HIT

High intensity interval training (HIIT) is a very popular training method. When used correctly it effectively improves cardiovascular conditioning, burns fat and promotes new muscle growth. In addition a relatively short HIIT session is sufficient to elicit substantial performance gains. Like any training method, understanding the basic physiological principles will make a big help to using it effectively. This article will explain a bit about this type of training and some of the pitfalls to watch out for.

HIIT is popular because it is time effective. An individual can burn a lot of calories in a short space of time. As the name implies it is an intense form of exercise. Our energy systems function on a simple mechanism of energy charge. The rate of energy (Adenosine Triphosphate/ATP) utilization in the muscle cell must be matched by an energy supply system. Slow rate of energy expenditure during low intensity work is supported by oxidation. Oxidation supplies a lot of energy but at a slow rate. High intensity work is supplied by the glycolysis and phosphate systems which have a much faster supply. Supply must meet the demand. There is often a slight lag between utilization and supply. This means that even during rest intervals and post exercise energy consumption is still elevated. In simple terms our metabolism is increased and we continue to burn more calories than at normal rest conditions. For this reason even though a 20min session burns, for example 500kcals, energy expenditure is raised throughout the day. A low intensity session lasting one hour may burn 800kcal with minimal elevation in metabolisms for the rest of the day. For this reason HIIT may actually burn more calories on a daily basis. This is why it is so effective at fat burning.

HIIT can also be performed with a strength endurance element, supporting a leaner physique!

In addition, the power output which is produced during the work period of HIIT is high. Higher power output during work periods are often effective in improving your conditioning. It also helps maintain strength and power simply by utilizing larger motor units. The main issue to consider with HIIT relates to energy supply. If we cannot supply the cells with adequate energy then they become damaged. This is known as metabolic stress. A certain degree of metabolic stress or damage can be reversed. This is what promotes new muscle growth. Moderate metabolic stress during training can, at times, be quite effective for promoting hypertrophy.

If we place too much stress on the muscle cells the damage can be irreparable. The cells will begin to die. When this happens on a regular basis muscle wastage can occur. It also places the body under larger amounts of general stress which will begin to impact on our immune system. There is a large list of potential health implications that this can eventually lead to.

Preventing this scenario is relatively easy but not always something we think about. One of the determinants to energy supply is our energy store. In the case of HIIT we need adequate stores of glycogen for an adequate supply of energy. If we do HIIT in a fasted state we are putting ourselves under severe metabolic stress, as there is little energy supply to fuel it. In addition the lack of energy will dramatically reduce performance so conditioning benefits may also be lost.

The take home message is this. Fuel up for intense exercise! Low intensity exercise can be done in a fasted state as the oxidative system works effectively to provide fuel. With intense exercise such as HIIT style training, you must have some glycogen stores or glucose in the bloodstream. If you are in a totally fasted, glycogen depleted state then consume some simple sugars close to training. By doing so you can maintain high intensity and reduce cell stress. You will still achieve an elevated metabolism that promotes fat burning. You also place the cells under just enough stress to help promote hypertrophy

It is important to understand training methods as the smallest oversight can cause more harm than good. HIIT is an effective tool but if it is not adequately fuelled it loses a lot of its benefits. It is a popular successful way to train and should be used in any program. Like any training method the process is the important part. It needs to be considered and managed properly in order to see the full benefit.

Our cardiovascular system is basically an engine. The bigger it is the more power we can produce. Like any powerful engine its performance is based on its efficiency and size. When we look at our body in terms of conditioning we should think of it like an engine. We must first build it and then fine tune it to be efficient for what we want it to do.

When we look at training we can look at it the same way. First we need to assemble the basic parts, this is the base miles in the offseason. This is what promotes the structural changes in our physiology. Our heart becomes larger and more powerful, capillarization occurs improving blood supply to the muscle fibers and in addition numbers of mitochondria increase within the cells. This process is gradual and is stimulated by large volumes of aerobic training. It is a relatively slow process but has a long lasting effect. Because longer duration is required the intensity must be relatively low in order to accumulate adequate volume without overtraining. This will gives us the foundation for our conditioning. Increasing aerobic capacity also has a vast amount health benefits associated, such as reduced blood pressure and a strong and efficient heart.

Once we build up a foundation we must then tune it. Now anaerobic style training comes into play. Anaerobic training up-regulates enzymes which promote glycolysis, the energy system utilised during high intensity. It also improves the ATP-CP energy system used during sprint type activity. The effects happen over a much shorter period of time and remain effective for a short period if training is not maintained.

HIIT has become popular because it yields results much quicker than LSD training. The issue is that the physiological changes that come from it are really only the icing on the cake. Without a strong base prior to HIT an athlete is neglecting a big part of their physiology. This is noticeable in a lot of team sports. An athlete may perform quite well at high intensity but struggle to utilise fat for fuel, causing him to tire late in a game. They also tend to recover relatively slower as their oxidative system does not have the capacity to remove lactate as effectively.

Athlete catching breath between play. Source:http://www.rugby365.com

If an athlete wishes to have good conditioning for their sport they must build a big engine to begin with and then tune it to be suitable to their activity. Whether they use threshold work or sprint intervals to do so will depend on the nature of the sport. The point I emphasise is that a strong aerobic base should never be neglected. Regardless if the sport is an endurance sport or not a strong aerobic system will be of great benefit to most athletes as it is still a major part of their physiology.

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HIIT, fat loss and muscle!

Building the engine!