From The Desk Of Clarence Bass
Interval Training May Provide Unique Health Benefits
McMaster University Professor Martin J. Gibala, PhD, has written an Invited Commentary in the May 2018 Current Sports Medicine Reports. Cleverly titled: “Interval Training for Cardiometabolic Health: Why Such A HIIT?”
As regular visitors know, Dr. Gibala has taken interval exercise training from the unique purview of elite athletes to a mainstay of fitness enthusiasts. Now it is health benefits, making interval training relevant for medical practitioners and health professionals.
Cardiometabolic health refers to your chances—good or bad—of having diabetes, heart disease or stroke. Cardiometabolic risk is particularly prevalent in patients having metabolic syndrome, which includes health markers such as waist size, cholesterol readings, blood pressure, and blood sugar.
Healthy living generally brings lower cardiometabolic risk and longer life. For interval training it means going beyond fitness to health.
Intensity versus Intermittency
Gibala begins by distinguishing between high-intensity interval training (HIIT) and sprint interval training (SIT). HIIT is relatively intense bouts of exercise (~80% of HR max) interspersed by periods of low intensity recovery, while SIT is several single bouts performed “all out.” He emphasizes that interval exercise does not have to be “especially intense” to elicit health benefits, “although a relatively high volume of exercise is required.” While that may be best suited for the general population, it runs into the commonly cited time-factor barrier to regular exercise.
With that brief introduction, Gibala moves on to newly emerging evidence that adaptations to interval training may not be solely due to intensity, but rather the fundamental nature of intermittent exercise. “For example, some of the cellular signaling pathways that regulate skeletal muscle mitochondrial biogenesis [creation] are activated to a greater extent after interval compared to continuous exercise, even when relative intensity is moderate and total work is matched.”
An example suggesting the superior health benefits of moderate-intensity intervals involves walking. Four months of interval walking (one hour 5 days a week) was superior to energy expenditure-matched continuous walking—for improving cardiorespiratory (heart, lung, and muscle) fitness, body composition, and glycemic control. “The interval protocol was more effective even though it involved only slight variation in intensity that corresponded to ~69% and ~63% of maximum heart rate, respectively, during alternating 3-min periods of fast and slow walking.”
HIIT a Time-Efficient Strategy
Gibala cites numerous studies showing time-efficient HIIT to be as effective as or more effective than moderate intensity continuous training (MICT) for improving cardiometabolic health.
This is evidenced by a recent meta-analyses of 65 intervention studies that concluded: “HIIT may serve as a time-efficient substitute or as a compliment to commonly recommended MICT in improving cardiometabolic health.”
Gibala writes that HIIT is superior for improving cardiorespiratory fitness in both healthy individuals and people with cardiometabolic diseases. That’s important because cardiorespiratory fitness “is as strong a predictor of mortality as established risk factors such as cigarette smoking, hypertension, high cholesterol, and type 2 diabetes and relatively small increases…are associated with considerably lower adverse cardiovascular event rates.”
Gibala continued: “The potential for HIIT to robustly improve cardiorespiratory fitness is noteworthy given that lower-intensity exercise…may not be sufficient to improve cardiorespiratory fitness for a substantial proportion of sedentary adults.”
Another meta-analysis concluded “that HIIT can be considered a more effective and time-efficient intervention for improving aerobic capacity and blood pressure as compared with other types of exercise in overweight and obese youth.”
There’s more, but this is enough to show that interval exercise training is indeed a “HIIT” for cardiometabolic health.
Is HIIT Safe?
All forms of exercise have their risks, but interval training has had more scrutiny than most.
A study from Norway compared the risk of supervised HIIT and MICT in 4,846 individuals in three cardiac rehabilitation sites.
In a total of 175,820 training hours where all patients performed both types of exercise, the absolute rate of complications was higher for high-intensity compared with moderate-intensity exercise (1 per 23,182 compared to 1 per 129,456 hours), but the overall risk of a cardiovascular event was low after both types of exercise.
“It must be emphasized that the individuals were engaging in a supervised training program after having undergone a full medical screening prior to participation,” Gibala stated. Susceptible individuals must, of course, be screened before any kind of exercise.
“On the whole, however, mounting clinical evidence supports HIIT as a safe therapy for the majority of individuals with elevated cardiometabolic risk,” another review study concluded.
Dr. Gibala offers a span of intensity and ways that are effective for improving indices of cardiometabolic health, making the benefits of interval exercise training accessible to practically everyone.
He begins with a study showing that 12 weeks of sprint interval training (SIT) improved indicators of cardiometabolic health (VO2max and insulin sensitivity) as much as traditional training despite a five-fold lower exercise volume and time commitment. “The sprint protocol involved a total of 1 minute of “all out” intermittent exercise set within a 10-minute time commitment, whereas the moderate training consisted of 50 minutes of continuous exercise, and both groups training three times per week.”
A drawback is that the SIT was performed on a specialized ergometer in a laboratory setting. Not a problem, says Gibala. “A recent study…used a more practical, constant-load cycle protocol that required <15 minutes per session, and reported that 18 sessions of training over 6 weeks improved VO2max and other cardiometabolic risk factors.”
Concept 2 Ski Erg is ideal for both HIIT and SIT, because of the superb
performance monitor which
He goes on to explain that brief bouts of intermittent stair climbing and bodyweight interval training have been shown to improve cardiorespiratory (heart, lung, and muscle) fitness in a time efficient manner.
With a little imagination, interval exercise training can help bring cardiometabolic health to the vast majority of people in time-efficient and enjoyable ways.
What’s next for HIIT?
“HIIT is like a promising new treatment on the market: it is showing considerable efficacy in small scale, early phase trials, but longer and more comprehensive studies are warranted,” Gibala begins. “Efforts to elucidate the role of exercise intensity in promoting healthy aging and longevity are of particular significance,” he continues.
Exploring “real world” protocols outside of laboratory settings are also needed.
Gibala ends by calling for more work from a behavioral standpoint. Is interval training more enjoyable—and more sustainable—than traditional steady state exercise?
Dr. Richard Winett, whose Master Trainer newsletter alerted me to Professor Gibala’s commentary, is concerned about the growing possibility of injury as we age. "As we age is exercise intensity associated with a better quality of life and longevity?" he asks.
I’m inclined to stress intensity—to keep fast fibers alive. And longer recovery periods between workouts. Dr. Winett tends toward less intensity and greater frequency. Both approaches are effective.
Exercise becomes more important with each passing year. We must keep looking for ways we enjoy and are willing to keep doing. My experience is that interval training fits the bill. It makes training more interesting—and more effective. As Dr. Gibala emphasizes, there are interval protocols to suit practically everyone.
For more information on the pros and cons of HIIT, SIT and MICT protocols, see The Psychology of Interval Training:
November 1, 2018
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