Lecture 33: Cardiovascular Response to Exercise and Physiological Adaptations

Question 1

What is the overall effect on the heart during exercise?

Answer 1

• Decrease parasympathetic activity
• Increase sympathetic activity
• Increase CO

Question 2

What happens to our heart rate during exercise? Give the units.

Answer 2

beats/min
▪ Increases from resting rate (~60bpm)
▪ Max HR = 220 – age
▪ Increases by 3-4 times

Question 3

What happens to stroke volume during exercise? Give the units.

Answer 3

mL/beat
* Increases from resting volume (~70mL)
* Increases by 1.5-2 times

Question 4

What happens to cardiac output during exercise? Give the units.

Answer 4

Volume/min
▪ HR x SV
▪ Increases from resting ~5 L/min
▪ Max ~40 L/min in elite athletes
▪ Increases by up to 8 times

Question 5

What is the overall effect on vessels during exercise?

Answer 5

• Increase sympathetic output to veins and arterioles in abdominal organs and kidneys
• Increase vasoconstriction in abdominal organs and kidneys

Question 6

What blood flow redistribution occurs during exercise?

Answer 6

Global vasoconstriction
Local vasodilation

Question 7

How does cardiac distribution change from rest to exercise?

Answer 7

Blood distribution % to:
* Skin increases slightly
* Heart & brain decreases (but more blood flow as CO has increased but % is lower)
* Viscera decreases
* Skeletal muscle increases

Question 8

Why is blood redistributed to skeletal muscle?

Answer 8

Largest increase in blood flow; to provide O2 and nutrients, and remove CO2 and waste products

Question 9

Why is blood redistributed to skin?

Answer 9

For heat loss

Question 10

Why is blood redistributed to the heart and brain?

Answer 10

Increased blood flow for the heart to meet increased demands

Question 11

Why is blood redistributed away from abdominal organs?

Answer 11

They’re less active during exercise

Question 12

What causes global vasoconstriction?

Answer 12

• Exercise stimulates SNS
  ▪ Noradrenaline released from sympathetic nerve terminals, binds to ⍺1 & ⍺2 receptors
  ▪ Vasoconstriction of arterioles
  ▪ Reduces blood flow

Question 13

What is functional sympatholysis?

Answer 13

Local vasodilation of skeletal muscle overrides the vasoconstriction from sympathetic vasoconstrictor nerves

Question 14

What are the 3 mechanisms of local vasodilation/decreasing TPR?

Answer 14

1. Working muscle metabolites act on smooth muscle of skeletal muscle arterioles
   causing vasodilation: metabolic regulation/active hyperemia
2. Muscle contraction compresses the outside of blood vessels causing reflexive vasodilation: mechanical feed-forward vasodilation
3. Adrenaline binds to B2 adrenergic receptors on smooth muscle of skeletal muscle arterioles and causes vasodilation
   * Blood flow is increased to working muscles

Question 15

What happens to MABP during moderate, steady-state exercise?

Answer 15

• CO increase = TPR decrease
  ▪ MABP is relatively constant

Question 16

What happens to MABP during high intensity exercise?

Answer 16

• CO increase > TPR decrease
  ▪ MABP increases: mostly due to increase in systolic pressure

Question 17

Normally, what is the result of stimulating baroreceptors?

Answer 17

Decreased sympathetic nervous activity

Question 18

Describe the normal baroreflex (during rest):

Answer 18

• Baroreceptors detect ↑ MABP and ↑ AP firing
  ▪ Activation of barosensitive neurons in medulla
  ▪ Inhibit SNS central command
  ▪ ↓ SNS output to the heart and blood vessels
  ▪ MABP ↓ returning to normal set point

Question 19

Describe the baroreflex during exercise:

Answer 19

• Mechano- and chemoreceptors in exercising muscle send info to the exercise ‘central command’
  ▪ MABP set point ↑

Question 20

What 2 responses occur during the exercise pressor response?

Answer 20

1. Exercise ‘central command’ activates neurons to inhibit barosensitive neurons in the medulla
   ▪ MABP ↑ but there’s no inhibition of the SNS central command
   ▪ ↑ sympathetic output to the heart and blood vessels
2. Exercise ‘central command’ directly
   stimulates SNS central command to ↑ SNS output

▪ MABP ↑ to exercise set-point

Question 21

How can muscle fibre types change with anaerobic training?

Answer 21

• More Type IIa – fast oxidative glycolytic
• More Type IIx/b – fast glycolytic

Question 22

How can muscle fibre types change with anaerobic training?

Answer 22

More Type I - slow oxidative

Question 23

What is anaerobic training and when do adaptations occur?

Answer 23

• High intensity, low rep training
  ▪ Anaerobic glycolytic
  system
  ▪ Adaptations occur within 3 weeks

Question 24

What are the 2 overall goals of anaerobic training?

Answer 24

1. Increase strength - due to muscle hypertrophy
2. Increase anaerobic capacity - due to sarcoplasmic hypertrophy & increased lactate threshold

Question 25

What is muscle hypertrophy?

