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Sprint interval and moderate-intensity cycling
training differentially affect adiposity and aerobic
capacity in overweight young-adult women.
Authors: Simon Higgins1; Michael V. Fedewa1,2; Elizabeth D. Hathaway1; Michael D.
Schmidt1; Ellen M. Evans1
Corresponding Author: Simon Higgins, Department of Kinesiology, Office 101D, Ramsey
Center, 330 River Road, University of Georgia, Athens, GA 30602-6554. Telephone: 706-461-
6776. E-mail: sh@uga.edu
Author Affiliations:
1 Department of Kinesiology, University of Georgia, 330 River Road, Athens, GA 30602-6554.
Email: Simon Higgins – sh@uga.edu, Elizabeth D. Hathaway – lizhath@uga.edu, Michael D.
Schmidt – schmidtm@uga.edu, and Ellen M. Evans – emevans@uga.edu.
2Department of Kinesiology, The University of Alabama, 2003 Moore Hall, Box 870312,
Tuscaloosa, AL 35487-0231. E-mail: Michael V. Fedewa - mvfedewa@ua.edu
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Abstract
Purpose: To examine the effects of sprint interval training (SIT) and moderate-intensity
continuous cycle training (MICT), with equal estimated energy expenditure during training, on
body composition and aerobic capacity. Methods: Body composition measured via dual-energy
x-ray absorptiometry and aerobic capacity (VO2peak) were assessed following 6 weeks of training
in previously inactive overweight/obese young women (n=52, 20.4 ± 1.5 yr, 30.3 ± 4.5 kg·m-2,
67.3% white). Training was performed in a group-exercise format that mimicked cycling classes
offered by commercial fitness facilities, and included 3 weekly sessions of either 30-second ‘all-
out’ sprints followed by 4 minutes of active recovery (SIT), or continuous cycling at 60-70%
heart rate reserve to expend a similar amount of energy. Results: Participants were randomized to
SIT or MICT, attended a similar number of sessions (15.0 ± 1.5 sessions vs. 15.8 ± 1.9 sessions,
P=.097) and expended a similar amount of energy (541.8 ± 104.6 kJ·session-1 vs. 553.5 ± 138.1
kJ·session-1, P=.250). Without significant changes in body mass (P>.05), greater relative
reductions occurred in SIT than in MICT in total fat mass (3.6 ± 5.6% vs. 0.6 ± 3.9%, P=.007)
and android fat mass (6.6 ± 6.9% vs. 0.7 ± 6.5%, P=.002). Aerobic capacity (mL·kg-1·min-1)
increased significantly following both interventions (P<.05), but the relative increase was 2-fold
greater in SIT than in MICT (14.09 ± 10.31% vs. 7.06 ± 7.81%, P<.001). Conclusion: Sprint
interval cycling reduces adiposity and increases aerobic capacity more than continuous
moderate-intensity cycling of equal estimated energy expenditure in overweight/obese young
women.
Keywords: High-intensity, Moderate-intensity, Central Adiposity, Equal Energy Expenditure,
Body Composition.
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Introduction
High-intensity interval training (HIIT) is a mode of exercise that is characterized by brief,
intermittent bursts of vigorous activity, interspersed by periods of rest or low-intensity exercise
(Gibala et al., 2012). HIIT has been investigated in many populations with consistent
improvements in body composition (Boutcher, 2011; Heydari et al., 2012) and aerobic capacity
(Gist et al., 2013; Sloth et al., 2013; Trilk et al., 2011; Weston et al., 2014). It has been suggested
that HIIT may be more efficient than traditional moderate-intensity continuous exercise training
protocols (MICT), producing greater adaptation from a similar training duration, comparable to
that produced by high-volume endurance-type training (Gillen and Gibala, 2014). The popularity
of HIIT reaches beyond the physiological adaptations (Gibala and McGee, 2008), with research
suggesting that it may also be more enjoyable than MICT (Bartlett et al., 2011). These
advantages give HIIT the potential to have a greater adherence rate than conventional exercise
interventions (Jung et al., 2015).
