1. Section 4
Macronutrient Metabolism
in Exercise and Training

2. Fuel for Exercise
 The fuel mixture that powers exercise generally depends
on:
• The intensity of effort
• The duration of effort
• The exerciser’s fitness status
• The exerciser’s nutritional status

3. Illustration of the contribution of COH, lipid, and protein during different exercise intensities:
*Assume that little or no proteins are being used for energy.
Rest Low-Intensity High-Intensity Mod-Intensity
Long Duration Short Duration Long Duration
Protein 2-5% 2-5% 2% 5-8%
COH 35% 40% 95% 70%
Lipid 60% 55% 3% 15%

5. Cross-Over
100
60
COH %
Fat %
30 70
10 50
Rest 25% 70% 100%
% of Maximal Aerobic Capacity

6. Effect of Training
100
60
COH %
Fat %
30 70
10 50
Rest 25% 70% 100%
% of Maximal Aerobic Capacity

9. Double Cross-Over
90
70
COH %
Fat %
50 50
10 30
Rest 1 10 20 40 80 120
Duration of Exercise (min)

12. 1. Emphasize Carbohydrates in the diet:
55-65% of total caloric intake
High quality carbohydrates (nutrient rich)
Low glycemic COH are preferred
2. Storage of COH
Liver glycogen COH Homeostasis During Exercise
Muscle glycogen
COH from
g.i. track
Used for muscle
In=Out contraction
Liver glycogen Blood Glucose Muscle glycogen
Adipose tissue
~400 kcal ~400 kcal ~1200 kcal
~a lot of kcal
Converted to Fat

13. 3. Use of COH during Training/Competition
•Below 50% intensity--fat utilization
•Above 50% intensity--primarily COH (intervals)
•Depletion of glycogen stores within 2 hours
headache, lightheadedness, nausea, fatigue, malaise
•Training enhances ability to use COH
•Training also enhanced the ability to use fat for energy
Why is ability to use fat so important? It saves the COH…
Estimation of energy available for muscle contraction:
Fuel Depot Kcal
Glycogen in muscle 480-1,000
Glycogen in liver 280-400
Adipose tissue 141,000-
Body proteins ~24,000

14. 4. Maintaining Glucose Levels During Exercise
•Hepatic glucose production--”Feed forward mechanism”
•Glucose feedings/drinks
•Absorption
-Start drinking early
-Cold
-Less than 8% (8 g of glu/oz of fluid) glucose
*Maltodextrin drinks (Exceed, GatorLode, UltraFuel)
-Adequate volume of fluid
-Good tasting
• Replenishing Glycogen Stores After Exercise
•Immediately after Ex-High glycemic foods are okay
•Thereafter: Avoid Glycemic Foods that produce an insulin response
•Replenish Glycogen Stores, don’t feed Fat Stores
• Carbohydrate Loading--Enhancing Glycogen Storage
•Time to fatigue is related to glycogen stores
•Repeated depletion during training--Increased storage

15. •Dietary Plan: 7 days before competition
-depletion: Day 1-exhausting exercise to deplete stores
Days 2 to 4-low COH diet
-loading: Days 5-7 high COH diet, no depletion
•If all goes well...can store 2x as much glycogen “Supercompensation”
-normal: 2 g glycogen/100 g muscle
-”loaded”: 4-5 g glycogen/100 g muscle
•If all does not go well...
-diarrhea/constipation/gas production
-1 g glycogen stored in 3 g of water
-fluctuations in plasma glucose, fatty acids, and cholesterol
-difficulty training during low COH period

18. Glycogen Depletion
 Blood glucose levels fall.
 Level of fatty acids in the blood increases.
 Proteins provide an increased contribution to energy.
 Exercise capacity progressively decreases.

19. Nutritional Strategies to Enhance Fat Oxidation During Exercise
Carbohydrate stores are limited within the body, and fat depots represent an enormous
source of potential energy.
However, fatty acid oxidation by muscle is limited, especially during exercise above
about 50% intensity.
Adipose Tissue Blood Plasma Muscle
Triglyceride Intra-muscular
(~77,000 kcal) Triglyceride
(~3,200 kcal)
Glycerol
FFA
Glycogen
(~2,000 kcal)
Albumin FFA Fatty acids
FFA Acetyl-CoA
Kreb’s cycle &
Electron Transport
Liver
Glucose
Glycogen (~450 kcal) ATP
(~1200 kcal)
Oxygen

20. Processes that limit fatty acid oxidation during exercise:
. External factors:
-aerobic training status of the individual
-habitual intake of fat
-ingestion of COH and fat just prior to exercise
-gender
-intensity of exercise
. Mobilization of fatty acids from adipose tissue: Lipolysis
-cleavage of fatty acids from triglyceride is dependent on activation of the enzyme,
hormone sensitive triglyceride lipase (HSL) in adipose tissue.
-Epinephrine and glucagon activate HSL
-Insulin and high blood glucose inhibit HSL
. Transport of fatty acids across the sarcolemmal membrane into muscle:
-Small fatty acids go into muscle by diffusion (8-12 C long)
-Longer fatty acids require:
Fatty acid binding proteins (FABP)
Fatty acid translocases (FAT)
Fatty acid transport proteins (FATP)
*FABP is higher in slow twitch muscles and is enhanced by training
. Transport of fatty acids across the mitochondrial membrane:
-Carnitine palmitoyltransferase I takes FA across outer mitochondrial membrane
-Carnitine palmitoyltransferase II takes FA across the inner mitochondrial membrane
-Transport dependent activity
. Oxidation of fatty acids:
-Dependent on the availability of oxygen
-Dependent on mitochondiral density
-Dependent on plasma concentrations of epi, glucagon, insulin, and glucose
-Dependent on exercise intensity

