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Journal of Obesity
Volume 2012, Article ID 480467, 8pages
doi:10.1155/2012/480467
Research Article
The Effect of High-Intensity Intermittent Exercise on
Body Composition of Overweight Young Males
M. Heydari,1J. Freund,2andS.H.Boutcher
1
1School of Medical Sciences, Faculty of Medicine, University of New South Wales, Sydney, NSW 2052, Australia
2St Vincent’s Hospital, Darlinghurst, NSW 2010, Sydney, Australia
Correspondence should be addressed to S. H. Boutcher, s.boutcher@unsw.edu.au
Received 4 January 2012; Revised 9 March 2012; Accepted 6 April 2012
Academic Editor: Giorgios P. Nassis
Copyright © 2012 M. Heydari et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
To determine the effect of a 12-week high intensity intermittent exercise (HIIE) intervention on total body, abdominal, trunk,
visceral fat mass, and fat free mass of young overweight males. Participants were randomly assigned to either exercise or control
group. The intervention group received HIIE three times per week, 20 min per session, for 12 weeks. Aerobic power improved
significantly (P<0.001) by 15% for the exercising group. Exercisers compared to controls experienced significant weight loss
of 1.5 kg (P<0.005) and a significant reduction in total fat mass of 2kg (P<0.001). Abdominal and trunk adiposity was also
significantly reduced in the exercising group by 0.1kg (P<0.05) and 1.5 kg (P<0.001). Also the exercise group had a significant
(P<0.01) 17% reduction in visceral fat after 12 weeks of HIIE, whereas waist circumference was significantly decreased by week
six (P<0.001). Fat free mass was significantly increased (P<0.05) in the exercising group by 0.4kg for the leg and 0.7 kg for the
trunk. No significant change (P>0.05) occurred in levels of insulin, HOMA-IR, and blood lipids. Twelve weeks of HIIE resulted
in significant reductions in total, abdominal, trunk, and visceral fat and significant increases in fat free mass and aerobic power.
1. Introduction
Obesity levels continue to increase in both developed and
developing countries [1]. As being overweight is associated
with numerous health problems, effective fat loss strategies
are required [2]. Although dieting has been the major fat
loss method, aerobic exercise programs have been shown to
increase cardiorespiratory fitness [3] and preserve fat-free
mass [4]. Most aerobic exercise interventions have consisted
of moderate-intensity steady-state exercise, for about 30 to
40 min for 3 to 4 days per week, over a four- to six-month
period. Disappointingly, these kinds of exercise programs
have resulted in minimal fat loss [5,6].
In contrast, high-intensity intermittent exercise (HIIE)
has been shown to result in greater fat loss [7]. For example,
Trapp et al. [8] conducted a HIIE program in young women
for 15 weeks with three 20 min sessions per week. HIIE con-
sisted of an 8 s sprint followed by 12 s of low intensity cycling,
repeatedfor20min.Anothergroupofwomencarriedout
an aerobic cycling protocol for 40 min each session. Results
showed that women in the HIIE group lost 2.5 kg of subcuta-
neous fat, whereas no change occurred with steady state aer-
obic exercise. Fat loss accruing through 15 weeks of HIIE was
attained with 50% less exercise time commitment and a simi-
lar energy expenditure to that of steady-state exercise. Impor-
tantly, the women in this study also showed a significant
0.6 kg increase in fat-free mass (FFM) after HIIE, whereas
FFM of the steady state exercise group was unchanged. The
lack of increase in FFM accompanying steady-state exercise is
in agreement with prior research in this area [9].
With regard to abdominal fat, 15 weeks of HIIE led to
a 0.15 kg reduction of fat in previously untrained young
women [8]. As women in this study possessed moderate lev-
els of abdominal fat it is feasible that the greater abdominal,
trunk, and visceral fat of men may show greater reductions
after exposure to HIIE. For example, Boudou et al. [10]stud-
ied older type 2 diabetic males and found that after 8 weeks of
HIIE, abdominal adiposity was decreased by 44%. Whether
regular HIIE will also reduce the abdominal and visceral fat
of young nondiabetic but overweight males is undetermined.
2Journal of Obesity
Therefore, the purpose of this study was to examine the
effects of 20 min bouts of HIIE, repeated three times weekly
for 12 weeks, on body composition of overweight males.
