Most of you have probably wondered what are the most efficient ways of expending body fat and burning the most calories? If you go to the gym you will often see people spending their time on a  treadmill, bike or cross trainer cruising along at a steady pace.  One of the reasons for this is that we have been brought up to think that long duration cardio is our main fat burning mechanism. This isn’t entirely true, so let me explain.

Let’s look at the correlation between 2 sources of energy.

The way your body works is that it uses a higher percentage of its fat stores as an energy source when taking part in lower intensity exercise (this is where the myth of the fat burning zone comes from) and more carbohydrates in higher intensity exercise. The reason being is carbohydrates are stored in the muscles as glycogen and the body has quick access to it. So the more intense the exercise the more carbohydrates you use and the less intense the more fats you use.

So how does the body use these two energy sources? This is where it gets tricky!

Let’s say you’re walking for 20 min at around 3 mph. This would result in 67% of energy deriving from fats and 33% of energy deriving from carbohydrates. At this pace you expend 4.8 calories a minute, 3.2 calories which come from fats and 1.6 calories which come from carbohydrate stores.So in total the amount you expend is 64 calories from fat and only 32 calories from the metabolism of carbohydrate. Imagine if you double the walking intensity to 6 mph for the same time. This increase would result in more carbohydrates being used as an energy source. So this time the expenditure is 54% from carbohydrates and 46% from fat. Due to the increase in pace, 9.75 calories are now burnt per minute, 5.2 from carbohydrates and 4.48 from fats. Therefore you have burnt 104 calories from carbohydrates and 90 calories from fats. In this case that’s a 40% increase of calories burnt from fat from exercise of higher intensity, however everyone’s metabolism functions differently and burns calories at different rates.





You may be saying to yourself, well if you’re going faster of course you will burn more calories! True, but what we just established is that the common myth of the low intensity “fat loss zone” isn’t technically very accurate.

HIIT is a much more intense form of training than walking and running at the pace I mentioned, so the body will burn an even higher amount of calories per minute. A study conducted by the university of Ontario actually showed the following results in some research they conducted.Researchers had 10 men and 10 women train 3 times per week, with one group doing 4 to 6,  30-second treadmill sprints (with 4 to 6 minutes of rest in between each), and the other group doing 30 to 60 minutes of steady-state cardio (running on the treadmill in the “fat loss zone” at 65% of their Maximum heart rate). After 6 weeks of training, the subjects doing the interval sprints had lost more fat.

But why?

So far we’ve established that working at a higher intensity burns more calories and although your main source of energy aren’t your fat stores, the amount of calories burnt from fat will still be higher than the ones of a long duration cardiovascular session. HIIT workouts put more stress on the body and significantly increases your heart rate because your muscles need more oxygen to work quicker. HIIT has also proven to have longer excess post-exercise oxygen consumption levels (EPOC). Following an exercise session, oxygen consumption (and therefore caloric expenditure) remains elevated as the working muscle cells restore physiological and metabolic factors in the cell.

During a HIIT session you are not only working on your cardiovascular system but also you’re training muscular endurance. It’s very dependant on the format of your session and the exercises you choose to see what main component you are working on, but the beauty of it is you can accommodate so many exercises and intervals allowing variation on different aspects of training and the added bonus of it never getting boring.

HIIT will actually help your muscles grow! Whereas doing long hours of cardio can result in burning muscle tissue.  MO Farah and long endurance athletes are good examples of this. Muscle hypertrophy (growth) sets range between 6 to 12 reps per set (depending on the exercise), and these are the kind of reps you should average for 20-30 seconds work, maybe even more! Increased muscle size means there is a higher storage capacity in the muscles and you can consume more calories before the extra calories get stored in the body as fat.

Most exercises can be performed in a HIIT format and a  great way to follow a HIIT program is by downloading or searching for Tabata on Youtube or Spotify . It automatically talks you through your work and rest periods. So whatever exercise it is you want to do, whether it is squats, burpess, lunges, press-ups, running, cycling try them as a HIIT session and see how you feel afterwards!

It’s important to carry out some long duration cardio training as well as HIIT for an effective training programme. We’ve established that HIIT can actually burn more calories than a long cardio session so find a good combination of both and you’re onto a winner. If you haven’t tried HIIT yet, give it a go, you’ll feel great after, it’s fun and you’ll burn those calories even when you’re sitting down!

For any further questions on training programmes please contact me. I’m happy to help!

Definitions: Long Duration Cardiovascular training is a continuous way of training at 65% to 75% of your maximum heart rate. Long duration cardio can be any exercise such as running, cycling, swimming at a constant speed etc… Your maximum heart is calculated through this calculation.

MHR= 220- your age 

High Intensity Interval Training (HIIT) is a method of training at which you are working between 75%-95% of your maximum heart rate.  For example;  a 20 second sprint followed by a 10 second rest. 

Fat Oxidation: This is a process by which the stored, giant lipid molecules (fats in the body) are broken back down into their smaller parts, triglycerides and fatty acids so they cab be used as energy.

EPOC: Excess post-exercise oxygen consumption (EPOC, informally called afterburn) is a measurably increased rate of oxygen intake following strenuous activity intended to erase the body’s “oxygen deficit”.



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