Effects of High-Intensity Interval Training for Weight Loss

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8th Feb 2020 Physiology Reference this


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High-intensity interval training as a method for weight loss and improving aerobic fitness


Introduction and definitions

This investigation will aim to consider how high-intensity interval training can be used as a method for weight loss and the improvement of aerobic fitness. High-intensity interval training (HIIT) also known as high-intensity intermittent exercise (HIIE) is a training method alternating short periods of intense exercise followed by a period of less intense active recovery with the duration depending on the participant’s fitness level.

Approach taken

The approach taken to present the findings of this investigation is to use four different subheadings (Principles of HIIT, HIIT program development, HIIT for fat loss and adaptations to aerobic endurance with the information being reported under the appropriate heading. The four subheadings represent the purpose of the investigation, how to achieve efficient results and what happens to the body. This investigation is predominately covered by Haff and Triplett (2015); however, it is realised that the information from this source may need to be combined with others. For example, Haff and Triplett (2015) reports on the program development for aerobic endurance, but doesn’t specifically cover weight loss. Haff and Triplett (2015) contains information from other researchers (Swank and Sharp. 2015; Reuters and Dawes. 2015). The main sources that used varied from sporting and health organisations as well as books and journals. It is worth noting that there is a wide range of knowledge reported in books, websites, journals and review articles, which can all be considered as suitable sources.

As this investigation is the review of current knowledge on high-intensity interval training as a training method it will be difficult to evaluate all the scientific information especially when considering how HIIT can be interpret ate differently for different participants 

Trustworthiness of sources

A wide range of books, journals and websites have been used as sources and the assumption can be made that these sources are credible and reliable. However, one of the journal articles about the ‘Impact of exercise intensity on body fatness and skeletal muscle metabolism’ is relatively outdated (Tremblay et al, 1994). Therefore, its credibility can be questioned, although many pieces of literature refer to this article so it is possible its credibility can be proven. It is also worth noting the websites used are organisations so their views could be seen as bias.

Main findings from the literature


Principles of High-intensity interval training

There is little knowledge and scientific evidence on the principles on HIIT. However, there is a lot attention given to the breakdown of this method of training. HIIT has been established as a growing trend that can be used by athletes and non-athletes. The focus of HIIT can be split into two stages (High-intensity training and interval training). Firstly, High-intensity training, will concentrate on performance efficiency and attain maximum outcomes and secondly, interval training targets time efficiency and when bought together it makes HIIT (High-intensity interval training). HIIT has been established by sporting professionals and literature as an effective method for fat loss due to due to it’s ability to simultaneously reduce fat and burn calories in a short period of time, which suggests why it has become a popular training method. Moreover, it can also be a beneficial training method to improve a person’s fitness level as well as cardiovascular health. Studies have shown that a more effective way to improve metabolic functions and respiratory and cardiovascular health may be to exercise at the body’s maximal limit with a less intense active recovery interval as it is believed to be more efficient than exercise at moderate intensity without rest intervals. There is not one specific method of conducting HIIT due to the fact participants respond in different ways and have different fitness levels. A few things that should be considered when developing a training program are: Exercise duration, Intensity, Recovery and Frequency, which will be discussed later on (Farms. 2018).

Studies into examining the effectiveness of high-intensity interval training have found that this method of training allows for the improvement to ‘sub-maximal and maximal exercise capacities, mitochondrial biogenesis, enzymatic markers associated with glycolysis, aerobic metabolism and b- oxidation and anthropometry’ (Earnest. 2008). It has also been suggested that these improvements occur with less caloric expenditure and within shorter periods of time than ‘traditional’ aerobic exercise (Tremblay. 1994).

To summarise, HIIT is an efficient method to achieve positive results by doing less, which we be beneficial for many due to the short duration period as time for exercise nowadays is scarce. By switching from short and intense periods of exercise to moderate intensity exercise periods, you’ll get more positive results than exercising for a longer period of time (Farms. 2018).

Weight loss

There is evidence suggesting that HIIT is an efficient method for weight loss. The reasoning for this is due to the intensity of the training as it doesn’t allow for the body to adapt to the intensity of the workout. When the the body starts to adapt at being at maximum levels, the intensity drops and once it starts to adapt to the lower intensity, it starts to increase. The constant changing of intensity has an increasing affect on a bodies resting metabolic rate (RMR) for approximately 24 hours after the workout has ended. Meaning that the body continues to burn more fat even when the participants stop exercising (Stones. 2017). As well as assisting individuals to loss weight quicker than normal or also maintains muscle mass and can even enhance the participants muscle mass with an appropriate training plan, which sets it apart from ‘traditional’ aerobic exercises as they are not known for maintaining muscle mass. Therefore, as HIIT can help develop lean muscle mass it can lead to better metabolism resulting in fat being burnt faster (Farms. 2018).

