For the past five years or so, high-intensity interval training,
or HIIT, has been one of the most popular and controversial forms of exercise.
Consisting of brief spurts of intense exercise interspersed with rest, various
versions of HIIT have been tested, tried, talked about and sometimes derided by
countless researchers, coaches, journalists, influencers and almost anyone else
interested in fitness.
اضافة اعلان
Gym franchises and online classes specialize in HIIT. Dozens of
scientific studies every month explore its benefits and drawbacks. By almost
any measure, HIIT is hot.
But plenty of questions remain about HIIT. Is it particularly
good for our hearts? Minds? Life spans? Waistlines? Is it better for us, long
term, than taking a brisk daily stroll? And what does “intense”
exercise even
mean?
With New Year’s exercise resolutions almost around the corner,
now seems the right moment to home in on HIIT, and how and why to try it. It is
also useful to explore the best way to do HIIT, as well as whether we need a
pricey heart rate monitor, gym membership, personal trainer and advanced math
skills to get started, or if sneakers, a handy hill and a distant tree can be
equipment enough.
What is HIIT?
With HIIT, you strenuously ride, run, swim, hop, crunch or
otherwise push yourself aerobically for a few minutes or even seconds, slow or
stop to rest for a few more minutes, and repeat that sequence three or four
times, or more. The aim is to “challenge” your cardiovascular system and
muscles during each interval without tipping yourself into abject exhaustion or
injury, said Martin Gibala, a professor at McMaster University in Hamilton,
Ontario, and prominent HIIT researcher.
Alluringly, HIIT workouts often require fewer than 10 minutes in
total to complete.
This exercise approach is not new, of course. Athletes looking
for performance boosts have threaded interval sessions into their broader
training since time immemorial. But today’s HIIT is often promoted as the only
exercise you have to do — and not an add-on to longer, moderate sessions.
Does HIIT work?
“For most people, there is no doubt that HIIT leads to larger
increases in VO2max” — or maximal oxygen uptake, a measure of our aerobic
fitness and endurance — “than exercise of a more moderate nature,” said Ulrik
Wisloff, a professor and head of the cardiac exercise research group at the
Norwegian University of Science and Technology in Trondheim, who has been
studying HIIT for more than 20 years.
A higher VO2max is strongly associated with greater longevity,
he added, suggesting that intervals are likely to have a more potent influence
on our life spans than, for instance, gentle walks.
HIIT also may help to reduce fat stores around our midsections
as effectively as longer, easier exercise, and it seems uniquely beneficial for
our brains.
“HIIT improves memory in younger and older adults” in ways that
standard, moderate exercise cannot, said Jennifer Heisz, a professor at McMaster
University and the author of the upcoming book “Move the Body, Heal the Mind,”
which will be published in March. Only strenuous exercise prompts the muscles
to produce a gush of the chemical lactate, she said, which then travels through
the blood to the brain, where it is known to promote the creation of new cells
and blood vessels, upping brain health and lowering our risk for dementia.
Most beguiling, HIIT workouts can be exceptionally brief. In a
famous 2006 study from Gibala’s lab, for two weeks one group of college
students pedaled stationary bicycles moderately for 90 to 120 minutes three
times a week, while another group grunted through four to six sessions of 30
seconds of all-out cycling followed by four minutes of recovery. The moderate
exercisers, who topped out at about 12 hours of exercise altogether, showed
improved measures of fitness and healthfully remodeled the inner workings of
their muscle cells. But the HIIT riders, who completed 12 total minutes of
intense exercise, grew just as fit or fitter and showed even more molecular
alterations inside their muscles.
Where HIIT falls short.
“It is neither practical nor advisable to be doing HIIT on a
daily basis,” said Jamie Burr, a professor at the University of Guelph in
Ontario, who has studied the physiological effects of many types of physical
activity. Health guidelines generally advise against this kind of exercise more
than three times a week, he said, to avoid burnout or injury.
But in that case, we are not exercising for at least four days
of the week, which can be problematic.
“There are a number of health benefits,” most of them related to
better blood sugar and blood pressure levels, he said, that occur only on days
when we exercise. When we skip working out, even if we did HIIT the day before,
our blood sugar and blood pressure control may slip, undercutting the long-term
metabolic gains from those earlier intervals.
So if you decide to do HIIT, plan to schedule other types of
exercise, he said, such as moderate walking, cycling, swimming, jogging or
calisthenics on most other days of the week.
Keep it simple. Consider fartleks.
Interested in trying HIIT now? Good, Wisloff said. “I would say
that everyone should aim for at least one HIIT session per week, for the sake
of health,” he said.
Choose whichever variety of HIIT appeals to you. You might try
one minute on, one minute off, meaning you push yourself for 60 seconds, rest
for 60, and repeat, or the four-minute interval workouts employed often in
Wisloff’s research, with four minutes of strenuous effort followed by four
minutes of rest.
Other researchers use four-second intervals, and I have tried
and enjoyed the 10-20-30 approach, which was pioneered by scientists in
Copenhagen, Denmark: You jog or otherwise exercise gently for 30 seconds, ramp
up the effort for 20 seconds and then sprint for 10 seconds before returning to
the easy half-minute jog.
But lately, I have settled into frequent fartleks. Swedish for
speed play, fartlek workouts involve picking a goal, such as a tree or light
pole up ahead, and speeding up until you reach it. No need to check your heart
rate or track each interval’s length, in time or distance, said Wisloff, who
also trains with fartlek. Use the natural contours of the landscape to shape
your exercise.
“This is perfect to do outside the gym,” he said, with little
expense or experience needed. Just dash toward the tree until it recedes behind
you, pick another landmark ahead, and you’ll be “HIITing” health and fitness
goals.
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