A category of HIIT which employs bouts of efforts at an even higher intensity and power
output than traditional HIIT protocols is sprint interval training (SIT). A typical SIT protocol
includes 30-second ‘all out’ efforts followed by 4 minutes of active recovery at a low-intensity
(Freese et al., 2015; Gibala et al., 2006). The effects of SIT have been explored in healthy
populations (Hazell et al., 2014; Macpherson et al., 2011; Whyte et al., 2010), and in some
clinical populations (Gibala et al., 2012). With regard to overweight/obese women who are
underrepresented in the SIT literature, positive effects on aerobic capacity and cardiovascular
function, post-exercise blood lipids, and perceived health status and mood have been reported
(Freese et al., 2014; Freese et al., 2015; Trilk et al., 2011). While studies have shown that the
benefits of SIT are similar to those of continuous exercise involving a greater volume of work in
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different populations (Gist et al., 2013; Kessler et al., 2012), the feasibility of overweight/obese
women adhering to these ‘all out’ efforts is unclear, as are the relative effects of the two types of
training when energy expenditure during training is equal. It is likely that in most studies, greater
effects of the higher exercise intensity and power output of SIT have been offset by greater
energy expenditure in the continuous training exercise regimens to which they have been
compared, resulting in relatively similar changes in outcomes of interest.
The ability of continuous exercise training to facilitate weight loss and positive body
composition change, in the absence of dietary compensation, is well established (Swift et al.,
2014). Studies examining SIT suggest similar effects (Gibala and McGee, 2008), with the
potential for greater benefits to body composition (Boutcher, 2011) than MICT. The few
reported SIT interventions in women have used training durations of 6-15 weeks (Hazell et al.,
2014; Trapp et al., 2008) and reported significant reductions in weight and adiposity. Moreover,
there is a small amount of research comparing SIT to MICT in inactive overweight/obese
women; one study to do so did not ensure equal exercise energy expenditure during training
(Keating et al., 2014). Indeed, total energy expenditure during an exercise session is a key
mechanism responsible for weight and body composition changes (Swift et al., 2014); however,
few studies involving SIT have controlled for this factor making it difficult to compare the
independent effects of exercise intensity on body composition. One study to investigate the
effects of exercise intensity on body composition showed that high-intensity continuous exercise,
matched on energy expenditure with a lower-intensity regimen, led to greater losses of visceral
fat and abdominal subcutaneous fat over 16 weeks in obese middle-aged women (Irving et al.,
2008); however, both regimens used continuous exercise protocols. Contrary to these findings,
some have argued that it is the volume, not the intensity, of exercise that leads to reductions in
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abdominal adiposity (Ross et al., 2015), thus, the potential for exercise intensity to mediate
magnitude of fat loss warrants further research.
It is also well established that aerobic exercise training improves aerobic capacity (Garber
et al., 2011; Gormley et al., 2008). Recent work comparing the relative effects of SIT and MICT
interventions on aerobic capacity in sedentary adults over 6 (Burgomaster et al., 2008; Cocks et
al., 2013), 12 (Keating et al., 2014), and 15 weeks (Trapp et al., 2008) reported similar
significant improvements in aerobic capacity regardless of training mode. Interestingly, although
SIT interventions lasted up to 4 months, SIT interventions of just 2 weeks have also significantly
improved aerobic capacity by an average of 9.5% (Whyte et al., 2010). The positive relationship
between the intensity of aerobic work and the magnitude of improvement in aerobic capacity is
accepted (Gormley et al., 2008); however, if the greater increase in aerobic capacity following
higher intensity work holds true with a SIT protocol of an even higher intensity and intermittent
nature is unknown, especially when work or exercise energy expenditure is equal. As interval
training becomes increasingly popular, more research is needed regarding the effect of exercise
intensity/pattern on body composition and aerobic capacity when using a SIT protocol,
controlling for energy expenditure, especially in overweight/obese women as SIT is understudied
in this cohort.
Thus in this context, the primary aim of this study was to examine the relative effects of 6
weeks of SIT compared to a MICT protocol of equal estimated energy expenditure on body
composition and aerobic capacity in inactive overweight/obese young women. We hypothesized
that the magnitude of changes in body composition and aerobic capacity would be greater in SIT
compared to MICT under training conditions of equal estimated energy expenditure.
