High-intensity interval training (HIIT) has become nearly synonymous with fat burning and weight loss. Early studies on HIIT featured elite male cyclists and concluded they got superior results training at 170 percent of their VO2 max—the greatest amount of oxygen their bodies could consume during exercise (V = rate, O2 = oxygen).1 That was the advent of a method called Tabata, named after the primary researcher.
That 1996 study slowly made its way to mainstream fitness classes and bootcamps. Since the original Tabata study, a significant body of research has featured different HIIT variations for various populations.
HIIT features repeated bouts of high-intensity effort ranging between 80 and 100 percent of peak heart rate followed by less intense recovery times.2 What does that feel like? Breathlessness and little to no movement to the point you can breathe through your nose again. The intervals are repeated a designated number of times depending on the protocol and the fitness level of the exerciser.
Interval training is not new and not only used with elite athletes. Patients with COPD and with asthma have long been advised to use interval training to support optimal performance and increase cardiovascular function.
The difference between use of interval training in clinical medicine and HIIT fitness applications is the intensity. This isn’t alternating a walk with a jog. This is truly all-out sprinting, whether by riding a bike, swimming or doing another activity.
The biggest advantage of HIIT is benefits similar to those of longer moderate or moderate-to-vigorous exercise in much less time. Results are promising.3 In some cases, just 30 minutes of HIIT a week can improve cardiometabolic markers of health equivalent to improvements from two and a half hours of traditional cardio.
If you’re busy, HIIT is extremely attractive because most workouts using HIIT range anywhere from 4 to 30 minutes. There’s no question HIIT has been proven to work. Still, there’s an important reason to evaluate whether you should try it and if you should, how.
Between 2012 and 2016, there was a 274 percent increase in the use of HIIT, but also a corresponding 144 percent increase in injury rates.4 So, for individuals prone to injury or with a tendency to overtrain, HIIT could be riskier.
Choosing modes of exercise with lower impact or varying impact if you do HIIT multiple times per week can reduce injury risk. For instance, perform HIIT by running hills one day and riding a bike another. Even with lower-impact forms of HIIT, the muscle damage is still significantly higher than with lower-intensity exercises, so consider recovery time between sessions as carefully as the training session itself.
The seductive calorie- and fat-burning promises of HIIT advocates may be exaggerated, depending on how you view them. Several studies have found that the extra calorie burn believed to occur after HIIT exercise, called the “after burn,” is relatively small. Collecting data during and after exercise energy expenditure, researchers found an increase of only 226 calories expended doing HIIT.5
Compare that to a longer exercise session at high but not HIIT level that burns 600–700 calories, and HIIT doesn’t look as good even though it’s time-sparing.6
For any human, doing the type of exercise that is enjoyable, convenient, and realistic in its time commitment may be the best way to reinforce regular sustained exercise. That is, if you love long walks, do more of that and inject HIIT for those times your regular routine doesn’t fit your schedule. Even so, consider small doses of HIIT to reap the cardio and power boost that lower intensity exercise can’t match.
The bottom line is, while 20 minutes of HIIT does burn both more fat and calories than 20 minutes of moderate exercise, it does not burn more calories or more fat than longer moderate-intensity exercise.
There’s another gap in assuming research results featuring one segment of the population apply to anyone. Many of these studies still feature healthy young men. Their hormones, of course, vary considerably from those of midlife women.
A few promising studies are emerging featuring female menopausal subjects. Estrogen deficiency, which occurs at menopause, changes metabolic adaptations to exercise.7
The advantage of short work intervals for women in midlife particularly is the reduction of cortisol response to exercise. Excess cortisol levels, already on the rise in women beginning
in their mid-40s,8 increase the risk of muscle and bone losses and detrimentally influence sleep and mood.
Provided intervals are kept short, HIIT mitigates the elevation of cortisol while still providing benefits. Monitor energy levels to find your personal sweet spot. Exercise should increase energy, optimize appetite and decrease blood sugar swings.
If the lure of short workouts with all the benefits of long sounds attractive, there’s plenty to choose from.
These three types of intervals have all been proven to work for midlife women. Consider your fitness status and injury risk, and choose a mode of exercise you enjoy.
HIIT: Originally, this option included only the “true Tabata” training of cycles of 20 seconds hard exertion and 10 seconds recovery, repeated eight times. Each set of eight cycles was done once or up to four times, separated by a minute of recovery each. It evolved to include a variety of shorter-work-to-longer-rest ratios, equal-work-to-rest ratios, and longer-work-to-rest ratios that vary considerably based on an individual’s status, goals and time.
But one problem with many HIIT-type workouts is incomplete recovery between high-intensity intervals. That damages both testosterone and mitochondria levels, two areas midlife and older adults want to nurture for energy and metabolism.9
SIT: Sprint interval training research with postmenopausal women was performed on sedentary bicycles, reducing the risk of injury.
Subjects trained for 20 minutes alternating between 8-second sprints and 12 seconds of light pedaling, bookended by a warmup and cooldown of 8 minutes each. Increases in cardiorespiratory fitness, fat loss and atypical lean muscle gains were significant findings.10
HIRT: High-intensity repeat training works similarly to HIIT and SIT with the unique difference that participants recover for as long as needed, even up to 3 minutes, before repeating a work interval.
It’s working if you’re able to repeat the initial effort. When you can’t maintain the same speed or distance in consecutive workouts, the session should end.
As a starting point, try four to six intervals alternated with full recovery. Do a slightly longer warmup and cooldown than in a low-intensity workout. Allow two to three days between interval training sessions.
Start with one session a week, progressing to two or three a week, not to exceed 50 minutes of total training, after which injury risk rises significantly.11
References:
Debra Atkinson, MS, CSCS, is CEO of Flipping 50 and creator of the Flipping50 Menopause Fitness Specialist course for trainers and health coaches. She is a medical exercise specialist with nearly four decades of experience. Her career has included teaching kinesiology at Iowa State University, giving international presentations to fitness professionals for major fitness associations, and serving as a subject matter expert for the American Council on Exercise. She’s a sought-after speaker for reframing aging and teaching how to do it, and her TEDx talk is “Everything Women in Menopause Learned about Exercise May Be a Lie.”