It was hypothesized that HIIE would result in significant
reductions in total abdominal, trunk, and visceral fat and a
significant increase in fat-free mass and aerobic power.
2. Subjects and Methods
2.1. Subjects. Forty-six inactive, overweight men were
recruited from a university population and randomly
allocated into either exercise (n=25) or control groups
(n=21). The exercisers and controls were similar in terms
of age (24.7±4.8and25.1±3.9 years) and body mass index
(BMI: 28.4±0.5and29±0.9 kg m−2). The study received
approval from a University Research Ethics Committee.
Forty-six subjects underwent initial testing, however, for
various reasons five withdrew from the exercise group and
three from the control group. There was no significant
difference for any variable between the nonadherents and
those males who completed the study.
2.2. Procedures. Subjects were advised to avoid strenuous
activity and caffeine consumption for 24 hours prior to test-
ing, and attended the laboratory after a 10-hour overnight
fast. Tests for all subjects in control and exercise groups were
completed at the same time of day. The Physical Activity
Readiness Questionnaire [11] was filled out and information
on subjects’ personal and familial medical history obtained.
Fasting blood (300 mL) was drawn at baseline, and at weeks
3, 6, and 12 from an antecubital vein in EDTA vacutainers.
An automated enzymatic method (Cholestech LDX, USA)
was applied to quantify blood lipid profiles and glucose
concentrations from whole blood. The remaining whole
blood in EDTA tubes was spun immediately in a chilled
centrifuge (Model Megafuge 1.0R, Heraeus, Germany) at 4◦C
and frozen at −86◦C for later analysis. Aerobic power was
assessed using a TrueMax 2400 Metabolic Cart (ParvoMedics
Inc, USA) and an electronically braked cycle ergometer,
Monark 869 (Monark, Sweden). For subjects who could not
achieve the criteria for ˙
VO2max, due to the strenuous nature
of the exercise session ˙
VO2peak was used as an indicant of
aerobic power.
2.3. Resting Metabolic Rate (RMR). Fasted subjects relaxed
in a reclined position for 30 minutes. Resting heart rate,
resting energy expenditure (REE), ˙
VO2,and ˙
VCO2were
assessed using a metabolic cart (TrueMax 2400 Metabolic
Cart, ParvoMedics Inc, USA).
˙
VO2represents the rate of oxygen utilised by subjects
during exercise, whereas ˙
VCO2represents the rate of carbon
dioxide exhaled. Subjects were advised not to sleep and
breathe naturally during testing. The first 10 minutes of data
collection were excluded from analysis to allow for subject
stabilization.
2.4. Diet. Subjects in both exercise and control groups
were advised to maintain their normal eating habits during
the study. On their first and last visit to the laboratory
subjects provided a 3-day diet inventory which was analyzed
using diet analysis software (SERVE Nutrition Management
Systems, Professional Edition, version 5, Australia).
2.5. Body Composition. A Dual Energy X-Ray Absorptiom-
etry (DEXA) scan with a Lunar Prodigy scanner (software
version 7.51, GE Corporation, USA) was used to measure
body mass and percentage body fat. Fat mass (FM) along
with FFM in kg was measured for the whole body. DEXA
also provided information on abdominal and trunk fat, as
indicators of central adiposity. Computerised tomography
(CT) scans (Philips Gemini GXL 16, the Netherlands) were
also used to measure abdominal and visceral fat distribution.
Axial slices (3 ×10 mm) were performed through the
abdomen at L2/L3 and L4/L5. Fat density of 0.9 mg/L was
assumed [12], and it was automatically selected at any tissue
between 150 to 50 Hounsfield Units (HU). Gemini software
(GXL Host system) was used to analyse the CT images.
Abdominal, visceral, and subcutaneous fat were determined
at the levels of L2/L3 and L4/L5. BMI was calculated by
dividing weight by height squared (kg m−2).
2.6. High-Intensity Intermittent Exercise Training. Subjects in
the exercise group completed supervised exercise (8 s sprint,
12 s recovery) continuously throughout each 20-min session.