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Methods
Study Population and Recruitment. This analysis was part of a parent study examining
the effect of SIT and MICT protocols on markers of metabolic syndrome risk. Women (n=60)
were recruited via email and print advertising and excluded if they were: current smokers (within
6 months), physically active (≥30 minutes of physical activity, ≥2 days per week), not aged 18-
24 yr, not enrolled at the University, <25 kg·m-2 BMI, varsity athletes, currently pregnant, or had
been pregnant within the previous 12 months. Individuals with any health condition that could
have been exacerbated by the exercise protocols, or for which the exercise may be unsafe were
not enrolled. The Institutional Review Board of the university approved all aspects of the
protocol and all participants provided written informed consent prior to participation.
Study Design and Exercise Interventions. This research study used a parallel-arm design
with participants stratified on BMI and subsequently randomized to a SIT or MICT group. All
sessions were performed on a friction-loaded stationary cycle ergometer which has the ability to
estimate energy expenditure based on power output (Keiser, Keiser M3 Indoor Cycle, Fresno,
California). Heart rate (HR) during exercise, ratings of perceived exertion (RPE), and estimated
energy expenditure from the Keiser ergometers were recorded during each exercise session to
ensure compliance with the training protocol. Participants assigned to the SIT group began each
exercise session with a 4-minute warm-up at a low resistance and pedal rate, followed by
repeated 30-second ‘all out’ sprints interspersed with 4 minutes of active recovery pedaling
against minimal resistance at a low pedal frequency. This exercise stimulus equated to 2.5-3.5
minutes of near-maximal effort interspersed with 16-28 minutes of recovery, along with a brief
cool-down period following each session. Training progression increased the number of sprint
repetitions from 5 during weeks 1 and 2, to 6 sprints during weeks 3 and 4, and 7 sprints during
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weeks 5 and 6. Participants assigned to the MICT group were instructed to cycle continuously at
an intensity of 60-70% heart rate reserve (HRR) for 20-30 minutes, with the duration of training
sessions systematically increased to maintain equal estimated energy expenditure between
groups. Training protocols were performed 3 times weekly in a supervised group-training format
which were led by trained research staff and mimicked cycling classes offered by commercial
fitness facilities.
Weight Status and Body Composition. Standing height was measured by a stadiometer
(Seca 242, SECA Corp, Hamburg, Germany) to the nearest 0.1 cm. Body mass was measured
with a digital scale (Tanita WB-110A class III, Tanita Corporation, Tokyo, Japan) to the nearest
0.1 kg. Subsequently, BMI was calculated as mass divided by height squared (kg·m-2). Whole
body and regional composition including absolute and relative adiposity (%Fat) and mineral free
soft tissue mass, designated herein as fat free mass (FFM), were measured via dual x-ray
absorptiometry (DXA; Lunar iDXA, v 11.30.062, GE Healthcare, Madison, Wisconsin).
Aerobic Capacity. Aerobic capacity (VO2peak) was measured with a maximal exercise test
whereby participants pedaled continuously on an electronically braked cycle ergometer, with the
workload increasing every 3 minutes in a graded manner (Lode Excalibur Sport 2000, Lode
B.V., Groningen, Netherlands). Oxygen uptake was measured using a computerized indirect
calorimetry system (ParvoMedics True Max 2400; ParvoMedics, Sandy, UT). HR was measured
continuously throughout the test (Polar FT1; Polar Electro, Kempele, Finland). The test was
terminated when traditional termination criteria were met for respiratory exchange ratio, HR,
RPE, volitional fatigue, or pedal rate dropped below 50 rpm. Aerobic capacity is expressed in
absolute terms (L·min-1), relative to body mass (mL·kg-1·min-1), and relative to fat free mass
(mL·kgFFM-1·min-1).
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Habitual Energy Expenditure and Reported Energy Intake. Energy expenditure was
measured objectively over a minimum 3-day continuous period using the Actiheart monitor
(CamNtech, USA), which uses both HR and an omnidirectional accelerometer movement sensor.
Reported energy intake was measured using the Automated Self-Administered 24-hour Recall
(ASA24), a Web-based tool modeled on the USDA’s Automated Multiple Pass Method (Subar et
al., 2012). Energy intake and expenditure data were collected over 3-day periods including 2
weekdays and 1 weekend day at baseline and during weeks 5-6 of the intervention (endpoint),
and are reported as average values.
