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The Potential for High-Intensity Interval
Training to Reduce Cardiometabolic
Disease Risk
Holly S. Kessler,
1,2
Susan B. Sisson
2
and Kevin R. Short
3
1 Section of Pediatric Emergency Medicine, University of Oklahoma Health Sciences Center, Oklahoma
City, OK, USA
2 Department of Nutritional Sciences, University of Oklahoma Health Sciences Center, Oklahoma City,
OK, USA
3 Section of Pediatric Diabetes and Endocrinology, University of Oklahoma Health Sciences Center,
Oklahoma City, OK, USA
Contents
Abstract................................................................................. 489
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490
2. High-Intensity Interval Training: Operational Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492
2.1 Maximal Oxygen Consumption Outcomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492
2.2 Glucose Metabolism Outcomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
2.3 Serum Lipid Outcomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
2.4 Blood Pressure Outcomes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503
2.5 Anthropometric Outcomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503
2.6 Mechanistic Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504
3. Conclusion ........................................................................... 505
Abstract In the US, 34%of adults currently meet the criteria for the metabolic
syndrome defined by elevated waist circumference, plasma triglycerides (TG),
fasting glucose and/or blood pressure, and decreased high-density lipoprotein
cholesterol (HDL-C). While these cardiometabolic risk factors can be treated
with medication, lifestyle modification is strongly recommended as a first-
line approach. The purpose of this review is to focus on the effect of physical
activity interventions and, specifically, on the potential benefits of incor-
porating higher intensity exercise. Several recent studies have suggested that
compared with continuous moderate exercise (CME), high-intensity interval
training (HIT) may result in a superior or equal improvement in fitness and
cardiovascular health. HIT is comprised of brief periods of high-intensity
exercise interposed with recovery periods at a lower intensity. The premise of
using HIT in both healthy and clinical populations is that the vigorous ac-
tivity segments promote greater adaptations via increased cellular stress, yet
their short length, and the ensuing recovery intervals, allow even untrained
individuals to work harder than would otherwise be possible at steady-state
intensity. In this review, we examine the impact of HIT on cardiometabolic
REVIEW ARTICLE Sports Med 2012; 42 (6): 489-509
0112-1642/12/0006-0489/$49.95/0
Adis ª2012 Springer International Publishing AG. All right s reserved.
risk factors, anthropometric measures of obesity and cardiovascular fitness in
both healthy and clinical populations with cardiovascular and metabolic
disease. The effects of HIT versus CME on health outcomes were compared
in 14 of the 24 studies featuring HIT. Exercise programmes ranged from
2 weeks to 6 months. All 17 studies that measured aerobic fitness and all seven
studies that measured insulin sensitivity showed significant improvement in
response to HIT, although these changes did not always exceed responses
to CME comparison groups. A minimum duration of 12 weeks was necessary
to demonstrate improvement in fasting glucose in four of seven studies (57%).
A minimum duration of 8 weeks of HIT was necessary to demonstrate im-
provement in HDL-C in three of ten studies (30%). No studies reported that
HIT resulted in improvement of total cholesterol, low-density lipoprotein
cholesterol (LDL-C), or TG. At least 12 weeks of HIT was required for
reduction in blood pressure to emerge in five studies of participants not al-
ready being treated for hypertension. A minimum duration of 12 weeks was
necessary to see consistent improvement in the six studies that examined
anthropometric measures of obesity in overweight/obese individuals. In
the 13 studies with a matched-exercise-volume CME group, improvement
in aerobic fitness in response to HIT was equal to (5 studies), or greater than
(8 studies) in response to CME. Additionally, HIT has been shown to be safe
and effective in patients with a range of cardiac and metabolic dysfunction. In
conclusion, HIT appears to promote superior improvements in aerobic fit-
ness and similar improvements in some cardiometabolic risk factors in com-
parison to CME, when performed by healthy subjects or clinical patients for
at least 8–12 weeks. Future studies need to address compliance and efficacy of
HIT in the real world with a variety of populations.
1. Introduction
According to the 2003–6 National Health and
Nutrition Examination Survey (NHANES), 34%
of all adults in the US meet the criteria for the
metabolic syndrome defined by the National
Cholesterol Education Program’s Adult Treat-
ment Panel III (NCEP/ATP III).
[1]
The NCEP/
ATP III criteria for the metabolic syndrome
includes at least three of the following risk factors:
increased waist circumference, elevated triglycerides
(TG), low high-density lipoprotein cholesterol
(HDL-C), elevated fasting glucose and elevated
blood pressure.
[2]
While these cardiometabolic risk factors
can be treated effectively with medication, life-
style modification is strongly recommended as a
first-line approach.
[3]
Most lifestyle intervention
programmes include behavioural, dietary and
physical activity components, but there is evi-
dence that regular exercise decreases cardiome-
tabolic risk independent of dietary interven-
tion.
[4,5]
Furthermore, regular aerobic exercise
also improves cardiovascular fitness,
[6,7]
a health
and function benefit that is not expected with a
medication-only treatment plan. Multiple studies
have shown an association between cardio-
vascular fitness and cardiovascular mortality, as
well as all-cause mortality in men and women of
all ages.
[8-10]
Thus, there is strong rationale to
emphasize exercise within lifestyle improvement
programmes that are designed to prevent or treat
the metabolic syndrome and its components.
Despite evidence that exercise is vital to good
health and disease prevention, only 64.5%of
adults in the US meet federal recommendations
of at least 150 minutes/week of moderate-intensity
or 75 minutes/week of vigorous-intensity aerobic
exercise.
[11]
One commonly cited barrier to exer-
cise is a lack of time.
[12]
Substituting some vigorous
490 Kessler et al.
Adis ª2012 Springer International Publishing AG. All rights reserved. Sports Med 2012; 42 (6)
exercise for some moderate-intensity exercise is a
way to improve fitness in a more time-efficient
manner. According to the 2008 Physical Activity
Guidelines,
[5]
1 minute of vigorous activity
counts for 2 minutes of moderate-intensity ac-
tivity, although currently there is not sufficient
evidence to support this claim for many health
outcomes. Nevertheless, including vigorous ac-
tivity as part of an exercise programme could
offer a more time-efficient approach to achieve
specific health goals for some individuals. In this
review, we examine the impact of high-intensity
interval training (HIT) on aerobic fitness and
metabolic outcomes.
HIT may offer similar health benefits com-
pared with continuous moderate aerobic exer-
cise (CME),
[13]
and may be more time-efficient
for improving maximal oxygen consumption
(.
VO
2max
).
[14,15]
HIT has been used for several
decades by athletes and coaches to improve ex-
ercise performance,
[16]
but its ability to improve
health outcomes in non-athletes has recently
generated new interest. HIT is characterized by
brief periods of high-intensity aerobic exercise
(typically >90%.
VO
2max
) separated by recovery
periods of lower-intensity aerobic exercise or
rest.
[17]
The recovery periods allow for brief pe-
riods of high-intensity exercise that would not be
sustainable for longer periods of continuous ex-
ercise. As a result of exercising at high intensity,
a shorter total duration of each exercise session
is required to complete an equal volume of
work compared with CME. Therefore, HIT may
provide an alternative mode of vigorous exercise
for people who do not possess the necessary fit-
ness level to perform continuous high-intensity
exercise.
The purpose of this review is to examine the
impact of HIT on clinical cardiometabolic risk
factors including glucose metabolism, serum lip-
ids, blood pressure and anthropometric out-
comes, including body mass index (BMI), body
composition and waist circumference. Additionally,
.
VO
2max
, while not a typical measurement of car-
diometabolic risk in most clinical settings, is
highly predictive of all-cause and cardiovascular
mortality.
[9,10]
The literature on aerobic exercise
training responses is mostly comprised of studies
that used CME. Thus, to determine the equiv-
alency or relative benefits of HIT, many HIT
studies have included a CME arm in which the
training volume (exercise energy expenditure)
was similar to or greater than the HIT arm.