The HIIE workload was set at 80–90% of each subject’s heart
rate (HR) peak at a cadence between 120 and 130 r.p.m
and recovery was set at the same amount of resistance but
at a cadence of 40 r.p.m. Subjects were instructed to keep
their exercise intensity at a level necessary to produce a HR
between 80–90% of HR peak. As subjects adapted to HIIE
training, workload was increased so HR stayed at the appro-
priate 80–90% HR peak level. HIIE was coordinated with a
prerecorded compact disc counting down each sprint in a 3-
2-1 manner. Subjects performed a 5-min warm-up and cool-
down on the bike prior to and after each exercise session. All
training cycling data included continuous recording of HR
and r.p.m, whereas rating of perceived exertion [13] (RPE)
was assessed at 5-min intervals.
2.7. Assays. Insulin was measured using commercially avail-
able ELISA immunoassay kits. The degree of enzymatic
turnover of the substrate was determined by dual wavelength
absorbance measurement at 450 and 620 nm (Dako K6219,
Denmark). HOMA-IR, an insulin resistance index [14], was
calculated as follows:
HOMA-IR =fasting insulin μIU/mL×fasting blood glucose (mmol/L)
22.5.(1)
Journal of Obesity 3
Tab le 1: Change in body composition, aerobic power, resting heart rate, RQ, resting energy expenditure, carbohydrate, and fat oxidation for
the high-intensity intermittent exercise and no exercise control group (N=38; mean and standard error).
Exercise Control
Pre∗Post Pre∗Post
Weight (kg) 87.8±2.786.3±2.7∗∗ 89 ±2.9 89.4±3.1
BMI (kg m−2)28.4±0.527.9±0.5∗∗ 29 ±0.9 29.1±0.9
Waist circumference (cm) 93.3±1.489.8±1.4∗∗ 93.7±1.995.1±1.9
Fat mass (kg) 29.8±1.627.8±1.5∗∗ 31.7±2.231.8±2.3
%Fatmass 34.8±1.132.8±1.1∗∗ 36.3±1.436.0±1.5
Fat-free mass (kg) 54.3±1.555.5±1.4∗∗ 53.8±1.354.2±1.3
˙
VO2peak (l min−1)3.0±0.13.4±0.1∗∗ 2.6±0.12.7±0.1
˙
VO2peak (mL kg−1min−1)34.2±1.039.4±0.8∗∗ 29.1±1.330.6±1.4
Work output (watts) 246.3±8.1 289.8±8.0∗∗ 224.4±7.3 225.9±6.3
HR (bpm) 62.2±2.557.9±1.8∗∗ 62.7±2.063.7±1.7
RQ 0.85 ±0.01 0.83 ±0.01∗∗ 0.82 ±0.02 0.86 ±0.01
REE (Kcal/day) 1793 ±54 1841 ±56 1788 ±58 1794 ±53
Carbohydrate oxidation (g/day) 232.6±14.3 201.5±13.1∗∗ 186.7±22.3 252.1±21.2
Fat oxidation (g/day) 93.8±6.6 106.1±6.5∗∗ 110.2±10.082.0±10.9
∗Pre vales were used as covariates for ANCOVA.
∗∗P<0.05, change in exercise group significantly greater compared to that of control group. BMI: body mass index; REE: resting energy expenditure; HR:
heart rate; RQ: respiratory quotient; REE: resting energy expenditure.
2.8. Statistical Analysis. Data were analysed with the Sta-
tistical Package for Social Science for Windows software
(SPSS 18, USA). To examine changes after the intervention,
an analysis of covariance (ANCOVA) was used to evaluate
differences between the two groups for variables that did
not violate ANCOVA assumptions. Preintervention values
were used as covariates. Where assumptions were violated, an
independent t-test was conducted on the difference scores.
The statistical analysis was considered significant when the
probability level was less than 0.05.
3. Results
There was no significant difference between the two groups
for body mass, BMI (Tabl e 1 ), and age prior to the training
program.
3.1. Exercise Heart Rates, RPE, and Work Load. The average
HR during the HIIE training sessions for the exercise group
was 160 ±9 beats min−1which corresponded to 88% of HR
peak and the average RPE was 13.6±0.5. Maximal work load
significantly increased in the exercise group (P<0.001) by
43.5 watts (Tab l e 1 ).
3.2. Response in Aerobic Power following the Intervention.
HIIE resulted in a significant increase in both absolute and
relative ˙
VO2peak (P<0.005) with absolute ˙
VO2peak being
increased by 13% and relative ˙
VO2peak by 15% (Tabl e 1 ).