Statistical Analysis. Statistical analyses were performed using SPSS for Windows (SPSS
22.0, Chicago, IL). After testing for violation of assumptions using standard procedures, baseline
differences between groups were assessed using independent t-tests. Pre- to post-intervention
changes in outcome variables were analysed using a 2x2 (GROUP*TIME) repeated measures
analysis of covariance (ANCOVA) with GROUP included as the between training group factor,
and TIME included as the within factor. Baseline values for outcome variables served as a
covariate. Post hoc pairwise comparisons with a Bonferroni adjustment for repeated contrasts
were used to identify specific treatment effects. As this is a secondary analysis from a parent
study, an a priori power analysis was not possible. However, given the sample size (n =52) in the
designated primary (fat mass) and secondary (VO2peak [mL·kg-1·min-1]) outcomes of interest,
post hoc power anaylsis revealed statistical power well in excess of 0.90 for both outcomes. To
further characterize the magnitude of change in SIT relative to the comparison group (MICT),
effect sizes (ES) are reported as unbiased standardized mean change using the equation
(Lipsey and Wilson, 2001) which was subsequently corrected for
sample size bias using hedges unbiased effect size estimate
(Hedges,
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1981). Statistical significance was set at an α level of P<.05. All data are expressed as mean ±
standard deviation (M±SD), unless otherwise indicated.
Results
Participant Characteristics and Adherence. Of the participants that completed the
intervention (n=60), seven participants were excluded based on <70% attendance (n=5 SIT; n=2
MICT) and one was excluded from analysis as an outlier (baseline fat mass values >3 SD from
the mean). Thus, the cohort (n=52) of young women (20.4 ± 1.5 yr) were on average obese (30.3
± 4.5 kg·m-2) and mostly white (67.3%) paralleling university racial/ethnic demographics (19.2%
Black, 5.8% Asian, 1.9% Hispanic, and 5.8% other). Groups did not differ on baseline
characteristics (P>.05; data not shown). Session attendance (15.0 ± 1.5 sessions vs. 15.8 ± 1.9
sessions, P=.097) and average energy expenditure (541.8 ± 104.6 kJ·session-1 vs. 553.5 ± 138.1
kJ·session-1, P=.250) was not different between SIT and MICT. No adverse events were reported
within either intervention group. Available complete total daily energy expenditure data (n=44)
indicated no change from pre- to post- intervention in either SIT (10,859.6 ± 1,406.7 kJ·d-1 vs.
10,719.4 ± 1,170.7 kJ·d-1, P=.544) or MICT (10,506.9 ± 1,315.0 kJ·d-1 vs. 10,591.8 ± 1,195.4
kJ·d-1, P=.956), with no significant GROUP*TIME interaction (P=.632). Complete dietary data
(n=51) indicated a main effect of time (P<.001) but no GROUP*TIME interaction (P=.308). Post
hoc analysis revealed no change in response to SIT (7,930.4 ± 2,203.7 kJ·d-1 vs. 7,688.5 ±
2,165.6 kJ·d-1, P=.356), but a significant reduction in MICT (8,367.2 ± 2,869.4 kJ·d-1 vs. 7,388.5
± 2,051.0 kJ·d-1, P=.013).
Mass & Body Composition. Changes in outcome variables are expressed in relative terms
within the main text and in absolute terms within Table 1. No changes in body mass occurred in
response to either of the exercise interventions (ES=.07, P=.118). A significant GROUP*TIME
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interaction was found for reductions in total fat mass (ES=.12, P=.007), with SIT reducing total
fat mass by 3.6% (P<.001) compared to 0.6% (P=.757) in MICT (Table 1, Figure 1A). A
significant interaction was also found for changes in %Fat (ES=.14, P=.013), with further
analysis indicating a 1% decrease in SIT (P<.001) and no change (-0.3%, P=.315) in MICT.
Similarly, a significant GROUP*TIME interaction (ES=.16, P=.002) existed indicating that
exercise intensity had differential effects on android fat mass with a 6.6% reduction in SIT and
no change (-0.7%) in MICT. Total body FFM did not change differentially (ES=.00, P=.983) or
within either group (both P>.05). The change in leg FFM was similar in both groups (ES=.03,
P=.557), increasing by 2.0% in MICT (P=.001) and 1.9% in SIT (P<.001).