A literature search of the PubMed database
was performed in March 2011 using the following
terms: ‘high-intensity interval training’ or ‘high-
intensity interval exercise’ combined with ‘weight
loss’, ‘obesity’, ‘body fat’, ‘diabetes’, ‘glucose’,
‘insulin’, ‘metabolic syndrome’ and ‘lipids’. Ad-
ditional relevant publications were identified by
using the PubMed ‘related articles’ link, as well as
reviewing the reference sections from the selected
studies. A similar search strategy was employed
using the OVID MEDLINE and SPORTDiscus
databases. Search results were limited to studies
examining HIT and at least one clinical cardio-
metabolic risk factor, studies examining non-
athletes/untrained participants, longitudinal studies
and English language articles. Cross-sectional
studies, animal studies, studies including diet in-
terventions with HIT, studies examining out-
comes in trained participants/athletes and studies
examining only non-clinical outcomes were ex-
cluded. Twenty-four peer-reviewed original research
articles were included in this review. Fourteen
of those studies were conducted as randomized
trials with a CME arm and 14 included a control
non-exercise arm. Only one of the included
studies was conducted in adolescents,
[18]
and
there were no studies in prepubescent children.
No year limit was applied, and the earliest study
found was from 1984. Studies included partici-
pants who had normal BMI (18.5–24.9 kg/m
2
), as
well as studies with overweight/obese participants
(‡25.0 kg/m
2
). While most of the studies included
healthy participants, five studies included partic-
ipants with cardiovascular disease,
[19-23]
one
study included participants with the metabolic
syndrome,
[24]
and one study included participants
with type 2 diabetes mellitus.
[25]
While studies
utilizing specific dietary interventions in combi-
nation with HIT were excluded, one study in-
cluded a 1-hour diet education seminar prior to
the start of training that had no apparent effect
on energy intake.
[26]
Study durations ranged from
2 weeks to 6 months.
Reducing Cardiometabolic Disease Risk with HIT 491
Adis ª2012 Springer International Publishing AG. All rights reserved. Sports Med 2012; 42 (6)
2. High-Intensity Interval Training:
Operational Definition
HIT is defined as vigorous exercise performed
at a high intensity for a brief period of time in-
terposed with recovery intervals at low-to-mod-
erate intensity or complete rest. The modes of
HIT training usually include running/walking on
a treadmill or cycling on a cycle ergometer. HIT
does not include resistance training. Two distinct
types of HIT are included in this review. Sprint
interval training (SIT) is usually characterized by
4–6 cycles of 30 second ‘all out sprints’ followed
by 4–4.5 minutes of recovery. Five SIT studies are
included in this review. Four SIT studies used leg
cycle ergometry as the mode of exercise,
[14,27-29]
and one study used treadmill running.
[30]
The ex-
tremely high intensity of SIT imposes some po-
tential health, safety and motivational concerns.
Therefore, the majority of studies using this ap-
proach have been performed with young healthy
people, although a few recent studies have begun
exploring whether SIT could be used in clinical
populations.
[29,31]
The other type of HIT, aerobic
interval training (AIT), is performed at a slightly
lower intensity than SIT but for longer periods of
time. Typically, the AIT exercise protocols in this
review used 4 minutes of high-intensity work at
80–95%.
VO
2max
followed by 3–4 minutes of re-
covery time, for 4–6 cycles performed on a tread-
mill or bicycle ergometer. In contrast to SIT, the
AIT approach has been used with young healthy
people and higher risk groups, including older
adults and patients with coronary artery disease
(CAD).
[20-23]
Many of the studies in this review
include a CME arm for comparison with HIT. In
contrast to SIT and AIT, CME is typically per-
formed at 50–75%.
VO
2max
. Some of these studies
that compared results of HIT versus CME con-
trolled for the total energy expenditure during
exercise. Thus, in order to achieve equal energy
expenditure, participants in the CME training
arms typically exercised ~15–20%longer than their
AIT counterparts. However, energy expended
during exercise has not always been matched
among comparison training groups. This is
especially true for the studies using SIT, in which
the total exercise time may be only 2–3 minutes
and the comparison CME group may perform a
traditional moderate-intensity exercise session
for 45–60 minutes.
[14]
2.1 Maximal Oxygen Consumption Outcomes
The 17 studies that examined the impact of
HIT on .
VO
2max
consisted of three SIT studies of
2- to 6-weeks’ duration
[14,29,30]
and 14 AIT stud-
ies of 4-weeks’ to 6-months’ duration (table I). All
but one treatment arm of a single study
[35]
dem-
onstrated an increase in .
VO
2max
after the SIT/
AIT programmes. All four studies of 4- to 8-weeks’
duration that included a CME arm, induced a
similar improvement in .
VO
2max
in both the SIT/
AIT and CME arms. Two of those investigations
used the SIT approach with young adults
[14,30]
and the other two studies used AIT in older adults
with CAD
[19]
and overweight/obese middle-aged
adults.
[26]
Nine AIT studies that lasted 10 weeks to
6 months also included a CME arm. In contrast
to the studies comparing SIT with CME, all but
one of the AIT studies reported that AIT resulted
in a significantly greater improvement in .
VO
2max
compared with CME training.
[35]
This includes
three studies in adults with CAD,
[20-22]
three
studies in young adults,
[15,38,39]
a study in obese,
middle-aged adults
[37]
and a study in middle-aged
adults with the metabolic syndrome.
[24]
An
exception to those findings was presented by
Thomas et al.
[35]
In that study, statistically similar
improvement in .
VO
2max
was achieved by the
CME group and an AIT group who performed
4·4-minute bouts of vigorous activity, although
a second AIT group who performed 8 ·2-minute
bouts of high-intensity exercise had no improve-
ment in .
VO
2max
over the 11-week training pro-
gramme. It is possible that the relatively small
group sizes (nine adults in the 8 ·2-minute bout
group) may have obscured the ability to detect
significantly different training responses in that
study.
Notably, AIT induced equal or superior im-
provement in .
VO
2max
in comparison with CME,
even when exercise time was less in the AIT group.
Due to the higher intensity of exercise, AIT exercise
sessions required less time than CME sessions to
492 Kessler et al.
Adis ª2012 Springer International Publishing AG. All rights reserved. Sports Med 2012; 42 (6)
Table I. Summary of cardiometabolic outcomes from studies using high-intensity interval training
Study Participant
characteristics
a,b
Study design Sample size
(n)
Intensity/duration of
exercise
Glucose regulation
c,d
Lipids
d,e
BP
d,f
Anthropometric
measurements
d
.
VO
2maxd
Babraj
et al.
[28]
16 young men,
normal BMI
Cycle
ergometer,
6 sessions in
2wk
SIT (16) 4–6·30 sec ‘all-out’
sprints, 4 min recovery
17–26 min/session
250 kcal/wk
OGTT AUC:
glucose fl12%
insulin fl37%
insulin sensitivity
(Cederholm index)
›23%
No change in fasting
glucose or insulin
Richards
et al.
[27]
31 young adults,
overweight
Cycle
ergometer,
6 sessions in
2wk
SIT (12)
SB (9)
CON (10)
SIT: 4–7·30 sec
‘all-out’ sprints, 4 min
recovery
SB:
as above for only 1
training session
Insulin sensitivity
(clamp technique):
SIT ›27%
No change in single
bout or CON
No change in fasting
glucose or insulin
Whyte
et al.
[29]
10 young men,
overweight/obese
Cycle
ergometer,
6 sessions in
2wk
AIT (10) 4–6·30 sec ‘all-out’
sprints, 4.5 min
recovery
24 h post-exercise,
fasting insulin fl25%,
insulin AUC fl15%
Insulin sensitivity
Index ›23%
Changes did not persist
72 h post-exercise
No change in fasting
glucose or glucose
AUC
No change in
TC, TG or
HDL-C
SBP fl5%at
24 h, change
did not
persist at
72 h
No change in
DBP
No change in
body mass
WC fl1.1%
›9.5%
Little et al.
[25]
8 older adults with
type 2 diabetes
mellitus, obese
Cycle
ergometer,
6 sessions in
2wk
AIT (8) 10 ·60 sec at 90%
HR
max
with 60 sec
recovery plus warm
up/cool down
Total time: 75 min/wk
48 h results:
Continuous 24 h
average blood glucose
fl13.2%
AUC 24 h glucose
fl13.5%
3 h post-prandial
glucose AUC fl29.6%
Continued next page
Reducing Cardiometabolic Disease Risk with HIT 493
Adis ª2012 Springer International Publishing AG. All rights reserved. Sports Med 2012; 42 (6)
Table I. Contd
Study Participant
characteristics
a,b
Study design Sample size
(n)
Intensity/duration of
exercise
Glucose regulation
c,d
Lipids
d,e
BP
d,f
Anthropometric
measurements
d
.
VO
2maxd
Hood et al.
