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HIIT VS Continuous Training

The obesity crisis has never been as big of a problem than it has right now as the current COVID-19 pandemic has illustrated the higher risk of vulnerability for those who suffer from obesity and the comorbid conditions. The prevalence of comorbidity relating to a persons weight has been very well documented for years amongst the scientific literature through the know associations of obesity and the likelihood of developing type 2 diabetes due to the pancreas inability to respond to insulin as a result of a lifetime of poor dietary choices.

With gyms re-opening across the US as of the 25th of July never has the debate of HIIT vs Continuous training been as relevant as it is now as people flock to the gyms in search of some normality and a vast amount of benefits both physically and mentally. However, if you want to make up for lost time or you simply just want to better your health in an effort to lower your risk of falling seriously ill in the middle of a global pandemic than you would want to employ a set of specific training methods which invoke the best physiological response in the shortest period of time.

It’s well documented that in today’s society’s the lack of exercise and physical activity has led to an increase in health problems that occur with obesity and its related illnesses. Obesity is part of a disease called metabolic syndrome which is often recognised by an increase in body fat percentage, particularly in visceral areas (ARDEKANI, 2004). Obesity and weight gain are strongly correlated to the development of chronic diseases such as hypertension, hyperlipidaemia and insulin resistance which all are risk factors for cardiovascular diseases. Epidemiological studies have shown that Obesity is also now recognised globally as a major cause of preventable ill health and death from all causes and multiple disabilities. An influential studt carried out in 2014 outlined obesity to be the second largest burden on the US’S economy costing the country 47 billion a year. The report also stated that 30% of the global population is now overweight or obese and this is set to rise to 50% of the population by 2030. Although the benefits of regular moderate exercise are well documented the HSE 2012 report showed that only 66% of men and 56% of women met the guidelines aged 19 and over for participation in at least moderate intensity activity (HSC12).This has led too much academic discussions as to which form of exercise is best to help tackle to epidemic and its health related problems. It has long been understood that there was a linear relationship between a person’s health and the amount of time you spent exercising, however even though this may be true HIIT has in some cases demonstrated a superior linear relationship with significant health markers and athletic performance. This prompted academics to study whether exercise intensity is as effective at producing the same if not better physiological responses within a significantly shorter period of time. The potential benefits are therfore two fold if HIIT can significantly improve health markers through the adaptations that are produced as a result of training intensity then it can also aid in the war against obesity as it will be much easier to convince a nation to participate in as little as four minutes of exercise!!

HIIT is considered to be a superior form of interval training, an exercise approach consisting of alternating periods of short intense bouts of anaerobic exercise with less-intense recovery periods. One of the earliest and most respected models for this type of training is the Tabata method. This method is made up of short bouts of high intensity work which last 20 seconds with short active recovery periods lasting 10 seconds. The process is repeated 8 times which totals to only 4 minutes total exercise. Evidence put forward amongst the scientific literature demonstrated that thr Tabata training protocol is as effective at prompting physiological benefits as traditional forms of long boring continuous training. The initial research  in 1996 undertook a comparative analysis which compared tje effects of Continuous training which was working at 70% of VO2max for 60 minutes with HIIT at 170% of vo2max. Following the 6 weeks of moderate intensity endurance training there was no significant effect on anaerobic capacity but found that 6 weeks of HIIT could improve anaerobic capacity and VO2 simultaneously. Unsurprisingly the findings from this study resulted in a number of HIIT programs being developed. Although there are many different ways HIIT training sessions can be performed great the core principals were still applied of all-out effort combined with either total rest or active recovery periods. However HIIT had not been commonly used among non-athletes and the general public, the proficiency of getting an intense workout and significant health benefits in a short period of time has the potential to engage people in physical activity. Hegerud et al study in 2007 put forward tje obvious sociological benefit to the wider public is the potential of consistently partaking in HIIT is far greater due to the known time/cost/reward relationship which influences all aspects of human behaviour.

Therefore the Tabata protocol may be an influential training method in reducing obesity levels decreasing the burden on the NHS and significantly reduce the risk of falling seriously ill in the middle of a global pandemic. This inevitably led to the introduction of commercial programs such as Insanity, P90X and Crossfit (FEITO, 2014). As our understanding of HIIT has increased, researchers have established that HIIT has many aerobic and metabolic benefits why also showing to help improve cardiovascular risk disease (CVD) risk factors (BUCHAN, 2011). A wealth of research has also proposed an exponential relationship between exercise intensity and the magnitude of the excess post oxygen consumption (EPOC) for specific exercise durations.  

A shared protocol used in various HIIT studies has been repeated Wingate tests which involves a series of 30 second cycling bouts at maximal effort against a supramaxial workload. Studies compared 6 weeks of Wingate HIIT training 3 times a week to traditional endurance training. Each HIIT session was made up of 4-6 bouts of 30 second sprints with 4 minute recovery periods in-between. The over-all amount of exercise at maximal effort is between 2-3 minutes. In spite of a 9 fold lower training volume with the HIIT group similar training induced changes in skeletal muscle in oxidative capacity and cardiovascular function were found (BURGOMASTER, 2008).The study also underlined that they found HIIT training to induce other adaptations commonly associated with endurance training such as; an increase in resting muscle glycogen content, an increase in whole body lipid oxidization and reduced glycogen utilization and lactate production during exercise. (HELGERUD, 2007) Research showed that training induced adaptation which occurred with HIIT are similar and in some cases greater to those that are found when participating in CT. 