There is evidence associating aerobic endurance training with the changing of body composition, with the assumption that nutritional consumption is correct. Aerobic training tends to decrease body fat percentage with prolonged training programs having a greater affect on body fat percentage (Swank and Sharp. 2015).

Literature has also shown that HIIT is a more efficient training method when compared to steady training methods for participants with the goal of losing weight. Although, whilst it is believed that the ‘fat burning zone’ is achieved during moderate-intensity steady state aerobic exercise and with it resulting in increased percentage of fat being burned during exercise, total caloric expenditure and the breakdown of fat are greater in an HIIT plan, resulting in significant fat loss. This was evident in the study conducted by Tremblay et al (1994), who compared 2 groups of participants with one taking part in an endurance training plan and the other taking part in a HIIT protocol. It was found that even though that there were lower energy costs at the end of exercise plan (120.4 versus 57.9 MJ), the participants showed a 9-fold reduction in skin-fold (Schoenfeld and Dawes. 2009).

Majority of developed exercise protocols that are designed for weight loss have focused on steady state exercise at moderate intensity. However, the results for these kinds of protocols have be insignificant. Gathered evidence mentions that high-intensity intermittent exercise (HIIE) may be a more efficient way of exercising with the goal to lose weight (Boutcher. 2011). Studies such as Trapp et al (2008) and Dunn (2009) both supported this. Both studies adopted similar methods with Trap et al (2008) conducted a 15 weeks and 20 minutes long HIIE program and Dunn (2009) conducting a 12-week program with a fish oil supplement and Mediterranean diet being incorporated. Trapp et al (2008) reported that a significant lose in subcutaneous fat (2.5kg) in the group taking part in the HIIE program than the group in the steady state exercise. Dunn (2009) reported similar results with a lose of 2.6kg subcutaneous fat. Regarding abdominal fat both studies reported significant reductions. These studies used women who had already low fat levels so suggested that it may be possible that the reduction in fat levels can greater in men with high levels of fat.   

There is a common theme amongst the literature supporting one another in the that HIIT is an efficient method of exercise, such as Schoenfeld and Dawes (2009) who reported the benefits of HIIT. The authors mention that HIIT can potentially increase the body’s ability to use lipids as an energy substrate, with the increase of enzymes that allow for beta-oxidation (Schoenfeld and Dawes. 2009). Moreover, other literature has observed HIIT as a more effective way to lose excessive body weight than continuous training at moderate-intensity (Sijie et al. 2012). High-intensity interval training is a method of training that has been suggested to be more time-efficient when being used to improve a participant’s body composition as well as disease (Gerosa-Neto et al. 2016).

Adaptations to aerobic endurance

Over time a participant can expect adaptations to their aerobic system to occur. Taking part in regular training will have effects on the cardiorespiratory functions and skeletal system. As training progresses the cardiovascular system becomes more efficient as the participants resting heart rate decreases and stroke volume increases. Moreover, the cardiac muscle is also affected as it increases in size, which allows for increased blood flow and supply (Bradley. 2018). During the adaptations, lung functions also improves. The muscles associated with the respiratory become stronger allowing for increased tidal volume and breathing frequency, resulting in more air being exhaled and inhaled. The strength of the diaphragm muscle also increases, allowing the participant to maintain regular breathing patterns, which is important due to the pressure being placed on the muscles caused by the forceful breathing that comes with exercise. Aerobic exercise also increases a participant’s maximum oxygen uptake, resulting in the bodies ability to utilise the oxygen increasing, which is vital during exercise, because as the intensity increases so does the bodies demand of oxygen (Bradley. 2018)

There is a wide range of research on the adaptations caused by aerobic endurance training. Aerobic metabolism is an important component in exercise. Aerobic metabolism produces ATP as energy using fats, proteins and carbohydrates. Athletes require appropriate training and conditioning for the aerobic metabolism as many sports require a constant demand of aerobic fitness. Training the aerobic system increases an athlete’s ability to sustain performance as well as their recovery rate. Aerobic training can cause reductions in body fat, increased VO2 max, running economy and cardiorespiratory functions. It can also lower blood lactate, increase density of capillaries and improve enzyme activity (Swank and Sharp. 2015). Training the aerobic system can cause a ‘5% to 30%’ increase in an athlete’s aerobic power. However, this increase is dependent on the current level of fitness when that start of the exercise has commenced (Astrand et al. 2003). The training intensity is an important part of exercise. As studies have shown that prolonged exercise with a high number of rest periods, the result on the aerobic system will be insignificant. Moreover, exercise with high intensity and short recovery periods have been proven to improve aerobic endurance (Swank and Sharp. 2015).  Aerobic fitness has an important part in determining performances in sport and everyday, it also has an impact on health. Relating to performance, the aims of aerobic fitness training is to increase an individuals maximal oxygen uptake (VO2 max) as well as lactate/ventilatory threshold (Baquet et al. 2003).

