Lit Review on High Intensity Interval Training
High intensity interval training (HIIT) is a new popular method of exercising that optimizes your workout by completing a series of short, high intensity exercise (90% of your maximum heart rate =220-age). , followed by longer, lower-intensity exercise (55 to 70 % of your maximum heart rate=220-age). High intensity interval training is said to be significantly more beneficial than other forms of cardiovascular workouts because it challenges the body differently and is more extreme then a moderate cardiovascular workout (Omidi, 2010).
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Moderate cardiovascular workouts do increase cardiovascular fitness and muscular fitness, but if there is a faster way to achieve your goals, then that method should be utilized. HIIT can increase the effects of cardiovascular fitness by increasing the mitochondrial abilities allowing the body to work more efficiently and muscular strength by challenging the muscles by changing the intensity of speed causing the muscle to use different fibers and energy stores (Omidi, 2010).
One study that shows the effects of improved cardiovascular fitness with HIIT researched the effects of low volume HIIT versus all-out sprint interval training. They study had 24 young males, age 24 to 26 that were then separated into three groups of 8: the sprint interval training group which, completed three to five cycling rounds of 30 seconds all-out and 4 minutes of recovery in between, the low volume HIIT group which completed six to ten cycling rounds with two minutes of recovery in between and the control group with no training.
The training lasted four weeks and the methods of Volume Oxygen consumption max test (VO2 max tests the maximum capacity of an individual’s body to transport and use oxygen during incremental exercise), time to exhaustion, and Wingate test to measure power output were compared before and after the four weeks of training. This study found that there was only significant improvement in power output with the all out sprint interval training group. But they found that sprint interval training and HIIT are very beneficial for VO2 and time to exhaustion for healthy individuals.
Bayati, 2011) Another study that shows the effects of improved cardiovascular fitness with HIIT, looked at the benefits to individuals with coronary artery disease (Gremeaux et al, 2011). The study showed the effects of different training methods on coronary artery disease patients after an acute coronary syndrome. The study took 27 individuals with coronary artery disease and separated them into three groups of 9; one with moderate intensity continuous exercise (MICE) at 70% of max HR, one at MICE at maximal 6 minute walk test HR, and one using HIIT.
The methods used were comparing VO2 peak, six minute walk test, and 200 meter fast walk test every two weeks for six weeks. Though this was a pilot study with a very small amount of individual; the study did find that peak VO2 improved in all groups and was higher in the HIIT group on average by 2 ml. min kg. This study was very basic and short and future research needs to look at the longer effects of HIIT on individuals with coronary artery disease. HIIT is beneficial to all for cardiovascular purposes, and it also is a significant benefit to muscular strength. Gremeaux, 2011)
A study done by Gurd et al, 2010 looked at the effects of a six week HIIT workout on the SIRT1 levels in human skeletal muscle. SIRT1 is the silent mating-type information regulator 2 homolog1; which signifies increases in gene expression of mitochondrial (mitochondrial biogenesis) and fatty acid oxidative genes increasing the rate of fat oxidation. Nine subjects performed six week high intensity interval training which consisted of three days a week, ten exercise intervals lasting four minutes with a two minute rest in between at a 90% VO2 power output during each four minute intervals.
The research methods for this study included taking a small frozen muscle sample and isolated the proteins then took a SIRT fluorometric assay kit to find the SIRT1 level before and after the six weeks of training. They found that after six weeks of HIIT there was a significant increase in SIRT1 levels concluding that with HIIT you can increase the body’s ability of mitochondrial biogenesis because with more mitochondrial abilities the better your body can produce energy for respiration and physical work and fat oxidation which can get you leaner faster.
Gibala’s, 2009, study agrees with their findings. Perry et al, (2008) also looked at fat oxidation in his study by focusing on the effects of HIIT on fat and carbohydrate metabolic capacities in skeletal muscle. This study had eight individuals begin a six week HIIT program that included using the cycle ergometer three days a week (a one hour interval consisting of ten four minute exercise intervals with 2 minutes of rest) for 6 weeks totaling 18 hours. Perry et al. s methods were to take muscle biopsies before during and after exhaustion during a VO2 peak test before and after the six week training.
They found that 18 hours of HIIT 3 days a week for over 6 weeks increased fat oxidation and skeletal muscle capacities. Another study completed by Forbes et al. (2008) looked at the effects of a short term HIIT on the phosphocreatine (PCr) recovery in skeletal muscle. PCr breakdown and resynthesis of PCr is directly related to mitochondrial content, the faster the breakdown and resynthesis the more efficient your mitochondria are working.
Their study took 14 young healthy individuals age 17 to 25 (seven experimental and seven control). The seven members of the experimental group were put on two weeks of HIIT with six training sessions on a cycle ergometer (first two, four intervals, second two, five intervals, third two, six intervals, all intervals lasted 30 seconds and had a four minute light cycle in between). The PCr levels were collected using phosphorous-31 magnetic resonance spectroscopy and then compared between the control and experimental groups.
Forbes et al. found that PCr recovery was improved by 14% with short term HIIT, which tells us that short term HIIT is a good way to increase oxidative capacity of skeletal muscle, which will increase our recovery and improve our muscular abilities. HIIT can increase the effects of cardiovascular fitness by increasing the mitochondrial abilities allowing the body to work more efficiently and muscular strength by challenging the muscles by changing the intensity of speed causing the muscle to use different fibers and energy stores.
The studies have shown that fat oxidation, VO2 capacities, and mitochondrial abilities can be increased with HIIT. However, it was found that the effect of HIIT on muscular strength is lacking in studies; circumference or power output increased is not thoroughly compared and may be beneficial in starting a HIIT routine. A thorough study comparing a moderate cardiovascular workout routine would also be beneficial to narrow down all benefits in one study to compare cardiovascular fitness and muscular strength.