Epidemiological data show that the majority of the adult population fails to meet recommended physical activity levels [
High intensity interval training (HIIT) could potentially provide health benefits in a time-efficient manner. This involves repeated bursts of vigorous exercise interspersed with low intensity recovery. There is growing evidence from healthy populations that HIIT leads to a range of cardiovascular and metabolic benefits that are similar to or greater in magnitude than those achieved with regular continuous aerobic exercise. These benefits include increased cardiorespiratory fitness [
On the basis of these metabolic and fitness benefits, it has been argued that HIIT could be used as a time-effective therapy for the management of body fat levels in overweight and obese individuals [
Whilst HIIT programs that are of low risk have been shown to produce cardiometabolic benefits (improvements in glycaemic control, insulin sensitivity, and skeletal muscle oxidative capacity) in people with coronary artery disease and chronic obstructive pulmonary disease [
We therefore conducted a randomized placebo-controlled trial to examine the effect of 12 weeks of HIIT versus continuous aerobic exercise versus a sham-exercise placebo control on body composition and cardiovascular risk factors in overweight, previously inactive adults. We hypothesized that HIIT would improve fitness and reduce body fat, trunk fat, and android fat and that these benefits would be comparable to those achieved with traditional continuous exercise training and could be achieved in 50–60% of the total time.
38 inactive (exercising < 3 days/week) and overweight (BMI 25 to 29.9) adult (18- to 55-year-old) men (
106 individuals were screened by telephone interview with 38 eligible volunteers undergoing initial assessment and randomization. Five participants did not complete the program (Figure
Flowchart showing the study process. M: male, F: female, HIIT: high intensity interval training, CONT: continuous aerobic exercise, PLA: placebo control group.
Volunteers were required to abstain from alcohol, over-the-counter medication, and strenuous exercise for 24 hours prior to baseline and postintervention testing. Randomization was undertaken after baseline assessments by equally distributed pregenerated list (
Cardiorespiratory fitness/work capacity was assessed by graded maximal exercise test on an electronically braked cycle ergometer (Lode Corival, The Netherlands) under the supervision of the study physician. After a 3-minute warm-up at 35 W and 65 W for women and men, respectively, intensity was increased by 25 W every 150 seconds until volitional fatigue. Heart rate, blood pressure, and 12-lead ECG were recorded at each stage of exercise and participants were verbally encouraged to perform to volitional fatigue. Rating of perceived exertion (RPE) was measured using the Borg scale [
Total body and regional fat distributions were measured by dual-energy X-ray absorptiometry (DEXA) (Lunar Prodigy, GE Medical Systems, Madison, WI, USA, software enCORE 2011 Version 13.60.033). The trunk region included the bottom of the neck line to the top of the pelvis, excluding the upper limbs. The android region (which incorporates abdominal subcutaneous and visceral adipose tissue) included the cut of the pelvic region to 20% of the distance between the pelvic cut and the bottom of the neck line, excluding the arms. The gynoid measure included the height equal to 2 times the height of the android region (Lunar enCORE-based X-ray Bone Densitometry User Manual Revision 6, September 2010). DEXA scanning and analyses were performed by an individual who was blinded to group allocation. Stature was measured to the nearest 0.1 cm by stadiometer (Tanita Best Weight, Seca Model 220, Germany). Waist circumference was measured in the horizontal plane, midway between the inferior margin of the ribs and the superior border of the iliac crest in deep expiration [
Venous blood (8 mL) was collected from the antecubital vein after an overnight fast (>10 hrs) into 2 serum separation tubes. The whole blood sample was stored at 4°C for 2-3 h prior to analysis by an accredited commercial laboratory (Douglass Hanly Moir Pty Ltd., Sydney, Australia). Analysis was performed on the same day as that of collection of serum glucose, insulin and lipids (including triglycerides (TAG), total cholesterol (TC), high density lipoprotein cholesterol (HDL-C), and low density lipoprotein cholesterol (LDL-C)), alanine aminotransferase (ALT), aspartate aminotransferase (AST), and high sensitivity C-reactive protein (hs-CRP). The other tube of blood was used for determination of serum free fatty acids (FFAs). These tubes were centrifuged at room temperature at 4000 g and serum was stored at −20°C before analysis.
