Week 1 - Exercise physiology

Question 1

What is ATP and how does it function?

Answer 1

The ‘currency’ of a muscle.

Actin-myosin cross-bridge cycling
- ATP-energised myosin head attaches to the exposed actin binding site
- Power-stroke occurs as one Phosphate ion dissociates (ATP→ ATP + Pi)
- ADP dissociates from cross-bridge but actin-myosin link remains intact
- New ATP releases the myosin head from actin site + cycle starts again

Question 2

Key things about ATP?

Answer 2

→ ATP is an essential part of muscle contraction
→ Continued muscle contraction requires a continual supply of ATP

Question 3

What are the methods of ATP synthesis?

Answer 3

Phosphocreatine
Anaerobic glycolysis

Question 4

How does phosphocreatine synthesise ATP?

Answer 4

→ Stored locally in the muscle
→ Very fast + powerful but short-lived system
→ Initial 2-10s of exercise

Creatine stimulates oxidative phosphorylation + PC is resynthesised using mitochondrial ATP during rest + recovery.

Question 5

How does anaerobic glycolysis synthesise ATP?

Answer 5

→ Dehydration of glucose into pyruvate
→ Quite fast + powerful, 10s-2mins
→ During onset of exercise or high intensity exercise, pyruvate is converted to lactate (anaerobic pathway)

Question 6

How does aerobic ATP synthesis occur (oxidative phosphorylation)?

Answer 6

• Occurs exclusively in the mitochondria
• Can metabolise carbohydrates, lipids or proteins
• Primary energy source during sustained, moderate activity
• Oxygen is the final electron acceptor in the electron transport chain
• Most efficient + sustainable system
• Slowest system
• Reliant on oxygen delivery to cells

Question 7

What energy supplies are used at different stages of exercise?

Answer 7

ATP-PCr → first 10s of exercise, very rapid reduction, rapidly used up e.g. sprint

Anaerobic glycolytic → peaks @ 20s of exercise, slowly decreases

Aerobic (oxidative phosphorylation) → takes longer to get going (60s), at this point oxidative mechanisms take over, in steady sustained exercise - main system for ATP synthesis.

Question 8

Oxygen uptake

Answer 8

Oxygen being taken up and used by muscle cells

Question 9

How does oxygen uptake change in steady-state exercise?

Answer 9

from rest e.g. sitting in chair

Oxygen uptake gradually increases until it meets the demand of the work rate.

Question 10

What is a cardio-pulmonary exercise test? (CPET)

Answer 10

Incremental ramp test

Question 11

How does oxygen uptake change in incremental exercise from rest?

Answer 11

O2 uptake is parallel to workload until plateau
Plateau = VO2 max

CO2 starts to increase at faster rate than work rate after certain point - shows anaerobic systems have been implemented e.g. anaerobic glycolysis → get extra ATP to meet demand

Question 12

Oxygen deficit + debt?

Answer 12

O2 deficit repayed during recovery period

→ Recovery depends on fitness + level of exercise/level of exertion

→Period of time taken for O2 uptake to increase to meet demand of person - creates lag - when exercise starts O2 takes longer to reach demand

Question 13

Co-ordination of what is required to meet the demands of exercise?

Answer 13

Interactions between mitochondria, muscle, cardiovascular and respiratory systems

Question 14

Factors influencing oxygen delivery?

Answer 14

DO2 - O2 delivery
VO2 - O2 uptake

Question 15

What is VO2 max?

Answer 15

Maximum rate of oxygen your body is able to use during exercise.

Question 16

What is DO2?

Answer 16

O2 delivery

= Arterial oxygen content X Cardiac output

Question 17

Arterial oxygen content?

Answer 17

Oxygen bound to haemoglobin + oxygen dissolved in plasma

Question 18

Cardiac output?

Answer 18

Heart rate X Stroke volume

Question 19

What is VO2?

Answer 19

O2 uptake

= (CaO2 - CvO2) x (SV x HR)

Question 20

What is SV x HR

Answer 20

Cardiac output

Question 21

What is CaO2 - CvO2

Answer 21

Difference between venous O2 content + arterial O2 content

Question 22

What is CaO2 - CvO2 influenced by?

Answer 22

→ Muscle blood flow
→ Capillary density
→ Mitochondrial density
→ Hb-O2 affinity (Bohr effect)
→ Muscle mass
→ Muscle fibre type
→ Nutrition (substrate) availability

Question 23

What are the different systems that have a response to exercise?

Answer 23

• respiratory
• cardiovascular
• coronary circulation
• peripheral circulation

Question 24

Respiratory response to exercise?

