Endurance athlete

Question 1

What boundary of energy production is used in endurance events?

Answer 1

CHO and glycolysis and so exercise is limited by the levels of glycogen as high rates of glycolysis deplete this

Question 2

What enhances oxidative metabolism in endurance events?

Answer 2

Facilitation of oxygen delivery. The diffusion distances of the myofibrils are reduced.

Question 3

What is the mitochondria involved in?

Answer 3

Involved in Ca2+ control, cell signaling, apoptosis and ATP production

Question 4

What are the features of the outer mitochondrial membrane?

Answer 4

• Contains roughly equal proportions of proteins and lipids
• Contains porins: channel-forming proteins allowing free diffusion of small ions and molecules (up to 10 kD)
• Relatively permeable

Question 5

What are the features of the inner mitochondrial membrane?

Answer 5

• High protein content (~ 80%)
• The density of the extensive cristae reflects respiratory activity of the cell
• Freely permeable to O2, CO2 and H2O
• Impermeable to most other ions and metabolites, thus requiring specific transporters or carriers, thus ion gradients are maintained across the inner membrane

Question 6

What is VO2max?

Answer 6

Maximum oxygen uptake (VO2max) is the upper limit of oxygen transport and utilisation attainable in any individual

Question 7

What size capacity for oxidative metabolism is required to minimise endurance performance?

Answer 7

High

Question 8

How many H+ are required to generate 1ATP?

Answer 8

4

Question 9

What is the ATP yield of NADH and FADH?

Answer 9

1 NADH yields 2.5 ATP (10 / 4)

1 FADH2 yields 1.5 ATP (6 / 4)

Question 10

What is running speed correlated too?

Answer 10

VO2 max and lactate threshold

Question 11

What determines the limit between moderate intensity and heavy intensity exercise?

Answer 11

Lactate threshold

Question 12

What is the total yield from complete oxidation of glucose?

Answer 12

32 (30 depends on whether the electrons associated with the cytoplasmic NADH are shuttled into the mitochondrion on the malate-aspartate shuttle (5 ATP) or the a-glycerophosphate shuttle (3 ATP))

Question 13

What is the overall reaction for oxidative phosphorylation with NADH as the electron source?

Answer 13

O2 + 2 NADH + 2 H+ + 5 ADP + 5 Pi –> 2 NAD+ + 5 ATP + 2 H2O *

Question 14

What are the controlling/ limiting factors of oxidative phosphorylation?

Answer 14

• Oxygen availability
• Phosphorylation potential [ATP] / [ADP] · [Pi]
• Oxidation reduction (redox) potential [NADH] / [NAD+]

Question 15

What is the maximal forward flux of oxidative phosphorylation dependent on?

Answer 15

1.Biochemical factors that limit the rate of substrate availability ([NADH], [ADP], [Pi]) e.g. Glycolyitic activity, TCA cycle activity, or NADH shuttles:

non-O2-dependent factors

2.O2 transport factors that limit the rate of oxygen delivery to the mitochondria. These include convective O2 transport in the blood and diffusive O2 transport between the capillary and the mitochondria:

O2-dependent factors

Question 16

Both O2-dependent and -independent factors are influenced by muscle fibre type because, compared to type II, type I fibres have:

Answer 16

Greater oxidative enzyme activity
Greater M-A shuttle activity
SS and IMF mitochondrial expression
Myoglobin content
More capillaries
Smaller area
Shorter O2-diffusion distances

Question 17

What percentage changes do we see from pre training?

Answer 17

VO2max	= 16%
LT = 30%
Capillary density = 20%
Fibre area = 20%
Succinate dehydrogenase (SDH) activity= 40% 
Cytochrome c activity = 40%

Question 18

Is it the delivery or the utilization that limits VO2max?

Answer 18

Over the first few weeks the intramuscular processes are increasing at a rate similar to the rate of VO2max increase with O2 delivery changing a much smaller degree over the same time. It takes longer for oxygen delivery to increase compared to utilisation

Question 19

What happens to LT in hypoxic and hyperoxic conditions in trained and untrained individuals?