[32]
7 middle-aged
adults, overweight
Cycle
ergometer,
6 sessions in
2wk
AIT (7) 10 ·60 sec at 80–95%
HR
res
with 60 sec
recovery plus warm
up/cool down
~20 min/session
72 h results:
Insulin sensitivity
(HOMA2%S) ›35%
Moholdt
et al.
[19]
59 older adults,
overweight, post
coronary artery
bypass graft
surgery
Treadmill,
5·/wk for
4wk
AIT (28)
CME (31)
AIT: 4 ·4 min at
90%HR
max
with 3 min
recovery plus warm
up/cool down
Total time:
38 min/session
CME: continuous
exercise at 70%
HR
max
for
46 min/session,
similar energy
expenditure as AIT
No change in fasting
glucose
(fasting glucose
elevated at baseline)
No change in
HDL-C, LDL-C,
or TG
No change in
body weight
AIT
›12.2%
CME
›8.8%
No
difference
between
groups
Burgomaster
et al.
[14]
20 young adults,
normal BMI
Cycle
ergometer,
SIT: 3 ·/wk for
6wk
CME: 5 ·/wk
for 6 wk
SIT (10)
CME (10)
SIT: 4–6·30 sec ‘all-
out’ sprints, 4.5min
recovery
1.5 h/wk
CME: 40–60 min
continuous exercise at
65%.
VO
2peak
4.5 h/wk
No change in
body weight
SIT ›7.3%
CME
›9.8%
No
difference
between
groups
Macpherson
et al.
[30]
20 young adults,
baseline BMI NR,
but calculated
from data
provided as
normal/borderline
overweight
Treadmill,
3·/wk for
6wk
SIT (10)
CME (10)
SIT: 4–6·30 sec
‘all-out’ sprints,
4 min recovery
CME: 65%.
VO
2max
,
30–60 min/session
Fat mass (kg):
SIT fl12.4%
CME fl5.8%
Lean mass (kg):
›1.0%in both
groups
SIT
›11.5%
CME
›12.5%
No
difference
between
groups
Musa et al.
[33]
36 young men,
normal BMI
Running,
3.2 km on
track 3 ·/wk
for 8 wk
AIT (20)
CON (16)
AIT: 4 ·800 m runs at
90%HR
max
with 1 : 1
exercise-to-rest time
ratio
~40 min/session
HDL-C:
AIT ›18.1%
TC/HDL-C
ratio:
AIT fl18.1%
No change in
TC
No change in
BMI or BF%
Continued next page
494 Kessler et al.
Adis ª2012 Springer International Publishing AG. All rights reserved. Sports Med 2012; 42 (6)
Table I. Contd
Study Participant
characteristics
a,b
Study design Sample size
(n)
Intensity/duration of
exercise
Glucose regulation
c,d
Lipids
d,e
BP
d,f
Anthropometric
measurements
d
.
VO
2maxd
Tsekouras
et al.
[34]
15 young men
mean BMI:
25.2 kg/m
2
(borderline
overweight)
Treadmill,
3·/wk for
8wk
AIT (7)
CON (8)
AIT: 4 ·4 min at 90%
.
VO
2peak
,
4 min recovery,
32 min/session
VLDL-C-TG:
AIT fl28%
No change in
body weight or
composition
AIT ›18%
Wallman
et al.
[26]
21 middle-aged,
obese adults
Cycle
ergometer,
4·/wk for
8 wk plus a 1 h
diet education
seminar prior
to start of
training
AIT (7)
CME (6)
CON (8)
AIT: 10 ·1 min at 90%
.
VO
2peak
, 2 min
recovery at 30%
.
VO
2peak
,
30 min/session
CME: 30 min
continuous exercise at
50%.
VO
2peak
, similar
energy expenditure as
AIT
No change in
TC, HDL-C,
LDL-C or TG
(TC elevated at
baseline)
No change in
BP
No change in
body mass
Upper body fat
mass:
AIT fl8%
CME fl3%
No change in
energy intake
for all 3 groups
AIT ›24%
CME
›19%
No
difference
between
groups
Rognmo
et al.
[20]
17 adults with
CAD, overweight
Treadmill,
3·/wk for
10 wk
AIT (8)
CME (9)
AIT: 4 ·4 min at
80–90%.
VO
2peak
,
3 min recovery, plus
warm up/cool down,
33 min/session
CME: 41 minutes
continuous exercise at
50–60%.
VO
2peak
,
similar energy
expenditure as AIT
No change in
resting BP
(SBP
elevated at
baseline)
No change in
body mass
AIT
›17.9%
CME
›7.9%
AIT ›
more than
CME
(p <0.01)
Thomas
et al.
[35]
36 young men
18–25 y
(BMI NR)
Treadmill,
3·/wk for
11 wk
AIT-1 (8)
AIT-2 (9)
CME (11)
CON (8)
AIT-1 : 6 ·4 min at
90–100%HR
max
,
4 min recovery
AIT-2 : 8 ·2 min at
90–100%HR
max
,
3 min recovery
CME: 8.04 km at
75–85%HR
max
(8 min/mile), time not
given
Similar energy
expenditure among
groups
No change in
TC or HDL-C
AIT-1
›19.9%
AIT-2: no
change
CME:
›7.1%
Continued next page
Reducing Cardiometabolic Disease Risk with HIT 495
Adis ª2012 Springer International Publishing AG. All rights reserved. Sports Med 2012; 42 (6)
Table I. Contd
Study Participant
characteristics
a,b
Study design Sample size
(n)
Intensity/duration of
exercise
Glucose regulation
c,d
Lipids
d,e
BP
d,f
Anthropometric
measurements
d
.
VO
2maxd
Moreira
et al.
[36]
23 middle-aged
adults, overweight
Cycle
ergometer,
3·/wk for
12 wk
AIT (8)
CME (8)
CON (7)
AIT: 20 ·2 min at 20%
above anaerobic
threshold, 1 min no-
exercise recovery,
60 min/session
CME: 60 min
continuous exercise at
10%below anaerobic
threshold, similar
energy expenditure as
AIT
Fasting glucose
g
:
AIT fl13%
CME fl14%
TC
g
:
AIT no change
CME fl16%
TG:
no change
BMI:
AIT fl1.4%
CME fl1.5%
WC:
HIT fl0.8%
CME fl1.8%
WHR:
HIT fl2.5%
CME no change
BF%:
HIT fl0.6%
CME fl0.9%
All outcomes
not different
between groups
Nybo et al.
[15]
28 young men
BMI NR,
Mean body fat:
24.3%
Treadmill,
3·/wk for
12 wk
AIT group:
completed
2.0 –0.1
mean –SD
sessions/
wk
CME group:
completed
2.5 –0.2
mean –SD
sessions/wk
AIT (8)
CME (9)
CON (11)
AIT: 5 ·2 min intervals
at 95%HR
max
,
recovery duration NR,
plus 5 min warm up.
20 min/session
CME: continuous
running at 80%HR
max
for 60 min
Fasting glucose:
AIT fl9%
CME fl9%
Glucose (2 h post-
glucose load):
AIT fl16.4%
CME fl12.5%
(fasting glucose
elevated at baseline)
No change in
TC, HDL-C,
LDL-C
TC/HDL-C
ratio:
AIT no change
CME fl15%
SBP:
AIT fl6%
CME fl6%
DBP:
AIT no
change
CME fl6%
Body mass:
AIT no change
CME fl1.2%
BF%:
AIT no change
CME fl1.7%
AIT
›14.2%
CME ›7%
AIT ›
more than
CME
(p <0.05)
Schjerve
et al.
[37]
27 middle-aged
adults,
obese
Treadmill,
3·/wk for
12 wk
2 supervised
sessions and
1 at-home
session/wk
AIT (14)
CME (13)
AIT: 4 ·4 min intervals
at 85–95%HR
max
with
3 min recovery, plus
warm up/cool down,
38 min/session
CME: continuous
exercise at 60–70%
HR
max
for 47 min,
similar energy
expenditure as AIT
No change in fasting
glucose, insulin,
C-peptide, or HbA
1c
No change in
TC, HDL-C, or
TG
(TC elevated at
baseline)
No change in
SBP
DBP:
AIT fl7%
CME fl9%
(DBP
elevated at
baseline)
Body weight:
AIT fl2%
CME fl3%
BMI:
AIT fl1.6%
CME fl3.0%
BF%:
AIT fl2.2%
CME fl2.5%
No change in
WHR
AIT ›33%
CME
›16%
AIT ›
more than
CME
(p <0.001)
Continued next page
496 Kessler et al.
Adis ª2012 Springer International Publishing AG. All rights reserved. Sports Med 2012; 42 (6)
Table I. Contd
Study Participant
characteristics
a,b
Study design Sample size
(n)
Intensity/duration of
exercise
Glucose regulation
c,d
Lipids
d,e
BP
d,f
Anthropometric
measurements
d
.
