Middle distance athlete Flashcards
What is the tolerance of an endurance athlete to serve and very heavy intensity exercise?
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
What is an endurance athletes muscle fibre proportions?
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
At what level is their critical power?
High ‘critical power’ (CP) demarking the upper limit to attain a steady-state
What happens below and above critical power?
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.
What is the difference in power output curves of a sprinter and an endurance athlete?
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.
What is a middle distance event?
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
What is the equation of the power duration relationship?
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
What does the equation for the power duration relationship show?
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
What is critical power?
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
What are the causes of the progressive increase in energy requirement during constant-power exercise?
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
What happens to muscle glycogen during a middle distant event?
“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
What happens to PCr levels during heavy intensity exercise?
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.
How is the rate of energy production met in heavy intensity exercise? and how does this differ to sprint?
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.
What is the ability to sustain exercise influence by?
The ability to meet the rate of energy production and therefore the ability of energy systems to respond quickly
How long does it take the glycolysis system too switch on and reach max rate?
5 seconds
How long does it take the oxidation of carbohydrates system too switch on and reach max rate?
CHO is variable. It responds with a delay and can take 3-15 mins to reach maximum flux
How long does it take the oxidation of fatty acids system too switch on and reach max rate?
2 hours after a decrease in the carb store
What happens to glycolysis in very heavy exercise?
- Is rapidly activated
- Has a high maximal rate of ATP provision relative to oxidative metabolism
- Has a high capacity relative to stored phosphates
What are the main substrates for glycolysis?
The main substrates for glycolysis are:
1) Glucose from the blood, and
2) Glycogen stored in muscle (and liver)
What is the net yield of glycolysis?
2ATP per glucose, or
3ATP per glycogen
Other than ATP what does glycolysis produce?
Sequesters a Pi when glycogen is the substrate
Reduces cytosolic NAD+ to NADH + H+
Produces 2 molecules of pyruvate
What is the fate of the cytoplasmic NADH?
malate aspartate shuttle
or
a-glyerophosphate shuttle
What are the key features of the malate aspartate shuttle?
Reversible
Dominant in type I fibres
Transfers electrons from cytosol to NAD+ in the matrix
Each 2 electrons yield 2.5 ATP
What are the key features of the a-glyerophosphate shuttle?
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
What is lactate dehydrogenase?
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
What causes an increase in lactate production?
If, at exercise onset, glycogen phosphoryalse (GP) an phosphofructokinase (PFK) activity outstrips pyruvate dehydrogenase (PDH) activity, then lactate production will increase
What are the activators for:
GP, PFK and PDH?
GP – [Ca2+], [Pi], [ADP], [AMP], adrenaline
PFK – [F-6-P], [ADP], [AMP], [Pi], [ammonia], [Ca2+]
PDH – [Ca2+], [pyruvate], [ADP]
What is a key activator of these enzymes at the onset of contraction?
Intracellular Ca,
What is the structure of LDH?
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
What happens to lactate concentration balance during very heavy exercise production?
production > clearance
What is La clearance via?
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
What are the two issues with lactate clearance?
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
When are lactate and pH at their highest / lowest retrospectively?
At the limit of tolerance
How is ingesting bicarbonate of aid?
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
What of the integration of energy pathways mean?
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.
What would slower communication between energy pathways mean?
A slower communication between sites of ATP utilisation and production would reduce the onset rate of adaptation of in energy provision from oxidative phosphorylation
