Evidence based exercise: Clinical benefits of high intensity interval training

Abstract

Background:
Aerobic exercise has a marked impact on cardiovascular disease risk. Benefits include improved serum lipid profiles, blood pressure and inflammatory markers as well as reduced risk of stroke, acute coronary syndrome and overall cardiovascular mortality. Most exercise programs prescribed for fat reduction involve continuous, moderate aerobic exercise, as per Australian Heart Foundation clinical guidelines.

Objective:
This article describes the benefits of exercise for patients with cardiovascular and metabolic disease and details the numerous benefits of high intensity interval training (HIIT) in particular.

Discussion:
Aerobic exercise has numerous benefits for high-risk populations and such benefits, especially weight loss, are amplified with HIIT. High intensity interval training involves repeatedly exercising at a high intensity for 30 seconds to several minutes, separated by 1-5 minutes of recovery (either no or low intensity exercise). HIT is associated with increased patient compliance and improved cardiovascular and metabolic outcomes and is suitable for implementation in both healthy and 'at risk' populations. Importantly, as some types of exercise are contraindicated in certain patient populations and HIIT is a complex concept for those unfamiliar to exercise, some patients may require specific assessment or instruction before commencing a HIIT program.

Full text

clinical
Evidence based exercise
Clinical benefits of high intensity interval training
Tim Shiraev
Gabriella Barclay
mortality.5–10 Exercise has been shown to be
an important additional strategy to a weight
loss program.11 However, in Australia, nearly
40% of males and 60% of females carry out
insufficient daily physical activity.12
Aerobic exercise has a marked impact on
cardiovascular disease risk. Benefits include
improved serum lipid profiles, blood pressure
and inflammatory markers as well as reduced
risk of stroke, acute coronary syndrome and
overall cardiovascular mortality.13–19 Additionally,
aerobic exercise is effective in the prevention and
management of insulin resistance and T2DM.20,21
A recent meta-analysis looking at the effect of
different levels of light or moderate physical activity
on all cause mortality demonstrated that 30 minutes
of moderate exercise five times per week (the basis
of most exercise prescription guidelines22) reduced
all cause mortality by 19% versus no activity.23
Importantly, as light or moderate aerobic exercise
can be carried out in an incidental manner, it is
potentially accessible and nondisruptive to most of
the population.
High intensity interval
training
Many exercise programs prescribed for fat reduction
involve continuous, moderate aerobic exercise
(CME), as per Australian Heart Foundation clinical
guidelines.22 However, such exercise programs
have been shown to fail to result in significant fat
loss.13,24
High intensity interval training (HIIT) involves
repeatedly exercising at a high intensity for 30
seconds to several minutes, separated by 1–5
minutes of recovery (either no or low intensity
exercise).25 The most common HIIT intervention
used in studies is the Wingate Protocol developed
in the 1970s.26 This involves 30 seconds of cycling
at maximum effort (at an intensity of over 90% of
maximal oxygen uptake, also known as 90% of VO2
Obesity rates in Australia are among
the highest in the world,1 with one in 4
adults being obese.2 Obesity increases
the risk of coronary heart disease, type
2 diabetes mellitus (T2DM) and stroke,
three of the top five causes of burden of
disease and injury in Australia.2 Dietary
modification is the mainstay of any
weight loss program3,4 and has been
shown to improve cardiovascular and
metabolic risk factors including blood
pressure, lipids, serum glucose, glycated
haemoglobin (HbA1c) and insulin
levels as well as reducing risk of acute
coronary syndromes, stroke and all cause
Background
Aerobic exercise has a marked impact on cardiovascular disease risk. Benefits
include improved serum lipid profiles, blood pressure and inflammatory
markers as well as reduced risk of stroke, acute coronary syndrome and overall
cardiovascular mortality. Most exercise programs prescribed for fat reduction
involve continuous, moderate aerobic exercise, as per Australian Heart
Foundation clinical guidelines.
Objective
This article describes the benefits of exercise for patients with cardiovascular and
metabolic disease and details the numerous benefits of high intensity interval
training (HIIT) in particular.
Discussion
Aerobic exercise has numerous benefits for high-risk populations and such
benefits, especially weight loss, are amplified with HIIT. High intensity interval
training involves repeatedly exercising at a high intensity for 30 seconds to
several minutes, separated by 1–5 minutes of recovery (either no or low intensity
exercise). HIT is associated with increased patient compliance and improved
cardiovascular and metabolic outcomes and is suitable for implementation in
both healthy and ‘at risk’ populations. Importantly, as some types of exercise are
contraindicated in certain patient populations and HIIT is a complex concept for
those unfamiliar to exercise, some patients may require specific assessment or
instruction before commencing a HIIT program.
Keywords
exercise therapy; risk factors; body weight
960
Reprinted from AUSTRALIAN FAMILY PHYSICIAN VOL. 41, NO. 12, DECEMBER 2012

