Response to Exercise

1
Response to Exercise
2
Muscular Response to Exercise

• Metabolic changes w/in a horse are more extreme
  than those of elite human athletes.
• Horses
• Very high VO2 max uptakes
• Very high levels of enzymatic activity
• Able to produce tolerate high levels of muscle
  lactate

3
Muscular Response to Exercise

• Oxygen uptake
• O2 uptakes increases
• 5ml/min/kg at rest
• 160ml/min/kg high intensity exercise
• Primarily in the locomotory muscles
• Hemoglobin
• Replaces download O2 w/ either
• Hydrogen ions
• CO2

4
Muscular Response to Exercise

• Blood Flow
• Increases in during exercise
• At rest, 15 or 4 liters/min of cardiac output is
  used by muscle.
• During exercise, muscle may demand up to 80 or
  200 liters/min of the total cardiac output.
• 40-fold increase

5
Muscular Response to Exercise

• Temperature
• As muscle activity increases, there is a
  progressive increase in muscle temp.
• 1oC increase can improve enzyme activity.
• Overheating has been associated with
• Weakness
• Fatigue
• Tissue damage

6
Muscular Response to Exercise

• Use of fuel stores
• Low intensity
• Type I, IIA, and then IIB
• Repletion opposite order
• Low to moderate intensity
• FFA primary fuel source during aerobic activity
• High intensity
• All muscles fibers recruited
• Glycogen usage and depletion greatest in type IIB
  least in type I

7
Muscular Response to Exercise
IIB
IIA
I
8
Muscular Response to Exercise

• Lactate Kinetic
• Anaerobic pathways recruited at 11-33 mph
• Speed at which this occurs varies with
• Breed
• Type of training
• Muscle fiber type
• Health
• Ground conditions
• Lactic acid dissociates into Lactate ions and H
  ions.
• It diffuses from areas of high conc. to low conc.

9
Muscular Response to Exercise

• Lactate Accumulation
• Its now accepted that with almost all
  intensities of exercise a degree of anaerobic
  metabolism and production of lactate occurs.
• At the lower intensities, very little or no
  change is seen in blood lactate concentrations.
• Removal keeps pace with production

10
Muscular Response to Exercise

• As intensity of exercise increases and
  progressively more type II fibers (and then
  especially type IIB (low oxidative fibers) are
  recruited
• energy production becomes increasingly dependent
  on
• anaerobic metabolism
• consequent formation of lactate
• muscle lactate concentrations have been reported
  in excess of 200 mmol/kg of dry weight or 20-35
  mmol/l.
• With the associated proton accumulation leading
  to a marked decrease in pH.

11
Muscular Response to Exercise

• With increasing intensity of exercise there is at
  first only a gradual increase in blood or plasma
  lactate concentration.
• But, a point is reached where a sharp rise in
  circulatory levels occurs.
• This point is referred to as the anaerobic
  threshold or more correctly, the onset of blood
  lactate accumulation (OBLA) or the velocity at
  which blood lactate reaches 4 mmol/l (VLA4) .

12
Muscular Response to Exercise
13
Muscular Response to Exercise

• Anaerobic threshold (OBLA) generally occurs
  between a blood lactate concentration of 2 and 4
  mmol/liter.
• For comparative purposes, OBLA generally has been
  given an arbitrary set point of 4 mmol/liter.
• OBLA occurs at an intensity of exercise below
  VO2max,
• this point depends on the fitness of the horse.

14
Muscular Response to Exercise

• At lower intensities of exercise, peak
  concentrations of blood or plasma lactate are
  seen immediately on the cessation of exercise.
• Below 10 mmol/l blood lactate conc. fall as soon
  as exercise is over.
• Following cessation of high-intensity exercise,
  lactate disappearance normally occurs at a linear
  rate.
• This can be hastened by submaximal exercise.
• Training also may increase the rate of removal of
  lactate.

15
Muscular Response to Exercise
60
40
16
Muscular Response to Exercise

• In the case of soreness
• Related to right after exercise
• Production of lactic acid
• Effects of the hydrogen ions
• Tissue edema
• Normally disappears shortly after exercise
• Warming down helps
• Related to later after exercise
• Delayed onset muscle soreness (DOMS)
• Structural damage
• Release of intracellular contents
• Creatine phosphokinase (CK)
• Aspartate amino transferase (AST)
• Subsequent inflammation

17
Regeneration of a Skeletal Muscle fiber

• Skeletal muscle
• 1. healthy fiber showing an intact sarcolemma.
• 2. Multi. subsarcolemma nuclei.
• 3. myofibrils in order
• Segmental disruption of fiber
• 4. w/ intact basement membrane.