Aerobic Capacity. A significant GROUP*TIME interaction (ES=.48, P<.001) existed
with SIT demonstrating a 2-fold (14.1%) increase in VO2peak (mL·kg-1·min-1) compared to the
7.1% increase in MICT (Table 1, Figure 1B). Similar interactions and changes were observed for
VO2peak expressed in absolute terms (L·min-1; ES=.49, P=.001) and relative to FFM (mL·kgFFM-
1·min-1; ES=.46, P=.002).
Discussion
The effect of exercise intensity on body composition and aerobic capacity in
overweight/obese young women was examined with 6-week SIT and MICT interventions
involving equal estimated exercise energy expenditure. In agreement with our hypothesis, the
major findings were: 1) exercise training intensity/pattern differentially affected adiposity, with
SIT eliciting significantly greater losses of total and central fat mass compared to MICT, and 2)
although both interventions led to a significant increase in aerobic capacity, SIT led to a nearly
2-fold greater increase in VO2peak than in MICT, regardless of expression.
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Body Mass and Composition. The absence of substantial change in body mass is not
surprising in light of the low energy expenditure of each session ~550 kJ, totaling ~10,000 kJ
over the 6-week intervention. However, the reported reductions in total and central fat mass in
favor of SIT are mirrored by an absolute reduction in body mass which neared significance
(p=.06) and was not seen following MICT. In support of these findings, a recent study using a 6-
week running SIT protocol of a similar duration and intensity to the present study (Hazell et al.,
2014), reported a 1.2 kg reduction in fat mass with only a 0.5 kg reduction in body mass, despite
presumably low exercise energy expenditure and no changes to dietary energy intake. The
significant reduction in energy intake within MICT of ~1000 kJ/day in the absence of body
composition change, along with the ~2500 kJ discrepancy between energy intake and
expenditure reported by participants is paradoxical and highlights the limitations of
methodologies for measuring free living energy intake. Indeed, part of the variance in body
composition change could be accounted for by changes in energy balance not captured by these
methodologies; however, these limitations are present in all such studies, similarly affecting
intervention groups. Moreover, most studies are consistent in their findings of reduced adiposity
following similar SIT protocols (Hazell et al., 2014; Macpherson et al., 2011), along with other
forms of high intensity interval work (Gillen et al., 2013; Heydari et al., 2012), which speaks to
the validity of the findings and strength of the lipolytic effect of high intensity interval training.
However, one study comparing SIT and MICT failed to show a beneficial effect of SIT, nor one
which was greater than MICT (Keating et al., 2014). In overweight/obese adults, 12 weeks of
MICT reduced android fat by 2.7%, whereas SIT led to no reductions in adiposity (P=.04)
(Keating et al., 2014). Notably, this intervention showed similar discrepancies in energy intake
and expenditure to the current data, and did not have equal work or exercise energy expenditure
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between groups which could have played a role in the contradictory findings, as by the final
week of training, exercise duration was 2-fold greater in MICT compared to SIT (Keating et al.,
2014).
Though reductions in adiposity have been consistently noted following SIT (Hazell et al.,
2014; Macpherson et al., 2011), much debate exists regarding the mechanisms that drive the
lipolytic effect of SIT (Boutcher, 2011), and how they might differ from MICT. One theory is
that an intensity driven hormone release occurs with SIT, which augments lipolysis (Bracken et
al., 2009; Nevill et al., 1996; Williams et al., 2013; Zouhal et al., 2008). Nevill et al., showed that
elevations in growth hormone were linked to peak power output, with greater concentrations
occurring following SIT than endurance work (Nevill et al., 1996). Furthermore, increased
production of the catecholamines epinephrine and norepinephrine in comparison to MICT has
also been reported in some studies (Bracken et al., 2009; Williams et al., 2013; Zouhal et al.,
2008), but not others (Sevits et al., 2013). Indeed, these hormones are important contributors to
lipolysis, however, in the case of increased catecholamine production, the high rate of lipolysis
does not appear to translate into augmented fat oxidation, leading only to high re-esterification
rates (Mora-Rodriguez and Coyle, 2000; Williams et al., 2013). More research is needed to
define the relationships among training regimen type, hormones released at supramaximal
intensities, and subsequent fat oxidation.
A second theory that has been considered to explain favorable changes in adiposity is a
higher excess post-exercise oxygen consumption (EPOC) throughout the remainder of the day.
