‘’HIIT or Hit it ‘till threshold’’


You probably hear quite often the term HIIT or High-intensity-interval- training when visiting a gym or attending a fitness group class. Moreover, if you are doing cross training, cross-fit, orangetheory or boot-camp training, HIIT is something you should be familiar with, as fitness instructors always refer back to it when explaining workouts, at which intensity you should aim for and for how long.


HIIT is one of the most popular types of training among not only athletes but people of all ages. It can be adjusted for all people of all fitness levels and special conditions such as obesity, metabolic syndrome, and diabetes. Now it starts to become even bigger and more popular as there are a number of research studies that have identified and confirmed its benefits towards cardiorespiratory and physical health. Today almost every sports center or gym has at least one fitness class of HIIT or they have programs that run every 30 minutes in the place with the training machines, where people can workout on the machines in a circuit way, implementing HIIT instead of running on the treadmill for 45 minutes.


High-intensity-interval- training can be defined as a training program of 20 to 60 minutes that involves repeated bouts of exercises followed by varied recovery times as stated by the American College of Sports Medicine (ACSM). HIIT is basically a cardio type of training that improves both aerobic and anaerobic fitness. It can also include weight exercise, plyometrics and exercises with elastic bands thus turning into a very dynamic type of training. HIIT workouts increase the burning of calories compared to traditional workouts especially after the training due to EPOC (1). EPOC (excess post-exercise oxygen consumption) is the amount of oxygen required to restore your body back to resting metabolic functions and this is the reason why you still burn calories after you have finished the workout. EPOC values increase after a HIIT workout due to high-intensity exercises and make our body burn 6 to 15% extra calories. To make it more simple, the main idea of HIIT is;


Working harder = higher oxygen intake = greater calorie burn


When I first heard of HIIT, it sounded to me too scientific and as a fitness freak, I wanted to try it. I was sick of the gym. Spending hours and hours on the treadmill, static bicycle or elliptical machine, waiting to reach the 15 or 20 minutes in order to get a bit sweaty and then spend 8-10 minutes on each machine just to train a group of muscles and then sit there watching everyone exercising while I was waiting for the next set…. and then again 10 more minutes on the treadmill to cool down. Too boring to be true right? Of course, if your goal is different such as muscle hypertrophy or corrective exercising, then there are appropriate training plans. But for me, my goal was to improve my physical health, increase my stamina, boost my metabolism and tone up. There are so many ways to make training enjoyable and intense in 30 minutes and HIIT is one of them. After my first HIIT training, I never trained at the gym the traditional way as it really changed my whole perspective about training. What I love about it, is that it can really push you to your limits but in the end you want more, thus making it addictive. In this article, I focus on the importance and benefits of HIIT. Furthermore, on the second part, I share a sample of HIIT workouts and some tips on how to create your own HIIT workout with or without gym equipment in different settings.





  1. Cardiovascular Health: HIIT due to the use of moderate-to-vigorous exercise intensities, contributes to the reductions of cardiovascular diseases (coronary heart disease, atherosclerosis, stroke etc) in both men and women by improving cardiac function (2). This is because the muscle of the heart is becoming stronger due to exercise and thus the stroke volume increases. Stroke volume is the amount of blood pumped by the heart to the circulation in order to reach our body cells. That is to say, our heart is able to pump more blood into our arteries without a lot of effort. Another benefit is that blood is able to flow more smoothly in the vessels thus reducing the risk of blood clots and hypertension (3). Moreover, numerous studies have shown that high exercise intensity was related to decreased all cause-mortality, independent of the duration of activity.


  1. Cardiorespiratory fitness: HIIT increases our heart rate. This causes our VO2max and stroke volume to increase thus improving heart circulation. VO2max is the maximum amount of oxygen that a person can utilize during very intense exercise. To produce the energy we need oxygen, therefore, the higher amount of oxygen we use the more energy we can produce.


  1. Insulin Sensitivity: Exercise improves insulin sensitivity and HIIT can be an effective and efficient type of workout. Insulin sensitivity means that your body cells are sensitive to insulin and therefore they are able to absorb the glucose. However, in people with diabetes type 2, there is a cell dysfunction when it comes to insulin. The body cells are not sensitive to insulin anymore and therefore they don’t absorb glucose anymore. As a result, these people have high levels of blood glucose which can cause a number of health problems. Research studies have revealed that generally exercise and high volume and intensity training can improve insulin sensitivity not only in diabetics but also in the healthy population where improvements can be noticed from the 2nd week of training (4,5,6). However, it should be noted that without the consumption of a balanced diet, it is hard for our bodies to achieve these improvements.


  1. Increased Metabolism: As I mentioned before during HIIT, EPOC elevates and makes us burn up to 16% of extra calories -that is around 80 to 100kcal, as it takes longer time to recover than moderate-intensity exercise (7,8). Additionally, HIIT helps you build lean muscle. Thus it gradually increases our metabolism, induces weight loss and long-term it can add up to our overall energy expenditure, which can be equivalent of 1 to 2kg (~2-6 pounds) of fat in a year, just from exercising (9).



