High Intensity Interval Training – HIIT

5 Minute Read

Lady performing an at home H.I.I.T workout
Lady performing an at home H.I.I.T workout

Introduction to HIIT Training

High intensity interval training, commonly referred to as HIIT, is an approach to training that requires participants to undertake exercise at around 80-95% of their age predicted maximum heart rate. However, many HIIT programmes do not actually monitor heart rate and so it is feasible that participants performing these programmes will be working at much higher intensities.

The recovery periods used may last equally as long as the work phase and are usually performed at 40-50% of a person’s estimated maximal heart rate; again this is often a feature of HIIT sessions that may not be controlled when heart rate monitors are not used.

Due to the intensity of HIIT, exercise sessions are typically much shorter than conventional workouts; this is what makes them appealing to many exercisers. A typical HIIT session will last anywhere between 20-60 minutes depending on the fitness level of the participants and the type of exercise being performed. However, some variations of HIIT, like Tabata Training for example, only require participants to perform as little as 4-minutes of total work.

H.I.I.T workout

Also known as high intensity intermittent exercise (HIIE) and sprint interval training (SIT), HIIT is an advanced approach to exercise that must only be used with conditioned exercisers. Prior to performing HIIT, participants are encouraged to establish a base level of fitness for a number of weeks or months to ensure that they are sufficiently conditioned.
Additionally, HIIT must only be used with participants that are apparently healthy and who do not belong to any special population group(s). Clearance from a G.P. may therefore be appropriate before partaking in HIIT, especially with those who have previously been sedentary. Prolonged inactivity increases coronary disease risks associated with high intensity exercise and many of these risks have no outward signs or symptoms. Caution is always the best approach in these circumstances.

HIIT can be performed using free body exercises like burpees, jumping jacks, high knees, and fast feet drills, or with mainstream cardiovascular activities like running, cycling, rowing etc. In fact, just about any form of strenuous exercise can be used to create a HIIT session, which is why the application of HIIT so broad.

HIIT has become increasingly popular in recent years because of the volume of research that has been undertaken in this field. According to a 2011 American College of Sports Medicine study that was presented at their annual meeting, just 2 weeks of HIIT can improve aerobic capacity to the same extent as 6-8 weeks of sub-maximal endurance training. A 2010 research review published in the International Journal of Medicine and Science in Sports reported that incorporating HIIT into a training programme could improve the exercise performance of well-trained adults by 2- 4% in less than a month.

Outdoor H.I.I.T workout

Prolonged aerobic exercise sessions have traditionally been promoted as the best approach to burn body fat. However, in recent years HIIT research has turned this theory on its head and has proven that there is in fact an alternative way to achieve the same, if not better results.

HIIT has a profound effect on metabolic rate, both during the exercise session and following the workout. In fact, a number of studies have reported that HIIT utilises around 80% of the body’s muscles, compared to around 40% in conventional aerobic training programmes. If more muscles are being recruited, greater energy expenditure is inevitable, even at the same exercise intensity. When exercise intensity is increased, as is the case with HIIT, energy expenditure rises exponentially. The sheer intensity of HIIT causes resting metabolic rate to increase dramatically; this means that those performing HIIT will be burning a greater amount of energy (including fat) during periods of inactivity, even while they are sleeping!
Another reason why high intensity training is effective at reducing body fat relates to how the body adapts to the increased release of insulin in active individuals. HIIT appears to significantly lower insulin resistance, which is a factor known to accelerate fat storage. When the body becomes more sensitive to insulin, skeletal muscles acquire a greater ability to burn glucose and fat.

Key Advantages of HIIT:

  • Develops both aerobic and anaerobic fitness – the aerobic benefits are typically delivered form the intense recovery demands
  • Improves resting blood pressure values
  • Improves cardiovascular health and reduces coronary disease risks
  • Increase the sensitivity to insulin, making glucose more readily available for exercise
  • Improves cholesterol profiles
  • Significantly increases metabolism, both during and following
  • Reduces body fat while maintaining muscle mass
  • Defers the point at which fatigue sets in during lower intensity periods of exercise
  • HIIT has a greater metabolic effect post exercise

Main Disadvantages of HIIT:

  • Highly strenuous and not suitable for de-conditioned participants
  • Nausea and vomiting may occur
  • High levels of discomfort during exertion
  • Fast changes in body position can cause blood pooling and dizziness
  • High levels of muscle soreness post exercise

Rhabdomyolysis may occur when performed excessively – this is the breakdown of muscle tissue that leads to the release of muscle fibre contents into the blood. These substances are harmful to the kidney and often cause kidney damage.


HIIT is a widely used training approach which has the potential to support personal training clients with their health, fitness, performance, and body transformation goals. if you want to learn more about how you can design and implement HIIT protocols, take a look as our personal training courses.

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