Many people with chronic health problems resign themselves to lives of modest activity or no activity at all, thinking vigorous exercise is unsafe or that they lack the stamina for it. But recent studies are proving just the opposite.
They are showing that high-intensity exercise may be even better than regular aerobic activities for many patients with conditions like heart disease, diabetes, stroke, pulmonary disease, arthritis and Parkinson's disease.
The studies strongly suggest that a more demanding but more efficient and often more enjoyable form of exercise known as high-intensity interval training, or HIIT, is not only safe for most patients but more effective at preventing or reversing the deficits associated with many chronic ailments.
Although once reserved for athletes seeking a competitive advantage and for healthy people wanting to burn more body fat, HIIT is now being studied as a treatment that is sometimes as effective as medication for many people with chronic health problems.
Researchers have found that repeatedly pushing the body close to its exercise limits for very brief periods, interspersed with periods of rest, is more effective than continuous moderate activity at improving cardiovascular, respiratory, metabolic and mechanical functions.
Instead of continuous movement for 20 or more minutes, as is typical for exercise walkers, joggers and cyclists, HIIT usually involves 30 to 60 seconds of exercise near the peak of a person's ability, followed by a comparable recovery period of easy activity, with the sequence repeated for a total of about 20 minutes three times a week.
"We know that exercise is good for people at risk of chronic disease, but people tend not to exercise," said Jonathan P. Little, a specialist in exercise physiology at the University of British Columbia at Okanagan. Yet he and other researchers report that study participants find interval training more enjoyable than continuous aerobic exercise, making it more likely that people will continue it on their own.
Various activities can be adapted to interval training, including cycling, swimming, walking and jogging, especially on a machine like a stationary bike or treadmill. But HIIT is possible indoors and out, for example by alternating sprints with more moderate exercise.
The intensity is tailored to an individual's starting ability. "The high-intensity component is set at 80 to 90 percent of the person's maximum aerobic capacity," Little said. Researchers commonly use exercise bikes and treadmills to adjust the pace mechanically.
However, high-intensity exercise, even just half a minute at a time, is not appropriate for everyone. In a recent report in the American College of Sports Medicine's Health & Fitness Journal, Little; his wife, Mary E. Jung, also at the University of British Columbia; and Marcus W. Kilpatrick of the University of South Florida wrote that HIIT "is only appropriate for low-risk individuals, moderate-risk individuals who have been cleared for vigorous intensities by a medical professional, and high-risk individuals who are under direct medical supervision during exercise training."
Among the physiological benefits of HIIT are the body's increased ability to use oxygen and insulin, as well as arteries that are more elastic than continuous moderate exercise can achieve. "We've seen, for example, that interval training is remarkably effective at lowering glucose levels in people with diabetes," Little said in an interview. "Just one session improves a person's glucose level."
A 12-week controlled study in Denmark of high-intensity interval walking for patients with Type 2 diabetes showed it helped control blood glucose levels better than continuous moderate exercise, even though the same number of calories was expended by both groups. Interval training also was more effective at enhancing the patients' physical fitness and reducing body fat relative to lean muscle tissue.
By making blood vessels better able to expand, HIIT can improve the cardiovascular system's ability to respond to added exertion. Oxygen-carrying blood can flow more smoothly through arteries that are wide open, which also reduces the risk of a vessel-blocking clot.
The body's ability to use oxygen efficiently improves markedly "after as little as two weeks of training" with HIIT, the researchers wrote. Peak oxygen uptake - the amount of oxygen an individual can use during intense exercise - is considered the best indicator of cardiovascular fitness and an independent predictor of illness and death in cardiac patients.
"Too many people think incorrectly that high-intensity exercise is only for athletes, that it's a heart attack waiting to happen," Little said. On the contrary, the research strongly suggests, it is more likely to reduce the risk of a heart attack.
In a 2012 report reviewing the effects of HIIT in patients with coronary artery disease and heart failure, researchers in Canada, France and Switzerland wrote that "HIIT appears safe and better tolerated by patients than moderate-intensity continuous exercise" and more effective at increasing patients' peak oxygen uptake, blood vessel flexibility and pumping ability of the heart.
Patients with chronic obstructive pulmonary disease are often unable to exercise long enough to gain needed health benefits. But they can do HIIT for long periods with less shortness of breath and leg discomfort, researchers at the National and Kapodistrian University of Athens have reported.
Stroke patients with persistent disabilities can also benefit from HIIT. As rehabilitation specialists at the University of Cincinnati wrote this month in BioPortfolio, stroke patients with residual weakness "enter a vicious cycle of limited activity and deconditioning." But while regular aerobic exercise can improve their function and cardiovascular health, preliminary studies, including one in Trondheim, Norway, suggest that patients do even better with HIIT. The Norwegian team reported that the improvements persisted for months after the six-week high-intensity exercise program ended.
And Polish researchers demonstrated that HIIT could alleviate the rigidity and excessive muscle tone that makes it difficult for Parkinson's disease patients to move their arms and legs. The researchers, from the University School of Physical Education in Krakow, Poland, showed in 11 patients with mild to moderate Parkinson's symptoms that eight weeks of HIIT, three times a week, on a stationary bike had a global benefit, improving both lower and upper body function.
Reductions in rigidity and stiffness correlated with an increase in a substance called brain-derived neurotrophic factor, which the researchers suggested could have stimulated the growth and function of nerves normally influenced by dopamine, the neurotransmitter that declines in Parkinson's disease.
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