Exercise physiology

Question 1

What is the Fick equation?

Answer 1

Equation used to calculate the VO2/VO2max 
VO2 = Q x (CaO2 - CvO2)
Where:
- Q = cardiac output 
- CaO2 = arterial O2
- CvO2 = venous O2

Question 2

What is the VO2 of a healthy 70kg male?

Answer 2

250 ml/min

3.6 ml of O2 consumed/min for each kg

Question 3

What is VO2 max?

Answer 3

highest O2 uptake during dynamic exercise

reached when O2 consumption remains at a steady state despite increase in workload

Question 4

What is anaerobic/lactate threshold?

Answer 4

the point where lactate begins to accumulate in the blood

*lactic acid is produced faster than it is metabolised leading to metabolic acidosis

Question 5

What adjustments occur in the cardiovascular system during exercise?

Answer 5

1. rise of cardiac output –> SV + HR

2. redistribution of blood to active muscles

Question 6

Where is there an increase in HR and vasoconstriction during exercise?

Answer 6

• HR is kept low by the action of the parasympathetic nervous system
• partial vasoconstriction arises from activity of the sympathetic nervous system
• in exercise there is a reduction in activity of the PNS and increase in activity of the SNS leading to increased HR and increased vasoconstriction
  The effect of this is increased venous return, increased EDV/preload and increased stroke volume (Starling’s Law)

Question 7

Why does the heart remodel as a long-term consequence of exercise?

Answer 7

• heart adapts to sustained increase in BP

- physiological change (increased cardiomyocytes + muscles mass)

Question 8

Compare heart remodelling in an athlete’s heart and a failing heart.

Answer 8

Athlete’s heart:

• increased muscle mass
• normal cardiac function
• reversible

Failing heart:

• increased muscle mass
• reduced cardiac function
• irreversible (cell death leading to fibrosis)

Question 9

Why does bradycardia occur in athletes?

Answer 9

• volume-induced cardiac hypertrophy
• increased resting EDV and SV
• causes reduction in HR

Question 10

Compare distribution of blood to the muscles at rest and at maximal exercise.

Answer 10

Rest: 20-25% of resting CO distributed to muscles (~1 L/min)

Maximal exercise: 80-90% increase in CO to muscles (~22L/min)
- brain: 750 –> 750; heart: 250 –> 1000

Question 11

Explain systemic mechanisms regulating distribution of blood.

Answer 11

• increased sympathetic outflow to heart + systemic resistance levels
• adrenergic receptors:
  1. alpha: vasoconstriction in gut and veins
  2. beta1: increased rate and force of myocardial contraction
  3. beta2: relax muscles, increase ventilation and O2 uptake and vasodilation of blood vessels (esp. to skeletal muscles)

Question 12

Explain local mechanisms regulating distribution of blood.

Answer 12

• involves blood vessels or surrounding tissues
• endothelial/myogenic mechanisms: NO relax smooth muscle cells resulting in vasodilation
• -> tissue factors: adenosine + inorganic phosphates, CO2, H+ and K+(released from contracting muscles)

Question 13

How does MAP change during exercise?

Answer 13

• Total peripheral resistance reduces (~ 1/3 of resting resistance) –> reduces diastolic pressure
• Mean arterial pressure = (CO x TPR) + CVP
• reduced TPR is offset by increased CO
• MAP increases only slightly

Question 14

What adjustments to the resp system occur during exercise?

Answer 14

• Pulmonary ventilation increases form 8l/min to 100l/min
• increase in ventilation due to increased respiratory rate and tidal volume (increased minute ventilation)
• in moderate exercise increased ventilation is proportional to work done
• in heavy exercise increased ventilation is not proportional to work done

Question 15

How does oxygen delivery to cells change during exercise?

Answer 15

• during exercise there is increased CO2, increased H+ and increase in temperature
• this reduced HbO2 binding affinity and therefore facilitates O2 delivery to cells

Question 16

What stimulates chemoreceptors during exercise?

Answer 16

Build up of CO2 –> major drive for ventilation

Plasma [K+] also increases during exercise = extra stimulus to peripheral chemoreceptors