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The VO2 Max series part 2: The heart

Oxygen and creating energy from it plays a large role in our fitness. One of the ways to measure fitness is by how efficiently our body utilise oxygen, the VO2 Max. We all breath the same air and more or less breath in the same amount of oxygen.
Now, why then are some people fitter than others?

In this instalment of the VO2 max series I'm going to answer questions like:
- Why does a fit person have a lower resting heart rate?
- What adaptations take place in the heart and why does this help you perform?

So before we start out it's important to understand how the heart functions.
Now it would be an insult to your intelligence to explain that the heart pumps blood around the body. I'm going to explain how the heart manages to do this more efficiently as you get fitter.

We'll start of with a little bit of terminology, the diastole and the systole components of the heartbeat. The diastole is the phase where the heart chambers fill themselves with blood, the systole is the phase where the heart ejects blood in to the Aorta.
Now you understand this I'm going to explain the end diastolic volume and the end systolic volume. The end diastolic volume is the volume of blood that is in the heart chambers at the end of the diastolic phase. The end systolic volume is the amount of blood in the chambers after ejection.
This means that if you want the heart function to improve, you need to INCREASE the end diastolic volume (more blood in the chambers) and DECREASE the end systolic volume (less blood left in the heart chambers after ejection).
So this breaks down in to two components, how can one create more space in the heart chambers? And how can one increase the strength of the heart muscle to eject more blood?

One method to increase the the space in the heart chamber is through steady-state cardio. You can imagine this as a run (or cycle) where you can still have a conversation and takes between 20 and 60 minutes. What you have to imagine is the amount of blood/min increases, which stretches the heart chambers, allowing them to increase in size.
Now how do you get more strength in the heart muscles?
Like with any muscle you need some form of resistance to increase it's strength. So how do you increase the resistance in the heart? You make more blood go through it. Interval training is especially suited to this.
When you train at a high intensity your heart will pump large volumes of blood towards your muscles. This increases your stroke volume (the amount of blood/beat) and your heart rate. Leading to an increased cardiac output. When you're resting in between your intervals your heart rate decreases, but your stroke volume does not (as much). This means your heart has to pump out more blood per minute, and viola, you have increased the resistance in your heart chambers and have given your heart muscles some strength work.

So people that have a lower resting heart rate not only have a larger heart (that can fill up with more blood) but also stronger cardiac muscles!


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