Answer 25

Increase in size and strength of skeletal muscles - Within a whole muscle each muscle cell/fiber gets bigger because each muscle fibril gets bigger

Question 26

What does increased contractile strength come from?

Answer 26

Increasing the SIZE of muscle cells/fibers (rather than adding more muscle fibres)

Question 27

What 3 factors increase the size and strength of skeletal muscles?

Answer 27

1. Increased protein synthesis ▪ More actin and myosin added to each muscle fibril: more contractile strength 2. Satellite cell activity ▪ Proliferate and fuse to existing fibers to make each muscle fiber bigger 3. Sarcoplasmic hypertrophy ▪ Increased volume of the sarcoplasm and sarcoplasmic components

Question 28

What is micro-trauma theory?

Answer 28

* Damage of muscle fibers ▪ 'Micro’ tears in small areas of a muscle fiber (not the whole muscle)

Question 29

What repairs muscle fibres and how do they do this?

Answer 29

Satellite cells ▪ Myogenic stem cells (build muscle) and are quiescent until activated ▪ Activated and migrate to heal micro tears ▪ Span micro tear to prevent further damage, differentiate into myoblasts and fuse with existing muscle fibers adding new myofibrils and more nuclei -> Increasing size of fibre -> More protein (actin and myosin) synthesis (nuclei) -> Increasing contractile strength

Question 30

What is sarcoplasmic hypertrophy?

Answer 30

▪ Increased volume of sarcoplasm ▪ No direct change in contractile strength ▪ Increased capacity for anaerobic glycolysis

Question 31

What is increased anaerobic capacity?

Answer 31

* Increased ATP & substrate stores (creatine phosphate, glycogen) ▪ Increased enzymes for anaerobic glycolysis

Question 32

What is myostatin?

Answer 32

* Increased with inactivity ▪ Causes atrophy ▪ Prevents excessive muscle growth ▪ Myogenesis regulator

Question 33

What is an increased lactate threshold?

Answer 33

Increase in exercise intensity before reaching lactate threshold

Question 34

What are myostatin inhibitors?

Answer 34

▪ Prevent muscle atrophy ▪ Could be used as a performance enhancer

Question 35

What is muscle atrophy?

Answer 35

Decrease in size and strength of skeletal muscles due to inactivity or denervation

Question 36

What type of training increases lactate threshold?

Answer 36

▪ High volume, maximal steady-state, interval workouts (80-90% of VO2max) ▪ Uses the anaerobic glycolysis energy system, producing lactate

Question 37

What muscle modifications does the build up of lactate/lactic acid trigger?

Answer 37

* Muscle fibres get better at tolerating lactate build up (buffering) ▪ Increased transport of lactate out of muscle cells + improved body systems to clear lactate from blood and use it as a fuel source ▪ Lactate accumulation reduced

Question 38

What is the benefit of training to increase lactate threshold?

Answer 38

Improved performance for both endurance athletes and speed & power

Question 39

What is aerobic training and when do adaptations occur?

Answer 39

* Low intensity training, high rep, longer duration endurance training ▪ Oxidative phosphorylation systems ▪ Adaptations occur within 4-6 weeks

Question 40

What is the overall goal of aerobic training?

Answer 40

Increase aerobic capacity - aerobic threshold and VO2max

Question 41

What is an increased aerobic threshold?

Answer 41

Sustain a higher level of exercise intensity for longer before needing to use anaerobic glycolysis and therefore increasing lactate production

Question 42

What is an increased VO2max?

Answer 42

Increased physical fitness, greater performance during aerobic endurance exercise

Question 43

How does VO2 change with exercise intensity?

Answer 43

Increase until maximum level = VO2max * Max O2 consumption at max exercise level

Question 44

What effect does aerobic training have on VO2 max and what are the benefits of this?

Answer 44

* Increases with aerobic training ▪ Limited by age ▪ Improved cardiovascular health ▪ Reduced risk of heart disease, diabetes, cancer, and stroke

Question 45

How can VO2 max be increased?

Answer 45

1. Increasing O2 SUPPLY to exercising muscle: cardiovascular adaptations 2. Increasing ability of exercising muscle to USE O2 to make ATP: muscle cell metabolic adaptations

Question 46

What effect does aerobic training have on heart rate?

Answer 46

* Max HR unchanged (determined by age) * Resting HR decreased, higher output at lower HR * Increased HR range during exercise

Question 47

What effect does aerobic training have on stroke volume?

Answer 47

* Increased SV at rest and during exercise * Remodelling of ventricular walls: moderate hypertrophy, increased ventricular volume & increased contractility

Question 48

What effect does aerobic training have on cardiac output?

Answer 48

Increase in max CO due to increases in HR and SV

Question 49

How does aerobic training result in an increased oxidative ATP synthesis capacity?

Answer 49

* Change in muscle fiber type to more type I fibres (oxidative) * Increased production of oxidative enzymes * Mitochondria biogenesis (make more mitochondria): increased oxidative phosphorylation