Although the positive relationship between exercise intensity and EPOC is well accepted (Bahr
and Sejersted, 1991), investigations into EPOC following SIT suggest that energy expenditure is
similar to that of MICT protocols (Kelly et al., 2013; Sevits et al., 2013; Williams et al., 2013),
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with changes in total daily energy expenditure being attributable to the energy cost of exercise
and any differences between protocols being too small in magnitude (~6-15% of the total oxygen
cost of exercise) to explain the changes in body composition (Kelly et al., 2013; LaForgia et al.,
2006). It is noteworthy that the recovery period between sprints is accompanied by an increased
EPOC, which contributes to overall energy expenditure above that which is captured by
measurement methods other than calorimetry (LaForgia et al., 2006). As such, the use of Keiser
ergometers to estimate energy expenditure and the lack of oxygen uptake data post-training
limits the mechanistic interpretation of our data as we cannot confirm differences in EPOC;
however notably, these limitations are balanced by the greater translational utility of this exercise
intervention.
A third, more recent hypothesis focuses on the potentially satiating effect of SIT,
reducing perceptions of hunger (Deighton et al., 2013; Williams et al., 2013), and in some cases
energy intake (Alkahtani et al., 2014; Sim et al., 2015). However, there remains question as to
whether a change in measured appetite translates to a reduction in energy intake, as
malalignment between the two have been reported (Deighton et al., 2013). As we were unable to
measure specific aspects of these proposed mechanisms, the explanation of greater fat loss
following SIT remains elusive and warrants further investigation.
Aerobic Capacity. Studies using a similar SIT protocol that employed an equal work or
exercise energy expenditure design between intervention groups are sparse. One study compared
6 sessions of 4-7 SIT bouts over 2 weeks to a MICT group working at an intensity below their
ventilatory threshold, with an equal estimated energy expenditure. This study found no
significant improvements in VO2peak in MICT but 7.5% (L·min-1) and 6.7% (mL·kg-1·min-1)
increases with SIT (Bailey et al., 2009). Conversely, a study by Keating et al. showed that in
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overweight adults, 12 weeks of training improved aerobic capacity to a similar extent in SIT
(22.3 ± 3.5%) and MICT (23.8 ± 3.0%) groups (Keating et al., 2014). A number of potential
moderators may explain the conflicting results from previous SIT and MICT comparisons
including study duration, MICT intensity, and lack of energy expenditure control in each
exercise group subsequently leading to different training volumes and limiting the interpretation
of the findings.
A recent meta-analysis summarizing the effect of SIT on aerobic capacity in young
healthy participants suggested that a SIT intervention would be expected to induce on average an
8% increase in VO2max relative to non-exercise control groups (Cohen’s d=.69) and that changes
would not be different from a moderate-to-vigorous-intensity continuous training intervention of
a similar duration (Cohen’s d=.04) (Gist et al., 2013). With the similarities between Cohen’s d
and the ES used in this analysis, an effect size of ES=.48 for increases in VO2peak (mL·kg-1·min-1)
suggests that the SIT protocol used in this study had a stronger effect on aerobic capacity than
reported in previous literature. However, this and similar reviews did not explore relationships
between equal exercise energy expenditure or work-matched interventions and outcomes of
interest, which makes the comparison of results difficult (Gist et al., 2013; Weston et al., 2014).
SIT has induced rapid improvements in both aerobic capacity and muscular oxidative
potential, with a meta-analysis showing several studies of a 2-week duration significantly
improving VO2max (Sloth et al., 2013). Within this review, it was suggested that the time-course
of adaptations to SIT may differ from MICT, the former eliciting peripheral adaptations at a
much faster rate than the latter. This has implications when looking at study duration and the
comparison of SIT and MICT interventions, pointing towards interventions with a shorter
duration being more likely to show superior improvements in aerobic capacity with SIT. Further
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research is needed to elucidate the effects of longer duration SIT interventions, with MICT
comparison groups, to identify the different time-course of adaptations as current reviews have
failed to resolve this issue (Gist et al., 2013; Sloth et al., 2013; Weston et al., 2014).