3.3. Total Body Mass and Body Fat Assessed by DEXA.
Total body mass significantly decreased (P<0.005) in
the exercise group (Tab le 1) by 1.5 kg (2%), whereas total
Fat mass change (kg)
0
1
2
Exercise group
Control group
−1
−2
−3
∗
Figure 1: Total fat change for the high-intensity intermittent
exercise and no exercise control groups (N=38, mean and standard
error). ∗Significantly different from control group (P<0.05).
FM significantly decreased (P<0.005) by 2.0 kg (6.7%;
Figure 1).TheFMofcontrolswasunchangedafter12
weeks (Ta b l e 1). Percent body fat in exercisers at pretest
was not correlated to changes in percent body fat after the
intervention (r=0.17, P>0.05).
3.4. Abdominal and Trunk Fat Assessed by DEXA. There was
a significant decrease in abdominal fat by 0.14 kg (6.6%)
for the exercise group (P<0.05) with no change for the
control group (Ta b l e 2). The exercise group also significantly
decreased (P<0.001) trunk fat by 1.4 kg (8.4%), whereas
trunk fat was slightly increased in controls (Tabl e 2 ).
4Journal of Obesity
Tab le 2: Regional changes in body composition for the high-intensity intermittent exercise and no exercise control groups (N=38; mean
and standard error).
Region of fat mass Exercise Control
Pre∗Post Pre∗Post
Leg fat (kg) 9.6±0.89.0±0.79.9±0.79.8±0.7
Leg lean (kg) 18.6±0.619.0±0.6∗∗ 18.5±0.618.5±0.5
Arm fat (kg) 2.7±0.22.5±0.2∗∗ 2.6±0.12.7±0.2
Arm lean (kg) 6.7±0.26.7±0.26.4±0.46.6±0.3
Abdominal fat (kg) 2.3±0.12.2±0.1∗∗ 2.4±0.22.4±0.2
Abdominal lean (kg) 3.7±0.13.7±0.13.5±0.13.5±0.1
Trunk fat (kg) 17.0±0.915.5±0.9∗∗ 17.2±1.217.3±1.3
Trunk lean (kg) 24.9±0.725.6±0.7∗∗ 24.0±0.823.9±0.7
∗Prevalues were used as covariates for ANCOVA.
∗∗P<0.05, change significantly greater compared to that of control group.
Arm
Fat free mass (kg)
0
5
10
15
20
25
30
Pre
Post
Trunk
Leg
∗
∗
Figure 2: Fat-free mass change for the high-intensity intermittent
exercise groups (N=38; mean and standard error). ∗Significant
difference between pre- and posttesting (P<0.05).
3.5. Regional Body Composition Assessed by DEXA. There was
no significant difference between groups in absolute FM loss
in the leg (P>0.05), whereas arm FM loss was greater for
exercisers (P<0.01; Tab l e 2 ).
Total, leg, and trunk FFM (P<0.05) were significantly
increased after 12 weeks of HIIE in the exercise group
compared to the control group, whereas arm FFM (P>
0.05) showed no significant change after the intervention
(Figure 2).
3.6. Abdominal, Visceral, and Subcutaneous Fat Mass Assessed
by CT. Total, abdominal, visceral, and subcutaneous FM at
levels of L2/L3 and L4/L5 were significantly reduced (P<
0.05) after 12 weeks of HIIE compared to the control group
(Tab l e 3 ). Abdominal fat decreased by 8.5% at L2/L3 and
6.6% at L4/L5. Visceral fat was significantly decreased (P<
0.05) by 17% at level L2/L3 and 10% at level L4/L5 (Tabl e 3 ;
Figure 3).
L2/L3
Visceral fat (g)
0
20
40
60
80
100
120
Pre
Post
L4/L5
∗
∗
Figure 3: Visceral fat change for the high-intensity intermittent
exercise and no exercise control groups (N=38; mean and standard
error). ∗Significantly different from control group (P<0.05).
3.7. Change in Body Composition after 3, 6, and 9 Weeks.
At weeks 3 and 6 there were no change in body mass and
BMI, however, after 9 weeks body mass (P<0.005) and
BMI (P<0.005) were significantly decreased. At the end of
the trial, body mass and BMI were significantly decreased
(P<0.001; Tab le 1), yet, at week 6, WC was significantly
lower than that at baseline, from 93.3 to 90.7cm (P<0.001).