Proliferation of the sarcolemmal membrane occurs
to compartmentalize the damaged area.
18
Regeneration of a Skeletal Muscle fiber

• 5 6. Macrophages infiltrate and phagocytize
  necrotic debris.
• 7 8. Satellite cells are activated and
  replicated to form myoblasts.
• 9. Myoblasts fuse to form myotubes.

19
Regeneration of a Skeletal Muscle fiber

• Synthesis of new myofilaments and formation of
  myofibrils progress, and myonuclei remain in
  central position.
• A repaired fiber with peripherally displaced
  nuclei following complete myofibrillogensis.

20
Muscular Response to Exercise

• Following exercise, a variable swelling of
  mitochondria with rounding and increased
  prominence of individual cisternae occurs.
• Restoration to normal ultrastructural appearance
  occurs about 1 hour after completion of exercise
• and at the same time as muscle pH and temperature
  return to normal.

21
Muscular Response to Exercise

• In addition to mitochondria changes, swelling of
  the SR has been observed.
• This may be associated with impaired SR function,
  as indicated by up to a 50 reduction in Ca2
  uptake by equine muscle following maximally
  fatiguing exercise.

22
Muscular Response to Exercise

• Muscle buffering
• Ability to both soak up and remove hydrogen ions
  from its cells.
• Compare to man horses have a 60 greater muscle
  buffering capacity.
• Potassium loss
• Intensity and duration of exercise can change
  plasma electrolyte concentrates.
• Sodium, potassium, and chloride
• Plasma K can increase 4 mmol/l to 10 mmol/l
• High H ions can impair Na-K pump

23
Muscular Response to Training

• Adaptations that take place w/in individual
  muscle fibers as a result of training depends on
• Age of horse
• Previous level and type of training
• Genetic make-up
• Intensity and type of work on muscle fibers
• Many changes that occur during training are more
  pronounced when a horse is trained for the first
  time.

24
Muscular Response to Training

• Top 10 ways in which muscle function can be
  improved in response to training.
• Increased capillarization
• Increased transit time
• Increased arterial-venous difference
• Increased oxidative capacity
• Increased activity of aerobic enzymes
• Increased capacity to use fat as a fuel
• Increased myoglobin content of muscle
• Increased glycogen content
• Increases in anaerobic muscle enzymes
• Improved motor skill

25
Muscular Response to Training

• Increased capillarization
• Increases capillary supply to muscle fiber
• Capillary density vs capillary number
• Capillary supple per unit volume of muscle fiber
• Training type primarily aerobic
• Muscle diameter vs capillary number
• Increased transit time
• Network of capillaries increase
• Blood flow is then slower transit time longer
• More time in which equilibrium can occur between
  oxygenated blood and working muscles.

26
Muscular Response to Training

• Increased arterial-venous difference
• Leads to more O2 being uploaded at muscle
• Greater extraction of O2 from bloodstream
• Venous blood lower in O2 content
• Increased oxidative capacity
• Shift in fiber type functions
• Type IIB to IIA
• Increase overall capacity of muscle to use O2 to
  breakdown fuel aerobically.
• Downside may loose speed and strength

27
Muscular Response to Training

• Increased activity of aerobic enzymes
• Citrate synthase (CS)
• Produces citrate in TCA cycle
• 3-hydroxyacyl-CoA dehydrogenase (HAD)
• beta-oxidation
• Increased capacity to use fat as a fuel
• Training increases mobilization of FFA from
  adipose tissue
• Glycogen sparing effect and thus delays onset of
  fatigue

28
Muscular Response to Training

• Increased myoglobin content of muscle
• Major increase seen type I fibers
• Leads to an increased O2 storage capacity
• Myoglobinuria dark urine, severe damage to
  muscle fibers
• Increased glycogen content
• Increases fuel store available for both anaerobic
  and aerobic energy production
• Storage is found mostly in horses with lots of
  large type IIB fibers

29
Muscular Response to Training

• Increases in anaerobic muscle enzymes
• Phosphofructokinase (PFK)
• Lactate dehydrogenase (LDH)
• Glycogen phophorylase (PHOS)
• Improved motor skill
• Movement skills requires a degree of conscious
  effort.
• With increase in skill come an increase in
  efficiency

30
The Effects of Detraining

• The period following either complete cessation of
  training or a marked decrease in training
  intensity.
• Training-induced adaptations in muscle is far
  slower in the horse than in other athletic
  species.
• Responses of the muscle to exercise are
  maintained for at least several weeks.
• Enzymatic activities and glycogen content may
  take up to 3 months to be reversed