high intensity interval training

If there is one issue that has over the years been very contentious among fitness experts, it would be no other than what is referred to as the Fat Burning Zone. A lot of heated discussions there have been with different experts offering divergent opinions on which is the best fat burning zone to be in to be able to effectively lose weight.

The fat burning zone as a phenomenon can be said to be a function of the intensity of your exercise which is often directly proportional to how much energy you are expending while performing any type of physical activity geared towards achieving some degree of weight loss.

Consequently, one major factor that is also linked to intensity and which has to be factored in when considering the fat burning zones is the source of the energy fuel being used. The muscles basically have three options of energy fuel which are proteins, carbohydrates, and fats and the decision of which one to draw from often depends on certain variables chief amongst which is the workout intensity.

These energy fuels can be found in either the bloodstream or the muscles. Carbohydrates in the bloodstream are found in the form of glucose while in the muscles they are in the form of glycogen – a mixture of glucose and water. Fats on the other hand are generally stored in the body tissues as triglycerides and made available in the bloodstream through a process called lipolysis.

The body usually goes into a "fight or flight" mode when it senses a threat or is under stress and exercise is generally categorized as a stressor to the body’s maintenance mechanism. Usually, the intensity of the workout will determine the most appropriate energy fuel type and source the muscles will decide to pick in order to most effectively handle any stress situation it finds itself.

The different intensity levels that can be experienced during a workout session are usually determined through a rating system referred to as the Rate of Perceived Exertion (RPE). It is somewhat of a personalized rating system as it is based on your current fitness level and overall perception of exercise level.

On a scale of 1 to 10, with 1 being minimum exertion and 10 being the most intense, the RPE intensity scale would be as follows: (a) Low Intensity (1 – 4); (b) Moderate Intensity (5-7); and (c) High Intensity (8-10).

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During low intensity workouts such as walking, fat is usually the primary source of energy due to the abundance of oxygen. At this stage, the muscles naturally prefer to use more of the fat from the bloodstream because it more in abundance than the stored fat in the muscles and then supplement it with some glucose. The body achieves this through a process called lipolysis whereby fats released from their storage sites in fat tissues are broken down and released into the blood stream. This is what is mostly referred to as the “fat burning zone”. However, as recent studies have shown this process doesn’t burn a significant amount of body fat to bring about considerable weight loss in any reasonable amount of time.

You get to moderate intensity level when you start working harder, let’s say running moderately at about 6 out of 10 on the RPE scale. To keep up with your increased pace, the muscles need more oxygen and energy fuel causing the heart to beat faster in order to get more blood to the muscles in the quickest possible time. The muscles at this point are also producing more heat which has to be released and the blood also attempts to carry this to the skin for perspiration in order to regulate the overall body’s temperature.

The increase in both of these activities suddenly make less blood available to be able to effectively continue the process of burning fat from the body fat stores and releasing them into the bloodstream. Thus lipolysis soon tapers off but the rate of fat burning in the muscles still continues to increase. This makes the muscles to turn to its own fat stores – triglycerides – in order to make up for the shortage. This stage is arguably the most optimal fat burning zone and which is recommended for most adults.

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Getting to the last three stages of the RPE scale (8, 9, and 10) – the high intensity stage – takes a lot of energy but also comes with its own reward. Entering stage 8 out of 10, the muscles virtually turn to carbohydrates due to lack of sufficient oxygen to metabolize its own fat store of triglycerides. With any further increase in intensity, the muscles now completely turn to its own glycogen store as its primary source of energy fuel.

Any further increase in intensity will have you stepping over into stage 9 of 10 or probably further into stage 10. At this point, you are basically exercising anaerobically – without oxygen – and your muscles generally start to fail. This is attributable to the production of lactic acid which is now building at a rate faster than it is being cleared out of the muscles.

At high-intensity, the body has virtually stopped making use of fat as in any form and completely switched over to burning carbohydrates – in form of glycogen – instead. Recent studies indicate that there are more benefits derivable from doing high intensity workouts due to an observed increased fat burning experienced after such workouts.

Physical activities where an anaerobic stage can be reached include sports such as football, rugby, soccer, basketball, and hockey. Anaerobic stages are reached during workouts through weight lifting or interval training.