There was a further WC reduction from week 6 (90.7cm)
to week 12, (89.8 cm), which was not significant (P>0.05).
Also the major reduction in visceral fat brought about by
HIIE appears to have occurred within the first six weeks as
reduction in waist circumference was significantly correlated
(r=0.57, P<0.05) with reduction in visceral fat (L4/L5) at
week six.
3.8. Response in Resting Metabolic Rate following the Inter-
vention. After the intervention exercise subjects had sig-
nificantly lower resting HR (P<0.01) and respiratory
quotient (RQ; P<0.01) compared to subjects in the control
group. There was no significant change in resting metabolic
Journal of Obesity 5
Tab le 3: Changes in computed tomography scan variables for the high-intensity intermittent exercise and no exercise control groups (N=
38; mean and standard error).
Exercise Control
Pre∗Post Pre∗Post
L2/L3 total fat mass (g) 564.0±22.3 538.0±21.4∗∗ 587.1±26.3 591.0±30.6
L2/L3 abdominal fat (g) 280.0±21.4 256.1±19.6∗∗ 304.8±26.5 311.9±30.6
L2/L3 visceral fat (g) 94.6±10.684.8±9.9∗∗ 102.1±11.5 101.5±11.4
L2/L3 subcutaneous (g) 177.3±16.3 161.7±14.7∗∗ 194.2±20.2 200.4±23.4
L4/L5 total fat mass (g) 576.9±24.3 555.7±21.7∗∗ 595.7±28.4 602.2±32.7
L4/L5 abdominal fat (g) 327.8±23.0 306.3±20.9∗∗ 346.5±27.3 355.5±31.0
L4/L5 visceral fat (g) 62.6±6.251.8±5.1∗∗ 69.7±9.767.3±8.4
L4/L5 subcutaneous (g) 259.7±22.1 247.8±20.0∗∗ 271.7±26.1 281.7±27.7
∗Prevalues were used as covariates for ANCOVA.
∗∗P<0.05, change significantly greater compared to that of control.
Tab le 4: Glucose, insulin, HOMA-IR, and lipid change for the high-intensity intermittent exercise and no exercise control groups (N=38;
mean and standard error).
Exercise Control
Pre Post Pre Post
Glucose (mmoL·l−1)4.86 ±0.14 4.97 ±0.10 4.91 ±0.14 4.91 ±0.14
Insulin (μU·mL−1)6.98 ±0.66 6.72 ±0.63 8.67 ±0.90 8.29 ±0.67
HOMA-IR 1.51 ±0.15 1.47 ±0.14 1.90 ±0.24 1.82 ±0.17
Total cholesterol (mmoL·l−1)4.18 ±0.25 3.97 ±0.24 4.59 ±0.21 4.36 ±0.18
Triglycerides (mmoL·l−1)1.20 ±0.27 1.18 ±0.36 1.52 ±0.21 1.31 ±0.18
High-density lipoprotein (mmoL·l−1)1.31 ±0.09 1.35 ±0.09 1.08 ±0.09 1.03 ±0.08
Low-density lipoprotein (mmoL·l−1)2.51 ±0.16 2.35 ±0.18 2.82 ±0.18 2.81 ±0.16
Very low-density lipoprotein (mmoL·l−1)0.48 ±0.07 0.43 ±0.10 0.66 ±0.09 0.56 ±0.09
TC: HDL ratio 3.51 ±0.32 2.99 ±0.20 4.62 ±0.31 4.52 ±0.27
rate after the intervention (P>0.05),however,subjects
in the exercise group had significantly higher (13%) fat
oxidation (P<0.001) and lower carbohydrate oxidation
(P<0.001) after the intervention compared to the control
group (Tab l e 1).
3.9. Response in Blood Variables following the Intervention.
Fasting glucose, plasma insulin, glucose, HOMA-IR, and
lipid levels were unchanged in the exercise compared to
the control group (P>0.05). For exercisers and con-
trols preintervention levels of insulin, glucose, HOMA-IR,
total cholesterol, triglyceride, low-density lipoprotein, high-
density lipoprotein (Tabl e 4 ) were within the normal range
for males of this age [15].