Results from the screening visit were used to determine the presence of metabolic syndrome using the International Diabetes Federation definition [
Participants were asked to maintain their habitual activity and eating behaviours for the duration of the intervention. Mean time spent in sedentary time, physical activity, steps per day, and daily energy expenditure were analysed by a triaxial accelerometer worn on the upper arm, which also estimated energy expenditure through galvanic skin response and heat flux (SenseWear, BodyMedia Inc., PA, USA) for three nonexercising days (two weekdays and one weekend day) during weeks 1 and 12. Accelerometers were worn for 24 h/day except during water-based activities such as showering. Participants also completed a diet diary and subjective physical activity questionnaire [
All exercise training in the intervention groups was supervised by an accredited exercise physiologist. Heart rate, RPE, and blood pressure were continuously monitored throughout training. Although it was not possible to be blinded to exercise group allocation, participants were blinded to the primary purpose of the study and the placebo group were instructed that the stretching/massage/fitball intervention was intended to reduce inflammation and body fat.
Description of exercise interventions.
Week | Frequency | Intensity | Session duration | Total weekly training time (including warm-up and cooldown, min) | |
---|---|---|---|---|---|
Work : recovery | Intervals (number) | ||||
HIIT | |||||
1 | 3 | 120% VO2peak: 30 W | 30 : 180 s | 4 | 60 |
2 | 3 | 120% VO2peak: 30 W | 30 : 120 s | 5 | 55.5 |
3 | 3 | 120% VO2peak: 30 W | 45 : 120 s | 5 | 59.25 |
4 | 3 | 120% VO2peak: 30 W | 45 : 120 s | 6 | 67.5 |
5–12 | 3 | 120% VO2peak: 30 W | 60 : 120 s | 6 | 72 |
CONT | |||||
1 | 3 | 50% VO2peak | 30 min | 108 | |
2 | 3 | 60% VO2peak | 40 min | 138 | |
3 | 3 | 65% VO2peak | 45 min | 144 | |
4 | 3 | 65% VO2peak | 45 min | 144 | |
5–12 | 3 | 65% VO2peak | 45 min | 144 |
HIIT: high intensity interval training; CONT: continuous aerobic exercise; W: watts; VO2peak: peak aerobic capacity.
Compliance was calculated as total number of sessions attended/total number of sessions available ×100. An intention-to-treat analysis was employed with group mean change scores imputed for dropouts. This single imputation method is valid when data is assumed to be missing completely at random independent of study intervention and group allocation [
The study population had an average BMI of
Baseline participant characteristics.
Characteristics | PLA ( |
CONT ( |
HIIT ( |
---|---|---|---|
Demographics | |||
Age (years) | 42.9 (2.8) | 44.1 (1.9) | 41.8 (2.7) |
Sex ( |
2/10 | 2/11 | 3/10 |
BMI (kg/m2) | 28.2 (0.6) | 28.5 (0.6) | 28.2 (0.5) |
Waist circumference (cm) | 90.9 (3.1) | 90.8 (2.1) | 92.4 (2.5) |
Metabolic syndrome (Y/N) | 2/12 | 3/13 | 2/13 |
Baseline habitual physical activity (Bouchard (kJ/Kg/day)) | 13.8 (0.6) | 13.7 (0.4) | 13.4 (0.3) |
Presented as mean (SE). PLA: placebo; CONT: continuous aerobic exercise; HIIT: high intensity interval training; M: male; F: female; BMI: body mass index.
There was a significant group × time interaction for change in
Outcome measures.
