High-Intensity Interval Training

The popularity of high intensity interval training is on the rise. High intensity interval training sessions are commonly called HIIT
workouts. This type of training involves repeated bouts of high intensity effort followed by varied recovery times.

A Complete Physical Activity Program
A well-rounded physical activity program includes
aerobic exercise and strength training exercise, but
not necessarily in the same session. This blend helps
maintain or improve cardiorespiratory and muscular
fitness and overall health and function. Regular physical
activity will provide more health benefits than sporadic,
high intensity workouts, so choose exercises you are
likely to enjoy and that you can incorporate into your
ACSM’s physical activity recommendations for healthy
adults, updated in 2011, recommend at least 30 minutes
of moderate-intensity physical activity (working hard
enough to break a sweat, but still able to carry on a
conversation) five days per week, or 20 minutes of more
vigorous activity three days per week. Combinations
of moderate- and vigorous-intensity activity can be
performed to meet this recommendation.
Examples of typical aerobic exercises are:
• Walking
• Running
• Stair climbing
• Cycling
• Rowing
• Cross-country skiing
• Swimming
In addition, strength training should be performed a
minimum of two days each week, with 8-12 repetitions
of 8-10 different exercises that target all major muscle
groups. This type of training can be accomplished using
body weight, resistance bands, free weights, medicine
balls or weight machines.

The intense work periods may range from 5
seconds to 8 minutes long, and are performed
at 80% to 95% of a person’s estimated maximal
heart rate, the maximum number of times
your heart will beat in a minute without
overexerting yourself. The recovery periods may
last equally as long as the work periods and are
usually performed at 40% to 50% of a person’s
estimated maximal heart rate. The workout
continues with the alternating work and relief
periods totaling 20 to 60 minutes.
What are the benefits of HIIT?
HIIT training has been shown to improve:
• aerobic and anaerobic fitness
• blood pressure
• cardiovascular health
• insulin sensitivity (which helps the exercising
muscles more readily use glucose for fuel to
make energy)
• cholesterol profiles
• abdominal fat and body weight while
maintaining muscle mass.
Why is HIIT Training so Popular?
HIIT training can easily be modified for people
of all fitness levels and special conditions,
such as overweight and diabetes. HIIT
workouts can be performed on all exercise
modes, including cycling, walking, swimming,
aqua training, elliptical cross-training, and in
many group exercise classes. HIIT workouts
provide similar fitness benefits as continuous

endurance workouts, but in shorter periods of
time. This is because HIIT workouts tend to
burn more calories than traditional workouts,
especially after the workout. The post-exercise
period is called “EPOC”, which stands for
excess postexercise oxygen consumption. This
is generally about a 2-hour period after an
exercise bout where the body is restoring itself
to pre-exercise levels, and thus using more
energy. Because of the vigorous contractile
nature of HIIT workouts, the EPOC generally
tends to be modestly greater, adding about 6
to 15% more calories to the overall workout
energy expenditure.
How do You Develop a HIIT Exercise
When developing a HIIT program, consider
the duration, intensity, and frequency of the
work intervals and the length of the recovery
intervals. Intensity during the high intensity
work interval should range ≥ 80% of your
estimated maximal heart rate. As a good
subjective indicator, the work interval should
feel like you are exercising “hard” to “very
hard”. Using the talk test as your guide, it
would be like carrying on a conversation, with
difficulty. The intensity of the recovery interval
should be 40-50% of your estimate maximal
heart rate. This would be a physical activity
that felt very comfortable, in order to help you
recover and prepare for your next work interval

