Exercise Metabolism CONTD.

Question 1

What does measurement of pulmonary gas exchange do?

Answer 1

provides a noninvasive technique to ‘estimate’ fuel utilization during exercise and involves measurement of
respiratory exchange ratio (RER)

Question 2

When must measurements of pulmonary gas exchange be performed?

Answer 2

During steady-state exercise (that is below lactate threshold) to be reflective of gases in tissues.
- Assumes that “0” protein is used as a fuel during exercise.

Question 3

What is the ‘crossover’ concept?

Answer 3

The shift from fat to CHO metabolism as
exercise intensity ↑

Question 4

What is the crossover concept due to?

Answer 4

• Recruitment of fast muscle fibres (abundance of glycolytic enzymes, fewer lipolytic enzymes)
• Increasing blood levels of epinephrine stimulate glycolysis and lactate production (inhibits fat metabolism by reducing the availability of fat as a
  substrate).

Question 5

Why does fat metabolism increase as exercise duration increases (at 40-59% VO2 max)?

Answer 5

Increased rate of lipolysis
*Breakdown of triglycerides (by lipases) glycerol + FFA.
*Stimulated by rising blood levels of several hormones
(epinephrine, norepinephrine and glucagon)

Question 6

Glycogen is depleted during prolonged (>2 hrs) high intensity exercise, what does this cause?

Answer 6

-↓ rate of glycolysis and production of pyruvate (important precursor for Krebs-cycle intermediates)
-↓ rate of Krebs-cycle activity

Question 7

What is the only way fats are metabolized?

Answer 7

Via Krebs cycle oxidation

Question 8

What is FATmax?

Answer 8

Highest rate of fat oxidation. Reached just before lactate threshold.

Question 9

What is lactate threshold?

Answer 9

The point at which blood lactic acid rises
systematically during incremental exercise

Question 10

What % of VO2 max does lactate threshold occur at in UT individuals?

Answer 10

50-60% VO2 max

Question 11

What % of VO2 max does lactate threshold occur at in endurance TRN individuals?

Answer 11

65-80% VO2max

Question 12

What else can lactate threshold be referred to as?

Answer 12

Anaerobic threshold

Question 13

What is onset of blood lactate accumulation (OBLA)?

Answer 13

The point at which blood lactate reaches >4mmol/L

Question 14

How is accelerated glycolysis a possible explanation for lactate threshold?

Answer 14

NADH produced faster than it is shuttled into mitochondria (exceeds transport capacity of the hydrogen shuttle mechanism)
Failure of this mechanism to keep up with the rate of glycolysis results in pyruvate accepting un-shuttled H+ to
form lactate

Question 15

How is recruitment of fast-twitch muscle fibres during intense, rapid exercise a possible explanation for lactate threshold?

Answer 15

LDH isozyme (exact form of the enzyme) in fast fibres has
a greater affinity for attaching to pyruvate → promotes lactate formation

Question 16

How is reduced rate of lactate removal from the blood a possible explanation for lactate threshold?

Answer 16

Blood flow to muscle prioritized over tissues responsible
(e.g., liver) for removing lactate

Question 17

What are the 4 possible mechanisms for lactate threshold?

Answer 17

• Low muscle O2
• Accelerated glycolysis due to epinephrine
• Recruitment of fast-twitch fibres
• Reduced rate of lactate removal

Question 18

How fast is lactate removal from the blood post-exercise?

Answer 18

Rapid. <60 mins

Question 19

What is the main benefit of lactate?

Answer 19

It can be used as a fuel source during exercise (cori cycle)

Question 20

What is the most likely cause of DOMS?

Answer 20

Likely microscopic injury to muscle fibres, resulting in slow cascade of biochemical events leading to inflammation and edema within injured muscle.

Question 21

What is the Lactate shuttle?

Answer 21

Produced in one tissue and transported to another to be used as an energy source