O R I G I N A L R E S E A R C H A R T I C L E Open Access
The acute effect of exercise modality and
nutrition manipulations on post-exercise resting
energy expenditure and respiratory exchange
ratio in women: a randomized trial
Hailee L Wingfield
, Abbie E Smith-Ryan
, Malia N Melvin
, Erica J Roelofs
, Eric T Trexler
, Anthony C Hackney
Mark A Weaver
and Eric D Ryan
Background: The purpose of this study was to examine the effect of exercise modality and pre-exercise carbohydrate (CHO)
or protein (PRO) ingestion on post-exercise resting energy expenditure (REE) and respiratory exchange ratio (RER) in women.
Methods: Twenty recreationally active women (mean ± SD; age 24.6 ± 3.9 years; height 164.4 ± 6.6 cm; weight
62.7 ± 6.6 kg) participated in this randomized, crossover, double-blind study. Each participant completed six exercise
sessions, consisting of three exercise modalities: aerobic endurance exercise (AEE), high-intensity interval running (HIIT),
and high-intensity resistance training (HIRT); and two acute nutritional interventions: CHO and PRO. Salivary samples were
collected before each exercise session to determine estradiol-β-17 and before and after to quantify cortisol. Post-exercise
REE and RER were analyzed via indirect calorimetry at the following: baseline, immediately post (IP), 30 minutes (30 min)
post, and 60 minutes (60 min) post exercise. A mixed effects linear regression model, controlling for estradiol, was used to
compare mean longitudinal changes in REE and RER.
Results: On average, HIIT produced a greater REE than AEE and HIRT (p< 0.001) post exercise. Effects of AEE and HIRT
were not significantly different for post-exercise REE (p= 0.1331). On average, HIIT produced lower RER compared to
either AEE or HIRT after 30 min (p<0.001andp= 0.0169, respectively) and compared to AEE after 60 min (p= 0.0020).
On average, pre-exercise PRO ingestion increased post-exercise REE (p= 0.0076) and decreased post-exercise RER
(p< 0.0001) compared to pre-exercise CHO ingestion.
Conclusion: HIIT resulted in the largest increase in REE and largest reduction in RER.
HIIT elicited the largest increase in post-exercise
HIIT resulted in the largest reduction in post-exercise
RER, increasing fat oxidation, compared to AEE
In combination with varying exercise modalities, PRO
intake elevated post-exercise REE and fat oxidation
(via RER) to a greater extent than CHO.
Integrating HIIT and pre-exercise PRO intake into
exercise routines for women, may have positive
implications on weight and body composition.
More than 60% of women in the United States are
overweight, and 1/3 of those women are obese . In
addition, 75% of normal weight women believe they are
overweight and 90% overestimate their body size . With
such high obesity and body dissatisfaction rates, it is
important for women to receive reliable health and weight
loss recommendations. In addition, lack of time has shifted
the focus on more practical time-efficient strategies for
* Correspondence: email@example.com
Department of Exercise and Sport Science, University of North Carolina, 209
Fetzer Hall, CB #8700, Chapel Hill, NC 27599-8700, USA
Full list of author information is available at the end of the article
© 2015 Wingfield et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction
in any medium, provided the original work is properly credited.
Wingfield et al. Sports Medicine - Open (2016) 2:11
For health and weight maintenance, aerobic endurance
exercise (AEE) is usually prescribed . However, more
recently, higher-intensity exercise modalities have been
suggested as more time-efficient strategies for improve-
ments in health and energy expenditure [4-6].
Post-exercise resting energy expenditure (REE) has been
reported to increase following a 20-min treadmill run
, while high-intensity interval training (HIIT) has
increased total caloric energy expenditure (EE) in half
the time . In addition, high-intensity resistance training
(HIRT) with short rest intervals has been shown to
commonly prescribed resistance training  of lesser
intensity and longer rest periods. While these three
common exercise modes seem to be successful at
expending calories, previous research has indicated that
high-intensity exercise stimulates similar increases in
post-exercise REE in comparison to lower intensity
exercise, in half the time [9,10]. Research is still conflicted
on whether aerobic or resistance exercise is more effective
for augmenting EE. Higher intensity exercise has also been
linked to higher rates of fat oxidation, measured by
respiratory exchange ratio (RER) [6,11,12].
The combined effect of varying exercise modalities and
pre-workout nutrition on energy substrate utilization and
EE in women is limited. Pre-exercise ingestion of protein
(PRO) has been found to increase post-exercise REE more
than that of pre-exercise ingestion of carbohydrate (CHO)
[13,14]. While women rely heavily on fat as an energy
substrate during exercise, previous data has demonstrated
theimportanceofpre-exercise feedings on augmenting
lipolysis . In addition, a higher rate of fat oxidation in
postprandial state, has been reported . Pre-exercise
nutrient timing and content may be important when
evaluating exercise substrate utilization in women.