The relationship of the work and recovery
interval is important. Many studies use a
specific ratio of exercise to recovery to improve
the different energy systems of the body. For
example, a ratio of 1:1 might be a 3-minute
hard work (or high intensity) bout followed by
a 3-minute recovery (or low intensity) bout.
These 1:1 interval workouts often range about
3, 4, or 5 minutes followed by an equal time
in recovery. Another popular HIIT training
protocol is called the “spring interval training
method”. With this type of program the
exerciser does about 30 seconds of ‘sprint or
near full-out effort’, which is followed by 4 to
4.5 minutes of recovery. This combination of
exercise can be repeated 3 to 5 times. These
higher intensity work efforts are typically
shorter bouts (30 seconds with sprint interval
What are the Safety Concerns with HIIT
Persons who have been living rather sedentary
lifestyles or periods of physical inactivity
may have an increased coronary disease risk
to high intensity exercise. Family history,
cigarette smoking, hypertension, diabetes (or
pre-diabetes), abnormal cholesterol levels
and obesity will increase this risk. Medical
clearance from a physician may be an
appropriate safety measure for anyone with
these conditions before staring HIIT or any
exercise training. Prior to beginning HIIT
training a person is encouraged to establish a
foundational level of fitness. This foundation
is sometimes referred to as a “base fitness
level”. A base fitness level is consistent aerobic
training (3 to 5 times a week for 20 to 60
min per session at a somewhat hard intensity)
for several weeks that produces muscular
adaptations, which improve oxygen transport to
the muscles. Establishing appropriate exercise
form and muscle strength are important before
engaging in regular HIIT to reduce the risk of
musculoskeletal injury.
Regardless of age, gender and fitness level,
one of the keys to safe participation of HIIT
training is for all people to modify the intensity
of the work interval to a preferred challenging
level. Safety in participation should always
be primary priority, and people should focus
more on finding their own optimal training
intensities as opposed to keeping up with other

How Many Times a Week Can You do
a HIIT Workout?
HIIT workouts are more exhaustive then
steady state endurance workouts. Therefore, a
longer recovery period is often needed. Perhaps
start with one HIIT training workout a week,
with your other workouts being steady state
workouts. As you feel ready for more challenge,
add a second HIIT workout a week, making
sure you spread the HIIT workouts throughout
the week.
Final HIIT Message
Interval training has been an integral part
of athletic training programs for many years
because a variety of sport and recreational
activities require short bursts of movement at
high intensities. Interval training is becoming
an increasingly recognized and well-liked
method of training. The incorporation of
interval training into a general conditioning
program will optimize the development of
cardiorespiratory fitness as well as numerous
other health benefits. Give HIIT a try.

Staying Active Pays Off!
Those who are physically active tend to live longer,
healthier lives. Research shows that moderate physical
activity – such as 30 minutes a day of brisk walking –
significantly contributes to longevity. Even a person
with risk factors like high blood pressure, diabetes
or even a smoking habit can gain real benefits from
incorporating regular physical activity into their daily
As many dieters have found, exercise can help you
stay on a diet and lose weight. What’s more – regular
exercise can help lower blood pressure, control blood
sugar, improve cholesterol levels and build stronger,
denser bones.
The First Step
Before you begin an exercise program, take a fitness test,
or substantially increase your level of activity, make sure
to answer the following questions. This physical activity
readiness questionnaire (PAR-Q) will help determine if
you’re ready to begin an exercise routine or program.
• Has your doctor ever said that you have a heart
condition or that you should participate in physical
activity only as recommended by a doctor?
• Do you feel pain in your chest during physical activity?
• In the past month, have you had chest pain when you
were not doing physical activity?
• Do you lose your balance from dizziness? Do you ever
lose consciousness?
• Do you have a bone or joint problem that could be
made worse by a change in your physical activity?
• Is your doctor currently prescribing drugs for your
blood pressure or a heart condition?
• Do you know of any reason you should not participate
in physical activity?
If you answered yes to one or more questions, if you are
over 40 years of age and have recently been inactive,
or if you are concerned about your health, consult a
physician before taking a fitness test or substantially
increasing your physical activity. If you answered no to
each question, then it’s likely that you can safely begin
Prior to Exercise
Prior to beginning any exercise program, including
the activities depicted in this brochure, individuals
should seek medical evaluation and clearance to engage
in activity. Not all exercise programs are suitable for
everyone, and some programs may result in injury.
Activities should be carried out at a pace that is
comfortable for the user. Users should discontinue
participation in any exercise activity that causes pain or
discomfort. In such event, medical consultation should
be immediately obtained.