Exercise

Question 1

What is the major determinant of maximal oxygen uptake?

Answer 1

Maximal cardiac output

Question 2

What anatomical and physiological capacities facilitate huge O2 fluxes?

Answer 2

• Heart size as a percentage of body weight. Elite dogs and horses hearts are about 2% of their body weight
• Spleen, horses are able to increase the CaO2. The blood is hypoxic because it is spending less time in the capillaries, but there is an increase in hematocrit so it evens out

Question 3

How much arterial O2 can running horses extract?

Answer 3

90%

Question 4

What relates closely to max VO2?

Answer 4

Mitochondrial density

Question 5

What are the VO2 response at the onset of moderate exercise?

Answer 5

• Capillary RBC velocity and flux increase with first contraction cycle
• O2 extraction goes down at the onset, this is because it is not the limiting kinetic factor

Question 6

What are some truths about microcirculation?

Answer 6

• Hematocrit in the capillaries is as low as 20-30% of systemic
• There are no anoxic loci within myocytes
• No precapillary sphincters
• No capillary recruitment. Most contain moving RBC

Question 7

During exercise what happens to ventilation?

Answer 7

It is increase because of increased breathing frequency and tidal volume

Question 8

What is phase I of the onset of exercise?

Answer 8

Increase in CO2 at the lungs because of increased cardiac output and feed-forward control by muscle receptors

Question 9

What is Phase II of the onset of exercise?

Answer 9

Arrival of venous blood from exercising muscles at the lung. Ve elevated to a steady state

Question 10

What is Phase III of the onset of exercise?

Answer 10

Steady state at which the level of ventilations is exactly regulated to maintain arterial PCO2 at 40mmHg

Question 11

What is different about respiratory frequency in quadrepeds?

Answer 11

Their breathing frequency is coupled with their stride. Frequency of breathing is locked in at certain speeds and in order to increase Ve they have to increase tidal volume

Question 12

What happens to arterial PCO2 in the horse during exercise?

Answer 12

Increases due to hypoventilation

Question 13

Why do horses allow their PCO2 to rise during exercise?

Answer 13

If they were to hyperventilate instead, the Va that would incur would surpass the limit of the respiratory system. By hypoventilation they keep the Va at a manageable level

Question 14

What are the three domains of intensity of constant speed exercise?

Answer 14

• Moderate- below lactate threshold
• Heavy- above lactate threshold
• Severe- substantially above the lactate threshold. VO2 nor blood lactate can be stabilized

Question 15

What happens to VO2 in moderate exercise?

Answer 15

Rises rapidly and reaches an early steady state

Question 16

What happens to VO2 in heavy and severe exercise?

Answer 16

It rises rapidly at first, then there is a slow component that delays the onset of a steady state