As suggested, another factor influencing the comparability of SIT and continuous
exercise results is the differing intensity of the continuous exercise comparison groups within the
current literature, with intensities of 65-80% VO2max (Esfarjani and Laursen, 2007; Keating et al.,
2014; Rowan et al., 2012), along with HRmax based methodologies (Sandvei et al., 2012). This
range of ‘moderate-to-vigorous’ intensities could logically elicit differential improvements in
aerobic capacity as previous research has shown that the intensity of continuous exercise is
generally linearly related to improvements in VO2max (Gormley et al., 2008). In the context of
this study, it is possible that the MICT exercise intensity was not high enough to elicit the same
magnitude of changes in just 6 weeks; however, further research looking at equivalent exercise
stimuli is needed to address this issue.
Conclusion. In summary, compared to a MICT protocol in which the same estimated
energy was expended, 6 weeks of SIT elicited significantly greater reductions in total and central
adiposity, and increases in aerobic capacity in overweight/obese young women. Aerobic capacity
improved 2-fold more with SIT compared to MICT, with increases in VO2peak being greater than
expected based on recent reviews. Our findings suggest that SIT is an effective means to rapidly
improve body composition and aerobic capacity in overweight/obese young women when
performed in a supervised group-training format.
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Acknowledgments: No sources of funding were used in preparation of this manuscript. The authors
declare no conflict of interest. Data collection was performed by SH, MVF, and EDH. Review of
literature and statistical analyses were performed by SH. Manuscript preparation and revision were
performed by SH, MVF, EDH, MDS, and EME. Preparation of the final document for submission was
performed by SH and EME.
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Table 1. Changes in body composition and aerobic capacity
Variable
MICT
(n=29)
Pairwise
P-value
SIT
(n=23)
Pairwise
P-value
GROUP*TIME
P-value
Body Mass (kg)
Baseline
83.1 ± 14.2
81.9 ± 12.2
Post
83.2 ± 14.6
.814
81.0 ± 11.5
.060
.118
Change
0.1 ± 1.8
-0.9 ± 2.5
Fat Mass (kg)
Baseline
36.1 ± 8.6
33.7 ± 7.9
Post
35.9 ± 8.5
.757
32.5 ± 7.1
<.001
.007
Change
0.2 ± 1.4
-1.2 ± 1.9
Fat Mass (%)
Baseline
44.5 ± 4.8
42.2 ± 4.8
Post
44.2 ± 4.4
.315
41.2 ± 4.8
<.001
.013
Change
-0.3 ± 1.1
-1.0 ± 1.4
Android Fat Mass (kg)
Baseline
3.1 ± 1.0
2.9 ± 0.9
Post
3.1 ± 1.0
.724
2.7 ± 0.8
<.001
.002
Change
0.0 ± 0.2
-0.2 ± 0.3
Whole Body FFM (kg)
Baseline
44.5 ± 6.9
45.6 ± 5.9
Post
44.8 ± 7.0
.149
46.0 ± 6.3
.208
.983
Change
0.4 ± 1.1
0.4 ± 1.5
Leg FFM (kg)
Baseline
24.6 ± 4.5
25.6 ± 4.0
Post
25.1 ± 4.5
.001
26.1 ± 4.1
<.001
.557
Change
0.5 ± 0.7
0.6 ± 0.8
VO2 peak (L/min)
Baseline
2.2 ± 0.3
2.3 ± 0.4
Post
2.4 ± 0.3
<.001
2.7 ± 0.3
<.001
.001
Change
0.2 ± 0.2
0.3 ± 0.2
VO2 peak (ml/kg/min)
Baseline
26.9 ± 4.5
29.1 ± 4.8
Post
28.8 ± 4.3
<.001
33.2 ± 4.4
<.001
<.001
Change
1.9 ± 2.1
4.1 ± 3.0
VO2 peak (ml/kg FFM/min)
Baseline
50.1 ± 7.0
51.6 ± 7.9
Post
53.6 ± 7.2
<.001
58.4 ± 6.4
<.001
.002
Change
3.5 ± 3.8
6.8 ± 4.8
Values are mean ± SD. FFM = Fat-free mineral-free soft tissue mass. All comparisons controlled for
baseline values using Analysis of Covariance with Bonferroni adjustment for multiple comparisons.
25
Figure Captions:
Figure 1. Magnitude of training induced changes in (A) absolute adiposity (kg) and (B) aerobic capacity
(mL·kg-1·min-1). Values are mean ± SEM. *Significant within group difference (P<.001). †Significant
GROUP*TIME interaction (P<.01).
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