VO
2maxd
Thomas
et al.
[38]
59 young adults
18–32 y
(BMI NR)
Mean BF%males,
14.5%; females,
24.5%
Treadmill,
3·/wk for
12 wk
AIT (15)
CME-1 (14)
CME-2 (18)
CON (12)
AIT: 8 ·1 min at 90%
HR
max
, 3 min
recovery,
500 kcal/session
CME-1: 4 miles at
75%HR
max
,
500 kcal/session
CME-2: 2 miles
at 75%
HR
max
, 250 kcal /
session
No change in
TC, TG, or
HDL-C
BF%
g
:
All exercise
groups
flBF%~3%
AIT
›10.2%
No change
in other
groups
Tjonna
et al.
[18]
42 adolescents,
mean age 14 y,
obese
Treadmill,
2·/wk for
12 wk
AIT (20)
CON (22)
AIT: 4 ·4 min intervals
at 95%HR
max
with
4 min recovery plus
warm up/cool down,
40 min/session
CON: group meetings
every 2 wk, undefined
group physical activity
sessions 3 times in
3mo
Fasting glucose:
AIT fl6%
CON no change
Fasting insulin:
AIT fl29%
CON fl19%
Glucose (2 h post
glucose load):
AIT fl12%
CON no change
Insulin (2 h post-
glucose load):
AIT fl27%
CON fl41%
Insulin sensitivity
(HOMA2%S):
AIT ›24%
CON ›10%
HbA
1c
:
AIT fl0.14%
CON fl0.13%
HDL-C:
AIT ›9.7%
CON no
change
No change in
TG
SBP:
AIT fl7%
CON fl2%
DBP:
AIT fl8%
CON no
change
MAP:
AIT fl8%
CON no
change
BMI:
AIT fl2.1%
CON no change
BF%
AIT fl1.3%
CON no change
No change in
WC
AIT ›11%
CON no
change
Continued next page
Reducing Cardiometabolic Disease Risk with HIT 497
Adis ª2012 Springer International Publishing AG. All rights reserved. Sports Med 2012; 42 (6)
Table I. Contd
Study Participant
characteristics
a,b
Study design Sample size
(n)
Intensity/duration of
exercise
Glucose regulation
c,d
Lipids
d,e
BP
d,f
Anthropometric
measurements
d
.
VO
2maxd
Wisloff
et al.
[21]
27 older adults
with post-
infarction heart
failure, normal
BMI
Treadmill,
supervised
training 2 ·/
wk plus at-
home outdoor
walking 1 ·/
wk for 12 wk
AIT (9)
CME (9)
CON (9)
AIT: 4 ·4 min at
90–95%HR
peak
, 3 min
recovery, plus warm
up/cool down,
38 min/session
CME: continuous
walking at 70–75%
HR
peak
for 47 min,
similar energy
expenditure as AIT
CON: advised to
follow advice from
physician regarding
exercise plus
supervised treadmill
walking once every
3wkat70%HR
peak
for
47 min
No change in fasting
glucose
(fasting glucose
elevated at baseline)
No change in
TC, TG or
HDL-C
(TC elevated at
baseline)
No change in
BP
(participants
were on BP
medications)
No change in
BMI
AIT ›46%
CME
›14%
AIT ›
more than
CME
(p <0.05)
CON no
change
Ciolac
et al.
[39]
34 healthy,
normotensive
young women
with family history
of hypertension,
normal BMI
Treadmill,
3·/wk for
16 wk
AIT (11)
CME (11)
CON (12)
AIT: 13 ·1 min at
80–90%.
VO
2max
,
2 min recovery,
40 min/session
CME: continuous
exercise at 60–70%
.
VO
2max
for 40 min,
similar
energy expenditure as
AIT
Fasting glucose:
No change
Insulin:
AIT fl35%
CME fl28%
Insulin sensitivity
(HOMA2%S):
AIT ›31%
CME ›27%
TC, HDL-C,
LDL-C and TG
did not change
Ambulatory
SBP:
AIT fl1.8%
CME fl2.4%
Ambulatory
DBP:
AIT fl2.8%
CME fl3.0%
BMI, WC, and
WHR did not
change
AIT
›15.8%
CME
›8.0%
AIT ›
more than
CME
(p <0.05)
Guimaraes
et al.
[40]
43 middle-aged
adults with
hypertension,
overweight
Treadmill,
3·/wk(2
supervised
and 1
unsupervised
session) for
16 wk
AIT (16)
CME (16)
CON (11)
AIT: 13 ·1 min at 80%
HR
res
, 2 min recovery
at 50%HR
res
,
40 min/session
CME: continuous
exercise at 60%HR
res
,
40 min/session
BP did not
change in
any of the
groups when
analysed
separately
h
(participants
were on BP
medications)
Continued next page
498 Kessler et al.
Adis ª2012 Springer International Publishing AG. All rights reserved. Sports Med 2012; 42 (6)
Table I. Contd
Study Participant
characteristics
a,b
Study design Sample size
(n)
Intensity/duration of
exercise
Glucose regulation
c,d
Lipids
d,e
BP
d,f
Anthropometric
measurements
d
.
VO
2maxd
Tjonna
et al.
[24]
28 middle-aged
adults with the
metabolic
syndrome,
overweight
Treadmill,
3·/wk for
16 wk
AIT (11)
CME (8)
CON (9)
AIT: 4 ·4 min intervals
at 95%HR
max
, 3 min
recovery, plus warm
up/cool down,
40 min/session
CME: continuous
exercise at 70%HR
max
for 47 min, similar
energy expenditure as
AIT
CON: followed advice
from family physician
Fasting glucose:
AIT fl4.3%
CME no change
Insulin sensitivity
(HOMA2%S):
AIT ›15%
CME no change
(fasting glucose
elevated at baseline)
HDL-C:
AIT ›22%
CME no
change
(HDL-C low at
baseline)
TG: no change
SBP:
AIT fl6.2%
CME fl7.6%
DBP:
AIT fl6.3%
CME no
change
MAP:
AIT fl5.4%
CME fl6.9%
(BP elevated
at baseline)
Body weight:
AIT fl3%
CME fl4%
BMI:
AIT fl2.3%
CME fl4.1%
WC:
AIT fl4.7%
CME fl5.7%
WHR: no
change
AIT ›35%
CME
›16%
AIT ›
more than
CME
(p <0.05)
Warburton
et al.
[22]
14 middle-aged
men with CAD,
treated with
bypass or
angioplasty,
overweight
Treadmill,
stair climber,
and cycle
ergometer,
2·/wk for
16 wk plus
continuous
exercise at
65%
HR
res
/.
VO
2res
3·/wk for
both groups
AIT (7)
CME (7)
AIT: 8 ·2 min at 90%
HR
res
/.
VO
2res
, 2 min
recovery,
30 min/session
(10 min/equipment)
CME: continuous
exercise at 65%
HR
res
/.
VO
2res
,
30 min/session
(10 min/equipment)
No change in
SBP or DBP
(participants
were on BP
medications)
Body mass:
AIT fl3.4%
CME fl4.7%
.
VO
2
at
anaerobic
threshold:
AIT
›31.8%
CME
›9.5%
AIT ›
more than
CME
(p <0.05)
Munk et al.
[23]
40 middle-aged
adults with
coronary artery
stents, overweight
Cycle
ergometer or
running,
3·/wk for
6mo
AIT (20)
CON (20)
4·4 min at 80–90%
HR
max
, 3 min
recovery, plus warm
up/cool down
33 min/session
No change in
BP
+BP
medications
BMI:
AIT fl2.2%
CON ›1.8%
AIT
›16.8%
CON ›
7.8%AIT ›
more than
CON
(p <0.01)
Continued next page
Reducing Cardiometabolic Disease Risk with HIT 499
Adis ª2012 Springer International Publishing AG. All rights reserved. Sports Med 2012; 42 (6)
achieve the same energy expenditure. Four AIT
studies of 10- to 12-weeks’ duration in which ex-
ercise energy expenditure was matched in the AIT
and CME groups showed a significantly greater
increase in .
VO
2max
in the AIT groups.
