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Exercise Physiology & Training > Ch 4: Exercise Metabolism > Flashcards

Ch 4: Exercise Metabolism Flashcards

1
Q

At rest, is ATP produced aerobically or anaerobically?

A

At rest, ATP is produced almost 100% aerobically

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2
Q

Oxygen consumption (VO2) provides an index of…

A

aerobic ATP production (aerobic metabolism)

During rest: 3.5 ml/kg/min

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3
Q

Blood lactate levels at rest

A

Because oxygen is readily available at rest, pyruvate enters the Krebs cycle rather than being converted to lactate… so blood lactate levels are low.

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4
Q

ATP and VO2 at the Onset of Exercise

A
  • ATP demand increases instantaneously
  • VO2 does not increase instantaneously
  • initial ATP production is through anaerobic pathways
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5
Q

For light to moderate exercise, steady state VO2 occurs within

A

1-4 minutes

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6
Q

Oxygen deficit

A

Lag in VO2 (oxygen consumption) at the onset of exercise

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7
Q

Why do trained individuals have lower oxygen deficit?

A
  • better developed aerobic bioenergetic capacity due to cardiovascular or muscular adaptations to exercise training

cardiovascular adaptations= more capillaries
muscular adaptations= greater mitochondrial value

  • aerobic metabolism is active earlier and less lactic acid is produced
  • reach steady state VO2 earlier
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8
Q

Why does oxidative phosphorylation not achieve full activation instantaneously at exercise onset?

A
  1. Inadequate oxygen supply to muscles at exercise onset
    • Mitochondria may not have oxygen molecules present and therefore available to participate in the ETC… thus restricting aerobic ATP production.
    • This may hold true for high intensity work
  2. Delay in stimuli (ADP and Pi concentrations) to fully activate oxidative phosphorylation
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9
Q

Oxygen Debt

A

Elevated VO2 (above resting levels) following exercise

  • it takes time for oxygen consumption to return to the levels it was at rest… goes down in curvilinear way
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10
Q

Rapid Phase of O2 debt

A
  • Resynthesis of PC
  • Restoration of muscle and blood oxygen stores
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11
Q

Slow Phase of O2 debt

A
  • Elevated HR and breathing
  • Elevated body temperature
  • Elevated hormones (epinephrine & norepinephrine)
  • Conversion of lactic acid to glucose (gluconeogenesis)
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12
Q

EPOC

A

excess post-exercise oxygen consumption

aka oxygen debt

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13
Q

Why is EPOC greater following High Intensity Exercise?

A
  • higher body temperature
  • greater depletion of PC (additional O2 required for resynthesis)
  • greater blood concentrations of lactic acid (additional O2 required for greater level of gluconeogenesis)
  • higher levels of blood epinephrine and norepinephrine
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14
Q

Bioenergetic Pathways for Short-term high-intensity exercise…

When does ATP come from ATP-PC system or glycolysis?

A
  • ATP comes mostly from anaerobic pathways

Whether ATP provision comes from the ATP-PC system or glycolysis depends on the length of the activity
- First 1-5 sec: ATP-PC system
- > 5 sec: shift to glycolysis
- > 45 sec: anaerobic and aerobic

at 60 seconds: 70% anaerobic/ 30% aerobic
at 2-3 minutes: 50%/50%

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15
Q

At the onset of exercise _____ is the main source of energy

A

Phosphocreatine

  • drops significantly
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16
Q

Because we use all PC up, we shift to

A

glycolysis

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17
Q

Bioenergetic Pathways for Prolonged Exercise

(How is ATP produced?)

A
  • ATP production primarily from aerobic metabolism
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18
Q

Steady state oxygen uptake can generally be maintained during prolonged submaximal exercise, except for in:

What causes the drift?

A
  1. Moderate intensity in a hot and humid environment
  2. High intensity in a thermoneutral environment

There is a drift in steady state caused by:
- increase in body temperature
- increase in intensity = increase in hormones and metabolic rate

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19
Q

VO2 max

A

Maximum capacity to deliver and utilize oxygen during exercise

  • When an increase in workload no longer evokes an increase in O2 consumption

Affected by genetics and training

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20
Q

Physiological factors that influence VO2 max

A
  • maximum ability of cardiorespiratory system to deliver oxygen to the muscle
  • ability of muscles to use oxygen and produce ATP aerobically
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21
Q

Fick Equation

A

VO2= CO x (a-v O2 diff)

describes the relationship between oxygen consumption, cardiac output and atrial venous oxygen difference

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22
Q

During early incremental exercise (lower intensity) most ATP comes from

A

aerobic sources

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23
Q

As exercise gets harder (higher intensity) blood lactate concentration

A

increases

24
Q

Lactate production occurs in

A

skeletal muscle- fast twitch

25
Q

Lactate removal occurs in

A

liver, heart, muscle

26
Q

Lactate threshold

A

aka “Anaerobic Threshold”
OBLA: onset of blood lactate accumulation

the point at which there is a sudden increase in the blood lactate concentration during incremental exercise

