Yesterday’s Inside Health - – item on very high intensity exercise prompted a number of people to question the evidence behind my advice for middle-aged and older people to limit the intensity of their work-outs to ensure their heart rate did not rise over 220 minus their age (ie 170 for a 50 year old, and 160 for a 60 year old).

This is a controversial area because there is so much individual variation – not surprisingly, one rule can not be applied to all.  There are no gold standard trials into the hazards of regularly pushing your heart rate above this suggested maximum but there are sound physiological reasons as to why it may be protective (very high intensity work-outs increase the metabolic demands of the heart, dramatically raise blood pressure and lead to twisting movements during contraction that are thought to increase the likelihood of disruption of materials deposited in artery walls).  That said, many people, including the middle-aged and elderly, can push themselves beyond this quite safely although they tend to be fitter than average individuals.  My advice was aimed at more sedentary folk concerned that their work-outs may be doing them harm.

But, perhaps the most important point to make is that more people have strokes in their beds than they do in the gym.  Experiences like Andrew Marr’s are actually quite unusual and should never put people off exercise – the benefits of which, far outweigh the risks for most of us.