[20,21,24,37]
Additionally, one AIT study of only 4-weeks’
duration resulted in an equal improvement in
.
VO
2max
in both the AIT and CME groups.
[19]
All
five of these studies required 15–20%less time in
the AIT group to achieve the same energy ex-
penditure as the CME group. Furthermore, in the
12-week AIT study by Nybo et al.,
[15]
the AIT
group, which exercised for only 20 minutes/
session, demonstrated a significantly greater in-
crease in .
VO
2max
compared with the CME group,
which exercised for 1 hour. Exercise energy expen-
diture for each group was not reported, however.
Similarly, SIT studies that included a CME
arm demonstrated comparable increases in .
VO
2max
even when exercise time and/or training volume/
energy expenditure were much less in the SIT arm.
In the 6-week study by Burgomaster et al.,
[14]
young adults had similar increases in .
VO
2max
in both the SIT and CME groups. SIT training
volume in this study was only 10%of CME train-
ing volume, and total time was 1.5 hours/week for
the SIT group compared with 4.5 hours/week for
the CME group. Likewise, in the 6-week study
by Macpherson et al.,
[30]
both the SIT and CME
groups demonstrated similar improvement in
.
VO
2max
. In this study, total exercise time was
6.75 hours/week in the SIT group and 13.5 hours/
week in the CME group (energy expenditure was
not reported).
Collectively, the available research strongly
suggests that both SIT and AIT induce signif-
icant increases in .
VO
2max
even when compared
with CME training of longer time duration and
similar or greater exercise energy expenditure.
Furthermore, in a SIT study of only 2-weeks’ du-
ration and an AIT study of only 4-weeks’ dura-
tion, both resulted in a significant improvement
in .
VO
2max
suggesting that HIT rapidly induces
changes in .
VO
2max
within a few training ses-
sions.
[19,29]
In conclusion, HIT consistently in-
duced significant changes in .
VO
2max
in a wide
variety of populations including adolescents,
[18]
young adults,
[15]
middle-aged adults
[24]
and older
a Mean ages of participants: young (18–39 y), middle-aged (40–59 y), older (over 60 y).
b Mean BMI values of participants: normal BMI (18.5–24.9 kg/m
2
), overweight (25.0–29.9 kg/m
2
), obese (‡30 kg/m
2
).
c Elevated baseline fasting glucose defined as ‡100 mg/dL or ‡5.6 mmol/L, baseline values were normal unless otherwise noted.
d Percentage change values given for post-exercise differences from baseline reaching statistical significance (p <0.05), unless otherwise noted.
e Elevated baseline TC defined as ‡200 mg/dL or ‡5.2 mmol/L, elevated LDL-C: ‡160 mg/dL or ‡4.1 mmol/L, elevated TG: ‡200 mg/dL or ‡2.3 mmol/L, low HDL-C: <40mg/dL or
<1 mmol/L for men and <50 mg/dL or <1.3 mmol/L for women, baseline values were normal unless otherwise noted.
f Hypertension defined as SBP ‡140 or DBP ‡90, baseline values were normal unless otherwise noted.
g Authors did not provide absolute numbers. Percentage change is approximate, estimated from bar graphs.
h Authors reported that mean 24 h and daytime DBP decreased after training when both exercise groups were analysed together. The decrease in DBP was greater in subjects with
baseline BP above the median value, but there was no difference between training programmes.
AIT =aerobic interval training; AIT-1 and -2 =AIT groups 1 and 2; AUC =area under the curve for a variable measured serially; BF%=body-fat percentage; BMI =body mass index;
BP =blood pressure outcomes; CAD =coronary artery disease; CME =continuous moderate-intensity exercise; CME-1 and -2 =CME groups 1 and 2; CON =control
group performing no intervention unless otherwise stated; DBP =diastolic blood pressure; HbA
1c
=glycosylated haemoglobin; HDL-C =high-density lipoprotein cholesterol;
HOMA2%S=homeostatic model assessment version 2 for insulin sensitivity; HR
max
=maximal heart rate; HR
peak
=peak HR; HR
res
=HR reserve; LDL-C =low-density lipoprotein
cholesterol; MAP =mean arterial pressure; NR =not reported; OGTT =oral glucose tolerance test; SB =single bout; SBP =systolic blood pressure; SD =standard deviation;
SIT =sprint interval training; TC =total cholesterol; TG =triglyceride concentration; VLDL =very low-density lipoprotein particle; .
VO
2max
=maximal oxygen uptake as a measure of
aerobic exercise capacity; .
VO
2peak
=peak .
VO
2
;WC =waist circumference; WHR =waist-to-hip ratio; flindicates decreased; ›indicates increased.
Table I. Contd
500 Kessler et al.
Adis ª2012 Springer International Publishing AG. All rights reserved. Sports Med 2012; 42 (6)
adults with CAD.
[23]
An increase in .
VO
2max
ap-
pears to be the most common outcome from HIT.
2.2 Glucose Metabolism Outcomes
Thirteen studies examined the impact of HIT
on measures of glucose metabolism, such as in-
sulin sensitivity, fasting glucose concentration
and results from oral glucose tolerance testing
(table I). The methods used to measure insulin
sensitivity in seven of these studies included the
hyperinsulinaemic euglycaemic clamp technique,
[27]
Cederholm index,
[28]
homeostasis model assess-
ment of fasting glucose and insulin
[18,24,32,39]
and
the Matsuda insulin sensitivity index from an oral
glucose tolerance test.
[29]
All seven of these stud-
ies showed significant improvement in insulin
sensitivity after HIT.
[18,24,27-29,32,39]
In three of
these studies, young adults performed SIT for
2 weeks on a cycle ergometer.
[27-29]
Of these three
studies, Whyte et al.
[29]
found that insulin sensi-
tivity was improved for 24 but not 72 hours after
the last exercise session. In contrast, the other two
SIT studies reported that insulin sensitivity in-
creased above the pre-training values at a single
measurement performed 48–72 hours after the
last training session.
[27,28]
A single AIT study of
only 2-weeks’ duration showed significant im-
provement in insulin sensitivity in overweight
middle-aged adults who performed only 20 min-
utes of exercise on a cycle ergometer.
[32]
Three
other treadmill AIT studies of 12- to 16-weeks’
duration demonstrated improvement in insulin
sensitivity in overweight/obese adolescents;
[18]
healthy, young women with a family history of
hypertension;
[39]
and middle-aged adults with the
metabolic syndrome.
[24]
Of the two AIT studies
that included a CME arm, one study showed
similar improvement in both groups,
[39]
and the
other study, performed with middle-aged adults
with the metabolic syndrome, showed improve-
ment only in the AIT group.
[24]
These results
suggest that AIT can be an effective strategy to
improve insulin sensitivity in patients who have
already developed the metabolic syndrome.
Eleven studies evaluated the effect of HIT on
fasting glucose concentration. The three SIT
studies of 2- to 4-weeks’ duration reported no
change in participants with normal fasting glu-
cose values at baseline,
[27-29]
and older adults with
CAD and elevated fasting glucose.
[19]
In the seven
AIT studies of 12–16 weeks, fasting glucose re-
sponses were inconsistent. Four of these studies
reported a reduction in fasting glucose in partic-
ipants with normal,
[18,36]
elevated
[24]
and bor-
derline
[15]
fasting glucose values before training.
In contrast, three AIT studies showed no change
in fasting glucose values in participants with
normal
[37,39]
or elevated
[21]
fasting glucose at base-
line. Six of these studies included a CME arm. Three
of these studies showed no change in fasting glu-
cose in either the AIT or the CME arm,
[21,37,39]
two studies showed similar reduction in both the
AIT and CME arms
[15,36]
and one study showed
reduction in the AIT group only.
[24]
All five HIT studies that reported values for
the oral glucose tolerance test (OGTT) reported
significant improvement in 2-hour glucose or
glucose area under the curve (AUC) measure-
ments.
[15,18,25,28,29]
Two of these were SIT studies
of 2-weeks’ duration in young men.
[28,29]
Whyte
et al.
[29]
reported a decrease in the insulin AUC at
24 hours, but this improvement did not persist at
72 hours post-exercise. One AIT study of only
2-weeks’ duration reported a decrease in glucose
AUC in older adults with type 2 diabetes mellitus
who performed 75 minutes/week of exercise on
a cycle ergometer.
[25]
The other two were AIT
studies of 12-weeks’ duration with overweight/
obese adolescents
[18]
and young, healthy men.
