heat carried from your internal organs to
skin by the blood radiates heat from skin's
surface.
CONDUCTION - Heat transferred from your body to any object or
substance in “DIRECT CONTACT” with it.
• Good conductors of heat like metal or light cotton clothing. Heat can pass
easily through such objects
• In cooler weather heat conduction can be minimized by wearing clothes made
of wool or fur which are poor conductors of heat but good insulators. Heat
cannot easily permeate such objects
Body Temperature Regulation
CONVECTION- Heat is
transferred AWAY FROM THE
BODY surface by the MOVEMENT
OF THE AIR AROUND YOU.
– The air close to your skin
becomes warm and rises,
allowing cooler air to take its
place next to the skin.
EVAPORATION - Evaporation occurs
when atoms or molecules escape
from the liquid and turn into a
vapor.
Sweat (liquid) wets the skin surface;
body changes liquid to water vapor
(gas); evaporation carries heat
away.
– humid conditions may cause
sweat to drip off body rather than
evaporate on the skin; sweat is
useless as a coolant in humid
environments.
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Dehydration to Hydration
• The fluid lost in sweat comes from the blood stream
• The plasma volume is the fluid reserve for sweat
• Fluid volume loss during aerobic exercise leads to dehydration
– The sensation of thirst signifies 2% dehydration,
cardiovascular and aerobic function is reduced.
– 5% dehydration, serious thermal injury risk. (heat exhaustion)
• Body can absorb 1 liter of fluid per hour.
• Replacing fluids (cool, dilute, small, and
frequent amounts) during strenuous
exercise is important:
– 1 cup at 41oF, every 10-15 minutes
– Drink without thirst to avoid dehydration
• Electrolytes (Na+, K+, Cl-) critical for body processes. Must
replaced in addition to fluids
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Consequences of
Dehydration
and Hydration
Importance of hydration
during exercise
 Optimize muscle strength
 Optimize aerobic capacity
 Prevention of thermal injury
which include dizziness,
cramping, fainting, heat
exhaustion and heat stroke
 Pool of fluid to draw upon
for sweat loss is the blood
stream.
 The cardiovascular system
is affected dramatically by
fluid losses.
http://weightwise.com/wpcontent/uploads/dehydration.jpg
Cardiovascular demise
during dehydration
 Plasma volume decreases
 Osmolarity of the blood
increases
 Blood pressure goes down.
 Constriction of the blood
vessels
 Increase in heart rate
 Decrease in heart filling
 Decrease in cardiac output
 Decreased sweating
 Increase in core body
temperature