SIT is a form of very intense interval training. You perform 3-5 intervals of very short maximal-intensity exercise working until you can’t sustain the intensity , followed by a prolonged recovery period. This would typically be 20-30 seconds of work followed by a 3-5 minute rest interval. SIT has an array of benefits, but can only be performed by already well-conditioned people who have no contrary health conditions.
HIT is much more appropriate to the general public or average gym goer. This involves work periods ranging from 30 seconds to three minutes working between 80-100% of your maximum heart rate with shorter recovery periods than SIT. There is no specific formula to HIT but as a rule of thumb I would recommend your recovery period should be at least the same as your work interval, and can become shorter as you get fitter.
Many of the benefits of HIT training have been vastly overstated by the media and marketers but there are definitely some advantages to it.
HIT training leads to greater EPOC (excess post-exercise oxygen consumption) when compared to continuous exercise. This means that after you have finished exercising, your body will continue to burn calories at a higher rate than normal. The evidence base is small, but at least one study has shown that you can match the training effect of continuous training in less time using a proper HIT protocol.
There have also been studies done which show that HIT is a great way of improving your VO2 Max. This is essentially a measurement of how fit you are and is linked to all-cause mortality (your chance of dying). Those with a higher VO2 max have a lower risk of death compared to their peers. If a proper HIT training protocol is followed with the correct intensity (how hard you are working) and duration (how long you are working for) it is certainly a time efficient way of improving your fitness levels.
HIT can essentially be used by anyone although if you have recently had a Health MOT and been advised to partake in moderate intensity exercise then I would look to improve your fitness and other health markers before embarking on a HIT training programme. If you haven’t had a Health MOT recently it may be wise to have one and see if HIT training is suitable for you.
For people who find continuous training monotonous HIT can be a great choice as the constant change of pace means that you are kept engaged throughout your workout.
The main reason to choose HIT is the time efficiency compared to continuous exercise but you must be willing to work at a hard enough intensity to compensate for the reduced time you spend exercising.
HIT training should be and is very hard when performed correctly. This intensity of exercise can be exhilarating and leave you feeling a real sense of accomplishment but for others it will not be enjoyable and for those who want more control over how they feel during a training session I would recommend fartlek or continuous exercise.
Example of a HIT session on a stationary or spin bike (19 minutes total)
Warm Up two minutes steady cycle low resistance
Cycle very hard at 90% effort level for 60 seconds on a high resistance
Recover for 90 seconds on a low speed and resistance
Repeat this interval five times in total
Cool down two minutes low resistance
Repeat three times per week with at least one day recovery in between