Lecture 10 - O2 uptake during exercise

Question 1

For a given exercise intensity there is..

Answer 1

a particular oxygen uptake

Question 2

how efficient are we at converting oxygen uptake to mechanical work

Answer 2

20%

rest goes into heat

Question 3

Why is there a lag in oxygen uptake at the onset of exercise or exercise transitions?

Answer 3

O2 transport

O2 utilisation - “metabolic inertia” - the mitochondrial respiration is a bit sluggish, takes times for enzymes to start working

An interaction between both mechanisms

Question 4

What are some determinants of VO2 kinetics (and hence the lag period)

Answer 4

Ca2+ activation of mitochondrial dehyrogenases and ATP synthase

ATP/ADP * Pi and NAD+/NADH

Mitochondrial PO2 - getting the oxygen into the mitochondria

all of these contribute to the slow lag in o2 uptake

Question 5

As you increase the exercise intensity, you also increase

Answer 5

the oxygen drift - the slow increase in oxygen uptake

Question 6

What are some potential explanations to the VO2 drift in increasing intensity or duration exercise?

Answer 6

80% due to the active muscles

recruitment of lower efficiency type II fibres (which you need after a while)

Reduced OXPHOS coupling efficiency (the amount of ATP you get per oxygen decreases = P-O ratio)

Elevated muscle temp - changes the dynamics

Elevated catecholamines

O2 cost of ventilatory and cardiac work

You also need more oxygen to oxidise fat (which is used more later)

Question 7

What happens in the period after exercise that requires Excess post-exercise oxygen consumption (EPOC)?

Answer 7

Resynthesis of ATP, CrP (happens quickly)

Restoration of myoglobin O2 stores - which normally serves as a buffer

Elevated HR, Ve temperature, hormones

Increased FFA metabolism

Mitochondrial “uncoupling”

Glycogen resynthesis - happens quickly

Question 8

What are some points on CrP resynthesis?

Answer 8

Occurs rapidly (t1/2 = 60-90s)

O2 dependent

Influenced by Muscle oxidative capacity

Creatine supplementation

Question 9

What is the metabolic fate of lactate?

Answer 9

Oxidation in skeletal and cardiac muscle - with LDH enzyme

(active recovery enhanced lactate removal)

Substrate for glycogen synthesis

Conversion to other metabolites (AAs)

Does not increase VO2 or cause muscle soreness

Question 10

What are the keys points on post-exercise muscle glycogen resynthesis?

Answer 10

Trained individuals have more Glycogen synthase activity

Degree of muscle glycogen depletion

GLUT- 4

CHO ingestion is important, you need it (amount, type, timing)

muscle damage - interferes with glycogen resynthesis