3.10. Diet. There was no significant change in macro- or
micronutrient content before or after the intervention for the
3-day diet diary of the exercise or control group. Macronu-
trient levels before and after the 12-week intervention are
shown in Tab l e 5 .
4. Discussion
The major findings of this study were that HIIE significantly
increased ˙
VO2peak and significantly reduced total, abdominal,
trunk, and visceral fat of young, overweight males. Also
trunk and leg fat-free mass was significantly increased after
HIIE.
The 15% increase in ˙
VO2max is similar to results of a pre-
vious study that used a 8 s/12 s HIIE protocol [8]. Talanian et
al. [16] also found that a HIIE program significantly elevated
aerobic power. In this paper the oxidative enzyme β-hydroxy-
acyl-CoA dehydrogenase was used as a marker of mito-
chondrial volume and showed that intermittent sprinting
enhances mitochondrial capacity. Different forms of HIIE
have also been shown to significantly increase aerobic power
[17,18]. Thus, collectively these data show that HIIE results
in significant improvements in aerobic fitness. The improve-
ment in cardiorespiratory fitness after HIIE is an attractive
feature of this mode of exercise as aerobic fitness has been
shown to be an important predictor of positive health [19].
That HIIE resulted in significant subcutaneous fat reduc-
tion supports prior research in women using a similar
protocol [8]. Results of the present study with males extend
these findings showing that HIIE is an effective and efficient
way of controlling body composition in both genders. With
regard to abdominal fat, it has been found that 15 weeks
of HIIE led to significantly reduced abdominal fat (0.15 kg)
in untrained young women [8]. The 0.13 kg decrease in
abdominal fat and 1.5 kg decrease in trunk fat found in
6Journal of Obesity
Tab le 5: Macronutrient levels before and after the 12-week-intervention (N=38; mean and standard error).
Exercise Control
Pre Post Pre Post
Kilojoules 8102 ±428 8142 ±414 8569 ±343 8642 ±343
% carbohydrate 43.6±1.842.9±1.546.2±1.846.8±1.9
%protein 19.8±1.119.5±1.118.2±1.118.3±1.5
%fat 36.4±1.737.5±1.435.7±1.734.9±1.4
% saturated fat 13.2±0.813.0±0.712.4±0.711.3±0.6
% monounsaturated fat 13.6±0.714.2±0.713.6±0.713.8±0.7
% polyunsaturated fat 6.3±0.67.0±0.76.3±0.66.5±0.7
Cholesterol (mg) 397.3±37.5 394.7±41.9 304.8±41.6 381.8±57.0
Fibre (g) 19.5±2.519.5±2.420.3±2.421.4±2.8
Sodium (mg) 2564 ±320 2709 ±335 2390 ±345 2547 ±335
the current study demonstrates that this effect is also present
in young males and supports findings by Boudou et al.
[10] who showed that 8 weeks of HIIE significantly reduced
abdominal adiposity in older diabetic males.
The significant 17% decrease in visceral fat found in the
present study extends the findings of Mourier et al. [20]who
showed a significant reduction in visceral fat measured by
MRI, following an exercise regimen consisting of steady-state
exercise and HIIE for 8 weeks. These findings also add to
the results of studies that have shown that aerobic training
interventions decrease visceral adipose tissue [21]. The
present study, however, appears to be the first to examine
the effects of 20 min bouts of HIIE on visceral fat of young
males. As visceral compared to overall obesity is more
strongly associated with cardiovascular disease risk [22] the
ability of HIIE to reduce visceral fat may have positive health
implications. For example, it was shown that reduction in
visceral fat was associated with improvement in glucose and
lipid metabolism, [3] whereas Okauchi et al. [23] found that
a reduction in visceral fat lowered the risk of atherosclerotic
cardiovascular disease. Interestingly, Ohkawara et al. [21]
estimated the optimal dose of aerobic exercise necessary to
significantly reduce visceral fat and concluded that 3,780 kcal
expended per week was needed. As an exercise session (e.g.,
cycling on a stationary cycle ergometer) lasting around an
hour at a moderate exercise intensity expends about 520–
550 kcal then to reach an optimal exercise caloric expenditure
of 3,780 kcal per week an individual would have to perform
approximately seven one-hour exercise sessions per week.
