The use of High Intensity Interval Training (HIIT) for maintaining good health
Post date: 29-Apr-2013 20:38:26
High Intensity interval training has come under the spotlight recently following Andrew Marr’s appearance on the BBC. He suffered a right carotid artery dissection and attributed its cause to a High Intensity Interval Training (HIIT) session that he had completed that day on a rower. As with many things in the world, but particularly those issues related to health and wellbeing, interesting personal stories are often given more column inches than large scale systematic reviews. With this in mind I thought it would be interesting to look at some of the evidence and point those interested towards some relevant reading.
What is High Intensity Interval Training?
Interval training is a method of training the body that utilises repeated bouts of higher intensity workload interspersed with periods of lower intensity. Most studies that have looked at the value of HIIT utilise repeated bouts of high intensity (≥75% VO2max/peak or RPE >15) for a short period (30s-5 min) separated by an active rest period of several minutes. What of the main attractions cited by many proponents of HIIT are that its use can be a timesaving alternative to long slow endurance training (1, 2) and that the structure of a HIIT session has been shown to be more enjoyable for exercisers (18), both points being suggested as increasing the likelihood that individuals will participate in regular physical activity.
Is it beneficial for health?
High Intensity Interval Training has been shown to elicit both central and peripheral adaptations (12,15,21) that result in improvements in maximal oxygen uptake, work economy, cardiac output and diastolic function. These beneficial adaptations have been noted in both healthy (4-6) and unhealthy populations (7,8,10,11) and have been shown to be beneficial for weight loss (8), reducing the risk of cardiovascular disease (11), part of a fitness programme for management of diabetes (17, 20) and has been used in various high risk populations as a form of primary prevention (7).
What are the risks?
The risks associated with high intensity intervals are related to acute cardiovascular events and musculoskeletal injuries. The use of HIIT has been shown to be safe in the general population and those with coronary artery disease or in cardiac rehab (3,9,16). Whilst the use of HIIT in clinical populations is still in its infancy, it has been reported that in 30,000 hours of cardiac rehabilitation patient-hours, the use of HIIT was not seen as the cause of any significant adverse events (3).
There can often be a difference between perceived risks and actual risks and it is worth considering the history of cardiac rehabilitation as it is not too long ago that post-surgery, patients were advised to avoid exertion of any type or physical activity. Evidence is now clear that a more active rehabilitation programme is more beneficial and so recent studies have recommended the use of a more vigorous exercise intervention than the low intensity cardiac rehab sessions that have been the norm over recent years.
Although not life threatening it is also worth considering the normal response to HIIT sessions. I regularly run Wingate tests in our lab (30s flat out on a cycle ergometer) and out of 20 young (18-21 years old) reasonably fit students most will feel light headed and drained, some will feel faint and occasionally one will find themselves on the floor or being sick. Many will also feel the effects for up to an hour afterwards feeling a bit shakey with weak legs. It might save time but participants won’t be good for much in the hour or so afterwards.
The causes of stroke
Major causes of stroke are high blood pressure and cerebral embolisms, and with high intensity exercise bouts individuals will experience periods of raised blood pressure as part of the bodies normal response to exercise. Carotid artery dissections have been noted in those after bouts of exercise (14, 24) but in a study of 200 carotid dissections (22) (mean age = 45; range 16-74) there were a range of causes, findings supported by another study (23) that examined the causes of a carotid artery dissection across a group of 130 people (130 patients (76 men, 54 women; mean age, 45±11 years). This study suggested that only 5% of these cases were due to irregular haemodynamic patterns and that the majority were as a result of cerebral embolisms. A quick look at the risk factors for cerebral embolisms and we find that recent major surgery, bed rest, cigarette smoking, fractures in the pelvis or legs, heart failure, medications, cancer, multiple trauma, paralytic spinal cord injury, malignancy, congestive heart failure, previous embolism, pregnancy, obesity and immobility are all amongst the risks but not high intensity exercise.
If we allow ourselves to take case studies as evidence then we can also look to the case of Michael Lynagh who was also in the news this month recalling how he had a stroke last year after playing golf and then having a meal with friends. He recalled how he was laughing at a friend’s joke and then started a coughing fit which resulted in the dissection of an artery supplying blood to the brain. Based on this we should maybe consider people are cautious about listening to jokes or coughing.
Some thoughts on the use of HIIT
· Too many health topics are polarised by the media. It doesn’t have to be one method, or its polar opposite. The greatest benefits are usually gained by a combination of training methods that are well planned and challenge the body in a variety of ways. In addition to considering long, slower bouts of activity and bouts of activity that utilise HIIT protocols, try incorporating a tempo training approach that lasts for 20-30 minutes but requires a moderate to high sustained intensity of exercise (ie how far can you go in 20 mins). Start with a slow speed and as you get fitter, up the pace but keep it consistent for most of the duration.
· One of the cited benefits of HIIT training is that it only takes 4 minutes and that this is perfect for those that lead busy lives (ie everyone). This is a rather simplistic view as each bout of high intensity exercise is followed by a longer period of low intensity. Add to this the feeling of tiredness and the excess heat generated during the high intensity bouts and participants won’t be finished much quicker. Exercise needs time and taking time over exercise has more benefits to mental health than cramming an exercise session into an already stressful day.
· Ensure an appropriate warm-up prior to the high-intensity session. This doesn’t mean static stretching as this is not an effective use of time but a progressive, incremental programme that allows the body to be ready for the high intensity efforts (a few minutes spent after the high intensity bouts will also aid in reducing the levels of blood lactate that will build up).
· Trainers could consider the measurement of blood pressure during an incremental stress test as this has been recommended in identifying those at risk of a stroke (13, 21)
· HIIT appears to present no more risk than other forms of exercise training and trainers could use this form of protocol to allow clients to pick and choose the exercise that suits their needs and limitations (19)
If you have any other thoughts on this subject then please let me know at firstname.lastname@example.org or tweet me @benjanefitness.
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