[15]
The study by Nybo et al.
[15]
included a CME arm,
and both groups demonstrated similar improve-
ment in 2-hour glucose values despite the 20-minute
training time in the AIT group compared with
1 hour in the CME group.
In summary, the research suggests that HIT
results in a significant improvement in insulin
sensitivity in a variety of populations and may be
equal or superior to the effect of CME. SIT studies
and/or studies of less than 12-weeks’ duration did
not show a change in fasting glucose. Results of
studies of at least 12-weeks’ duration were in-
consistent, but the outcomes suggest that AIT
may be more effective in lowering fasting glucose
in young or middle-aged adults than in older
adults. A notable exception was the improvement
Reducing Cardiometabolic Disease Risk with HIT 501
Adis ª2012 Springer International Publishing AG. All rights reserved. Sports Med 2012; 42 (6)
in oral glucose tolerance, which was recently
demonstrated in older people with type 2 dia-
betes.
[25]
When compared with CME, AIT seems
to be at least as effective in lowering fasting glu-
cose in those cases where a reduction was re-
ported. Studies of both SIT and AIT all showed
improvement in at least one value from the
OGTT, and the one study that included a CME
arm showed similar improvement in the OGTT,
even with training time of 20 minutes in the AIT
group compared with 1 hour in the CME group.
[15]
Whyte et al.
[29]
reported significant changes in
insulin sensitivity and insulin AUC at 24 hours
that did not persist at 72-hours post-exercise.
Other authors showed significant results at 48
and 72 hours, but many did not report the time-
line for testing glucose metabolism from the last
bout of exercise (see table I). Controlling the
timing of post-training tests is important to de-
termine if improvements are due to the acute ef-
fect of the last bout of exercise or the cumulative
effect of exercise training.
2.3 Serum Lipid Outcomes
Fourteen studies examined the effect of HIT
on serum lipids (table I). The following measure-
ments of serum lipid metabolism are included in
this review: total cholesterol (TC), HDL-C, low-
density lipoprotein cholesterol (LDL-C), TG and
very low-density lipoprotein cholesterol TG
(VLDL-C-TG). Twelve studies examined the ef-
fect of HIT on HDL-C, but only one of these
studies included participants with low base-
line HDL-C.
[24]
AIT studies of less than 8 weeks
and the single SIT study with lipid outcomes
reported no change in HDL-C. Of the ten stud-
ies that lasted at least 8 weeks, only three dem-
onstrated an increase in serum HDL-C.
[18,24,33]
Two of these three studies were performed with
younger people with normal baseline HDL-C
including a 12-week study with adolescents
[18]
and an 8-week study with young adult men.
[33]
The third study showed that HDL-C increased in
response to 16 weeks AIT performed by middle-
aged adults with the metabolic syndrome and
very low baseline HDL-C values.
[24]
None of the
nine studies that included a CME arm showed
improvement in the HDL-C concentration in the
CME group. However, Nybo et al.
[15]
showed a
decrease in the TC : HDL-C ratio in the CME
group only, an index reflecting a relative im-
provement in HDL-C. It is possible that this re-
sult was related to the fact that the CME group
exercised for 60 minutes/session, but the AIT
group only exercised 20 minutes/session. Exercise
energy expenditure was not reported in that study
and it appears likely that the exercise volume in
the CME group exceeded that performed by the
AIT group.
There was little or no impact of HIT on the other
serum lipid measurements. None of the ten studies
examining the effect of HIT on TC showed a de-
crease in TC using either AIT
[15,21,26,33,35-39]
or
SIT.
[29]
However, the baseline TC was normal in
all but three of the AIT groups,
[21,26,37]
and
therefore the chance for improvement was likely
limited. Of the eight studies that included a CME
arm,
[15,21,26,35-39]
only one study showed a decrease
in TC in the CME group but not in the AIT group
in overweight, middle-aged adults who trained
for 12 weeks.
[36]
None of the four studies that
evaluated LDL-C reported changes in response
to either AIT or CME programmes,
[15,19,26,39]
although none of these studies used participants
with elevated baseline values. Similar to the find-
ings on LDL-C, none of the ten studies that
examined the effect of HIT on TG demonstrated
changes in response to AIT
[18,19,21,24,26,34,37-39]
or
with SIT.
[29]
All of these studies included partic-
ipants with normal baseline TG values except
for one in which mean TG concentration was
borderline elevated.
[21]
Of the eight studies that
examined TG that included a CME arm, none
showed improvement in TG in either the HIT or
the CME group.
[19,21,24,26,36-39]
In the only study
that examined VLDL-C-TG,
[34]
the fasting con-
centration of this lipid component decreased in
overweight young men after 8 weeks of AIT
training.
In summary, HDL-C has been the only serum
lipid measurement shown to improve in response
to AIT. A minimum duration of 8 weeks was
necessary to see improvement in HDL-C, although
only three of ten studies that lasted at least
8 weeks showed improvement in HDL-C. The
502 Kessler et al.
Adis ª2012 Springer International Publishing AG. All rights reserved. Sports Med 2012; 42 (6)
studies that demonstrated improvement in HDL-
C were performed with young participants or in
participants with very low baseline HDL-C val-
ues. None of the studies reviewed reported a
beneficial effect of HIT on TC, LDL-C, or TG. It
is possible that the duration of the studies was not
long enough to observe improvement in serum
lipids, as the CME groups in most of the studies
did not show any improvement either. These find-
ings are consistent with the scientific literature,
which suggests that moderate- or high-intensity
aerobic exercise improves HDL-C, but does not
frequently improve TC, LDL-C or TG.
[41]
Fur-
thermore, significant weight loss or change in
body composition may be required to achieve
improvements in TC, LDL-C, and TG.
[42]
2.4 Blood Pressure Outcomes
Twelve studies examined the impact of HIT
on blood pressure (table I). Studies of 2- to
10-weeks’ duration did not show a change in
blood pressure with AIT.
[20,26]
However, the sin-
gle SIT study that measured changes in blood
pressure did show a transient decrease in systolic
blood pressure (SBP) at 24 hours post-exercise
that did not persist at 72 hours in ten overweight/
obese young men who performed 2 weeks of SIT
on a cycle ergometer.
[29]
In participants who were not being treated
with antihypertensive medication, all five AIT
studies of 12- to 16-weeks’ duration showed a
decrease in blood pressure in a variety of popu-
lations. Four of these studies included a CME
arm for comparison. A 12-week study of obese,
middle-aged adults with baseline elevated dia-
stolic blood pressure (DBP) showed improvement
in DBP in both the HIT and CME groups.
[37]
A 16-week study of middle-aged adults with the
metabolic syndrome and baseline elevated SBP/
DBP showed improvement in SBP in both the
HIT and CME groups, but improvement in DBP
in the HIT group only.
[24]
A 16-week study of
young, normotensive females with a family his-
tory of hypertension showed improvement in
both SBP and DBP in both the HIT and CME
groups.
[39]
A 12-week study of young males with
borderline elevated SBP showed improvement in
the HIT and the CME group,
[15]
but only a de-
crease in DBP for the CME group. Because the
baseline DBP in the HIT group was normal in
that study, the lack of change in the DBP may not
be meaningful. Additionally, the AIT group in
that study exercised only 20 minutes, whereas the
CME group completed 60 minutes per session, a
difference that likely resulted in greater energy
expenditure by the CME group. Lastly, a 12-week
AIT study of overweight/obese adolescents with
borderline elevated SBP showed improvement in
both SBP and DBP,
[18]
but did not include a
CME arm for comparison.
All four AIT studies of at least 12-weeks’
duration in which there was no change in blood
pressure were performed with subjects already being
treated with antihypertensive medication.
[21-23,40]
Three of these studies reported baseline blood
pressure measurements.
[21,23,40]
Because all three
studies showed well controlled baseline blood
pressure on the antihypertensive medications, the
lack of change in blood pressure with exer-
cise training is not unexpected. The study by
Guimareas et al.
[40]
did not show significant
changes in either exercise group when the AIT
and CME groups were analysed separately, but
the authors reported that mean 24-hour DBP and
daytime DBP were decreased when the exercise
groups were analysed together.
[40]
In summary, the available data suggest that
measureable improvements in blood pressure
can be achieved with AIT training of at least
12-weeks’ duration in participants who are not
already being treated effectively for hypertension.
AIT of at least 12-weeks’ duration seems at least
as effective as CME in lowering blood pressure in
individuals with baseline-elevated measurements,
even if training time is less in the AIT arm com-
pared with the CME arm.
