October 8, 2013

Katharine D. Currie1 and Maureen J. MacDonald2
1International Collaboration on Repair Discoveries (ICORD), University of British Columbia, Vancouver, British Columbia, Canada
2Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada

Originally Published in the CSEP member newsletter, Communiqué, October 2013

Interval exercise, which involves brief bouts of high-intensity exercise at a near maximal level separated by bouts of rest or lower-intensity exercise, is a type of exercise that was once primarily used by athletes but is becoming increasingly more widespread in its use. There is conclusive evidence from studies in young healthy individuals that interval exercise training is capable of improving many indices of health and fitness. More recently, research studies have started to examine the health benefits of interval exercise training in clinical populations, such as individuals with coronary artery disease (CAD). This field of research is still developing and there are still many unanswered questions including “what is the most effective exercise program to improve fitness after a heart attack?”

In this study, we asked men with CAD who were part of an outpatient cardiac rehabilitation program to train twice per week for 12 weeks using either a short-duration interval exercise program or the current exercise prescription typical of most cardiac rehabilitation programs which involves longer-duration endurance exercise of a moderate-intensity. The interval group performed 20 minutes of exercise consisting of ten, 1-minute intervals at approximately 90% of their peak effort separated by 1-minute intervals at 10% of their peak effort. The endurance group performed 30-50 minutes of exercise at 60% of their peak effort. Peak effort was determined using a peak exercise test, which was performed before the initiation of both exercise programs. Briefly, individuals were asked to cycle as long as possible on a stationary bike while resistance was gradually increased. Peak effort was determined as the highest level of resistance reached during the test.

We wanted to see the effects of the exercise programs on fitness, resting heart rate variability, and heart rate recovery. Heart rate variability describes how much heart rate changes with each beat, while heart rate recovery describes how fast heart rate drops immediately following exercise. Both of these heart rate measures tell us about how the nervous system controls heart rate, and how the heart can respond to challenges. All three of our outcome measures are useful indicators of the risk of death, and therefore are important to measure in cardiac rehabilitation programs. Although the interval group performed less exercise (20 minutes vs. 30-50 minutes), we found a similar increase in fitness in both the interval and endurance exercise groups. Heart rate variability and heart rate recovery were unchanged following training in both groups; however, both groups had normal values to begin with. We believe the normal values may have been caused by their cardiac medications, which they were taking for 5-6 months before beginning our study. Overall, the findings of this study build on the previous findings in healthy young individuals, and suggest short-duration interval exercise is suitable for patients with CAD, despite some generally held concerns that intense exercise is not appropriate for cardiac rehabilitation programs. All participants in this study were medically cleared to participate and were capable of performing the near-maximal exercise for the brief intervals described. We also experienced no adverse events during training. In summary, we propose that you can achieve improvements in fitness and other health outcomes with a shorter duration of exercise, as long as you are exercising at a high intensity level.


Applied Physiology, Nutrition, and Metabolism 2013: 38(6): 644-650.

This article is a summary of an article published in Applied Physiology, Nutrition & Metabolism. If you intend citing any information in this article, please consult the original article and cite that source. This summary was written for the Canadian Society for Exercise Physiology and it has been reviewed by the CSEP Knowledge Transfer Committee.

The CSEP Knowledge Translation Committee supports the translation of research-based knowledge for the practical application of improving the health of Canadians through the publication of this article.