21. Strategies to Enhance Fatty Acid Oxidation During Exercise:
1. Caffeine ingestion before and during exercise:
stimulates lipolysis
enhances FA oxidation
decreases utilization of muscle glycogen
How? Not sure...
May be sympathomimetic (like epinephrine)
May stimulate fat mobilization directly
2. Fat feeding before exercise:
enhances fat metabolism during exercise
-probably by increasing FFA levels in the blood
does not prolong exercise or spare glycogen
3. Maintain low insulin levels prior to exercise
avoid high glycemia foods that stimulate insulin and inhibit HSL
pseudo-insulin resistance during exercise precludes this response
4. Long, slow, gradual, and continuous warm-up prior to exercise.
helps to maintain resting fatty acid levels during exercise
5. High state of aerobic fitness.
enhances oxygen delivery to cell
enhances fatty acid deposits in muscle
enhances blood flow to the cell
increases density of fatty acid binding proteins (FABP), fatty acid translocases (FAT),
and fatty acid transport proteins (FATP)
enhances mitochondrial density
5. Other unsuccessful things that have been tried:
-high fat diets/high fat sports bars
-high protein diets
-L-carnitine supplementation

22. Nutrient Utilization During Exercise
Percent contribution of aerobic and anaerobic energy pathways during exercise:
Duration of Maximal Exercise
Seconds Minutes
Time 10 30 60 2 4 10 30 60 120
% Anaerobic 90 80 70 50 35 15 5 2 1
% Aerobic 10 20 30 50 65 85 95 98 99

23. Nutrient Related Fatigue:
-Depletion of muscle glycogen and liver glycogen
“bonking”
“hitting the wall”
“carrying the piano”
“trip to Oz”
-Possible reasons for fatigue and depletion:
-Use of blood glucose as energy for the CNS
-Use of glucose as a primer for fat metabolism
-Significantly slower rate of energy release from fat compared to carbohydrate breakdown
-*Hepatic glucose production
When exercise begins – muscles take glucose from the
blood (exercise stimulated glucose uptake). This could make an
individual hypoglycemic if there were no compensatory mechanisms.
At the onset of exercise a sympathetically-mediated feed-forward mechanism
called hepatic glucose production prevents hypoglycemia during exercise
(but it also speeds the use of liver glycogen stores).
-Why fat metabolism is limited during exercise:
-FFA mobilization from adipose tissue
-FFA transport to muscle via blood
-FFA uptake by muscle cells
-FA mobilization from intramuscular fat
-FA transport into mitochondria
-FA oxidation in mitochondria

24. Preventing nutrient related fatigue:
1.Optimize carbohydrate stores before exercising
2. Optimize fat utilization during exercise
-slow and gradual warm-up
-continuous exercise
-adequate cutaneous blood flow
3. Glucose replacement during exercise
4. Training
-increases ability to utilize fats
-increases glycogen storage capacity
Effect of Training
100
60
30 70
10 50
Rest 25% 70% 100%
% of Maximal Aerobic Capacity

25. Training-Induced Adaptations That Increase Lipid Metabolism:
-facilitates lipolysis
-increased capillary perfusion of muscle to deliver lipids
-improved FA mobilization, transport, and oxidation
-increased mitochondrial density
-increased number of enzymes for β-oxidation

26. Protein Use During Exercise
 Serves as an energy fuel to a much greater extent than
previously thought
• The amount depends upon nutritional status and the
intensity of exercise training or competition.
• This applies particularly to branched-chain amino
acids that oxidize within skeletal muscle rather than
within the liver.

27. Protein Use During Exercise (cont.)
 Exercise in a carbohydrate-depleted state causes
significant protein catabolism.
 Protein synthesis rises markedly following both
endurance- and resistance-type exercise.

28. Protein Requirements
 Re-examining the current protein RDA seems
justified for those who engage in heavy exercise
training.
 One must account for increased protein breakdown
during exercise and the augmented protein
synthesis in recovery.

29. Gender Differences
 Women derive a smaller proportion of energy from
carbohydrate oxidation than do men during submaximal
exercise at equivalent percentages of aerobic capacity.
 Following aerobic exercise training, women show an
exaggerated shift toward fat catabolism, whereas men
do not.

30. Training-Induced Metabolic Adaptations
 Carbohydrate:
 Trained muscle has an augmented capacity to catabolize
carbohydrate aerobically for energy (less lactic acid)
 Due to an increased oxidative capacity of the mitochondria and
increased glycogen storage
 Greater fat use during submaximal exercise, less reliance on
muscle glycogen and blood glucose
 Lipids:
• Increases the ability to oxidize long-chain fatty acids
• Improves the uptake of FFAs
• Increases muscle capillaries and the size and number of muscle
mitochondria
• Protein:
 One must account for increased protein breakdown during
exercise and the augmented protein synthesis in recovery.
 American diet provides a heartily sufficient reserve

31. Influences of Diet
 The following diets are counterproductive for weight
control, exercise performance, optimal nutrition, and
good health:
• Starvation diets
• Low-carbohydrate, high-fat diets
• Low-carbohydrate, high-protein diets