PLA | CONT | HIIT |
|
|||||||
---|---|---|---|---|---|---|---|---|---|---|
Baseline | Post | Baseline | Post | ES (95% CI) | Baseline | Post | ES (95% CI) | ES (95% CI) HIIT versus CONT | ||
Body composition (DEXA) | ||||||||||
Trunk fat (g) Trunk fat (%) | 16562.1 (1203.6) 44.6 (2.3) | 17073.4 (1290.7) 45.6 (2.5) | 17337.5 (742.1) |
16627.8 (721.8) 44.2 (1.9) | −0.46 |
16142.5 (1153.2) 43.8 (1.5) | 15840.5 (1158.5) 43.5 (1.6) | 0.64 |
−0.79 |
0.70 |
Android fat (g) |
2724.0 (215.0) 48.2 (2.1) | 2874.5 (259.8) |
2884.5 (135.3) |
2736.3 (112.3) |
−0.32 |
2791.2 (184.7) |
2736.6 (200.7) |
0.86 |
−0.91 |
0.04** |
Gynoid fat (g) |
5792.1 (306.9) |
5776.0 (321.3) |
6273.0 (375.3) |
6138.1 (424.1) |
−0.59 |
5540.3 (391.2) |
5468.8 (442.9) |
−0.34 |
−0.28 |
0.28 |
Total body fat (g) |
31432.8 (2064.9) |
32131.8 (2370.2) |
33134.1 (1669.6) |
32114.91 (184.0) |
−0.64 |
30421.5 (2087.9) |
30229.1 (2408.9) |
0.22 |
−0.73 |
0.049** |
Total lean body mass (g) | 42374.8 (2892.6) | 42516.5 (3531.1) | 43637.8 (1873.8) | 44205.2 (2364.3) | 0.36 |
42211.6 (1360.7) | 42787.9 (1608.8) | 0.35 |
0.05 |
0.89 |
|
||||||||||
Anthropometrics | ||||||||||
Weight (kg) | 77.2 (3.5) | 78.6 (3.8) | 80.7 (1.5) | 79.9 (1.8) | −0.52 |
76.1 (2.7) | 76.3 (3.0) | 0.21 |
−0.84 |
0.30 |
Waist circumference (cm) | 90.9 (3.1) | 90.1 (3.2) | 90.8 (2.1) | 87.2 (1.7) | 0.24 |
92.4 (2.5) | 90.6 (2.5) | 0.27 |
−0.05 |
0.76 |
Hip circumference (cm) | 108.0 (1.6) | 108.8 (1.7) | 108.7 (1.4) | 107.5 (1.5) | 0.19 |
104.9 (2.1) | 106.2 (1.9) | 0.25 |
−0.13 |
0.53 |
|
||||||||||
Fitness | ||||||||||
Work peak (W) | 114.4 (16.6) | 118.4 (17.5) | 128.8 (10.2) | 160.2 (12.3) | 1.41 |
134.7 (8.5) | 164.7 (10.8) | 1.17 |
0.49 |
<0.001** |
VO2peak (mL/kg/min)* | 22.3 (1.8) | 22.3 (1.7) | 24.0 (1.2) | 28.3 (1.5) | 1.63 |
25.3 (10.4) | 30.4 (1.4) | 1.76 |
0.23 |
<0.001** |
|
||||||||||
Biochemistry | ||||||||||
AST (U/L) | 23.5 (2.4) | 18.7 (1.0) | 21.9 (2.1) | 20.1 (1.2) | −0.14 |
27.3 (3.9) | 22.5 (1.8) | −0.27 |
0.12 |
0.24 |
ALT (U/L) | 26.7 (5.5) | 17.6 (2.5) | 22.0 (4.5) | 17.0 (1.8) | −0.12 |
36.7 (8.8) | 24.2 (4.8) | −0.23 |
0.08 |
0.22 |
Fasting glucose (mmol/L) | 4.1 (0.2) | 4.3 (0.1) | 4.3 (0.1) | 4.4 (0.1) | −0.45 |
4.4 (0.2) | 4.3 (0.1) | −0.32 |
−0.19 |
0.41 |
Insulin (mU/L) | 7.3 (0.7) | 8.7 (1.2) | 8.6 (1.4) | 7.9 (1.1) | −0.39 |
8.0 (1.1) | 7.4 (0.7) | −0.47 |
0.12 |
0.31 |
hs-CRP (mg/L) | 1.9 (0.4) | 1.7 (0.3) | 4.0 (1.6) | 2.9 (0.8) | −0.49 |
3.4 (0.8) | 3.6 (1.3) | −0.71 |
0.03 |
0.45 |
|
||||||||||
Lipids | ||||||||||
Total cholesterol (mmol/L) | 6.1 (0.2) | 5.4 (0.2) | 5.3 (0.3) | 5.5 (0.2) | −1.55 |
5.4 (0.3) | 5.4 (0.2) | −1.46 |
0.25 |
0.02** |
HDL (mmol/L) | 1.6 (0.1) | 1.5 (0.1) | 1.4 (0.1) | 1.4 (0.1) | −0.21 |
1.7 (0.2) | 1.7 (0.2) | −0.59 |
0.46 |
0.20 |
LDL (mmol/L) | 4.0 (0.1) | 3.4 (0.1) | 3.3 (0.3) | 3.6 (0.2) | −1.70 |
3.2 (0.2) | 3.2 (0.2) | −1.21 |
−0.38 |
0.02** |
Triglycerides (mmol/L) | 1.2 (0.1) | 1.1 (0.1) | 1.2 (0.2) | 1.1 (0.1) | −0.30 |
1.3 (0.1) | 1.3 (0.2) | −0.39 |
0.20 |
0.40 |
Free fatty acids (umol/L) | 318.9 (34.5) | 484.6 (106.5) | 426.6 (42.0) | 460.6 (54.1) | −0.89 |
415.6 (47.9) | 493.8 (119.4) | −0.34 |
−0.48 |
0.71 |
|
||||||||||
Blood pressure | ||||||||||
SBP (mmHg) | 117.7 (5.3) | 116.5 (4.7) | 122.8 (4.6) | 118.5 (3.2) | 0.32 |
116.2 (3.9) | 110.6 (3.2) | 0.81 |
−0.27 |
0.10 |
DBP (mmHg) | 74.3 (2.5) | 73.7 (2.8) | 78.4 (2.8) | 74.9 (2.5) | 1.00 |
76.8 (2.3) | 73.9 (2.4) | 0.61 |
0.25 |
0.13 |
Presented as Mean (SE). PLA: placebo; CONT: continuous aerobic exercise; HIIT: high intensity interval training; DEXA: dual-energy X-ray absorptiometry; VO2peak: peak aerobic capacity; AST: aspartate aminotransferase; ALT: alanine aminotransferase; hs-CRP: high sensitivity C-reactive protein; HDL-C: high density lipoprotein cholesterol; LDL-C: low density lipoprotein cholesterol; SBP: systolic blood pressure; DBP: diastolic blood pressure. *Estimated from