A key point for metabolic adaptations is the metabolism of fat for fuel during exercise. Due to the significantly reduced time of total exercise of HIIT and its proposed benefits over traditional CT its effectiveness for burning fat has been studied meticulously. (EMBERTS, 2013) Cites Burgomaster 2005 study saying that HIIT was shown to stimulate the fat burning process more rapidly than CT. Perry et ell 2008 study showed that after 6 weeks of HIIT F oxidation was noticeably higher and CHO oxidation lower.  The main ATP resynthesis pathway during CT would be expected to rely mainly on aerobic energy turnover where as HIIT relies on anaerobic metabolism hence we see greater utilisation of F during the 6 week study Perry carried out. HIIT has also shown to increase the amount and size of mitochondria cells and is referred to as an increase in mitochondria density. This means that with increased mitochondria density the body is able to breakdown more CHO & F during aerobic exercise resulting in more energy available (Burgomaster et al 2008). 

Another significant metabolic factor HIIT has shown to increase is the upsurge excess post oxygen consumption (EPOC). Whilst exercising the body’s need for oxygen increases which means that oxygen uptake (VO2) increases also to meet the specific needs. After exercise VO2 doesn’t return to resting levels straight away thus we get EPOC. VO2 is one of the most commonly assessed variables in the study of exercise physiology. Understanding of oxygen consumption allows us to document the precise determination of energy expenditure also the measurement of the overall physiological stress imposed by exercise. The body roughly burns 5 calories of energy in order to consume 1 litre of oxygen. Hence the greater amount of oxygen utilised both during and after a workout will results in an increase of net calories burned.  Exercise that places a greater demand on the anaerobic energy pathways throughout the workout causes an increase in the need for oxygen after the workout, thus enhancing the post-exercise energy expenditure. HIIT has been glorified because of its potential to dramatically increase EPOC compared to traditional continuous training. EPOC is the caloric after burn after an exercise session, oxygen consumption remains higher as the working muscles restore physiological and metabolic factors to their original levels. In their review article, Laforgia, Withers and Gore (2006) noted that exercise intensity studies indicate higher EPOC value with HIIT training than with CT. The review quantified at higher intensity’s when energy is required immediately anaerobic pathways provide the ATP much more rapidly.  

However EPOC only encompasses 6-15% of the net total oxygen cost of the exercise (BORSHEIM, 2003). To put into perspective if someone was to burn a 1000 calories during HIIT this means that at best they will burn an additional 150 due to EPOC. Also the greater EPOC was only seen in untrained individuals trained individuals saw there metabolic rate return to normal faster. However Borsheim’s study did state that HIIT may have a more chronic effect on resting metabolic rate (RMR) which at times made it hard to differentiate between this and the EPOC effect.  

The ACSM 2010 guidelines recommend people burn a minimum of a 1,000 kcals a week due to physical activity if they want to better their health this equates to 150-300 kcals per session. Also they state that in order to enhance weight loss an energy expenditure should be around 2000 kcals or greater. There’s an abundance of research to show that EE has a greater correlation with intensity of exercise as it does with the duration of exercise.  A study done in 2013 by Emberts tested the EE of 16 subjects following the Tabata protocol and found them to be expending between 240-360kcals per session equalling on average 15kcals a min. Upon reflection of that paper and the ACSM guidelines it’s clear to see that Tabata clearly poses great benefits when looking at EE as it falls well within the recommended EE per session but in considerably shorter than traditional CT. However the role of exercise in the maintenance of body mass is not primarily facilitated by the amount of energy expenditure whilst your exercising as studies have shown the increase EPOC and resting RMR to play a significant role. Overall, HIIT claims to be better than endurance training since participants receive the same health and fitness benefits in a shorter period of time. 

Blood lactate concentration (BLC) is one of the most often measured parameters during clinical exercise testing as well as during performance testing of athletes. While an elevated may suggest ischemia or hypoxemia, it’s also considered a normal physiological response to exertion. When VO2 doesn’t meet the needs of the body during exercise CHO is broken down for energy and makes lactic acid (LA). 

 In response to maximal exercise lasting 30-120 seconds, peak La values of 15–25 mM can be seen 3–8 minutes post exercise. BLC is a better indicator of exercise intensity than heart rate. At rest and during most exercise conditions, whole blood values are on average 70% of the corresponding plasma values. Although Lactate its self is not thought to be detrimental to performance as once thought, high levels indicate that the body has been placed under significant amount stress due to exercise. Therefore being a good indicator as to how strenuous and demanding the exercise was on the body’s working muscles and complex systems. A study done by (KAPPENSTEIN, 2015) looked at BLC in adults and children following a repeated sprint protocol deemed that active recovery is much more efficient suggesting an elevated oxidative metabolism during active recovery minimizing the accumulation of LA within the blood. The key aim of this paper is to present a threefold report which reviewed current research and then discus’s the data collected then evaluate which type of training is more efficient when looking at EE, VO2, BLC & utilisation of CHO and F. 

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