Anne Aurand / The Bulletin

An overweight man, burdened with luggage, sprints through the airport to avoid missing a flight. An out-of-shape woman frantically shovels snow piled between her home and her car, rushing to get to work.

These everyday scenarios require bursts of extreme exertion that humans should be appropriately conditioned to withstand. Many are not.

“That's high intensity. That's when you have a heart attack,” said Chris Cooper, a local physical therapist with Therapeutic Associates. “Exerting yourself higher than you're trained for, that's unsafe.”

One solution could be high-intensity interval training. Pretty much everyone could benefit from it, Cooper said.

High-intensity interval training, loosely described as spurts of intense exercise broken up by short periods of rest, has long been used by elite athletes to improve performance and by fitness enthusiasts to burn fat and increase muscle.

It's also becoming accepted as a preventive tool to improve the heart and lung health of older and unconditioned people. Studies have shown that it improves the function of blood vessels and the heart and might lower the risk of chronic diseases.

Some evidence suggests that it might be safe and effective in the rehabilitation of patients with cardiac disease, although this idea is still controversial — many question whether heart patients should be pushing the limits of their exertion.

What is it?

High-intensity interval training can be done a number of ways, although running and cycling appear to be the most researched and most common forms. Intervals can be performed on a treadmill, a stationary bike, or by bustling up a stairwell at work. It can be jump-roping, burpees, squats, lunges or pushups.

It's the intensity that's key. To improve your body you have to push it harder than it's used to being pushed. A lot harder. But pushing your body to its limit can only be done for a brief period of time. People's hearts, lungs and muscles can't sustain that sort of effort the way they can endure a slower-paced, 60-minute jog or bike ride.

There's no standard recommendation for the type or amount of interval training a person should do. Research reports, scientists, physical therapists and personal trainers all describe different recipes for an interval workout. Basically, workout plans cater to each individual's needs and goals.

But there is a common theme: go hard for some duration of time between 30 seconds and five minutes. Then slow it down for a minute (or four). Repeat a few times. Generally speaking, going “hard” is determined by an individual's perceived exertion. An elite athlete's workout will look a lot different than an unconditioned cardiac patient's, while they each work at 90 percent of their maximum effort (See “Getting technical”).

The time factor

Many people cite lack of time as their excuse for not exercising. With growing knowledge about high-intensity interval training, that excuse no longer flies.

Proponents of high-intensity interval training emphasize that it takes hardly any time at all — mere minutes — to provide measurable health benefits.

The Centers for Disease Control and Prevention recommends adults get five hours of moderate-intensity aerobic exercise or 2.5 hours of vigorous-intensity aerobic exercise plus two sessions of muscle-strengthening workouts weekly.

Or, you could spend less time working out harder and get comparable results, according to Mark Smith, an applied physiologist based in California who has, among other things, been a personal trainer and health consultant.

“Compared to 60 minutes of endurance training, a high-intensity intermittent workout, lasting less than four minutes, produced a comparable increase in VO2 max, while simultaneously increasing the anaerobic capacity,” Smith wrote in a 2008 research paper called “Sprint Interval Training, It's a HIIT.”

(VO2 max is a person's maximum ability to process oxygen during exercise. Anaerobic capacity refers to a person's maximum effort and how long it's sustainable.)

Smith does not dispute the value of longer, moderate-intensity training, he wrote, but he argues that interval training has matched if not surpassed it in terms of cardiovascular health and fat loss, and within a significantly smaller time commitment.

A study published in the Journal of Physiology in 2006 illustrates this.

Researchers divided 16 men equally into interval training and endurance training groups to compare the effects of each type of exercise. Over two weeks, the interval training group did six interval workouts, each consisting of four to six repetitions of 30-second “all-out” cycling with four minutes of recovery between each repetition, a workout time of 20-30 minutes. The endurance group did six endurance workouts that consisted of 90 to 120 minutes of continuous cycling at an easier effort.

After two weeks, both groups showed similar improvements in cycling time trials and similar physiological adaptations in muscle oxidative capacity, lactic acid processing and glycogen content — muscle fuel.

Most notably, according to the study, is that training time was 90 percent lower in the interval training group.

For fitness

Bouncing back and forth between aerobic and anaerobic exercise will challenge and strengthen the heart and pulmonary system, resulting in greater fat and calorie burning, muscle mass retention and overall cardiovascular fitness, said Kyle Will, a personal trainer in Bend.

Such workouts were shown to be more effective than consistent, moderate-intensity training in terms of improving VO2 max and other functions that are correlated with cardiac health, according to a 2007 study published in the journal Medicine&Science in Sports&Exercise.

The concepts of interval training are incorporated into many classes and workouts at clubs and gyms around Bend. It can go by many different names, including Tabata, circuit training, functional fitness and CrossFit.

The American Council on Exercise named interval training as one of the top fitness trends of 2012.

For disease prevention

Exercise in general is a known, cost-effective intervention that can help prevent many chronic diseases. Newer research is showing that shorter time commitments of more intense exercise might be even more effective at managing health problems.