Habitual energy intake and energy expenditure.
PLA | CONT | HIIT |
| ||||
---|---|---|---|---|---|---|---|
Baseline | Postintervention | Baseline | Postintervention | Baseline | Postintervention | ||
Energy intake | |||||||
Fat (g/day) | 92 (11) | 78 (8) | 101 (12) | 87 (8) | 86 (11) | 79 (11) | 0.80 |
% intake | 32 (3) | 30 (1) | 35 (2) | 34 (1) | 33 (3) | 33 (2) | 0.98 |
Carbohydrate (g/day) | 265 (21) | 238 (14) | 268 (23) | 252 (22) | 227 (13) | 209 (20) | 0.28 |
% intake | 43 (2) | 42 (2) | 43 (3) | 42 (2) | 41 (2) | 41 (2) | 0.80 |
Protein (g/day) | 116 (10) | 111 (13) | 108 (10) | 98 (10) | 103 (11) | 95 (8) | 0.67 |
% intake | 20 (1) | 20 (2) | 17 (1) | 18 (1) | 19 (1) | 19 (1) | 0.46 |
Total energy intake (kJ/day) | 10319 (893) | 9283 (578) | 10523 (917) | 9527 (830) | 9403 (776) | 8190 (867) | 0.44 |
Energy expenditure | |||||||
Total energy expenditure (kJ/day) | 10354 (609) | 9990 (557) | 10527 (462) | 9989 (521) | 10414 (368) | 10506 (450) | 0.58 |
Steps/day | 9897 (1271) | 7243 (1240) | 9740 (1036) | 8374 (956) | 9212 (820) | 8989 (890) | 0.42 |
Sedentary time, <3 METS (hours/day) | 20:19 (0:58) | 18:57 (1:31) | 21:51 (0:11) | 20:54 (1:09) | 20:47 (0:41) | 21:27 (0:01) | 0.11 |
Moderate activity, |
1:29 (0:13) | 1:17 (0:15) | 1:25 (0:12) | 1:13 (0:13) | 1:31 (0:07) | 1:41 (0:01) | 0.57 |
Total self-reported energy expenditure (Bouchard score, kJ/Kg/day) | 13.8 (0.6) | 14.2 (0.8) | 13.7 (0.4) | 13.7 (0.4) | 13.4 (0.3) | 13.6 (0.4) | 0.79 |
Presented as mean (SE). PLA: placebo; CONT: continuous aerobic exercise; HIIT: high intensity interval training; METS: metabolic equivalents,
Body mass did not change significantly in any group (
Effect of 12 weeks of high intensity interval training (HIIT) or continuous aerobic exercise (CONT) or control (PLA) on relative percent change in (a) body mass, (b) total lean mass, and (c) total body fat. Circles show individual percentage change from baseline and horizontal bars show mean group percentage change from baseline. Values are means ± SE;
Effect of 12 weeks of high intensity interval training (HIIT) or continuous aerobic exercise (CONT) or control (PLA) on relative percent change in (a) trunk fat, (b) android fat, and (c) gynoid fat. Circles show individual percentage change from baseline and horizontal bars show mean group percentage change from baseline. Values are means ± SE;
There was no significant difference between groups for change in waist or hip circumference. Neither systolic nor diastolic blood pressure changed in any group (Table
There was no significant group × time interaction for changes in fasting serum AST, ALT, hs-CRP, triglycerides, HDL-C, insulin, or glucose (
Accelerometry data for one participant were omitted from analysis due to not wearing the accelerometer for the required period. Another participant refused to wear the accelerometer and therefore postintervention data for habitual physical activity and energy expenditure were available for
Correlations were performed using combined data from all study participants. Change in android fat was not significantly correlated with change in daily dietary energy intake (
This is the first study to examine the efficacy of HIIT versus that of continuous aerobic exercise training on body fat levels in previously inactive, overweight adults for whom an improved fat distribution is sought. Using a 12-week randomized placebo-controlled design, we showed that HIIT resulted in a similar improvement in work capacity to that induced by continuous aerobic exercise in this cohort. Moreover, the HIIT-induced improvement in fitness was achieved in only ~50–60% of the time taken for the same gain in fitness via continuous aerobic exercise (60–72 versus 108–144 minutes per week). However, although HIIT has been suggested to be effective for the management of body fat levels [
