Middle distance athlete

Question 1

What is the tolerance of an endurance athlete to serve and very heavy intensity exercise?

Answer 1

Relatively poor tolerance to severe and very-heavy intensity exercise – lower expression of type II muscle fibres and less well developed anaerobic energy provision pathways

Question 2

What is an endurance athletes muscle fibre proportions?

Answer 2

A greater proportion of type I muscle fibres and a high expression of aerobic enzymes, high capillarity and therefore well adapted aerobic energy provision pathways

Question 3

At what level is their critical power?

Answer 3

High ‘critical power’ (CP) demarking the upper limit to attain a steady-state

Question 4

What happens below and above critical power?

Answer 4

Below critical power the heavy exercise domain is well sustained as physiological processes become constant and sustained in a steady state. Continued exercise above steady state is not achievable as biochemical and physiological processes change so exercise becomes less sustainable.

Question 5

What is the difference in power output curves of a sprinter and an endurance athlete?

Answer 5

Sprinters have a lower critical power and so more anaerobic and cant sustain power outputs for longer periods of time. But the lower curvature means that they can maintain higher power outputs for a longer period of time.

Endurance athletes have poor tolerance to serve exercise as they have a lower expression of type II fibres and a less well developed anaerobic energy provision. but they have a higher critical power and so can sustain higher power outputs for longer.

Question 6

What is a middle distance event?

Answer 6

Middle distance sporting events are generally considered to last between ~2 and ~30 minutes, and are therefore bounded by the biochemical and physiological determinants of the “power-duration relationship

Question 7

What is the equation of the power duration relationship?

Answer 7

W´ = Tlim * (W – CP)

where:
Tlim is the tolerable duration of exercise
W is the power output (Watts)
CP is the critical power asymptote
W´ is the curvature constant of the hyperbola

Question 8

What does the equation for the power duration relationship show?

Answer 8

This equation describes the tolerable duration of a constant power output in terms of two parameters:

W´ that reflects the capacity of anaerobic energy systems
CP that describes the upper limit for wholly aerobic energy provision

Therefore, the high rates of power production in middle distance events integrate aerobic and anaerobic energy provision

A large W has a large curve like a sprinter whereas a low value has a sharp curve and is more likely to be an endurance athlete

Question 9

What is critical power?

Answer 9

Critical power (CP) demarks the upper-limit for the attainment of a steady-state

Exercise above CP is characterised by a progressive increase in energy requirement during constant-power exercise

Question 10

What are the causes of the progressive increase in energy requirement during constant-power exercise?

Answer 10

The causes of this are currently unknown but are likely to be related to the consequences of progressive muscle fatigue during exercise

Exercise below CP allows steady states to be achieved in:

1) Muscle and pulmonary gas exchange: VO2, VCO2
2) Arterial blood lactate concentration: [La-]a
3) Arterial acid-base status: pHa, [HCO3-]a, PaCO2
4) Muscle [PCr]
5) Muscle [Pi]
6) Intramuscular pH

Question 11

What happens to muscle glycogen during a middle distant event?

Answer 11

“middle distance” events generally are thought to be too brief to completely deplete muscle glycogen - although the average of the whole muscle may not reflect the status within individual muscle fibres

Question 12

What happens to PCr levels during heavy intensity exercise?

Answer 12

Pcr levels drop but there are still significant levels of phosphocreatine left at the limit of tolerance of exercise and so the capacity to supply the energy is met in heavy intensity exercise.

Question 13

How is the rate of energy production met in heavy intensity exercise? and how does this differ to sprint?

Answer 13

This is met through the integrated action of the phosphate, glycolytic and aerobic energy systems. These determine the limit of tolerance.
In sprint ATP and Pcr are depleted and this creates a limitation.

Question 14

What is the ability to sustain exercise influence by?

Answer 14

The ability to meet the rate of energy production and therefore the ability of energy systems to respond quickly

Question 15

How long does it take the glycolysis system too switch on and reach max rate?

Answer 15

5 seconds

Question 16

How long does it take the oxidation of carbohydrates system too switch on and reach max rate?

Answer 16

CHO is variable. It responds with a delay and can take 3-15 mins to reach maximum flux

Question 17

How long does it take the oxidation of fatty acids system too switch on and reach max rate?

Answer 17

2 hours after a decrease in the carb store

Question 18

What happens to glycolysis in very heavy exercise?

