High-intensity interval training (HIIT) is an exercise regime which has steadily increased in popularity due to its accessibility, versatility and numerous health benefits. Engaging in regular physical activity is extremely important to maintain good health and prevent chronic disease, however muvh of the population are inactive with lack of time being a major limiting factor.
Worldwide, nearly 1.8 billion adults are at risk of disease due to not enough physical activity. The World Health Organization recently updated their guidelines and recommended partaking in at least 150 to 300 minutes of moderate-intensity physical activity - or 75 to 150 minutes of vigorous-intensity aerobic exercise per week to achieve meaningful health benefits.
Read on to find out what high intensity interval training is, how it can improve health and longevity and tips to get started.
HIIT is categorized as exercise with repeated short bursts of intense activity followed by a brief period of recovery or low intensity exercise. The aim is to reach maximal or near-maximal effort during the short bursts. This means reaching >90% oxygen uptake or >75% of maximum power or 80-100% of your maximum heart rate which can be calculated by subtracting your age from 220.
There are many methods used for practising high-intensity interval training. As a general guidance, the length of high-intensity training should be the same as the rest period, such as60 seconds activity followed by 60 seconds of rest - or 30 second activity followed by 30 seconds of rest.
As fitness improves, the length of the rest period could be shortened. For example, a regime called Tabata involves 20 seconds of exercise at maximum effort and 10 seconds rest repeated for eight cycles, so for a total of four minutes. A typical HIIT session would last a maximum of 20 minutes.
Examples of exercises used in HIIT are:
HIIT using body weight exercises gives great versatility and can be carried out at home very easily.
Research has shown that HIIT induces multiple physiological adaptations which results in improved exercise capacity, cardiovascular and metabolic health.
Read on to find out more about the benefits.
Cardiovascular complications are a leading cause of mortality in those with poor metabolic health. Through high intensity intervals, a HIIT workout is designed to challenge the cardiovascular system.
HIIT has been shown to increase peak oxygen consumption known as peak VO2 or VO2 max, this is the gold standard measure of cardiorespiratory fitness. Increasing the VO2 max increases the amount of oxygen that your heart can pump around your body, thereby improving the efficacy of oxygen delivery and cardiovascular fitness.
An accumulation of evidence has shown that aerobic fitness (VO2 max) is the strongest predictor of future health, all cause-mortality and cardiovascular risks.
In systematic review and meta-analysis HIIT has been shown to be superior to moderate-intensity continuous training (MICT) in increasing cardiorespiratory fitness in both healthy individuals and those with metabolic diseases such as diabetes and high blood pressure as well as cardiovascular disease.
Additionally, HIIT has also been shown to improve heart health through improving cardiac function as well as reducing cardiovascular risks such as blood pressure.
As well as impacting cardiovascular health and fitness, HIIT has also been shown to influence metabolism, and studies have shown that HIIT can increase metabolism for hours after exercise.
This is known as the excess post-exercise oxygen consumption (EPOC) effect. EPOC refers to the increase in oxygen consumption and metabolism after exercise which occurs as the body recovers.
The duration and extent of EPOC is dependent on the intensity of the workout. A longer period of increased metabolism or EPOC after exercise is subsequently associated with an increased period of energy consumption and calorie burn even after you’ve stopped exercising.
It has been widely proven that exercise promotes fat loss and improves cardiorespiratory fitness. In a systematic review and meta-analysis of HIIT versus MICT on fat loss and cardiorespiratory fitness in young and middle-aged adults, HIIT and MICT resulted in a significant improvement in body composition and cardiorespiratory fitness.
HIIT resulted in a slightly greater improvement in waist circumference, percentage fat mass and abdominal obesity. Although the study indicates that the advantages of HIIT versus MICT was limited, HIIT was found to be more enjoyable and time saving. HIIT has also been shown to reduce visceral (organ) and hepatic (liver) fat, which in turn reduces cardiovascular disease risk.
It is known that resistance training is the gold standard for improving strength and muscle mass. It has been found, however, that high-intensity interval training performed at maximal aerobic capacity places high tensile stress on skeletal muscle and can somewhat resemble the demands of resistance training. A small randomized controlled trial comparing resistance training to high-intensity interval resistance training (HIIRT) in young adults showed that HIIRT improves muscle mass and muscle strength.
A significant barrier to lack of physical activity is time and it is the most prominent self-reported reason for individuals’ poor engagement in physical activity. One huge benefit of HIIT is that it is time efficient without losing any of the health benefits. With regimes as short as 20 minutes, HIIT can easily be incorporated into a busy schedule.