Answer 24

→ Minute Ventilation increases:
- 8L/min at rest
- >200ml during exercise

→ Depth of breath increases before the rate of breath
Respiratory muscle uses:
- 2% of total VO2 at rest
- 11% of total VO2 during exercise
- Up to 50% of VO2 during exercise in the obese

Question 25

Why does depth of breathing increase before the rate of breath?

Answer 25

Due to afferent feedback from proprioceptors in exercising joints/muscles.

Question 26

Key points about respiratory response to exercise?

Answer 26

→ Ventilatory reserve exists beyond the observed ventilation during maximal exercise in healthy individuals
→ Most of the response comes from muscle/joint proprioceptors
→ Arterial PCO2 + PH remain relatively constant during most exercise intensities - means minimal role for chemoreceptors
→ Anticipatory response increases breathing rate + depth before exercise

Question 27

Cardiovasular response to exercise?

Answer 27

→ CO (HR x SV) - increases up to 5x during exercise (5L/min to 25L/min)
→ HR increases linearly with work rate up to 3X
→ SV increases rapidly at first then plateaus <2x
→ Cardiac output is the limiting factor to oxygen delivery in the healthy individual

Question 28

What is stroke volume?

Answer 28

The amount of blood pumped out of the left ventricle during each systolic cardiac contraction

Question 29

Why is cardiac output the limiting factor to O2 delivery?

Answer 29

Most people have cardiac limitation to their maximal exercise tolerance.

Blood is not pumped out to the muscles fast enough to supply oxygen to the working muscles during exercise.

Question 30

Coronary circulation response to exercise during exercise? (not maximal)

Answer 30

→ Coronary arteries receive blood during diastole

→ During exercise:
- increased flow to coronary vessels (due to increased cardiac output)
- vasodilation of coronary vessels
- reduced duration of diastole with increased HR

Question 31

Coronary circulation response during maximal exercise?

Answer 31

• 6x increase in oxygen demand from the left ventricle
• 5x increase in coronary circulation

Question 32

Peripheral circulation response to exercise?

Answer 32

→ Blood flow is redistributed from non-vital organs to the muscles e.g. digestive tract - 25% of VO2 @ rest, falls to 5% during vigorous exercise.

→ Blood flow to the skin increases for heat dissipation

→ Arterioles vasodilate - up to 25x increased blood flow

→ Mean arterial pressure (BP) remains fairly constant

Question 33

Why does blood pressure remain fairly constant during exercise?

Answer 33

Mean arterial pressure = CO x Total peripheral resistance

Mean arterial pressure means a combination of systolic + diastolic BP figures.

During exercise cardiac output increases and arterioles vasodilate which decreases the total peripheral resistance which is why BP remains mostly

Question 34

Physiological responses to endurance training at rest?

Answer 34

Stroke volume → increase
Heart rate → decrease
Cardiac output → same
a-vO2 →same
Systolic blood pressure → decrease
Diastolic blood pressure → same
Blood volume → increase
Capillary density → increase
Mitochondrial density → increase

Question 35

What does mitchondiral density do?

Answer 35

makes O2 uptake more efficient

Question 36

What is minute ventilation?

Answer 36

respiratory rate x tidal volume

Question 37

Physiological responses to endurance training at submaximal exercise?

Answer 37

Same as rest apart from:

→ increased a-vO2 difference
→ decreased diastolic blood pressure

Question 38

Physiological responses to endurance training at maximal exercise?

Answer 38

Stroke volume → increase
Heart rate → decrease or stay the same
Cardiac output → increase
a-VO2 difference → increase
VO2 → increase
Systolic BP → stay same
Diastolic BP → decrease
Blood volume → increase
Capillary density → increase
Mitochondrial density → increase

Question 39

Physiological responses to High Intensity Interval Training (HIIT)

Answer 39

Increase in:
→ VO2 peak
→ High density lipoproteins
→ Adiponectin, insulin sensitivity and b cell function
→ PGC
→ Maximal rate of Ca2+ uptake
→ Availability of nitric oxide
→ Cardiac function
→ Enjoyment of excercise
→ Quality of life

Decrease in:
→ Systolic + diastolic blood pressure
→ Triglycerides and fasting glucose
→ Oxidative stress and inflammation
→ FATP-1 and FAS

Question 40

Brief summary of exercise physiology?

Answer 40

• Exercise demands oxygen and a substrate are increase
• Chemical, mechanical and thermal stimuli affect alterations in function

→ The body firstly uses immediately energy sources that include ATP
→ Alternatively, utilisation of the Adenylate Kinase Reaction as well as the Phosphocreatine system are important
→ Resynthesis of ATP from energy-dense substrates via Glycolysis and fat metabolism