A HIIT program can be constituted either by aerobic exercises, such as running or cycling, or by strength exercises, which naturally requires recovery a period between exercises. It is clear, however, that both aerobic and strength exercises can be combined together to create a multitude of different training schemes. Within these programs, the High Intensity workouts can last from a few seconds (e.g. the strength training) up to several minutes (e.g. the aerobic training), with the aim to reach 80%-95% of maximum heart rate when performing cardiovascular exercises. When performing strength based exercises the load can be very close to the maximum (1RM), or to a slightly smaller percentage of that. In this last case, it is necessary to increase the number of repetitions in order to achieve muscular exhaustion. The workout, typically consists of alternating periods of rest and activity, for a total duration of 20-60 minutes. Another method is to replace the rest period with another exercise, creating a training session of extreme intensities, with a much shorter duration than traditional training sessions. In this case the second ‘I’, meaning Interval, should be removed thus creating the HIT acronym (high intensity training).
The duration is much shorter than traditional training workouts.
Energy expenditure is higher than a traditional workout per time unit. This has a further metabolic effect on the post workout caloric expenditure, called EPOC (Excess Post-exercise Oxygen Consumption). This is identified as an additional energy requirement from the body to recover from a workout, back to a pre-workout state. After a HIIT program, EPOC is generally higher in comparison to traditional workouts for the first two hours post exercise.
This training is often executed in fitness classes, and group training interaction. The constant switch between aerobic and anaerobic exercises are perceived as being more engaging and exciting.
High intensity training can bare serious risks if poorly managed. These risks belong to the cardiovascular and osteoarticular domain. People with hypertension or with a history of coronary ischemia should pay much more attention. The high number of repetitions and the high velocity of execution, could additioanlly determine the onset of joint and tendon problems within the Muscle-Skeletal system. In order to perform HIIT and HIT programs efficiently, high level of technical skills are required (e.g. Squats or deadlift). This means that these exercises are limited to people with good coordination skills and motor control. In conclusion, HIIT is not a completely innovative training methodology. However, the essence that stands behind this method should be understood. The approrpriate metabolic intensity should be considered for each individual, respecting the ability to execute the exercise correctly form a technical and coordinative perspective.