  1. Convenience: ΗΙΙΤ does not necessarily require any expensive equipment or a gym. You can perform HIIT anywhere with or without dumbbells, kettlebells, medicine balls or elastic bands. You can get very creative by doing exercises using your own body weight such as push-ups, burpees or jump-squats. Moreover, by doing HIIT, even for 20 minutes, is long enough to train your whole body muscles, ameliorate your endurance and burn a sufficient amount of calories. In other words, instead of exercising for 1 hour or 90 minutes, you exercise for 20 to 60 minutes accomplishing the same quality of workout, ‘’leaving nothing out’’.

These are some of the main health benefits of HIIT. Another benefit which I did not mention above is better mental health. As you might know, exercise causes our bodies to produce the ”happy hormones” which are adrenaline, dopamine, and oxytocin and have an antidepressive effect on our mental function. This is why most of the times after your workout, you are in a good mood and feel very energetic.


Final Notes

One thing I would like to point out about HIIT is that it can be a bit dangerous for a beginner or someone who has never trained before. The reason I am saying that is because, someone who does not exercise very often or who have never exercised before, most of the times has very weak core muscles. Weak core muscles, decreased stability and balanced are associated with high risk of injuries and bad posture. Moreover, they make it very difficult and tiring to perform any exercise. For example, someone who does not have strong abs, cannot perform right a push-up. Long-term wrong execution of exercises can cause further musculoskeletal problems. Therefore I would strongly recommend to first spend some period of time working on stabilization and core strength for a period of time 3-4 weeks (as recommended by NASM[1]). Then you can proceed to HIIT, unless you suffer from joint or other health issues where you should consult your healthcare practitioner.


Last but not least, make sure you train with a qualified professional as he/she has knowledge on physiology, anatomy, and biomechanics. He or she knows how to show correct technique and execution of exercises, how to prevent any injuries during the session and how to design an effective training plan. There are a lot of ‘’self- taught’’ trainers that base their expertise on their personal experience and on their own workouts and yes most likely they have a very muscular body. But they lack one main factor which is necessary for every professional, and that is knowledge.


[1] National Academy of Sport Science




  1. LaForgia, J., Withers, R. and Gore, C. (2006). Effects of exercise intensity and duration on the excess post-exercise oxygen consumption. Journal of Sport Sciences,24, 12, 1247-1264.


  1. Wisløff, U., Ellingsen, Ø., & Kemi, O. (2009). High-Intensity Interval Training to Maximize Cardiac Benefits of Exercise Training?. Exercise And Sport Sciences Reviews37(3), 139-146. http://dx.doi.org/10.1097/jes.0b013e3181aa65fc


  1. Ciolac, E. G. (2012). High-intensity interval training and hypertension: maximizing the benefits of exercise? American Journal of Cardiovascular Disease2(2), 102–110.


  1. Keshel, T. E., & Coker, R. H. (2015). Exercise Training and Insulin Resistance: A Current Review. Journal of Obesity & Weight Loss Therapy5(0 5), S5–003. http://doi.org/10.4172/2165-7904.S5-003


  1. Borghouts, L., & Keizer, H. (2000). Exercise and Insulin Sensitivity: A Review. International Journal Of Sports Medicine21(1). http://dx.doi.org/DOI: 10.1055/s-2000-8847


  1. Gibala, M., Little, J., MacDonald, M., & Hawley, J. (2012). Physiological adaptations to low-volume, high-intensity interval training in health and disease. The Journal Of Physiology590(5), 1077-1084. http://dx.doi.org/10.1113/jphysiol.2011.224725


  1. Gonzalez, P., Lizee, T., Gehring, L., Charter, M., & K Witzke, K. (2016). Heart rate and excess post-exercise oxygen consumption of whole body hight-intensity-interval training vs moderate-intensity exercise. International Journal Of Exercise Science: Conference Proceedings8(4).


  1. Schaun, G.Z., Alberton, C.L., Ribeiro, D.O., Pinto S.S. (2017) Acute effects of high-intensity interval training and moderate-intensity continuous training sessions on cardiorespiratory parameters in healthy young me. European Journal of Applied Physiology 117: 1437. https://doi.org/10.1007/s00421-017-3636-7


  1. ACE (2016). Could EPOC Help Solve the Obesity Epidemic?. (2016). org. https://www.acefitness.org/education-and-resources/professional/prosource/october-2016/6091/could-epoc-help-solve-the-obesity-epidemic



  1. Photo by Scott Webb on Unsplash
  2. Photo by Alexander Redl on Unsplash
  3. Photo by Cyril Saulnier on Unsplash


Lydia Chrysoula

Author Lydia Chrysoula

Lydia is an Oxford Brookes (Uk) graduate with a bachelor degree in Nutrition Science. She is also certified Personal Trainer by the National academy of sports medicine, and Zumba Instructor. She has travelled in different places all over the world as travelling is her favourite hobby. She has spent a semester of her studies in Melbourne, Australia, focusing on sports nutrition, psychology and health behaviour change.

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