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Interval exercise as treatment for cardiovascular diseases?

Aerobic exercise benefits are well established, and it is easily the most prescribed exercise modality among physicians. Aerobic exercise has been convincingly shown to improve all measures of cardiac health. This month, however, we want to focus on a less-known exercise modality called high-intensity interval training (HIIT). HIIT is gaining popularity as it may provide unique benefit in the realm of cardiovascular disease risk modification.

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High-Intensity Interval Training: Mechanisms and Rationale

HIIT is cardiovascular exercise, but rather than maintaining a steady pace over the course of an exercise session, it involves undulating patterns of high intensity followed by lower-intensity recovery. Usually the protocol involves a work-to-recovery ratio of 1:2 to 1:4, depending on the fitness of the participants. The theory behind interval training is that the heart, like all muscles, needs to be challenged to repair and grow stronger. Interval training allows the advantage of a harder challenge with less risk because each high-intensity bout is followed by recovery. If done correctly, the heart is forced to alternate between sympathetic stimulation and parasympathetic recovery. This, it is argued, is a more functional exercise because it trains heart rate recovery and heart stimulation. Since many cardiac events come from sudden unexpected anaerobic challenges like shoveling the first winter snow, running through the airport to catch a plane, or walking up a large flight of steps, HIIT is believed to help the body prepare for these challenges by teaching the heart to work hard and recover quickly.

Interval training and Parasympathetic Activity of the Heart

Heart rate variability (HRV) and spontaneous cardiac baroreflex (SBR) provide functional measures of cardiac parasympathetic activity. The April 2005 issue of Clinical Autonomic Research showed the effect of interval training on both. (1) Eleven healthy elderly men, mean age 74, underwent an intensive 14-week interval training program involving nine 1-minute bouts of exercise at 85% maximum heart rate (MHR) followed by 4 minutes' recovery at 65% MHR. Aerobic capacity increased 18.6%, while the HRV showed a significant parasympathetic shift at night from pre- to posttraining. The cardiac baroreflex response was also improved, with 10 of the 11 participants showing a favorable response.

Interval Training and Intermittent Claudication

A 2006 study in the Journal of Vascular Nursing reported an observational study on HIIT for patients with peripheral arterial disease. (2) A total of 47 patients were included in the study. They were asked to walk on a treadmill to maximal claudication pain 6 times in each exercise session, with 3 minutes of recovery in between. Once a patient could walk continuously for 6 minutes without reaching maximal pain, the speed and/or grade was increased. A rehabilitation score was calculated as the product of speed and grade achieved by the participants. Results showed that HIIT led to clinical improvement in symptoms and a higher tolerable workload by patients. No adverse effects were seen from the treatment, suggesting those with peripheral arterial disease can both tolerate and benefit from HIIT.

Interval Training and Heart Failure

Wisloff et al. in Circulation (June 19, 2007) shed some light on the cardiovascular effects of HIIT versus traditional aerobic training for heart-failure patients. (3) Twenty-seven patients with stable postinfarction heart failure were randomized to either aerobic exercise (70% MHR) or HIIT (95% MHR for 4 minutes separated by 3 minutes at 50%-70% MHR) 3 times a week for 13 weeks, or to a control group. The control group patients were told to follow the exercise advice of their family doctors, and met for 47 minutes of walking at 70% MHR every third week. All groups exercised on a treadmill. The major finding was that HIIT was superior to traditional aerobic training with regard to reversal of left ventricular (LV) remodeling, aerobic capacity, endothelial function, and quality of life. With respect to LV remodeling, in the HIIT group the LV diastolic and systolic diameters decreased by 12 % and 15%, and estimated LV end-diastolic and end-systolic volumes dropped by 18% and 25%, respectively. Prohormone brain natriuretic peptide (proBNP), a marker of hypertrophy and severity of heart failure, declined by 40% in the HIIT group. There was no change in the traditional aerobic group or control group in LV remodeling, pointing to a rather profound effect of HIIT over traditional aerobic exercise in this patient population.

Safety and Other Measures

HIIT has been shown to be safe and well tolerated in COPD (chronic obstructive pulmonary disease), (4), (5) postbypass, (6) congestive heart failure, (3) and even heart transplant patients. (8) As discussed, HIIT may realistically mimic real-world challenges. It also can be tailored into a self-paced format that is safe, tolerable, and beneficial for many cardiovascular conditions. (7-14) It was shown in one study to have more favorable effects on ST segment changes than traditional aerobic exercise, in addition to the positive effects on heart rate variability. (1), (13-14)

Exercise Prescription

Obviously, physicians prescribing exercise for high-risk patients will not want to completely abandon traditional aerobic exercise in favor of HIIT. Traditional aerobic exercise is well established in both treatment and prevention of cardiovascular diseases. More studies need to be done on HIIT, but it appears it may have some unique cardiovascular benefits. Here are some considerations when prescribing this form of exercise.

