Physiology of Exercise

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					Module: Principles of

Session 2: Exercise Physiology
         James Fern
        Learning Outcomes
 LO1   - Understand the diverse requirements
  for ATP production and the different
  metabolic pathways that meet these
 LO2 - Be able to explain the different
  demarcations that separate the exercise
 LO3 - Be able to list the adaptations to
  training that lead to improved exercise
            Biological Work
In pairs discuss and create a list of tasks the
body performs everyday that can be described
as “biological work”?

                Muscle Contraction
                Digestion & Absorption
                Gland Function
                Establishment of Gradients
                Synthesis of New Compounds

First Law of Thermodynamics
 Conservation of Energy
   Energy can not be “Created” or

 Our body simply transforms energy
What is ATP?
o   Adenosine molecule bound to three
    phosphate groups.
o   Chemical “fuel” for all processes in body
o   Food “energy” (kcals) used to “rebuild” ATP
o   Potential Energy
o   Phosphate bonds - “high energy bonds”

     1.   How much can we “store” in the human body?
     2.   Where do we store it?
 Aerobic vs. Anaerobic
  Energy Production
    No  O2 required/available
    for energy production

 Aerobic:
     O2required for energy
               Metabolic pathways
   To maintain a constant supply of ATP
    several metabolic pathways are used.
        Some are located in the cytosol and some in
         the mitochondria.
1. Cytosol
  ATP production via the anaerobic breakdown
  of PCr, glucose, glycerol and carbon fragments
  of deaminated amino acids.
2. Mitochondria
  Aerobic ATP production via the Krebs cycle, β
  oxidation and the electron transport chain
         Phosphocreatine (PCr)
 Acts as an energy reservoir to overcome
  the storage limitations of ATP.
 Fat and glycogen are the major sources
  for maintaining ATP synthesis.
 However some comes directly from the
  splitting of a phosphate from PCr.
 Speed of ADP phosphorylation from PCr
  considerably exceeds anaerobic energy
  transfer from glycogen, because of the
  activity rate of creatine kinase (CK).

    What happens if intense exercise exceeds
    ~10 seconds?
Cellular oxidation
       Majority of energy for
        phosphorylation comes from the
        oxidation (burning) of dietary
        carbohydrates, lipids and proteins.
       This process continually provides
        hydrogen atoms from the catabolism
        of these macronutrients.
       The mitochondria contain carrier
        molecules that remove electrons
        from hydrogen (oxidation) and
        eventually pass them onto oxygen
       ATP synthesis occurs during these
        oxidation-reduction reactions that
        take place in the ETC.
         Electron Transport Chain
   During cellular oxidation hydrogen atoms are not
    merely turned “loose” into intracellular fluid.
       Instead, dehydrogenase enzymes catalyze hydrogen’s
        release from the nutrient substrate.
   Co-enzyme NAD+ and FAD accept pairs of
    electrons (energy) from hydrogen.
       The substrate is oxidized by giving up its hydrogen - by
        gaining this hydrogen NAD+ and FAD reduce to become
        NADH and FADH2.
   The NADH and FADH2 formed from the
    breakdown of food provide energy-rich molecules
    as they are carrying electrons with high energy-
    transfer potential.
          Electron Transport Chain
   Located on the inner membrane of
    the mitochondria cytochromes pass
    along the electrons carried by
    NADH+ and FADH2.
    Substrate Phospharylation
 Catabolism   of the macronutrients serves
  one vital function - to phosphorylate ADP
  to ATP.
 This involves 3 important stages:
  Stage 1. Digestion and absorption of large food molecules into
  smaller subunits for use in cellular metabolism.

  Stage 2. Degradation of amino acids, glucose and fatty acid and
  glycerol units into acetly-coenzyme A. Small amount of ATP
  produced at this stage.

  Stage 3. Within in the mitochondria acetly CoA degrades to CO2
  and H2O with a large amount of ATP produced.
                                  Refer to handout 1 (Fig 6.9)
                      Energy from food
   CHO is the only substrate who’s stored energy
    generates ATP anaerobically (vital for nervous tissue)
       Important implications for performances that require rapid
        energy release above levels supplied by aerobic

 Aerobic  hydrolysis of CHO occurs
more rapidly than energy production
from fatty acid breakdown, thus
depleting glycogen reserves early
during endurance performance
significantly reduces power output in
the later stages.
List   some common steps taken to prevent this.
                  Energy from food
Glycolysis (see handout 2, Fig 6.11)
 Occurs in the cytosol.
 A cells capacity for glycolysis is crucial for
  performances requiring max effort lasting upto 90
 PFK vital role in:
        Conversion of fructose 6-phosphate to fructose 1, 6-
        1 glucose (6 carbon) converts to 2 pyruvate (3 carbon).
   Fast Twitch fibres contain comparatively large quantities of PFK
             Glucose                                   Anaerobic

 Energy                      H+

          Pyruvic Acid (2)              Lactic Acid (2)
                                        Inter Cellular Fluid
                       CO2   &    H+
Acids                                                     Aerobic
          Acetyl Co-A (2)

                                   Energy          ATP
              Cycle                H+        To ETC
       ATP – CP Energy System

Small amount of ATP stored
 80-100 g in whole body, must be re-synthesized
 Enough for a few seconds of explosive all-out exercise

CP: immediate energy source for ATP rebound
 CP stored in larger quantities
      Where and how much?

