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Should I exercise longer or harder for weight loss?

Exercise Post Oxygen Consumption (EPOC)

 

During exercise most of you would have noticed you get warm, your body starts to sweat and you feel your heart and breathing rate increase. When you stop exercise it is not as easy as turning off the switch, in fact your body continues to burn energy at a greater rate following exercise. This process is called exercise post oxygen consumption (EPOC) or oxygen debt. It is typically the amount of oxygen needed to restore metabolic function.

 

We have a very important fuel source in our body and this is called ATP, we produce this through a variety of different means however to keep it simple it is either from aerobic (oxygen) or anaerobic (without oxygen) pathways. If we think of oxygen in the air like going on a driving holiday and the muscle being the end destination it is obvious that between A and B a period of time must exist. For this reason our body is very good at using anaerobic ATP as fuel during times when oxygen is less available or the drive is slower than normal. When you start exercising you may notice it feels hard or you feel tired, then as you warm up the exercise feels easier. If we exercise at a steady state eventually the oxygen supply will meet the demand, if there is an increase in training intensity (increased demand) then unless we supply more oxygen the body will revert back to using anaerobic sources. After we stop exercising, it is the balance between oxygen supply and demand during the session that results in EPOC to support the following processes:

 

1.     Replenish ATP stores in the muscle

2.     Resynthesis glycogen from lactate (a product of intense exercise)

3.     Restore oxygen levels in the blood to normal

4.     Restore body temperature to normal

 

If we look at the above and think about exercise intensity, a greater intensity means a greater tax on the system (i.e. decreased ATP stores, increased Lactate, lower oxygen content in the blood and higher body temperatures) and the greater the EPOC. There are two benefits here 1) you increase the work in the session because the intensity has increased and 2) you burn more energy after the session because the cost to return your body to rest is greater.

 

EPOC describes the process after exercise so how do we influence EPOC to get better results?

 

There are three ways shown to increase EPOC, High Intensity Interval Training (HIIT), high intensity resistance exercise (HIRT) and through a combination of these two modes.

 

HIIT

HIIT training helps increase the intensity of the exercise as it often involves high intensity efforts interspersed with low intensity activity. There is a greater intensity and the constant stop start does not allow your body to reach a steady state so you your oxygen debt or EPOC is larger.

 

HIRT

HIRT can be equally effective as it involves large muscle group resistance exercise with short recovery. We will introduce some HIRT sessions in the coming weeks, however body weight exercise is a great way to increase anaerobic energy supply.

 

COMBINATION (HIIT AND HIRT)

HIRT and HIIT training together, brutal and very horrible sessions however each helps to amplify the other. Adding resistance training exercise to a HIIT session has shown to increase the metabolic demands of the resistance exercise (i.e. you burn more for the same movement). You could perform a set of HIIT efforts and then with little rest go straight into a body weight resistance circuit, this is the foundation of our Cycle X classes

 

Is more better? 

One important fact about EPOC is it is influenced by intensity and not duration. We have a limited supply of anaerobic energy so once it is used up then the intensity has to be reduced to continue or the exercise has to stop. Because we have a limited supply of Anaerobic energy that means we have a limited capacity of EPOC as these are generally tightly linked. The key message is to train hard not long if you are trying to increase your EPOC.

 

 

Summary:

1.     Metabolic energy (ATP) is supply through two main pathways aerobic (with oxygen) and anaerobic (without).

 

2.     Exercise Post Oxygen Consumption (EPOC) is the amount of energy needed to return your body to rest following exercise

 

3.     EPOC is influenced by intensity and not duration ~ Train hard not long

 

4.     High intensity interval training (HIIT) and High intensity resistance training (HIRT) are both ways to increase EPOC.

 

5.     You can combine these two methods to reduce the amount of time needed in a session to maximise the EPOC

 

6.     Greater intensity in a session means greater expenditure after a session