Wednesday, September 12, 2007

Notes - VO2max

VO2max is the maximal rate at which you can inspire oxygen (O2) from the environment and transfer to the muscles within the body during exercise. It can be measured using specific equipment which measures the O2 you breathe during a graded exercise test.

VO2max is largely influenced by genetics and heredity.

For an individual, the variables that determine VO2max are cardiac output (CO) (the amount of blood you pump with each heart beat) and the aVDO2 difference (the concentration of 02 in the arteriole blood minus the concentration of O2 in the venous blood, basically the amount of 02 you extract out of the blood as it rushes past the working muscle cells).

VO2max = CO * aVDO2

Cardiac Output is dependant upon:

Stroke Volume (SV) – the amount of blood pumped out of the hearts ventricle each beat.

Heart Rate (HR) – the amount of beats per minute

CO = HR * SV

With proper training, these mechanisms and the variables that influence them increase 1.) The amount of blood you get to the muscle with max exercise 2.) The amount of oxygen you can extract from the blood as it travels past the exercising muscle.

An increase in VO2max from endurance training is primarily the result of an increase in CO. In turn, the most influential variable to increase CO is the increase in stroke volume after training (aVDO2 plays a small role in increasing VO2max, it has more influence over work capacity at sub-maximal workloads).

Reasons for an increase in SV (and hence, CO)

1. An increase in the heart’s left ventricular dimension – the chamber becomes larger thereby storing more blood for each beat.

2. Increased contractility of the heart. The heart beats a little harder thereby decreasing the amount of blood volume left in the ventricle after it contracts.

3. An increase in the plasma volume (PV) of the blood (hypervolemia). With training you can increase the amount of blood in your body by as much as 20%. The Frank Starling Mechanism says that as the PV increases the end diastolic volume (EDV) (the amount of blood sitting in the left ventricle right before beating) thereby causing an increase in SV which increases CO.

↑ PV → ↑ EDV → ↑ SV → ↑ CO

Therefore, an increase in CO through specific endurance training means that at any given absolute sub-maximal workload there is less stimulation of the sympathetic nervous system (because blood pressure is maintained easier). This is the reason HR decreases (at rest and for a given absolute sub-maximal workload) after a block of training. There is also less blood flow redistribution during a given absolute sub-maximal workload due to an increased CO. This increases exercising blood lactate clearance, absorption of ingested food, and an increase in the formation of glucose by the liver. All of which make you a stronger endurance athlete.

Main point – Increasing your VO2max can benefit your performance at sub-maximal workloads, including lactate threshold, and this is primarily the result of an increase in the volume of blood you pump through your body during exercise.

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