For example, Dr. Viviane Ugalde, a physiatrist at The Center: Orthopedic&Neurosurgical Care&Research in Bend, said research has shown high-intensity interval training to be superior to continuous exercise in the following conditions:

• It increases exercise tolerance and reduces shortness of breath in people with emphysema/chronic obstructive pulmonary disease.

• It increases walking distance without cramps for patients with poor arterial circulation (a condition called claudication).

• It improves aerobic capacity in cardiac patients and improves insulin sensitivity in metabolic syndrome (obesity and “borderline” diabetes).

• It reduces risk of developing hypertension in persons with a family history of hypertension.

It might be helpful in managing Type 2 diabetes, too. Researchers at McMaster University in Canada recently published a study in the Journal of Applied Physiology that said six high-intensity exercise sessions over the course of two weeks (equating to 30 minutes of high-intensity training per week) rapidly lowered blood sugar levels in Type 2 diabetics and increased skeletal muscle mitochondrial capacity, a marker of metabolic health.

Dave Cieslowski, a physical therapist with Focus Physical Therapy in Bend, said the mechanism by which it works has to do with muscle cell physiology. Studies out of McMaster University have said that high-intensity interval training triggers cellular changes in the muscles.

Martin Gibala, the kinesiology department chair at McMaster, who was involved with those studies, wrote in a 2007 paper: “While the underlying mechanisms are unclear, metabolic adaptations (from high-intensity training) could be mediated in part through signaling pathways normally associated with endurance training.”

Bottom line: It makes a person's metabolism run higher so they burn more calories and fat, even after they're done exercising.

And those physiological changes to muscle cells apply to heart muscles as well, Cieslowski said, which helps the heart function in its optimal capacity.

For cardiac and pulmonary rehabilitation

A pioneer in high-intensity interval research, Jan Helgerud, a professor of medicine at the Norwegian University of Science and Technology, has been studying the use of high-intensity interval training for years. He said it can be an effective form of rehabilitation and medical treatment. His collection of research suggests that high-intensity interval exercise has a positive effect on stroke survivors, patients with coronary artery disease, peripheral arterial disease, chronic obstructive pulmonary disease and others.

But, “The high intensity aerobic intervals as a treatment and rehabilitation for patients is still controversial,” Helgerud wrote in an email. “It does take some time to get rid of old fashion treatment, however, there has been what I would say a very positive development in the last couple of years. It has been a hot topic on several medical research conferences, and medical doctors and physical therapists have taken the new knowledge into their practice.”

The physical therapists interviewed for this story said they often discuss the idea with their patients, but if those patients are recovering from something major like a heart attack, they are long past their original cardiac rehab phase.

St. Charles Health System is not prescribing high-intensity interval training to its patients who have had cardiac surgery or conditions like chronic obstructive pulmonary disease, said spokeswoman Lisa Goodman. “It's too risky for the population we serve,” she said.

Courtney Lynn, a clinical care coordinator and exercise specialist in St. Charles Bend's cardiopulmonary rehabilitation lab, said high-intensity training would add too much stress to a patient who has recently experienced a heart attack, heart transplant, stent, valve repair or bypass surgery.

“They are in a recovery state, and we're not going to overwork the heart. We want them at a moderate pace,” she said.

Plus, these patients tend to be on various medications that can affect blood pressure and heart rate, she said. Rehabilitation plans are catered to each patient. Patients' blood pressure and heart rates are monitored while they exercise. Cardiac and pulmonary rehabilitation usually includes about 36 sessions, she said. After that, they are advised to check with doctors before they start their own exercise programs.

Helgerud agrees with this. A 2004 study of his said, “Selected exercise testing should be performed at the discretion of a physician before vigorous exercise in patients with known cardiovascular problems.”

The study addressed the fact that “individuals with cardiac disease seem to be at an increased risk for sudden cardiac arrest during vigorous physical exercise compared to healthy individuals. However, aerobic exercise is clearly beneficial in lowering mortality compared to a sedentary lifestyle.”

Exercise can also trigger myocardial infarction — heart attack — but the relative risk of that happening during or soon after exertion is greater in people who don't regularly exercise, the study said.

“To be short,” Helgerud said, “inactivity is what's killing us.”

Helgerud said it was a “pity” that high-intensity interval training apparently is not widely accepted as a form of medical rehabilitation, but he believes the practice “will be the common medical treatment in the future.”

Power up with fitness classes like TRX Unleashed

TRX Unleashed is just one example of a wide variety of classes found in regional gyms and clubs that incorporate the concepts of high-intensity interval-style exercise.

For this exercise, participants repeat the lunge movement for 30 seconds, followed by 10 seconds of rest, before moving to the other leg or to another exercise.

Anderson, a personal trainer, designed a sequence of variations of squats, pushups, plank poses and more. Participants hold the straps for leverage and balance but work against their own body weight to build strength. The straps are unstable enough that executing movements requires engaging all sorts of ancillary muscles, especially in the core section, to stay balanced.

Anderson also interspersed 30-second “cardio blasts,” such as running in figure eights around small cones on the ground, or jumping over the cones in a line.

TRX is the company that designs and sells the suspension system — manipulatable straps with handles that suspend from an anchor near the ceiling.