             1. Stored in the cytosol
             2. Up to 6 times more CP
                than ATP can be stored.
                               Energy Transfer Systems and Exercise
 % Capacity of Energy System

                                             ATP - CP

                               10 sec   30 sec            2 min   5 min +
Capacity for aerobic
resynthesis of ATP
          O2 uptake during exercise
   Oxygen Uptake: Use of oxygen
    by the cells for aerobic
       VO2 – Relative (ml/kg/min) and
        Absolute (l/min)
       VO2max = Max O2 uptake, transport
        and utilization possible by individual
       Quantification of Aerobic Capacity
VO2max : Max Oxygen Uptake
     Further increases in exercise intensity
      (further energy requirement), results in
      NO increase in VO2.
     Additional energy is produced via anaerobic
                                                Exercise of Increasing Intensity
Oxygen Consumption (ml/kg/min)





                                      Stage 1    Stage 2   Stage 3   Stage 4       Stage 5   Stage 6
    What effects our capacity to produce
 Nutritional status
 Training status
 Acid-base balance (cellular environment)
 Genetics
         Energy Systems and Exercise

   Anaerobic/Aerobic energy is always being
       Exercise intensity/duration determines the ratio or
        relative contribution.
   How can we estimate the ratio between
    aerobic vs. anaerobic energy production during
    a given task?
            •Respiratory exchange ration: RER
              •VCO2/VO2 - ranges from 0.7~1.15
              •Lipid = 0.7
              •CHO = 1.00
                Lactic Acid

Byproduct of Anaerobic Metabolism.


Energy                      H+

         Pyruvic Acid (2)        Lactic Acid (2)
                         Lactic Acid
   Causes Fatigue
        Irritation of local muscle contractile function
        Decreased pH of cellular environment & bloodstream
        Accelerated depletion of glycogen stores
   Training can increase lactate tolerance and decrease
    lactate formation for a given workload.

   How?
    Possibly by limiting the ability of the enzyme LDH
    (lactate dehydrogenase) to compete for pyruvate.

                                            (Wasserman et al., 1985)
Blood Lactate Threshold (Tlac)

 The  demarcation between the moderate
  and heavy exercise domains.
 1st increase in blood lactate above
  resting value during incremental
 Exercise intensity at Tlac is associated
  with a non-linear increase in VE (Tvent).
 Blood Lactate Threshold (Tlac)
 Constant   rate intensity exercise below Tlac
  Can be sustained without an appreciable
  increase in blood lactate.
  HR and ventilation reach an early steady

  state, subjects perceive the exercise to be
  relatively easy.
  Can be sustained for several hours.

  What factors will lead to termination?
      Blood Lactate Threshold (Tlac)
   If constant intensity                  12

    exercise is                            10                 Severe
    performed just
    above the Tlac then
    blood lactate           Lactate (mM)

    increases above                        4

    resting levels and                     2                                      Moderate
    eventually stabilizes                  0

    around 2-5mM.                               0   10   20        30

                                                               Time (mins)
                                                                             40      50      60
Effect of Training on Blood Lactate /
          Lactate Threshold
[Blood Lactate]



                  25%   50%         75%         100%
                        Percent of VO 2 max
What Effects Lactate Threshold ?

     Aerobic capacity
     Fiber type

 Training
     Aerobic capacity
     Fiber type
     Adaptations
Physiological Adaptations with Training

  in capillaries ( Density)
  aerobic enzymes
  mitochondria (# and size)
  Pain tolerance to lactic acid
        Blood Lactate Threshold

 Lactate   appearance in the bloodstream
     Powerful predictor of aerobic exercise
     Higher Tlac = Improved “performance”
     Lactate curve shifts to the right.
     Lactate Processing

                    Cori Cycle

Muscle Cell                                Liver

Glucose                                    Glucose /

   Pyruvate                           Pyruvate

          Lactate                Lactate
 Skinner,  J.S., McLellan, T.H., (1980), The
  transition from aerobic to anaerobic
  metabolism, Research Quarterly for
  Exercise and Sports, 51, 234-48.
 Wasserman, K., Beaver, W.L., Davis, J.A.,
  (1985), Lactate, pyruvate and the lactate-
  to-pyruvate ratio during exercise and
  recovery, Journal of Applied Physiology,
  59, 935-40.
     Recommended reading
 McArdle,  Katch & Katch 5th Ed - Energy
 transfer in the body (Section 2, Ch6, pp.