Is High Intensity Training (HIT) safe?

People who have not done exercise for a while might feel nervous about doing anything that sounds “intense”. This is understandable and we certainly recommend that if you are very unfit you start gradually. If you have any doubts about your health check with your doctor before starting any new exercise regimes.

Clearly there are risks as well as benefit to doing anything and exercise is no exception. The evidence, however, points overwhelmingly to the fact that the risks of not doing exercise greatly outweigh the risks of doing it.

The greatest risk of injury while doing exercise is that you will overdo it and pull a muscle. You might decide to sprint before you are warmed up or try and heave some weights that are well beyond your limits. All I can say is “don’t”. Your body needs time to adjust to any new regime.

Don’t push it too hard to start with.

Once you have injured yourself the chance of injuring yourself again is that much greater. All our exercises have a graduated approach.

The real fear, however, is that doing exercise, particularly intense exercise, will lead to a heart attack or stroke.

This anxiety has been fanned by what happened to the very popular news broadcaster, Andy Marr. In January 2012 he had a stroke which he was fortunate to survive and which he is still slowly recovering

It’s been suggested that his stroke could have been caused by doing too much strenuous exercise. Based on newspaper reports it seems he had the stroke some hours after doing a prolonged and vigorous workout on a rowing machine. It also appears that he had previously had at least one silent stroke and was under a lot of stress.

Having a serious stroke is a dreadful thing to happen. Andy Marr was quite young to have a stroke, but it is not uncommon in someone in their 50s.  Around 150,000 people in the UK have a stroke each year and there are 67,000 deaths. It is a leading cause of disability.

The commonest causes of stroke are high blood pressure, smoking, a large stomach, poor diet, lack of physical activity, high levels of bad cholsterol, diabetes, drinking too much, stress, depression, and heart disorders.

Exercise, particularly exercise that raises blood pressure, could (in theory) trigger a stroke. We have no real evidence it does and it would anyway be more likely to happen to someone who was heaving weights in a gym that someone doing aerobic exercise because lifting weights leads to bigger transient changes in blood pressure.

It is more likely that the prolonged and vigorous movement involved in working out on a rowing machine caused sheering damage, a tear to the blood vessels in his neck, vessels that had been weakened by his earlier, undetected stroke. The truth is, we’ll never know.

The forms of HIT we describe in Fast Exercise do not involve prolonged exertion and have been extensively studied to ensure they are safe.

These studies include trials done with people who have a previous history of heart attacks and strokes.

In a large study, published in 2012, Norwegian researchers compared the risks of having a heart attack or stroke after doing HIT or moderate intensity exercises in a group of high-risk patients. They took 4846 patients with coronary heart disease from rehabilitation centres and randomly allocated them either to moderate intensity training or to HIT. The 94 patients who did moderate training, such as walking or jogging, put in a total of 129,456 hours of exercise. The HIT group did their exercise more intensely, but put in far fewer hours, a total of 46,364.

During a grand total of 175,820 hours of training in this high-risk group of patients there was one fatal heart attack and no strokes. This was in the moderate training group. There were two non-fatal heart attacks, in the HIT group, and no strokes.

If you were wondering if it is wise to exercise at all if you have coronary heart disease the answer is a resounding “yes”. The evidence is very clear that it exercising, even if you have had a heart attack, is likely to prevent further damage.

The researchers’ conclusion was that the risks, even in those with existing heart disease, of moderate or intense exercise are low, and that ‘considering the significant cardiovascular adaptations associated with high intensity exercise, such exercise should be considered among patients with coronary heart disease’.

Similarly, in a review paper from 2012, ‘High intensity interval training in cardiac rehabilitation’, the authors looked at all the studies they could find that tested HIT in patients with coronary artery disease or heart failure. They concluded that ‘HIT appears to be safe and better tolerated by patients than moderate intensity continuous exercise’.

They go on to say that it is superior to standard exercise when it comes to producing improvements in heart function and quality of life.

However, if you answer yes to any of the questions below, we would recommend you consult your doctor before starting this or any exercise program.

  1. Do you feel pain in your chest when you do physical activity?
  2. Have you been told by your doctor that you should only do physical activity recommended by a doctor because you have a heart condition ?
  3. Have you had any chest pain in the past month when not doing physical activity?
  4. Do you lose your balance as a result of dizziness or do you ever lose consciousness/collapse?
  5. Do you have a bone or joint problem (eg  back, knee, or hip) that could be made worse by exercise?
  6. Is your doctor currently prescribing medication for your blood pressure or heart condition?
  7. Are you currently pregnant or have you given birth in the last 2 months?
  8. Do you know of any other reason why you should not do physical activity?