Our demonstration that HIIT induced a similar improvement in fitness to that of continuous aerobic exercise confirms recent reports which have examined the effect of HIIT on cardiorespiratory fitness in a range of populations [
To avoid risk of cardiovascular and musculoskeletal events during training we chose a HIIT protocol that is likely to involve less risk for overweight previously sedentary people than that of an “all-out” sprinting protocol. HIIT protocols can vary in exercise intensity, timing of the work : recovery cycles, type and intensity of recovery, and the number of intervals, making comparison between studies problematic. However, generally in clinical populations (e.g., coronary artery disease, chronic obstructive pulmonary disease, type 2 diabetes, and chronic heart disease), HIIT programs use 60–240-second efforts of near-maximal or maximal aerobic exercise, with interspersed recovery periods, and have been shown to elicit a range of cardiovascular and metabolic benefits but with cardiovascular strain minimised [
It is now well established that regular exercise can lead to preferential fat, including visceral fat reduction (even in the absence of weight loss). Aerobic exercise significantly increases hormone-stimulated adipose lipolysis and subsequent circulating fatty acid availability, which when combined with the sustained increase in metabolic rate (VO2) results in increased uptake and oxidation of fatty acids in working muscle [
We acknowledge that the small sample size in this study (38 enrolled, 33 completed) limits the ability to draw some conclusions about the relative potency of CONT versus that of HIIT from our trial. This affects the majority of studies in this area, as compliance with specific exercise interventions requires intensive supervision. Similarly it is difficult to definitively exclude the impact that changes in lifestyle, outside of the exercise intervention, can have on body fat outcomes in this type of research. For example there was a small reduction of android fat in PLA, and such changes are common in clinical trials under free living conditions where participants may alter their behaviour [
Overall, the results from this study show that continuous aerobic exercise training is effective for improving fat distribution independently of weight loss, but the HIIT intervention employed did not improve fat distribution. However, despite using 50–60% of the total training time employed in the CONT intervention, HIIT significantly improved work capacity in previously inactive and overweight adults.
High intensity interval training
Continuous aerobic exercise
Placebo
Peak work capacity
Dual-energy X-ray absorptiometry
Glucose transporter type 4
Body mass index
Electrocardiogram
Rating of perceived exertion
Peak rate of oxygen consumption
Region of interest
Serum separation tube
Triglyceride
Total cholesterol
High density lipoprotein cholesterol
Low density lipoprotein cholesterol
Alanine aminotransferase
Aspartate aminotransferase
High sensitivity C-reactive protein
Free fatty acid
Systolic blood pressure
Diastolic blood pressure
Maximal heart rate.
Shelley E. Keating, Elizabeth A. Machan, Helen T. O’Connor, James A. Gerofi, and Amanda Sainsbury declare no conflict of interests. Nathan A. Johnson has received honoraria for speaking engagements for Merck Sharp & Dohme. Ian D. Caterson has performed and still performs clinical trials of obesity treatment and prevention some of which have been funded by the government but others by the pharmaceutical industry. Current trials are funded by the NHMRC [
This research was supported by funding from the Ramaciotti Foundation (Establishment Grant: Nathan A. Johnson). The funding body had no role in the design of the study, collection and analysis of data, or decision to publish.