When evaluating exercise and nutritional responses in
women, it is important to consider hormonal variances,
such as the sex-specific hormone estradiol that varies
throughout the menstrual cycle. Estradiol has been
shown to have an impact on REE [17-19]. Controlling
for estradiol concentrations in metabolic evaluations is
crucial for determining the practical effects an interven-
tion may have . High-intensity aerobic exercise has
been shown to stimulate increases in cortisol , a
stress hormone that regulates energy substrate utilization
by mobilizing amino acids from skeletal muscle and
promoting gluconeogenic activity . Elevated corti-
sol concentrations have been reported as a primary
hormonal factor augmenting exercise adaptations from
high-intensity exercise, as well as impacting rates of
To date, no investigations have evaluated the com-
bined effects of varying exercise modalities and acute
nutritional supplementation in women. Therefore, the
purpose of the current study was to examine the effect
of common exercise modalities, AEE, HIIT, and HIRT,
combined with pre-exercise CHO or PRO ingestion, on
post-exercise REE and RER in women.
To test the study hypotheses, a randomized, crossover,
factorial design was used. After preliminary resting heart
rate, body composition, and strength testing, each
participant completed six randomly ordered exercise
sessions consisting of three exercise modalities: AEE,
HIIT, and HIRT; and two acute randomized nutritional
interventions: CHO and PRO (Figure 1). Participants
performed each exercise mode twice, with a different
nutritional intervention each time. Salivary samples were
collected before each exercise session to determine
estradiol and cortisol concentrations and after each
exercise session to determine cortisol concentrations.
Exercise sessions were performed at the same time of day,
within 2 h, with at least 48 h between each session, and the
order was randomly assigned using random allocation soft-
ware (version 1.0.0; Isfahan, Iran). Subjects were instructed
to stay well hydrated, to be 3 h postprandial, to refrain from
caffeine 5 h prior, and to refrain from strenuous exercise
24 h prior to all exercise sessions.
Twenty-one eumenorrheic, college-aged, recreationally
active women were enrolled to participate in this study; one
participant withdrew due to unrelated injury. Twenty
women (n= 20) completed the study (Table 1) and were
included in the statistical analyses. The study protocol was
approved by the University’s Institutional Review Board,
and all procedures followed were in accordance with the
Helsinki Declaration of 1975, as revised in 2008. Prior to
participation, all participants provided written informed
consent and completed a health history questionnaire. To
be included in this study, participants had to be a woman
between the ages of 18 and 35 and be recreationally active,
defined as accumulating 1 to 5 h per week of aerobic and/
or resistance exercise, excluding competitive athletes.
Participants were excluded if they were unfit, pregnant,
had any cardiovascular or neuromuscular health risks,
had injuries, or had any heart, lung, kidney, or liver disease.
Heart rate reserve measurement and body composition
Participants reported to the Applied Physiology Laboratory
after an 8-h fast, where they rested for 15 min. Resting
heart rate (RHR) was measured using a polar heart rate
USA), while age-predicted maximal heart rate (MHR) was
Wingfield et al. Sports Medicine - Open (2016) 2:11 Page 2 of 11
determined. Exercise target heart rate (THR) was calculated
using the Karvonen equation [THR = ((MHR −RHR) %
intensity) + MHR] . During each exercise bout, heart
rate (HR) was measured using the aforementioned HR
monitor. Exercises were matched for caloric expenditure
(pilot data not published), opposed to time, in order to
control for exercise length.
For baseline data, whole body composition was mea-
sured using a Hologic Dual Energy X-ray Absorptiometer
(DEXA, Hologic Discovery W, Bedford, MA, USA) using
the device’s default software (Apex software version 3.3).
The device uses rectilinear fan beam acquisition to give a
three-compartment assessment of body composition,
including fat mass (FM), lean mass (LM), and percent
body fat (% fat). After removing all metal objects, subjects
laid supine in the middle of the platform with hands
facedown near their sides. Subjects were instructed to
remain still and breathe normally for the duration of
the scan. All scans were performed by the same
DEXA-certified technician. The device was calibrated
according to the manufacturer recommendations
before testing to ensure valid results. Previous
test-retest reliability in our lab were FM: ICC = 0.98,
SEM = 0.85 kg; LM: ICC = 0.99, SEM = 1.07 kg; % fat:
ICC = 0.98, SEM = 1.0%.
Maximal strength test
In a standard post-absorptive state, each participant
performed a one-repetition maximum (RM) strength test
for bench press and leg press, using free weights and a
spotter, according to standard guidelines previously used
in this laboratory. After a 5-min warm-up and light
stretching, participants were familiarized with the
equipment and the motion of the movements. Each
participant then performed eight to ten repetitions at
50% of their predicted 1RM. After a 1-min rest period,
each participant performed four to six repetitions at 80%
of their predicted 1RM. Following a 1-min rest period,
the weight was increased to an estimated 1RM load,
which participants lifted one time. After each successful
set of one repetition, the weight was increased until a
failed attempt occurred, within four attempts. Two to
three minutes of rest was given between 1RM attempts.