HIIT has multiple proven physical health benefits but how does it affect our mental well-being? Studies have shown that HIIT can improve mental health outcomes in both the healthy population and those with physical illness. It has been suggested that it improves depression severity, perceived stress as well as sleep, and psychological distress.
With busy schedules, being able to easily fit a workout into a daily routine is extremely important. HIIT is appealing due to its versatile and accessible nature. There are many exercises which do not require equipment such as jumping jacks, sprinting and high knees, this means a HIIT workout can be performed easily at home or in a local outside space, also keeping cost to a bare minimum. The workout can be tailored based on individual fitness levels - for example beginners can start with a longer recovery period which can be steadily reduced over time.
As mentioned HIIT has been shown to improve muscle strength and mass. Sarcopenia is a disease related to ageing and a growing health concern. It is a syndrome characterised by generalized and progressive loss of skeletal muscle mass and strength. This results in adverse outcomes such as poor quality of life and physical disability.
Physical inactivity is a risk factor for developing sarcopenia. HIIT has subsequently been proposed as a promising way to combat age-related muscle loss. A review of current literature has concluded that HIIT is a feasible method for treating sarcopenia; however, various studies were limited by small sample sizes and lack of intervention studies. Further research involving sarcopenic patients is required.
A meta-analysis has also shown that HIIT can promote improvement in functional movement in older adults, however it is unclear if it is superior to MICT.
An estimated 129 million people in the United States have at least one chronic disease. This includes heart disease, obesity, diabetes and hypertension. HIIT has been shown to reduce risk factors for chronic diseases.
Risk factors include heart rate, blood pressure, waist circumference, body weight, body mass index, blood sugar and cholesterol. Many of these factors are encompassed in a condition metabolic syndrome, those with metabolic syndrome are at increased risk of diabetes, cardiovascular disease and stroke.
Interval training has been shown to decrease the risk of cardiovascular disease, breast cancer, metabolic syndrome, rheumatoid arthritis known to cause back pain and osteoarthritis.
Furthermore, HIIT has been shown to improve insulin resistance as well as promote skeletal muscle adaptations that result in improved glucose tolerance and enhanced skeletal muscle fat oxidation to reduce the risk of diabetes. It has also been shown to reduce blood sugar, body fat, blood pressure and heart rate in obese individuals. It is more effective when performed at least three times per week for at least 12 weeks.
The benefit of exercise on health and life span is well known and it delays the onset of age-related disease. Little is known, however, about the effects of exercise at a genetic level on health and life span.
A small randomized controlled trial found that HIIT can reduce an mRNA measure of biological age in sedentary middle aged adults. It indicates that exercise might improve health and longevity by influencing age-related transcriptional processes.
Furthermore, we know that the length of telomeres is one of the main indicators of biological age which undergo shortening with each cycle of cell division. Telomere length is positively associated with cardiorespiratory fitness and physical activity levels. A recent review demonstrated that aerobic exercise training and/or endurance exercise appears the most effective in maintaining telomere length.
There are other ways in which you can improve longevity such as diet, read to find out more.
Getting Started with HIIT
When choosing the right routine there are a few factors to take into consideration.These include:
Find out more about ways to improve heart health.
If you are new to HIIT or exercising, start slow and allow your body to adapt, aim to start with one to three workouts per week and take rest days. It is also advisable to start with body weight exercise and introduce weights slowly.
To avoid injury, it is really important to warm up and cool down appropriately. Take rest days and avoid over training.
HIIT has generally been found to be safe and enjoyable for those with and without health conditions, but it is important that it is tailored to the individual based on their fitness and medical history.
Those who are deconditioned, recovering from injury, suffer with medical conditions or are elderly should consult their physician prior to starting a HIIT regime and ensure they are monitored throughout.
The key to incorporating HIIT successfully into your lifestyle is to create a schedule and be consistent. It can be added on to the start of your normal workout routine
You should not be doing HIIT more than three times per week. Try to balance HIIT with other forms of exercise such as resistance training or endurance.
High-intensity interval training has many health benefits, it results in improved cardiovascular fitness, muscle mass and fat loss and reduces the risk of chronic disease and promotes mental wellbeing. It has been found to be an enjoyable and time-efficient way to exercise, resulting in its increased popularity.
If you are new to HIIT or have any underlying health conditions, it is important to consult your physician prior to starting a HIIT regime.
We understand that HIIT is not for everyone but engaging in regular physical activity is of utmost importance for your health span and longevity.
It is important to make empowered and positive choices regarding your lifestyle to promote health and wellbeing. This includes HIIT if you feel it is right for you.
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