High intensity interval training (HIIT) has received a lot of attention recently because it has many impressive health benefits for seemingly modest physical effort. The main benefits are:

1) significant Increase in VO2 scores,  which is a measure of heart and lung health (cardiorespiratory fitness)  -   i.e. an increase in fitness and an indicator of future health.

2) An improvement in glucose metabolism representing a reduced risk of diabetes (lower insulin resistance).

3) A significant reduction in fat mass of the whole body and possibly a contribution to weight loss.

Amazingly, the benefits are better than doing 'moderate intensity exercise' for 30 minutes, five times a week (e.g. jogging or cycling).

So what does the exercise regime entail?

The principle is an intense short burst of activity followed by rest and repeated three times. The easiest way to do this would be on an exercise bike or by sprinting (running), but any exercise is okay as long as your can do it 'intensely', so swimming would also be fine.  Riding a bike is best and easiest and there is less impact on the joints. If you are 'unfit' then you can start by cycling for 20 seconds as hard as possible or until you have to stop. The idea is to significantly raise the heart rate and become breathless. Once your heart rate has settled and you have stopped breathing deeply you repeat the 20 second intense burst of cycling. When you have recovered again,  complete your last 20 second burst. You have done one minute of intense exercise and this is to be repeated three times a week. Once your body is able to cope with 20 seconds it is probably necessary and better to increase the exercise to 30 seconds for every burst. 

Although there appears to be no significant decrease in blood pressure from HIIT exercise, it seems that 'Grip strength Dynamometry' may reduce blood pressure by as much as 16 %. This is where you grip a stress ball, tennis ball or even rolled up sock for two minutes at 30% of maximum strength, followed by a two minute rest, repeated four times in each session, three times a week. You can do this even from the comfort of your armchair!  So doing HIIT and the Grip strength exercise would appear to be a heathly combination with not too much effort!!

Sources : Wikipedia.org   bupa.co.uk  bbc.co.uk (Trust me, I'm a doctor)