17. Maximal oxygen uptake: determinants & limits Flashcards
What is maximal oxygen uptake?
A measure of the combined abilities of the cardiovascular and respiratory systems to deliver oxygen and the active skeletal muscle to consume oxygen.
It is commonly used as a measure of “cardiorespiratory fitness”
What is maximal oxygen uptake determined by?
Combination of genetic endowment and physical training
What is the rate limiting factor for maximal oxygen uptake?
Oxygen delivery
What is the relationship between VO2 and exercise intensity in respect to training/sedentary?
Linear relationship
There is no difference in mechanical efficiency between different levels of training, there is however, a diff in maximal O2 uptake. It is much higher in athletes.
Therefore your range is determined by both genetics + training. Your body mass can alter your maximal oxygen uptake.
Describe the heritability of VO2 max.
Looking at monozygotic/dizygotic twins, can determine that there is more variation in dizygotic twins
Familial aggregation observed when families trained together, estimating that 51% VO2 max is heritable.
Potential limitations to maximal VO2
- RESPIRATION
* VE, V/Q
* diffusion
* Hb-O2 affinity - CENTRAL CIRCULATION
* [Hb], [HbO2]
* arterial BP
* CO (HR, SV) - PERIPHERAL CIRCULATION
* Oxygen to non-exercising regions
* muscle bld flow
* vascularity - capillary density, vascular conductance, diffusion, O2 extraction (Hb-O2 affinity) - METABOLISM
* substrate delivery
* muscle mass (fibre size & number)
* [energy stores]
* [myoglobin]
* [mt] - oxidative potential
What is the relationship between muscle mt capacity and oxygen delivery capacity?
Muscle mitochondrial oxidative capacity exceeds the oxygen delivery capacity.
VO2 max vs systemic O2 delivery
(VO2 max is maximal oxygen consumption)
Maximum oxygen delivery is by max cardiac output and arterial oxygen content, therefore the two are closely correlated (though not necessarily indicative of causation).
higher oxygen delivery = higher VO2 max
Limitations to muscle O2 delivery & uptake
VO2 will often, if not always coincide with the leveling off in maximal cardiac output (with is largely a function of stroke volume). The increase in HR can’t compensate for the decrease in time in diastole.
Therefore a consequence of this is the following are maxed out at high intensity ex:
- leg blood flow
- leg oxygen delivery
- leg VO2
Things that can affect central circulation & VO2 max
- acute hypervolemia (untrained subject given plasma volume expander to maintain bld volume — can increase VO2 max; effect dampened/missing in trained subject — [Hb] diluted with training, acquire sports anemia)
- blood doping (remove bld, train, put it back in)
- erythropoietin (stimulant of RBC production)
- altitude training?
Why does CO limit leg muscle blood flow during maximal exercise?
Also limits leg oxygen delivery, because it must maintain MAP to maintain cerebral perfusion
If only a small muscle mass is active/recruited for exercise, the heart can afford to give as much blood as the active muscles want. However as you increase the active muscle mass, you cannot afford to perfuse that much muscle
Relationship between VO2 max and capillary density
Generally, individials with higher VO2 max = higher muscle capillary density.
*if you want to increase CO, must also increase the plumbing that delivers it to the contracting muscle (cap. density)
What is muscle diffusion capacity influenced by?
- surface area
- where the mitochondria are (groups of them found in subsarcolemmal, intermyofibrillar regions)
- diffusion distance
- mitochondrial morphology
R/ship between VO2 max & muscle diffusion capacity
People with higher tissue diffusion capacity have higher VO2 max
R/ship between VO2 max and muscle oxidative capacity
Linear relationship
As you increase muscle ox capacity, you increase the pull on your oxygen delivery system