Answer 19

It decreases in hypoxic and increased in hyperoxic in endurance athletes

It decreases in hypoxic and stays the same in hyperoxic in untrained individuals

This may reflect that VO2max and LT in untrained subjects is limited muscle O2 utilisation, but that O2 delivery is the limiting factor in trained athletes

In all subjects hypoxia reduces LT, but hyperoxia only increases LT in some

This may reflect a limitation of mitochondrial NADH oxidation, causing an increase in cytosolic redox potential and increasing [lactate]/[pyruvate] (L/P)

Question 20

What does it mean that ATP remains constant during endurance exercise?

Answer 20

Most of the control of VO2 by the phosphorylation potential ([ATP] / [ADP] · [Pi]) is exerted through changes in [ADP]
[ADP] is buffered through the creatine kinase reaction
therefore, (when intracellular pH is constant)

Question 21

What control does Phosphorylation potential: [ATP] / [ADP] · [Pi]

Answer 21

Appears to exert a tight control over oxidative phosphorylation in vivo during endurance exercise, at least in healthy subjects when NADH and O2 are in abundance
However, under some conditions either O2 or NADH (or both) can become limited

Question 22

What is the TCA cycle regulated by?

Answer 22

Substrate availability
Allosteric factors
Product inhibition
Competitive feedback inhibition by intermediates further along the cycle

Availability of Acetyl CoA
regulated by pyruvate dehydrogenase (PDH)

Availability of oxidised reducing equivalents
NAD+ for the three dehydrogenase reactions
Isocitrate dehydrogenase (ICD)
a-ketogluterate dehydrogenase (a-KD)
Malate dehydrogenase (MDH)
FAD for one dehydrogenase reaction
Succinate dehydorgenase (SDH)

Allosteric control of 3 non-equilibrium reactions
ICD, a-KD, and Citrate synthase (CS)

Question 23

What does NADH drive from?

Answer 23

• Cytosolic NADH shuttled into the mitochondrion (supplies electrons to FAD if a-glycerophosphate shuttle is used)
• Tricarboxylic acid (TCA) cycle (supplies electrons to FAD in succinate dehydrogenase)

Question 24

What changes are seen in a Cycle ergometry to exhaustion at 70% VO2max?

Answer 24

Fumarate, Malate, succinate, isocitrate, citrate and Oxaloactetate all increase from rest to 5 mins but then progressively fall

2-oxogluterate (a-ketogluterate) falls immediately

Oxaloactetate falls below resting levels by exhaustion

Question 25

What happens during endurance exercise to reactants on span I (right hand side) compared too span II?

Answer 25

Throughout endurance exercise reactants on the ‘right hand side’ (span I) of the TCA cycle are maintained at much lower levels than span II reactants
Span I= Cit, Iso, 2OG
Span II= Suc, Fum, Mal. Oxa

In addition, it has been suggested that TCA cycle flux may exceed PDH activity at the limit of tolerance during high intensity exercise

This might contribute to the reduction in span I intermediates at the tolerable limit of endurance exercise

Question 26

What does endurance exercise require?

Answer 26

Endurance exercise requires the limited muscle glycogen stores to be maximised by a high reliance on oxidative energy provision, however, the response time for oxidative phoshporylation is relatively slow compared to the other energy systems

Question 27

What is seen following exercise training?

Answer 27

Following exercise training oxidative energy provision is maximised by increases in mitochondrial density, oxidative enzymes, capillarity, and myoglobin

Question 28

What are sensitive to limitations in O2 delivery?

Answer 28

VO2max and LT are sensitive to limitations in O2 delivery

Question 29

Where is control of oxidative phosphorylation predominantly exerted?

Answer 29

through the phoshphoryaltion potential, but may be limited by mitochondrial O2 and NADH availability