According to the American Heart Association (AHA 2004), over 79 million Americans have one or more forms of cardiovascular disease (CVD). One in three deaths in the U.S. is attributable to CVD (AHA 2004). As well, CVD deaths lead the list of the top five deadliest diseases in the world (see Table 1 on page 20).

The overall objective of cardiac rehabilitation is to restore and maintain physiological, psychological, social and occupational status in patients with coronary artery disease (CAD) (a narrowing of the coronary arteries that supply blood and oxygen to the heart). This intervention also seeks to assist patients with their resumption of daily recreational activities. Traditionally, the primary method of training patients enrolled in cardiac rehabilitation has consisted of continuous aerobic activities designed to improve and maintain aerobic fitness.

While high-intensity interval training has been employed and shown to be an effective exercise modality to improve maximal aerobic power in healthy, active populations of men and women, few studies have evaluated the effect of interval training on the health status of patients with CVD. Warburton and colleagues note that, according to their preliminary data, patients with cardiac disease also obtain health benefits from interval training. The purpose of the study was to examine the underlying benefits of interval training with highly functional patients with CAD.


The 14 volunteers in the Warburton
et al. study were men (average age 56 years; average weight 190 pounds) who had undergone bypass surgery or an angioplasty (a medical procedure in which a balloon is used to open narrowed or blocked blood vessels of the heart) and were ≥ 6 months postsurgery. The subjects were in stable condition and highly functional, with peak aerobic capacities ≥ 31 milliliters per kilogram of body weight per minute (ml/kg/min), which is about 9 METS. A MET, which equals 3.5 ml/kg/min, is a physiological concept that represents a simple procedure for expressing the energy cost of physical activities as multiples of resting metabolic rate. The researchers grouped the subjects by age, weight and aerobic capacity into one group (

  1. = 7) of traditional aerobic training and another group (
  2. = 7) of interval training.

Training Sessions

Both training groups were required to train 2 days per week over this 16-week study. The traditional aerobic group completed a 10-minute warm-up followed by 30 minutes of continuous aerobic exercise at 65% of heart rate reserve (the difference between resting heart rate and maximum heart rate), which is also equivalent to 65% of their VO2 reserve. In addition, the subjects performed a standardized resistance training program, followed by a 10-minute cool-down. The interval training group performed the same warm-up, resistance training and cool-down segments as the traditional group. However, the interval training group’s aerobic workout consisted of 2-minute, high-intensity bouts at 90% of heart rate reserve followed by 2-minute, low-intensity bouts at 40% of heart rate reserve, for the 30-minute cardiovascular bout.

Both groups’ training sessions used three different modes of activity: combined arm and leg ergometry, treadmill exercise and stair stepping. All subjects were also encouraged to participate each week in three additional training sessions consisting of continuous aerobic exercise at 65% of their heart rate reserve. The researchers confirmed that the volume of the exercise (aerobic and resistance training) performed by both groups in this study was the same.


The traditional aerobic and interval training groups showed statistically significant and similar improvements in aerobic capacity during this 16-week training study, as measured by a maximal treadmill test (subjects were tested before and after using a Bruce maximal stress test protocol, commonly employed in cardiac rehabilitation programs). However, the interval training group showed a significantly greater treadmill time to exhaustion, exercising twice as long as the traditional aerobic group in a specific treadmill test to exhaustion. In this exhaustion test, the subjects exercised at 90% of their heart rate reserve until they voluntarily stopped. This test is valuable for measuring endurance capacity, with the later minutes of the test demonstrating anaerobic capacity markers.

Warburton and colleagues explain that as subjects near the end of their aerobic capacity in the exhaustion test, they recruit energy from the anaerobic energy systems. Although not statistically different, both groups showed improvements in systolic and diastolic blood pressure, pulse pressure (the difference between systolic and diastolic pressure and a function of stroke volume), artery compliance (extensibility of arteries to facilitate blood flow) or rate-pressure product (a measurement of the heart muscle’s oxygen consumption, calculated by multiplying heart rate times systolic blood pressure).

Practical Application

With the pervasiveness of heart disease in all societies throughout the world (see Table 1, above), fitness professionals and personal trainers should be very familiar with the risk factors for CAD (see Table 2 on page 21). This investigation demonstrates that functional CAD male
patients, with aerobic capacities ≥ 31 ml/
kg/min, can perform interval training in addition to a continuous cardiovascular exercise program. However, care should always be taken, as some patients will posses higher functional abilities than others. It is imperative to conduct proper screening and obtain extensive health evaluations and physician approval to ensure adequate client safety during exercise.

Perhaps the most notable finding of this study was the significantly greater time to exhaustion observed in the interval training group. As the authors highlight, “It does appear to lead to adaptations that allow for a greater tolerance to a strenuous exercise challenge. These adaptations would be of particular benefit for the performance of many activities of daily living.” The bottom line message to share with your physically active and stable CAD clients is that the inclusion of interval training may enable them to function more efficiently during the day and for lengthier periods of time.

Source: Adapted from World Health Organization. 2004.
Source: Adapted from American College of Sports Medicine. 2006. ACSM’s Guidelines for Exercise Testing and Prescription (7th ed.). Philadelphia: Lippincott Williams & Wilkins.