In contrast, subjects in the present study exercised for only
one hour per week. Also Donnelly et al. [24]conducted
16 months, 5 hours of aerobic exercise per week program
with overweight young males and recorded a 23% decrease
in visceral fat. Thus, it appears HIIE can bring about
significant decreases in visceral fat with programs that are
both significantly shorter in length (e.g., 16 months versus
3 months) and have less exercise commitment per week (5
hours versus 1 hour). Also the major decrease in visceral fat
brought about by HIIE may have occurred within the first
six weeks as reduction in visceral fat was correlated with
reduction in waist circumference (r=0.57, P<0.05) at week
six after which waist circumference did not further decrease.
Although the effect of HIIE on FFM has not been
extensively examined, one study using DEXA found that
trunk muscle mass was significantly increased in young
females by 0.6 kg after 15 weeks of HIIE, [8] whereas another
study using MRI showed a significant increase in thigh
muscle cross sectional area of older males and females after
HIIE [10]. The 1.2 kg increase in total FFM found after
HIIE in the present study confirms the ability of this type
of exercise to increase FFM. However, the length of this 12-
week intervention was 3 weeks less than that conducted by
Trapp et al. [8] that used females as subjects. As exercise HRs
and relative exercise intensity of the two trials were similar
it appears that males responded with a similar decrease in
total fat but a greater increase in FFM after HIIE. FFM
increase in the trunk after HIIE was 0.7 kg for males and
0.4 kg for females, whereas in the legs was 0.4 kg for males
and 0.1 kg for females. Thus, males compared to females
recorded greater increases in FFM in the trunk and legs.
This characteristic may be important for fat loss programs
as it has been shown that muscle mass is typically decreased
after dietary restriction [25] and is typically unchanged after
aerobic exercise training [9]. The significant increase in
leg FFM may also reflect important metabolic adaptations
resulting in enhanced insulin sensitivity [26].
Possible mechanisms underlying the HIIE-induced fat
loss effect are undetermined but may include enhanced exer-
cise and postexercise fat oxidation and suppressed postex-
ercise appetite [7]. For example, Burgomaster et al. [26]and
Talanian et al. [16] have shown that 6 to 7 sessions of HIIE
had significant increases in whole body and skeletal muscle
capacity for fatty acid oxidation. The excess postexercise
oxygen consumption response to HIIE does not appear to
have been examined, however, it is feasible that the signif-
icant levels of catecholamines generated during acute HIIE
[27] could elevate postexercise fat oxidation. The significant
catecholamine response to HIIE is in contrast to moderate,
steady-state aerobic exercise that results in small increases
in epinephrine and norepinephrine [28]. Also the high
Journal of Obesity 7
levels of catecholamines produced by HIIE may underlie its
ability to reduce visceral fat, as catecholamines have been
shown to drive lipolysis and are mainly responsible for fat
release from visceral fat stores [29]. Also significantly, more
β-adrenergic receptors have been found in visceral compared
to subcutaneous fat [30] suggesting that
HIIE may have greater potential than steady-state exer-
cise (e.g., jogging, cycling) to reduce visceral fat. Further-
more, increased fat oxidation after HIIE may occur as a result
of the need to remove lactate and H+and to resynthesize
glycogen. Uncoupled respiration, protein turnover, and
sympathetic nervous system activity may also contribute to
increased energy expenditure and fat oxidation after exercise
[9]. Finally, HIIE may also have a suppressive effect on
appetite as exposing rats to hard exercise has been repeatedly
reported to reduce food intake [31].
As this HIIE program required minimal time commit-
ment, it has implications regarding subject compliance with
exercise interventions. Thus, physical activity prescriptions,
which require the least effort, while still producing adequate
reductions in subcutaneous and visceral fat are likely to be
optimal [9] and HIIE would seem to fall under this category
as subject’s total exercise commitment was 60 min per week.
In conclusion, 20 min of HIIE, performed three times per
week for 12 weeks, resulted in significant reductions in total
body, abdominal, trunk, and visceral fat and a significant
increase in fat-free mass of overweight young males.
Acknowledgments
The authors wish to thank Diabetes Australia for supporting
this project (Grant no. RM06599) and also would like to
thank Chau Tran, Joshua Lane, Roger Burrell, and Lucas
Webb for help with data collection.
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