Exercise reduced burden of atrial fibrillation

Vegard Malmo. Foto: Andrea Hegdahl Tiltnes / NTNU“Time in atrial fibrillation and symptoms of the disease were reduced, and exercise capacity, cardiac function, lipid levels and quality of life were improved in the patients preforming high intensity interval training”, PhD candidate at CERG and medical doctor at St. Olavs Hospital,  Vegard Malmo.

He is first author in the paper “Aerobic Interval training reduces the burden of atrial fibrillation in the short term: A randomized trial” recently published in Circulation. In this study, 51 persons with non-permanent atrial fibrillation (AF) were randomized either to high intensity interval training (four 4-minute intervals at 85-95% of peak heart) rate three times a week for 12 weeks or a control group (continuing their earlier exercise habits). Minutes of AF each day was monitored continuously with an implanted recorder. In addition cardiac function, exercise capacity, lipid status, quality of life and AF symptoms were assessed.

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When every percent counts – new CERG publication

High-intensity exercise is shown to be protective against coronary heart disease (CHD) and is established as a popular and time saving exercise method. But what about people who already have a heart disease? Earlier, these patients were told to exercise, but only with moderate intensity to protect the heart from further damage. However, during the last few years it has been found that high-intensity exercise does not represent a greater risk of adverse events in these patients – on the contrary, this type of exercise is very beneficial even for this patient group.

Several studies comparing high intensity interval training with moderate exercise have found greater effect of higher intensity. But high do you have to go during the intervals? What are the characteristics of the “ideal” interval training session? This was the main question of a new study from Moholdt and colleagues from CERG, in this months Journal of Science and Medicine in Sport. In order to identify the most important predictor of improved fitness in CHD patients, the researchers analyzed data from four randomized, controlled trials conducted at the center. The main outcome was change in VO2max, peak oxygen uptake, which is a well-established measure of fitness and predictor of mortality. Subjects (n=112) were aged 18+ and had established CHD. The exercise period lasted for 12 weeks, and exercise was performed by either running/walking on treadmill, uphill walking outdoors or group training, after the 4×4 model.

CERG researcher Trine Moholdt during testing.

CERG researcher Trine Moholdt during testing.

Interestingly, when baseline and post-training VO2max was compared, the researchers found that the amount of training sessions had no impact on fitness, neither had the age of the subjects or baseline peak oxygen uptake. On the other hand, the intensity of training played a key role in improving VO2max and seems to be the most important characteristic of an effective interval session.

The traditional advice in interval training is that in the intensive periods, heart rate should be 85-95% of HRmax. However, this range is rather wide, and this study suggests that it is not indifferent where in the range you place yourself. Overall, VO2max increased by 11.9 % after an average of 23.4 training sessions during the 12 week period for all subjects. But, an intensity of >92 % of HRmax in the high-intensity periods was shown to be more effective than lower intensity (e.g. 85-88%), indicating that there is a dose-response relationship even within the HR zone of 85-95%.

It may seem like minor details, but people who start exercising intervals often have lots of questions on how to do it practically. How much incline on the treadmill? Can I short down to 2 calm minutes in-between the 4 minutes of high intensity? Why 4 minutes and not 5? Knowing that pushing oneself up to >90 % of HRmax may save you from an extra training session with lower intensity that week, gives meaning to the process of investigating even minimal details.

The four studies included patients with established CHD, either presented as acute coronary syndrome or angina pectoris. However, it is reasonable to believe that even small adjustments in intensity may be efficient also for healthy persons. So why don’t you push yourself the last 2-3 percents when you are exercising anyway?

Maria Henningsen, CERG