HIIT

by Uday

Question: I have been doing hiit for quite some time (almost 2 months). i have been performing sprints that last for approximately 15 mins. i do 6-8 repetitions of these 3 days a week. i am on a good and balanced diet. i have benefited a lot from it but am confused between this 15 sec interval and a longer(40-60 sec) interval.

i know longer intervals stimulate immediate fat loss but please tell me the scientific reason behind this and the 15 secs interval????and i would like to tell you that i am 20 yrs old and a fitness freak.

please also mention all the aspects that strictly need to be kept in mind while performing HIIT (be it duration, intensity, rest between intervals etc.)

what is the basic concept that exhausts the inter-muscular energy reserves(glycogen and triglycerides) completely. are the stores also exhausted after weight training in the gym???

Answer: Ok, This is a fairly complex question so its going to be a long answer. I’ll answer this question in terms of why warp speed fat loss picked longer rather than shorter intervals.

For this discussion we will consider short intervals to be around the 15 second mark and longer ones over 90 seconds of intense exercise. In both sets you exercise as hard as you can for the whole interval, the only difference is the intensity you are able to exercise at. Now it’s the intensity that causes different reactions in your body.

For an explanation of both of these types of intervals it’s important to understand that during the intense interval the muscle stops using energy from your blood stream and starts using stored muscle energy, called muscle glycogen.

This stored energy is the secret to how you lose fat, the muscle needs to be replenished after HIIT training and the easiest way to do this is to draw from your blood cells. The great thing though is that this is the energy usually used to run your body’s normal functions, so your body has no choice but to substitute this by using up fat stores, the kind you are trying to get rid of.

So with this in mind, how do the two types of intervals differ?

Let’s start with the shorter interval. This is all about adaptation. The first thing to realize is that your muscles are not constant things, they are always changing. If you have ever broken an arm or leg you would have noted with shock how fast your muscles withered. So your muscles are sitting there trying to figure out what they will be used for, and their best guess is what they have just been through.

So when you trigger a huge amount of force in a short amount of time through the muscle, a number of mechanisms are there trigger the changes. The most important one in HIIT is called AMPk which stands for activated protein kinase.

Now this has a number of positive effects on your body:

Increased volume of storage for muscle energy, more energy will go into running your muscle rather than being stored as fat.

Your body starts portioning its carbs and storing them in muscle, more of the carbs you eat will be stored as muscle energy rather than fat

Mitochondria are the transport system for energy to reach the muscles. These mitochondria grow in volume and in number, in so allowing your body to ‘catch and transport’ more energy instead of letting it go past into the fat cells.

It creates a metabolic change in the body which burns fat called EPOC. This can last for up to 40 hours after the exercise

Your body starts saving energy for repletion after exercise rather storing it to fat.

These changes take time and regular HIIT but are maximized by making HIIT more intense.

So now let’s look at the longer intervals and the reasons why they were picked for Warp Speed Fat Loss.

Firstly you get these adaptions with longer intervals, just not as quickly. Longer intervals greatest asset remains in the immediate effects it has. Now with the shorter intervals, point number 4. indicated that HIIT induced a state called EPOC which caused the body to burn fat for many hours after the exercise. Now with longer intervals the same thing happens except it burns a whole lot more fat than the shorter interval.

Muscle glycogen stores normally sit at about 100mmol/kg for normal active people but if you do HIIT on a low carbohydrate diet you can drop this level below 70mmol/kg. This is where your body really starts burning a lot of fat to quickly to replenish it stores.

Now warp speed fat loss is all about losing as much fat as possible in the shortest possible time so it would definitely focus on longer intervals to try and achieve this.

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