Work-to-recovery ratios should be shorter for the more fit and longer for the less fit or frail. A beginning exercise protocol for a younger fit person wanting to optimize cardiac prevention would be a work-to-recovery ratio of 1:2. More frail and less fit clients will want to start with a work-to-recovery ratio of 1:4 or greater.

Also, the use of heart rate monitors and perceived exertions ratings are advisable with any kind of exercise in high-risk populations. Interval training involves keeping the heart rate low (40%-60% MHR) during the recovery and peaking it higher during the work (80%-95% MHR). However, because there are other factors that can interfere with heart rate, such as beta blockers, it is advisable to use exertion rates. In most individuals, 85% of maximum heart rate corresponds to the ability to speak during exercise, while 40%-60% MHR is near rest or light exertion, where talking is easy and relaxing. Instructing patients on these parameters is useful.

In addition, HIIT is a good opportunity to teach patients about heart rate recovery (HRR), which has been shown to be a powerful indicator of all-cause mortality. A simple way to find HRR is to subtract your HR 2 minutes after exertion from your MHR immediately after exertion. A HR that drops less than 12 beats per minute is considered abnormal and should be evaluated. Normal HRR is a decrease between 15 and 25 beats per minute. A drop greater than 25 beats per minute is an indication of a very fit person.

Notes

(1.) Pichot et al. Interval training in elderly men increases both heart rate variability and baroreflex activity. Clin Auton Res. 2005;15:107-115.

(2.) Adams et al. High-intensity interval training for intermittent claudication in a vascular rehabilitation program. J Vasc Nurs. 2006:24:46-49.

(3.) Wisloff et al. Superior cardiovascular effect of aerobic interval training versus moderate continuous training in heart failure patients: a randomized study. Circulation. 2007;115:3086-3094

(4.) Kaelin et al. Physical fitness and quality of life outcomes in a pulmonary rehabilitation program utilizing symptom limited interval training and resistance training. J Exerc Physiol [online]. 2001;4(3):30-37.

(5.) Butcher et al. The impact of exercise training intensity on change in physiological function in patients with chronic obstructive pulmonary disease. Sports Med. 2006;36(4):307-325.

(6.) Meyer et al. Interval versus continuous exercise training after bypass surgery: a comparison of training-induced acute reactions with respect to the effectiveness of the exercise methods. Clin Cardiol. 1990;13(12):851-861.

(7.) Tanasescu et al. Exercise type and intensity in relationship to coronary heart disease in men. JAMA. 2002;288(16):1994-2000.

(8.) Pokan et al. Effect of high-volume and -intensity endurance training in heart transplant recipients. Med Sci Sports Exerc. 2004;36(12):2011-2016.

(9.) Kaelin et al. Physical fitness and quality of life outcomes in a pulmonary rehabilitation program utilizing symptom limited interval training and resistance training, J Exerc Physiol [online]. 2001;4(3):30-37.

(10.) Butcher et. al. The impact of exercise training intensity on change in physiological function in patients with chronic obstructive pulmonary disease. Sports Med. 2006;36(4):307-325.

(11.) Meyer et al. Interval versus continuous exercise training after coronary bypass surgery: a comparison of training-induced acute reactions with respect to the effectiveness of the exercise methods. Clin Cardiol. 1990;13(12):851-861.

(12.) Meyer et al. Interval training in patients with severe chronic heart failure: analysis and recommendations for exercise procedures. Med Sci Sports Exerc. 1997;29(3):306-312.

(13.) Ehsani et al. Improvement of left ventricular contractile function by exercise training in patients with coronary artery disease. Circulation. 1986;74:350-358.

(14.) Warburton et al. Effectiveness of high-intensity interval training for the rehabilitation of patients with coronary artery disease. Am J Cardiol. 2005;95(9):1080-1084.

by Jade Teta, ND, CSCS, and Keoni Teta, ND, LAc, CSCS

jade@metaboliceffect.com | keoni@metaboliceffect.com
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Title Annotation:Exercise is Medicine
Author:Teta, Jade; Teta, Keoni
Publication:Townsend Letter
Article Type:Report
Geographic Code:1USA
Date:Jun 1, 2009
Words:1525
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