Most common questions in an endurance training - A sensible approach

If you are a health and fitness professional, No doubt, you will get a ton of training related questions, I am going to share few information on frequently asked questions by my clients about an endurance training (Aerobic Training). Of course there is a lot of questions around the globe. Here i came up with the three questions.

1. How does an exercise training improve volume of maximal oxygen uptake (VO2max) ?

 To answer this question. I have to remind fick's equation to you all. 

VO2max = (Maximal cardiac Output * Maximal arteriovenous oxygen difference) or in simple term

 Maximal oxygen uptake = (Systemic Blood Flow * Systemic O2 extraction)

From the fick's equation , you can see VO2max is directly affected by it product(see above equation).

The maximal oxygen uptake increases due to increase in cardiac output or arteriovenous oxygen difference or both . Cardiac output is the amount of blood ejected from the left ventricle per minute and cardiac output is the product of Heart Rate and Stroke volume (amount of blood pumps put per beat). Arteriovenous oxygen difference is the amount of oxygen removed from arterial blood used by tissues.

When you are following a proper training protocol with an appropriate incremental in an intensity can increases your endurance performance by increase in stroke volume and heart rate remains same or decreases. Here i have got an another question,

2. What causes maximal stroke volume and maximal arteriovenous oxygen difference to increase as a result of endurance training?

Stroke Volume:

 (Please note:  Training will not increase the maximal hear rate, instead heart rate decreases with prolonged training). So increase of Cardiac Output comes from increase in Stroke Volume. But how?

Endurance training increases stroke volume through 

• Increase in End Diastolic Volume (EDV) (or) (Preload)
• Increased in Cardiac Contractility
• Decrease in Total Peripheral resistance (Afterload)

Increase in End Diastolic Volume (EDV) in other words Increase in the amount of blood present in left ventricle before contraction. This can be achieved through increase in plasma volume , Increase in blood filling time and venous return and increase in ventricular volume. Prolonged endurance training increases the volume of left ventricle with little change in ventricular wall thickness. Increases stroke volume at rest results from increased stretch of myocardium with larger End Diastolic Volume (EDV) and increased ventricular filling time associated with slow Heart Rate

Increased cardiac contractility:

Refers to the strength in cardiac muscle contraction, Endurance training changes little in left ventricle thickness and it can be contract the chamber with greater force thus results in increased stroke volume.

Decreased Total Peripheral Resistance:

When the Heart contracts against total peripheral resistance , stroke volume will be reduced. 

'Trained muscles offers less resistance to blood flow during maximal exercise due to reduction in sympathetic vasoconstriction activity to the arterioles of trained muscles so that mean arterial pressure(average arterial pressure during single cardiac cycle) remains unchanged'

Arteriovenous oxygen difference:

Training induced increase in arteriovenous oxygen difference due to increased extraction from the blood. It occurs due to increase in "capillary density". Enlarged capillary density in trained muscle accommodates larger blood flow during exercises. Thereby increased mitochondrial volume decreases the distance for diffusion and  the mitochondria and slow the rate of blood flow to more time for oxygen diffusion from capillary to muscle fiber. From this explanation, I have received an another question from my client which is

3. How endurance training increases mitochondrial volume?

 Both endurance training and high intensity interval training increases the synthesis of new mitochondria (mitochondrial biogenesis) resulting an increased volume of "sacrolemmal mitochondria"

 and "Intermyofibrillar mitochondria" in the trained muscle fiber. (Please note: Exercise training increases the volume of mitochondria and not increased the number of mitochondria)

In the bottom line,

There is no doubt endurance training has most beneficial effect on many systems. In this article i have just focused a few things from cardiorespiratory physiology to give an answer for the questions which have asked. simply endurance training increases amount of blood pump out from the chamber per beat and per minute then decreases the heart rate and little change in left ventricle wall thickness. It can also increases mitochondrial volume to boost performance.whatever the goal you have incorporating an aerobic training program in your schedule is must. American College of Sports Medicine recommends

to do 150 mins per week of aerobic training with moderate intensity (40-59% of VO2max) has more beneficial.