Every person requires a basic level of cardiorespiratory fitness, which needs to be trained with many researchers agreeing with that HIIT being an efficient training method (Swank and Sharp. 2015). There is a growing interest into HIIT with a wide range of literature supporting the efficiency of HIIT for promoting positive health-related changes in an adult population. However, there isn’t much research on the effect of HIIT on a younger population. A systematic and meta-analysis study by Costigan et al (2015) set out to evaluate the effects of HIIT on adolescent’s health. It was find that there was a significant improvement in the participant’s cardiorespiratory fitness and a reduction in their body fat percentage.

Aerobic endurance program development

Developing an exercise program is an important matter as it can have significant impacts on the results of the exercise. Exercise programs may have to be altered for each individual as people respond differently. However, it is reported that an individuals gender isn’t a cause for altering exercise programs (Reuter and Dawes. 2015). In the case of clinical populations as there may be health issues that a coach needs be aware of to reduce the risk of aggravation (Dalleck. 2019).

As mentioned before there are a number of variables that need to be considered such as; ‘exercise mode, training frequency, training intensity, exercise duration and exercise progression’. Exercise mode is the specific activity completed by an athlete. Therefore, the program should try and copy this to promote positive adaptations. Regarding non-athletes, it may be useful to ask for preferences. The frequency refers to the number of sessions a week and relates to current fitness levels and for athletes the stage of the current season.  The current fitness levels may influence the training frequency as more recovery days may be required for the individuals with the low fitness levels. Choosing the relevant training frequency is a vital part of developing part of developing a program as too much cause overtraining or possible injury. Recovery is believed to reduce the risk factors. Lack of recovery can result in an athlete’s inability to train at the set intensity of the exercise session. Furthermore, recovery allows for the reduction of fatigue, which is necessary for achieving optimal performance levels (Barnett. 2006). It is also believed that recovery develops the benefits already gained (Reuter and Dawes. 2015).

The level of training intensity correlates to the adaptations associated with aerobic exercise. For example, the higher the intensity the more significant the adaptations will be. As we know high-intensity exercise increases cardiorespiratory functions, which allows for more oxygen to be delivered to muscles (Reuter and Dawes. 2015). Exercise duration is often dependent on intensity as higher the intensity tends to mean shorter durations and vice-versa (Reuter and Dawes. 2015). Exercise progression is dependent on the individual goals as this can affect in the increase of frequency, intensity and duration and the reduction of recovery times. It is reported that there should be approximately a 10% increase of these variables (Hagerman. 2012). However, as important progression is the coach needs to be cautious of overtraining, which may be caused by the increase of intensity and duration mid-session (Dalleck. 2019).

According to the literature we now know that HIIT is an efficient training method for weight loss and the improvement of aerobic fitness.  An example of a HIIT program is set out in table 1.

Table 1: Example of HIIT programs for sedentary and recreationally trained individuals (Ross et al. 2016

Main recommendations for coaching/instructional practice

This study has investigated has reviewed a wide range of evidence from credible literature, of the benefits of HIIT and how to achieve the most effective results. The recommendations below focus on the protocols of HIIT and how they can be manipulated to increase efficiency. However, it is important to note that these are the main personal recommendations of this study after being reread and refined with a focus in the development of a HIIT protocol.

Recommendation 1

As we know from the evidence that HIIT is an effective method of training to increase a person’s fitness level and for weight loss. It is recommended that a coach incorporates different training loads by manipulating times (recovery and duration) and the choice of exercises. They also suggest that a coach use exertion scale (ranging between 9-10) so they are able to track intensity.


Recommendation 2

The literature of this investigation provides evidence that evaluates the best methods of instructing HIIT. Throughout the investigation these factors keep appearing regardless of goals, such as adequate recovery, finding the correct intensity, duration and frequency. Therefore, a coach will need to adapt each protocol to each participant as their fitness level and physical ability may differ from one another.

Recommendation 3

A coach also has a duty of care towards the participants so they will need to make it safe, which also applies to the participants who self coaching. It is suggested that the coach conducts pre-screening to assess if the participants suffer from any health problems. Moreover, the coach needs to be sure the participants are prepared correctly and recover, which is done by insuring they are properly hydrated with sufficient nutrition, appropriate clothing and take part in a warm-up. Post exercise the coach will need to make sure take part in a cool-down and rehydrate. A coach will also need to set an appropriate intensity and make sure the participants adhere to that intensity as the smallest extension of intensity can be the difference between high-intensity and overloading. well as educating the participant on when to rest, for example chest pain, muscle/skeletal pain or fatigue.



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