[15,24,37]
No change was
observed for those patients who were already
being treated effectively for hypertension, but the
true impact of HIT on their blood pressure may
have been masked by medication.
2.5 Anthropometric Outcomes
Seventeen studies examined the impact of HIT
on anthropometric measurements that relate to
Reducing Cardiometabolic Disease Risk with HIT 503
Adis ª2012 Springer International Publishing AG. All rights reserved. Sports Med 2012; 42 (6)
obesity (table I). The anthropometric mea-
surements included in this review were body
weight, BMI, body-fat percentage (BF%), lean
body mass percentage, waist-to-hip ratio and
waist circumference.
Four of the studies that examined the impact
of HIT on anthropometric measurements were
performed in participants whose BMI was within
the normal range (20–25 kg/m
2
); there were no
changes in body size or composition in response
to exercise training in any of these investiga-
tions. These interventions consisted of a 6-week
SIT programme in young adults,
[14]
two AIT
programmes of 8- to 16-weeks’ duration in young
men and women
[33,39]
and a 12-week AIT pro-
gramme in older adults with CAD.
[21]
Three of these
studies included a CME arm in which there was also
no change in body size or composition.
[14,21,39]
Eleven studies measured anthropometric chang-
es in overweight or obese participants. Of the five
studies of 2- to 10-weeks’ duration,
[19,20,26,29,34]
only one reported significant changes. In that
investigation, waist circumference decreased by
2.4 cm in young obese men who performed SIT
for 2 weeks on a cycle ergometer.
[29]
This reduc-
tion in waist circumference seems unexpected
after only 2 weeks in a study without a diet in-
tervention and a total exercise time of 2–3minutes
per session for six sessions. In contrast to those
shorter studies, the six AIT studies that lasted
3–6 months all showed improvement in anthro-
pometric measurements in response to AIT in a
variety of populations. Three AIT studies of
12–16 weeks performed by middle-aged adults on
a treadmill demonstrated reductions in BMI and
BF%,
[37]
BMI and waist circumference
[24]
and
BMI, waist circumference, waist-to-hip ratio and
BF%.
[36,37]
Overweight/obese adolescents who
performed 12 weeks of AIT on a treadmill ex-
perienced a decrease in BMI and BF%.
[18]
In two
studies of adults with CAD, 16 weeks of AIT on a
mix of aerobic exercise equipment resulted in
decreased body mass,
[22]
and 6 months of AIT on
a cycle ergometer resulted in decreased BMI.
[23]
Seven studies with overweight/obese partici-
pants had a CME comparison group. The three
shorter studies, lasting up to 10 weeks, showed no
changes in anthropometric measurements in
either the AIT or CME groups.
[19,20,26]
In com-
parison, the four studies of 3- to 6-months’
duration showed similar improvements in BMI,
body mass and/or waist circumference in the AIT
and CME groups.
[22,24,36,37]
The equivalency of
anthropometric changes in those studies may be
attributable to the fact that total exercise energy
expenditure was similar between AIT and CME
exercise programmes.
[24,37]
Three studies (one SIT and two AIT) exam-
ined the impact of HIT on BF%. In MacPherson
et al.,
[30]
young, healthy men and women with
baseline BF%of 18–21%who performed 6 weeks
of SIT on a treadmill showed a significant re-
duction in fat mass (1.7 kg), compared with the
CME group (0.8 kg). Furthermore, the SIT pro-
tocol required only half the time of the CME
protocol (6.75 hours/week vs 13.5 hours/week).
In Thomas et al.,
[38]
young men (baseline BF%
<20%) and women (baseline BF%<30%) were
randomized to perform either 12 weeks of AIT on
a treadmill or a volume-matched CME protocol.
Both the AIT and CME arms showed similar
significant reductions in BF%of ~3%. In a study
by Nybo et al.,
[15]
young men with an initial mean
BF%above normal (‡22.3%) who performed
AIT or CME on a treadmill for 12 weeks dem-
onstrated a reduction in BF%only in the CME
group (1.7%decrease in BF%). This outcome, as
noted in prior sections, may be due to the fact
that the AIT group appears to have performed
less exercise volume than the CME group.
In summary, these results suggest that AIT of
at least 12 weeks’ duration is likely to induce fa-
vourable anthropometric changes in overweight/
obese individuals with results similar to CME.
Thus, AIT may be a more time-efficient approach
to achieve the beneficial effects of exercise on
body size and composition. SIT studies with
programmes longer than 2 weeks are needed to
evaluate the impact of SIT on anthropometric
outcomes.
2.6 Mechanistic Considerations
Like the focus of this review, most of the exist-
ing HIT investigations have reported the effects
of exercise on clinical and functional outcomes.
504 Kessler et al.
Adis ª2012 Springer International Publishing AG. All rights reserved. Sports Med 2012; 42 (6)
Some studies, however, have included bio-
chemical and molecular outcomes that have
begun to provide mechanistic support for adap-
tations to HIT that could result in improved
physical function. In skeletal muscle, for example,
AIT was shown to induce an increase in the
transcription factor, peroxisome proliferator-
activated receptor g-coactivator-1a(PGC-1a),
which is a master regulator of oxidative pheno-
type. This increase occurred in patients with obesity,
heart failure or the metabolic syndrome,
[21,24,37]
but was absent in CME comparison groups. An
increase in PGC-1acould drive adaptations in
mitochondrial biogenesis and glucose transport-
ers that contribute to the increases in .
VO
2max
and oral glucose tolerance. Similarly, those same
studies demonstrated that skeletal muscle sarco-
plasmic reticulum calcium uptake was increased
by AIT but not CME.
[21,24,37]
This response is
expected to increase the ability to perform high-
intensity muscle contractions. Increased abundance
of transcripts for PGC-1a, glucose transporter 4
and oxidative pathway genes have been demon-
strated in response to acute or short-term SIT;
although, to our knowledge, comparisons of these
responses to CME have not yet been reported.
[14,32,43]
In addition to muscle adaptations, changes in
cardiac and vascular function in response to
HIT have been reported that may account for
improvement in .
VO
2max
and blood pressure. For
example, in response to AIT, flow-mediated di-
lation of the brachial artery, a measure of vas-
cular endothelial function, was increased in obese
adults and adolescents and adults with the me-
tabolic syndrome.
[18,24,37]
This response may
result, in part, from the increased nitric oxide
availability, as reported in response to AIT but
not CME.
[24]
One SIT study also showed an in-
crease in flow-mediated dilation in healthy adults
following 6 weeks of training, although the CME
comparison group had a similar improvement.
[44]
Notably, however, the SIT group performed only
2–3 minutes of exercise per session while the CME
group completed 40–60 minutes per session. There-
fore, the total exercise volume was not matched in
that study. HIT has also been reported to result in
an increased cardiac stroke volume in obese women
and cardiac failure patients,
[21,45]
and improved
cardiac output in middle-aged adults.
[46]
Although
the picture is still emerging, these initial ob-
servations suggest that HIT induces changes in
skeletal muscle and the vascular system that
could contribute to potentially greater health and
functional adaptations compared with CME.
3. Conclusion
Our review and interpretation of the existing
literature suggests that SIT and AIT are effective
for improving insulin sensitivity and .
VO
2max
,
with results equal or superior to CME (table II).
In contrast to the rapid and consistent improve-
ments reported for insulin sensitivity and .
VO
2max
for both SIT and AIT, changes in other cardio-
metabolic risk factors vary with the type and
programme duration of HIT training. AIT stud-
ies of at least 12 weeks showed a decrease in BMI
or BF%in overweight/obese individuals that was
Table II. Summary of primary cardiometabolic outcomes from
high-intensity interval training studies
Major outcomes Comments
flBMI or BF%in
overweight/obese:
6/6 AIT studies ‡12 wk
No change in AIT studies <12 wk. One
2 wk SIT stud y: flWC. Results
comparable with outcomes of CME
groups
›Insulin sensitivity:
3/3 SIT and 4/4 AIT
studies
Results comparable with outcomes of
CME groups
›HDL-C:
3/10 AIT studies ‡8wk
No change in AIT studies <8 wk. No
change in single 2 wk SIT study.
0/9 studies with CME groups showed
improvement in HDL-C with CME.
Longer intervention may be required to
show more consistent improvement with
HIT
flBP in subjects NOT on
anti-hypertensive
medication:
5/5 AIT studies ‡12 wk
AIT studies <12 wk did not show flin BP.