Answer 18

• Is rapidly activated
• Has a high maximal rate of ATP provision relative to oxidative metabolism
• Has a high capacity relative to stored phosphates

Question 19

What are the main substrates for glycolysis?

Answer 19

The main substrates for glycolysis are:

1) Glucose from the blood, and
2) Glycogen stored in muscle (and liver)

Question 20

What is the net yield of glycolysis?

Answer 20

2ATP per glucose, or

3ATP per glycogen

Question 21

Other than ATP what does glycolysis produce?

Answer 21

Sequesters a Pi when glycogen is the substrate
Reduces cytosolic NAD+ to NADH + H+
Produces 2 molecules of pyruvate

Question 22

What is the fate of the cytoplasmic NADH?

Answer 22

malate aspartate shuttle
or
a-glyerophosphate shuttle

Question 23

What are the key features of the malate aspartate shuttle?

Answer 23

Reversible
Dominant in type I fibres
Transfers electrons from cytosol to NAD+ in the matrix
Each 2 electrons yield 2.5 ATP

Question 24

What are the key features of the a-glyerophosphate shuttle?

Answer 24

Irreversible
Generally lower activity than M-A shuttle but has a 25% greater expression in type II fibres
Transfers electrons in cytosol to FAD in the inner membrane
Each 2 electrons yield 1.5 ATP

Question 25

What is lactate dehydrogenase?

Answer 25

A near-equilibrium reaction that catalyses the reversible conversion of pyruvate to lactate

LDH has an activity and Keq virtually guarantees lactate production, particularly with increasing glycolytic rate

Question 26

What causes an increase in lactate production?

Answer 26

If, at exercise onset, glycogen phosphoryalse (GP) an phosphofructokinase (PFK) activity outstrips pyruvate dehydrogenase (PDH) activity, then lactate production will increase

Question 27

What are the activators for:

GP, PFK and PDH?

Answer 27

GP – [Ca2+], [Pi], [ADP], [AMP], adrenaline
PFK – [F-6-P], [ADP], [AMP], [Pi], [ammonia], [Ca2+]
PDH – [Ca2+], [pyruvate], [ADP]

Question 28

What is a key activator of these enzymes at the onset of contraction?

Answer 28

Intracellular Ca,

Question 29

What is the structure of LDH?

Answer 29

A tetramer composed of four monomers
Each monomer can be one of two isoforms:
Heart = H or Muscle = M
The H form is more sensitive to pyruvate inhibition and is postulated to be less prone to La- formation
The M form has a greater affinity for pyruvate and is postulated to promote La- formation

Question 30

What happens to lactate concentration balance during very heavy exercise production?

Answer 30

production > clearance

Question 31

What is La clearance via?

Answer 31

Intercellular lactate shuttle:
Moncarboxylate (MCT) symporter – the charged La- ion cannot diffuse on its own so is transported with a proton (H+), then oxidised by
- Highly oxidative skeletal muscle
Cardiac muscle (up to 60% of blood La-)
Other tissues with low [La-] e.g. liver, kidney, brain

Question 32

What are the two issues with lactate clearance?

Answer 32

a-adrengergic activity causes vasoconstriction in liver, kidney, and inactive muscle thereby reducing lactate removal from the blood

2) Adrenaline reduces lactate uptake by muscle

Question 33

When are lactate and pH at their highest / lowest retrospectively?

Answer 33

At the limit of tolerance

Question 34

How is ingesting bicarbonate of aid?

Answer 34

Ingestion of sodium bicarbonate has been suggested to reduce pHi during intense exercise

Very little (if any) HCO3- enters the muscle, however, the increased extracellular buffering capacity and lower H+ allow protons to leave active muscle at a faster rate

Therefore more intracellular La- and H+ can be cleared for the same reduction in pHi

Question 35

What of the integration of energy pathways mean?

Answer 35

Phosphocreatine (PCr) may act to communicate between the ATPase (myofibrils, Ca2+ pumps) and the mitochondrion

This communication is thought to be better developed in type I muscle fibres and less sensitive in type II muscle fibres perhaps due to the greater glycolytic flux that interacts with the PCr system and creceases communication.

It is the integration of the energy delivery systems that allow power during very heavy intensity exercise. The PCr system plays the key role in communication between the muscle myofibril and mitochondria.

Question 36

What would slower communication between energy pathways mean?

Answer 36

A slower communication between sites of ATP utilisation and production would reduce the onset rate of adaptation of in energy provision from oxidative phosphorylation