clinicalEvidence based exercise – clinical benefits of high intensity interval training
max) separated by 4 minutes of recovery, repeated
4–6 times per session, with three sessions
per week.25,27 This results in only 2–3 minutes
of exercise at maximum intensity and 15–25
minutes of low intensity exercise per session,
making it a time efficient method of exercise. Less
demanding protocols may be utilised for sedentary,
overweight patients, which is important to
remember considering the target patient population
for exercise as prevention and management of
cardiovascular and metabolic disease.
HIIT vs continuous
moderate exercise
High intensity interval training has been shown to
significantly reduce subcutaneous fat, especially
abdominal fat,27 as well as total body mass,28,29
and to improve VO2 max (a marker of physical
fitness)30 and insulin sensitivity.31 In comparison
with CME, HIIT burns more calories and increases
postexercise fat oxidation and energy expenditure
more than steady-state exercise.32 Further, HIIT
decreased total cholesterol and LDL-cholesterol,
while increasing HDL-cholesterol33 and VO2 max32
more than CME. Interestingly, in a 2008 study,
fat loss was significantly increased after HIIT,
while fat loss did not change in CME patients
versus controls,31 ie. there was no difference in
fat loss between subjects carrying out CME and
the inactive subjects. In a study that highlights
the efficacy of HIIT, subjects carrying out HIIT
demonstrated improvements in endothelial
function, VO2 max, body mass index (BMI), body
fat percentage, blood pressure and glucose
regulation, more so than a group receiving dietary
and psychological advice in addition to CME.29
Perhaps most importantly, increased exercise
energy expenditure (such as with HIIT) as assessed
by metabolic equivalents (METs) has been shown to
result in a reduced risk of cardiovascular events in
both males18 and females,17 and decrease all cause
mortality.34 However, long term studies are needed
to specifically assess the effect of HIIT on overall
mortality.
HIIT effects in high risk
populations
In patients with cardiovascular disease, HIIT was
shown to be superior to CME in reducing blood
pressure,35 improving endothelial function,35–37 lipid
profiles,38 VO2 max,38 left ventricular37 and overall
myocardial function,35 as well as reversing left
ventricular remodelling in heart failure patients.37
Patients with metabolic syndrome who carry out
HIIT have been demonstrated to have improved
endothelial function, insulin signalling, blood
glucose and lipogenesis.29
Studies carried out in T2DM patients
demonstrated reduced blood glucose and increased
mitochondrial capacity and GLUT4 expression after
only 2 weeks of three 20 minute sessions of HIIT
per week,39 and have been shown to significantly
improve glucose tolerance at 6 months with no
such changes in CME subjects.40
Importantly, HIIT programs are not only
effective, but are also safe. HIIT has been used
effectively in patients with diabetes,39 stable
angina,41 heart failure37 and after myocardial
infarct,38 as well as postcardiac stenting42 and
coronary artery grafting.43
Further research is still required into the effect
of HIIT versus CME in cohorts with cardiometabolic
diseases, especially observation of long term
outcomes. Similarly, elucidation of the efficacy
of HIIT in certain patient populations is needed,
such as in those who have recovered from a
cerebrovascular event or in those suffering from
peripheral arterial disease.
Patient perspectives
A common reason given for not exercising is time
constraints,44 and long term adherence to exercise
programs is often less than 50% at 6 months.45 HIIT
allows equal or improved outcomes for markedly
less time investment and has the potential to be
associated with higher rates of adherence46 due
to the varied protocol leading to less boredom,29,47
although this remains controversial.48 In one study,
similar changes were seen over a 6 week period
in both HIIT subjects and CME subjects, although
HIIT subjects performed only 20% of the exercise
duration performed by the CME group,49 making it
an extremely efficient intervention.
Potential disadvantages of
HIIT
Injuries are often a concern when beginning any
exercise program (particularly one such as HIIT),
especially in elderly and sedentary patients. While
musculoskeletal injuries may occur, they are not
more common in groups performing HIIT50 versus
other forms of exercise and can be minimised
with careful selection of exercise equipment,
for example cycling instead of walking. A recent
systematic review demonstrated no cardiac or
other potentially lethal events across seven HIIT
studies in patients with coronary artery disease,51
suggesting HIIT is very safe when performed in a
controlled environment, although prescription of
such exercise must be considered on an individual
patient basis.
Due to the extreme energy expenditure
required in the interval phases of HIIT, high levels
of motivation are required. While effective in
controlled trials, and perhaps associated with
higher adherence levels (as discussed above),
studies to assess long term adherence rates to HIIT
are still needed.
Importantly, as some types of exercise are
contraindicated in certain patient populations52
and because HIIT is a complex concept for those
unfamiliar to exercise, some patients may require
specific assessment or instruction in HIIT from an
exercise physiologist or physiotherapist.
Conclusion
High intensity interval training has been shown to
have numerous clinical benefits for both healthy
and ‘at risk’ populations. General practitioners
are encouraged to discuss with their patients the
concept of ‘evidence based exercise’ and using HIIT
as part of their exercise program.
Authors
Tim Shiraev BSc(Hons) is a final year medical
student, University of Notre Dame, School of
Medicine, Sydney, New South Wales. timothy.
shiraev1@my.nd.edu.au
Gabriella Barclay BSc(Nutrition)(Hons), is a dieti-
cian, St Vincent’s Hospital, Sydney, New South
Wales.
Conflict of interest: none declared.
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