  • represents an increased reliance on glycolysis
27
Q

Possible explanations for Lactate Accumulation with Incremental Exercise

A
  1. Low muscle oxygen (hypoxia)
  • low levels of oxygen in individual muscle cells
  1. Accelerated glycolysis
  • increased epinephrine and norepinephrine at 50-60% VO2 max… stimulates glycolytic rate
  • H+ from NADH+H+ that is produced in glycolysis must be shuttled into mitochondria
  • During intense exercise, shuttling is not fast enough, so NADH + H+ accumulates
  • to regenerate NAD to keep glycolysis going NADH+H donates its H+ ions to pyruvate and lactate is formed
  1. Recruitment of fast-twitch fibers (harder exercises)
  • Type of lactase dehydrogenase present in fast twitch fibers promotes the formation of lactic acid from pyruvic acid
  1. Reduced lactate removal
  • as exercise intensity increases, muscles receive a greater % of cardiac output
  • blood is shunted away from the liver (a site of lactate removal)

the liver forms glucose from lactate (gluconeogenesis)

28
Q

Intracellular Lactate shuttle

A

Lactate is produced in the cytoplasm of a muscle fiber and can be taken up by the mitochondrion within the same fiber and used as fuel

29
Q

Intercellular Lactate shuttle

A

25% is used for gluconeogenesis in the liver

75% is used in muscle aerobic metabolism

Cori Cycle
- lactate in the blood travels to slow-twitch myocytes and cardiac myocytes, where it is then converted back to pyruvate

30
Q

Lactic acid is removed more rapidly with

A

light exercise in recovery

optimal intensity: 30-40% of VO2 max

31
Q

Lactic acid removal post exercise evidence

A
  • 70% of lactic acid is oxidized (used as a substrate by heart and skeletal muscle)
  • 20% is converted to glucose
  • 10% is converted to amino acids
32
Q

Where does the lactate threshold appear in untrained individuals vs trained individuals?

A

untrained: 50%-60% of VO2 max

trained: 65%-80% of VO2 max

33
Q

Lactate threshold represents an increased reliance on

A

glycolysis

34
Q

DOMS

A

delayed onset muscle soreness

  • occurs 24-48 hours after exercise
35
Q

Reasons it is not true that lactate causes DOMS

A
  • lactic acid removal is rapid and levels return to normal within an hour following exercise
  • soreness is rare following routine exercise
36
Q

What causes DOMS?

A

microscopic injury to muscle fibers resulting in a slow series of biochemical events leading to inflammation and swelling within the injured muscle

37
Q

effects of training on lactate threshold

A

trained individuals can reach higher work rates before LT occurs

38
Q

RER

A

Respiratory Exchange Ratio

  • estimates contribution of carbohydrate and fat to energy metabolism during exercise

aka Respiratory Quotient (R or RQ)

VCO2/VO2

39
Q

For RER to be used as an estimate of substrate utilization during exercise…

A

must be at steady state

40
Q

RER= 0.70

A

100% fat
0% carbohydrates

41
Q

RER= 0.85

A

50% fat
50% carbohydrates

42
Q

RER= 1.00

A

0% fat
100% carbohydrates

43
Q

Using RER to estimate fuel utilization assumes that…

A

protein is not used as a fuel during exercise

44
Q

Protein contribution in fuel

A
  • proteins contribute less than 2% of the substrate used in exercise less than one hour
  • may reach 5-10% during the final minutes of prolonged exercise (3-5 hours)

proteins play a minor role as a substrate during exercise

45
Q

How does diet govern fuel selection during exercise?

A

high fat, low carbohydrate promote high fat metabolism

46
Q

How does exercise intensity govern fuel selection during exercise?

A
  • low intensity (<30% VO2 max) exercise relies on fat for fuel
  • high intensity (>70% VO2 max) exercise relies on carbohydrates
47
Q

How does exercise duration govern fuel selection during exercise?

A

low intensity prolonged exercise increases fat utilization

48
Q

How does exercise training govern fuel selection during exercise?

A

endurance trained individuals use more fat and less carbohydrates than less-fit individuals during prolonged exercise at the same intensity

49
Q

Practical use of the lactate threshold?

A
  • predicting endurance performance
  • a marker of training intensity
50
Q

As exercise intensity increases, how is fat and carbohydrate metabolism affected?

A

As the exercise intensity increases, there is a progressive increase in carbohydrate metabolism and a decrease in fat metabolism.

51
Q

The “crossover point”

A

As the exercise intensity increases, there is a progressive increase in the contribution of carbohydrate as a fuel source.

  • as the exercise increases above the crossover point, a progressive shift occurs from fat to carbohydrate metabolism
52
Q

What causes the “crossover”?

A
  1. recruitment of fast fibers

fast fibers have more glycolytic enzymes but less mitochondrial and lipolytic enzymes (enzymes responsible for fat breakdown). Meaning they are more equipped to metabolize carbohydrates.

  1. increasing blood levels of epinephrine

High levels of epinephrine increase phosphorylase activity, which causes an in-crease in muscle glycogen breakdown; this results in an increased rate of glycolysis and lactate production. Increased production of lactate inhibits fat metabolism by reducing the availability of fat as a substrate.

53
Q

the absolute amount of fat metabolized during exercise is typically greatest at

A

higher intensities that are below the lactate threshold

54
Q

At higher intensities, the total energy expenditure

A

increases, even if the contribution of fat as fuel decreases

55
Q

Optimal exercise intensity to use fat as a fuel source depends on

A
  • percentage of energy derived as fat
  • total energy expenditure
56
Q

Carb or fat metabolism during prolonged moderate intensity exercise?

A

during prolonged moderate intensity exercise there is a shift from CHO to fat metabolism

  • lipolysis (breaking down fats) is a slow process and the rate increases only after several minutes of exercise

Exercise Physiology & Training (10 decks)

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