Of the three ATP production mechanisms,
the aerobic energy system has the highest capacity.
But it is very low in terms power that it permits the athlete.
Despite its low power, the aerobic energy system is a critical energy system for
almost all sport participants.
It not only permits the athlete to perform over an extended period of time,
it also supports the creatine phosphate energy system and glycolysis.
There are several field tests available that are designed to assess
the quality of an athlete's aerobic energy system.
The multi-stage fitness test, also known as the B-test,
the yoyo test, or the shuttle run test and some athletes even refer to it as
the suicide test, is a commonly used field test.
This test is based on a controlled,
gradual increase in speed as the athletes run between 2 lines 20 meters apart,
until they can no longer keep up the designated pace.
There are many apps that you can use to pace the athletes during the test.
Most apps started 8 kilometers per hour as you see here.
I've speeded up the time, so in this particular example
the red dot that's moving backwards and forwards is the athlete running between
the markers that are set 20 meters apart, as shown on the diagram.
Athletes must reach the line on or before the next beep.
The longer they keep going, the higher their VO2 max is predicted to be.
After one minute, the speed is increased to 8.5 kilometers per hours,
as is indicated here.
Then after two more minutes, the speed is increased again and so on.
Notice the athletes stopped at this point here.
V02 max is 15.5 mils per kg per minute.
Now, don't worry about these numbers for now.
We're going to come back and talk about them more in a little bit.
Now, theoretically,
the point where the athlete can no longer keep the correct pace is
the upper limit to which the mitochondria can use oxygen to produce ATP.
The term VO2 max is used to describe this upper limit to
the athlete's aerobic capacity.
There are three important functional characteristics
contributing to the athlete's aerobic capacity.
And these include first the athlete's cardiac output, and
cardiac output depends on coronary bloodflow, in addition to how
effectively the cardiac muscle contracts and how efficiently it uses oxygen.
And hearts differ in these characteristics.
The second is the oxygen carrying capacity of the blood, and
this depends on the amount of hemoglobin located in the red blood cells.
And once again, athletes will differ in the amount of oxygen
that they're able to carry in their blood.
And the third is the mitochondrial effectiveness.
Many factors influence the delivery of oxygen to the mitochondria,
including the density of capillaries surrounding the muscle,
the density of the mitochondria itself and
how efficiently the mitochondria themselves work to produce ATP.
While trained athletes have mitochondria with a greater
capacity to grab and use oxygen effectively,
the VO2 max is always lower than its genetic potential in the untrained.
