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Macronutrient Metabolism in Exercise and Training .ppt

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					  Integrated Metabolism

Macronutrient Metabolism
 in Exercise and Training
                 Fuel for Exercise

§   The fuel mixture that powers exercise
    generally depends on the intensity and
    duration of effort, and the exerciser’s fitness
    and nutritional status.
             Fuel and the Intensity
                   Continuum

§   For all-out, short-duration efforts the
    intramuscular stores of ATP and PCr provide
    the required energy for exercise.
§   Examples
    §   100-m dash
    §   Lifting heavy weights
           Fuel and the Intensity
                 Continuum

§   For intense exercise of 1 to 2 minutes
    duration, glycolysis provides the energy.
§   For top performance in all-out 2-minute
    exercise, a person must possess a well-
    developed capacity for both aerobic and
    anaerobic metabolism.
          Fuel and the Intensity
               Continuum

§   When exercise progresses beyond several
    minutes, the aerobic system predominates
    with oxygen uptake capacity becoming the
    important factor.
        Sources of Energy for
           ATP Synthesis

§   Liver and muscle glycogen
§   Triacylglycerols within adipose tissue and
    active muscle
§   Amino acids within skeletal muscle donate
    carbon skeletons
Carbohydrate Use During Exercise


§   Muscle glycogen and blood glucose serve as
    primary fuels during intense anaerobic
    exercise.
§   Glycogen stores also play an important role
    in sustained high levels of aerobic exercise.
§   The liver releases glucose for use by active
    muscle as exercise progresses from low to
    high intensity.
Carbohydrate Use During Exercise


§   Carbohydrate availability in the metabolic
    mixture controls its use.
§   Carbohydrate intake dramatically affects its
    availability.
Carbohydrate Use During Exercise


§   Trained muscle has an augmented capacity
    to catabolize carbohydrate aerobically for
    energy.
§   Due to an increased oxidative capacity of the
    mitochondria and increased glycogen
    storage.
       Carbohydrate Versus Fat

§   Compared to fat, carbohydrate generates
    about 6% greater energy per unit oxygen
    consumed.
              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.
                Influence of Diet

§   A carbohydrate-deficient diet rapidly
    depletes muscle and liver glycogen.
§   Low carbohydrate levels profoundly affect
    both anaerobic capacity and prolonged, high
    -intensity aerobic exercise.
               Influence of Diet

§   When carbohydrates are low, exercise
    intensity decreases to a level determined by
    how well the body mobilizes and oxidizes fat.
§   Carbohydrate depletion during prolonged
    exercise coincides with a reduced exercise
    capacity.
           Low Carbohydrate Diets

§   These diets rapidly deplete muscle and liver
    glycogen.
§   A low-carbohydrate diet makes it extremely
    difficult, from the standpoint of energy
    supply, to engage in vigorous physical
    activity.
         Fat as an Energy Substrate

§   Fat supplies about 50% of the energy
    requirement during light and moderate
    exercise.
§   Stored fat becomes more important during
    the latter stages of prolonged exercise.
§   During prolonged exercise, fatty acids
    provide more than 80% of the energy
    requirements.
     Sources of Fat During Exercise

§   Fatty acids released from adipocytes
§   Delivered to muscles as FFA bound to
    plasma albumin
§   Circulating plasma triacylglycerol bound to
    lipoproteins as very low-density lipoproteins
    and chylomicrons
§   Triacylglycerol within the active muscle
    itself
         Fat as an Energy Substrate

§   Aerobic training increases fatty acid
    oxidation, particularly the fatty acids derived
    from active muscle during moderate-
    intensity exercise.
        Fat as an Energy Substrate

§   Enhanced fat oxidation spares glycogen.
§   Trained individuals may exercise at a higher
    absolute levels of submaximal exercise
    before experiencing glycogen depletion.
                Influence of Diet

§   A high-fat diet stimulates adaptations that
    augment fat use.
§   Reliable research has not yet demonstrated
    consistent exercise or training benefits from
    such dietary modifications.
       Endocrine Regulation of
         Substrate Utilization

§   Epinephrine, norepinephrine, glucagon, and
    growth hormone activate lipase
§   Causes lipolysis and mobilization of FFA
    from adipose tissue
§   Exercise increases plasma levels of
    lipogenic hormones, increasing the supply
    of fatty acids to the muscles.
                        Hormones

n       Hormones influence substrate:
    §    Availability
    §    Mobilization from body tissue stores
    §    Uptake at tissue site of utilization
    §    Uptake within tissue itself
    §    Trafficking among storage, oxidation, and/or
         recycling
             Protein Use During Exercise

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

§   Exercise in a carbohydrate-depleted state
    causes significant protein catabolism.
§   Protein synthesis rises markedly following
    both endurance and resistance-type
    exercise.
            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.

				
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