HIIT is an interval-type of exercise that has become very popular in recent years. According to American College of Sports Medicine studies, incorporating HIIT into a training program could improve the exercise performance of well-trained adults by 2-4% in less than a month.

Also known as High-Intensity Intermittent Exercise (HIIE) and Sprint Interval Training (SIT), HIIT is an advanced exercise concept used mainly with clients that are apparently healthy, and do not belong to any special population groups.

HIIT consists of short bursts of intense exercises that typically last between 15-60 seconds followed by a brief recovery period. The participant is expected to work at 80-95% of their age-predicted maximum heart rate and rest at 40-50% of the estimated maximum heart rate. In the absence of heart rate monitor, then the RPE scale is used. The Rate of Perceived Exertion (RPE) is a subjective scale of 1-10 measuring the effort level, with 1 being sitting on a couch relaxing, and 10 being at the peak performance zone. For an effective HIIT session, we aim for an effort level of around 8-10, depending on the exerciser's fitness level.

Due to the intensity of the approach, HIIT sessions are structured in short timed blocks lasting 4-8 minutes for a total of 20-60 minutes depending on the participants' fitness levels and types of exercise. For Tabata Training that is a variation of HIIT, the session is structured in 4-minute blocks.

HIIT training is not limited to a specific exercise type. It can be performed using bodyweight exercises such as sit-ups, high knees, press-ups, or typical cardiovascular activities like running, rowing and cycling or even with free weights in a circuit style. Essentially, any strenuous exercise can be used to create a HIIT session making this approach so broad both in a gym environment or outdoors.

HIIT has a great effect on metabolic rate both during the session and following the exercise. As HIIT requires extended muscle recruitment, higher energy expenditure is achieved. The intensity level causes the resting metabolic rate to increase remarkably; those regularly performing HIIT will be burning a higher amount of energy while maintaining muscle mass during periods of inactivity - even in their sleep!

This training approach has many benefits, but due to the strenuous activity there are significant drawbacks:

• Not suitable for exercisers that belong to special population groups; clearance from a GP may be appropriate
• A base level of fitness needs to be established
• Discomfort, dizziness or even nausea may occur because of fast changes in body position
• Muscle soreness post-workout

HIIT is perfect for those with busy schedules or anyone looking to challenge themselves and see noticeable improvements quickly. 

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