No change with AIT in subjects taking
anti-hypertensive medication. Results
comparable with CME outcomes
›.
VO
2max
:3/3 SIT and
14/14 AIT studies
Results comparable (5 studies) or
superior (8 studies) with all studies that
included CME group
AIT =aerobic interval training; BF%=body-fat percentage; BMI =
body mass index; BP =blood pressure; CME =continuous moderate-
intensity exercise; continuous moderate-intensity exercise; SIT =
sprint interval training; .
VO
2max
=maximal oxygen uptake as a
measure of aerobic exercise capacity; WC =waist circumference;
›indicates increased; flindicates decreased.
Reducing Cardiometabolic Disease Risk with HIT 505
Adis ª2012 Springer International Publishing AG. All rights reserved. Sports Med 2012; 42 (6)
comparable with CME outcomes. AIT studies of
at least 12 weeks also demonstrated a decrease in
blood pressure in individuals not already being
treated with antihypertensive medications, and
results were comparable to CME outcomes in
individuals with elevated-baseline measurements.
HIT has not been shown to induce improvements
in serum lipids with the exception of an increase
in HDL-C in some AIT trials that lasted at least
8 weeks. Furthermore, CME was not found to be
effective in raising HDL-C in any of the nine
studies that included a CME arm. Longer study
duration may be necessary to show a more con-
sistent increase in HDL-C in response to HIT.
HIT may offer a modest advantage in time
efficiency over CME, since many of the beneficial
adaptations to exercise can be achieved in
~15–20%less time per typical AIT versus CME
exercise session. This is particularly true for
.
VO
2max
, since multiple AIT studies showed that
AIT exercise sessions requiring 15–20%less time
than a matched work volume of CME resulted in
equal or greater improvement, compared with
CME. Additionally, improvement in .
VO
2max
was
similar to CME results in individuals performing
SIT exercise despite 50–90%less exercise time
and an apparently large but unquantified differ-
ence in energy expended, compared with CME.
Furthermore, two other studies where AIT
training time was 15%less than CME training
time showed equal or superior improvement in
the AIT group for several other outcomes, includ-
ing anthropometric changes, blood pressure, fast-
ing glucose, insulin sensitivity and HDL-C.
[24,37]
Nybo et al.
[15]
showed equal improvement in SBP
and fasting glucose in groups assigned to AIT
and CME even though AIT training time was
only one-third as long (20 minutes, with intensity
reaching 95%maximal heart rate (HR
max
) for
5·2 minute intervals), compared with CME
training (60 minutes at 80%HR
max
).
An important concern is the safety of HIT for
patients with CAD. SIT has not been studied in
this population, but the results from five AIT
studies support the premise that supervised AIT
is safe in patients with cardiovascular disease,
since no training-related adverse events were re-
ported in a total of 72 patients in these five trials
conducted for 4 weeks to 6 months.
[19-23]
Fur-
thermore, in a study by Guiraud et al.,
[31]
circu-
lating troponin T, a marker of myocardial
ischaemia, remained within the normal range in
20 patients with CAD who performed a single
session of AIT. Of the four studies performed
with CAD patients that also included a CME
arm, three showed significantly larger increases in
.
VO
2max
in the HIT group, compared with the
CME group.
[20-22]
For example, older adults with
post-infarction heart failure who were randomly
assigned to a 12-week AIT programme for 3 days
per week on the treadmill had a 46%increase in
.
VO
2max
, whereas a CME group matched for ex-
ercise energy expenditure demonstrated only a
14%increase in aerobic capacity.
[21]
Additionally,
patients in this study also experienced significant
increases in the stroke volume, cardiac output and
ejection fraction in the AIT group but not in the
CME group. Considering the predictive value of
.
VO
2max
for future cardiovascular events, HIT
should be considered as an effective alternative
training method for patients with CAD.
For several reasons, HIT may not be appro-
priate or optimal for everyone. HIT is highly
structured and requires at least initial supervision
in untrained individuals. Also, HIT may require
medical clearance due to the high-intensity nature
of the exercise. Although high-impact exercise,
such as running on a treadmill may not be an
appropriate training method for people with, or
at-risk for orthopedic problems, alternatives such
as walking on an inclined treadmill or stationary
cycling may offer the same benefits without risk
of injury. HIT also requires a high degree of
motivation to achieve the targeted intensity level
and may not be the preferred method of exercise
for all people. However, the authors of two
studies that compared HIT to CME incidentally
noted that participants in the HIT group reported
that they found the varying intensities of exercise
to be motivating. The participants in the CME
group, in contrast, found the exercise training to
be quite boring.
[21,24]
These anecdotal reports
suggest that some people may be more likely to
adhere to a HIT exercise programme as opposed
to a CME programme. Identification of people
who may be more likely to adhere to different
506 Kessler et al.
Adis ª2012 Springer International Publishing AG. All rights reserved. Sports Med 2012; 42 (6)
training styles is an important area of study for
future research.
Several strengths and limitations of this review
warrant discussion. One of the strengths was that
no year limit was applied to the PubMed search
criteria. Therefore, studies that met the criteria
were retrieved from as early as 1984. Addition-
ally, we included studies using both healthy par-
ticipants and people with cardiovascular disease
or the metabolic syndrome. One of the limita-
tions is that this is not a systematic review with
rigorous standards for inclusion/exclusion of
potential articles and meta-analytic statistics.
However, in our assessment, the HIT literature
is not yet extensive enough to perform this type
of formal review. The duration of the available
studies, type of exercise, selection of outcomes
and participant characteristics vary too widely,
and many studies have not included a compar-
ison exercise group matched for exercise energy
expenditure. Nevertheless, as the current sum-
mary demonstrates, there appears to be enough
evidence to conclude that HIT is at least as ef-
fective as CME for several important health
outcomes. Another limitation, that reflects a gap
in the literature, is that only five SIT studies were
found to have met the criteria for this review, and
the longest duration of these was only 6 weeks.
Therefore, the true efficacy of SIT on cardiome-
tabolic risk is not yet known and further studies
of longer duration are needed before the effects
of SIT on clinical outcomes, safety and feasibility
can be fully evaluated. Lastly, only one study in-
cluded adolescents as subjects, and none of the
studies included pre-adolescent children. Despite
the finding that AIT was shown to produce many
of the same cardiometabolic benefits in obese ado-
lescents as shown in adults, further corroboration
from paediatric investigations is warranted.
In conclusion, HIT is an effective method of
exercise to improve some cardiometabolic risk
factors such as BMI, BF%, insulin sensitivity and
blood pressure, as well as peak aerobic capacity,
as summarized in table II. Additional investiga-
tion is needed with people who have low-baseline
HDL-C and elevated fasting glucose, to clarify
the impact of HIT on these two risk factors.
Combining HIT with dietary interventions to
assess their separate and combined effects on
serum lipids and obesity is another important
future area of study. AIT exercise programmes
lasting longer than 6 months and SIT program-
mes of greater than 6 weeks are needed to evaluate
the long-term impact of HIT on cardiometabolic
risk. Compared with CME, HIT may be a more
time-efficient mode of training as vigorous ex-
ercise requires less time than CME to achieve the
same benefits. The time savings, intensity varia-
tion and improved fitness may contribute to
increased long-term adherence to an exercise
programme for some individuals. Future studies
need to address whether compliance and efficacy
with HIT is an effective alternative to CME in the
real world with a variety of populations for im-
proving fitness and cardiometabolic risk factors.
Acknowledgements
Susan B. Sisson is supported by a University of Oklahoma
Health Sciences Center Vice President of Research Seed Grant
for study entitled Sitting Versus Light Activity and Cardio-
vascular Disease Risk: Influence of a High Fat Meal.KevinR.
Short is supported by grant number P20RR024215 from the
National Center for Research Resources (NCRR), a component
of the National Institutes of Health (NIH). Holly S. Kessler has
received no funding and the authors have no conflicts of interest
to declare that are directly relevant to the content of this review.
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Correspondence: Dr Holly S. Kessler MD, Section of
Pediatric Emergency Medicine, University of Oklahoma
Health Sciences Center, 940 Northeast Thirteenth Street,
2G-2300, Oklahoma City, OK 73104, USA.
E-mail: Holly-Kessler@ouhsc.edu
Reducing Cardiometabolic Disease Risk with HIT 509
Adis ª2012 Springer International Publishing AG. All rights reserved. Sports Med 2012; 42 (6)
