12/02/2014 07:19 GMT | Updated 13/04/2014 06:59 BST

High Intensity Training (HIT)

As you may have seen, the latest craze in exercise is High Intensity Training (or HIT) which promises all the benefits of regular exercise but in a fraction of the time; maybe as little as 12 minutes a week. This seems a whole lot more palatable than the usual activity "prescription" of at least 30-minutes of moderately intense exercise on most days of the week - which most of us just don't do. Here's how HIT works.

Suppose you use a stationary exercise bike as your activity of choice. You start with a warm-up of a few minutes to get the muscles supple and the blood flowing. You then pedal absolutely flat out - as hard as you can - for 60-seconds, followed by a rest for about 1 minute before repeating three times more (so 4 in all). The recommendation is to perform this routine three times a week, so you have a weekly total of just 12 minutes HIT. According to researchers this is enough to gain all the benefits of regular exercise - though clearly in a fraction of the time. Can this really be true?

The answer is a heavily qualified "yes". There are certainly good studies showing improvements in insulin and glucose metabolism as well as aerobic fitness (oxygen consumption) as a result of HIT. However, many important questions remain. For example, evidence collected over many decades shows that regular physical activity of 30 minutes on most days will cut the risk of heart disease by around 50%. We simply don't know whether a similar benefit could be achieved using HIT because we have no long-term studies. Moreover, a study of up to 10,000 former Olympic athletes published in the British Medical Journal showed that athletes competing in high-intensity sports such as cycling, boxing and rowing, did not live longer than those involved in low-intensity sports such as cricket and golf.

The last point to make is that, for the average middle-aged man and woman, HIT could be very risky. The television journalist and presenter Andrew Marr said that the stroke which almost killed him occurred in the middle of an intense workout on his home rowing machine. During hard exercise, blood pressure (BP) levels can become very high, putting a huge strain on the heart and circulation. This is especially true in older people who may already have raised blood pressure and other underlying health problems.

So should you consider HIT? If you are under 50-years of age, have no underlying health problems and a clean bill of health from your GP, including a normal BP, you may benefit from regular sessions of HIT. If you don't fall into this category, regular brisk walking will do nicely!