Functional Training Institute

HIIT vs SIT – Wednesday Wisdom

HIIT vs SIT - Wednesday Wisdom

Strictly speaking, there are two different types of interval training programs that are likely to be most relevant to you, the functional training practitioner. They are:

  1. High-Intensity Interval Training (HIIT)
  2. Sprint Interval Training (SIT)

The first type of interval training (HIIT) you are already familiar with, but how familiar are you with the second type of interval training, known as sprint interval training? Are they the same? The short answer is no, they are not the same, despite their similar names.  In the figure below we can see how these two interval training regimes differ:


The primary difference between HIIT and SIT is HIIT, despite what the name may suggest, reaches hard, but not MAXIMAL intensities. Whereas SIT, does require maximal and even supramaximal intensities. Clearly, one of these types of interval training programs is more appropriate for well trained, and conditioned clients and the other is not.  In fact, it is only HIIT programs that have been shown to be safe to use in clinical populations, such as those clients with cardiovascular disease and diabetes. However, this should not be taken as a license to inflict painful, highly intense workouts to some of your more vulnerable clients, preferably as an essential reminder that carefully prescribed HIIT sessions, can be part of a client’s training sessions if they are well planned. So to summarise, HIIT differs from SIT primarily by training intensity. SIT sessions are characterised by training intensities that are maximal or supramaximal, which implies the client would be expected to work at maximal intensities for the duration of the interval. In contrast, HIIT does not require maximal training intensities, in fact, most studies show very welcome improvements in fitness, and reductions in body fat can be achieved with training intensities around 80-85% of maximal heart rate, which for many is very achievable on an ongoing basis.  In our next article, we will look at some great examples of HIIT programs that target both fitness and fat loss, more importantly, these programs may well be very compatible with many functional training tools.

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