Section+4+exercise+metabolism%2 c+macronutrients+during+ex

Section 4Section 4

Macronutrient Metabolism in Exercise and Training

Fuel for Exercise 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

Rest Low-IntensityLong Duration

High-IntensityShort Duration

Mod-IntensityLong Duration

Protein 2-5% 2-5% 2% 5-8%

COH 35% 40% 95% 70%

Lipid 60% 55% 3% 15%

Illustration of the contribution of COH, lipid, and protein during different exercise intensities:

*Assume that little or no proteins are being used for energy.

Cross-OverCross-Over

% of Maximal Aerobic CapacityRest 25% 70% 100%

Fat

%

CO

H %

60

30

100

50

70

10

Effect of Training

% of Maximal Aerobic CapacityRest 25% 70% 100%

Fat

%

CO

H %

60

30

100

50

70

10

Double Cross-Over

Duration of Exercise (min)

Rest 1 10 20 40 80 120

Fat

%

CO

H %

70

50

90

30

50

10

Importance of Carbohydrates for Athletes

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

Muscle glycogen

Blood Glucose~400 kcal

Adipose tissue~a lot of kcal

Liver glycogen~400 kcal

Muscle glycogen~1200 kcal

COH fromg.i. track

Converted to Fat

Used for musclecontractionIn=Out

COH Homeostasis During Exercise

Fuel Depot KcalGlycogen in muscle 480-1,000Glycogen in liver 280-400Adipose tissue 141,000-Body proteins ~24,000

3. Use of COH during Training/Competition

Below 50% intensity--fat utilization

Above 50% intensity--primarily COH (intervals)

Depletion of glycogen stores within 2 hoursheadache, lightheadedness, nausea, fatigue, malaise

Training enhances ability to use COH

Training also enhanced the ability to use fat for energyWhy is ability to use fat so important? It saves the COH…

Estimation of energy available for muscle contraction:

4. Maintaining Glucose Levels During Exercise

Hepatic glucose production--”Feed forward mechanism”Glucose feedings/drinksAbsorption

-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 okayThereafter: Avoid Glycemic Foods that produce an insulin responseReplenish Glycogen Stores, don’t feed Fat Stores

• Carbohydrate Loading--Enhancing Glycogen Storage

Time to fatigue is related to glycogen storesRepeated depletion during training--Increased storage

Dietary Plan: 7 days before competition

-depletion: Day 1-exhausting exercise to deplete storesDays 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

Glycogen DepletionGlycogen Depletion

Blood glucose levels fall.

Level of fatty acids in the blood increases.

Proteins provide an increased contribution to energy.

Exercise capacity progressively decreases.

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(~77,000 kcal)

Glycerol

Albumin

FFA

FFA

Liver

Glycogen(~1200 kcal)

Intra-muscularTriglyceride(~3,200 kcal)

Glycogen(~2,000 kcal)

Acetyl-CoA

Kreb’s cycle &Electron Transport

ATPGlucose(~450 kcal)

Fatty acids

Oxygen

FFA

Processes that limit fatty acid oxidation during exercise:1. 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

2. 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

3. 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 training4. 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

5. 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

Strategies to Enhance Fatty Acid Oxidation During Exercise:1. Caffeine ingestion before and during exercise:

stimulates lipolysisenhances FA oxidationdecreases 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 blooddoes not prolong exercise or spare glycogen

3. Maintain low insulin levels prior to exerciseavoid high glycemia foods that stimulate insulin and inhibit HSLpseudo-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 cellenhances fatty acid deposits in muscleenhances blood flow to the cellincreases 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

Nutrient Utilization During Exercise

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

Percent contribution of aerobic and anaerobic energy pathways during exercise:

Duration of Maximal Exercise Seconds Minutes

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 productionWhen 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

Effect of Training

% of Maximal Aerobic CapacityRest 25% 70% 100%

60

30

100

50

70

10

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

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 -oxidation

Protein Use During Exercise 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.

Protein Use During Exercise (cont.)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.

Protein RequirementsProtein 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.

Gender DifferencesGender 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.

Training-Induced Metabolic AdaptationsTraining-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

Influences of DietInfluences 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