Figure 1 Experimental protocol schematic. REE, resting energy expenditure (kcal/day); RER, respiratory exchange ratio; CHO,
carbohydrate; PRO, protein; HRR, heart rate reserve; AEE, aerobic endurance exercise; HIIT, high-intensity interval run; HIRT, high-intensity
Table 1 Descriptive statistics for all subjects (n= 20) at
Mean ± SD
Age (years) 24.6 ± 3.9
Height (cm) 164.4 ± 6.6
Weight (kg) 62.7 ± 6.6
Fat mass (kg) 17.6 ± 4.0
Lean mass (kg) 42.5 ± 4.4
Percent body fat (%) 28.2 ± 4.8
Wingfield et al. Sports Medicine - Open (2016) 2:11 Page 3 of 11
After the 1RM tests, participants performed a multiple-
RM strength test for four accessory exercises: alternating
stationary lunge, overhead shoulder press, biceps curls,
and overhead triceps extension. With free weights and a
spotter, participants performedeachexercisewitha
weight they could lift for one set of no less than three,
and no more than ten repetitions. The weight for each
exercise, set by the lab assistants, was based on each
participant’s past strength training experience. If the
participant was unable to perform the exercise for three
repetitions or was able to perform more than ten repeti-
tions, the weight was decreased or increased, respectively,
and the test was redone. A 2- to 3-min rest was given
between each exercise.
The multiple RM obtained from the strength tests was
used to estimate 1RM for the accessory exercises using
the following equation :
0:522 þ0:419 −0:055 RTFðÞ
where RepWt = amount of weight lifted (lbs) with each
repetition and RTF = amount of repetitions to fatigue.
Once the participant’s 1RM was determined for all ex-
ercises, 80% to 85% was calculated for the 6RM to 8RM
used for the HIRT sessions.
Energy intake assessment
All participants completed a baseline 3-day food record
to assess their regular nutrient intake. Participants were
educated on food portions and were asked to eat similar
diets the day prior to each exercise session to facilitate
similar macronutrient profiles. Nutrition intake was an-
alyzed using a nutrition software program (The Food
Processor, version 10.12.0, Esha Research, Salem, OR,
USA). On average, subjects ingested 2,078.7 ± 679.9
kcal, 253.7 ± 97.6 g CHO (approximately 48.8% CHO),
84.3 ± 29.9 g PRO (approximately 16.2% PRO), and 80.9 ±
36.7 g of fat (approximately 35.0% fat) per day.
Saliva collection and analysis
In order to account for possible energy substrate utilization
differences between the exercise sessions, estradiol was
measured. Estradiol concentrations were determined by a
2.5 to 5.0 mL saliva sample prior to each exercise bout,
using an ELISA assay for salivary estradiol-β-17 (estrogen)
(Salivary 17β-Estradiol Enzyme Immunoassay Kit,
Salimetrics, LLC, State College, PA, USA). To ensure
valid saliva collection results, participants were asked
to avoid drinking alcohol for 12 h and eating a major
meal for 3 h prior to giving saliva samples. Participants
were asked to rinse their mouth with water 10 min prior
to saliva collection, to remove food residue. To avoid
blood in saliva collections, participants were asked to
avoid brushing teeth for 45 min and obtaining dental work
for 48 h prior to giving saliva samples. All samples were
maintained at 4°C no longer than necessary before freez-
ing them at −20°C. Intra-assay precision coefficient of
variation (CV) for estrogen was 8.7% to 18.6%; inter-assay
precision CV was 3.9%. Due to the physiological role of
estradiol-β-17 on energy substrate utilization in women
[17,19], baseline estradiol levels were used as covariates in
the REE and RER analyses.
Cortisol was measured to account for the stress re-
sponse from each modality of exercise. Cortisol concen-
trations were determined by a 2.5 to 5.0 mL saliva sample
prior to and following each exercise bout, using an ELISA
Assay for salivary cortisol (Salivary Cortisol Enzyme
Immunoassay Kit,Salimetrics, LLC, State College, PA,
USA); the aforementioned protocol for collection and
storage was used. Once all samples were collected, smaller
subsamples were pooled between the two supplements to
produce one pre- and one post-exercise sample to deter-
mine the effect of each modality on cortisol, independent
of treatment. Intra-assay precision CV for cortisol was
12.0% to 17.1%; inter-assay precision CV was 4.9%.
After providing a saliva sample and immediately prior to
beginning each exercise session, in a double-blind fashion,
participants orally ingested 25 g of CHO (maltodextrin) or
PRO (whey isolate; Elite Whey Protein Isolate, Dymatize
Nutrition, Farmers Branch, TX, USA) mixed with 6 oz of
water in an opaque bottle. Treatment order was randomly
assigned using random allocation software. In accordance
to the CONSORT guidelines, nutritional products were
blinded by the company prior to arrival to the laboratory.
All participants and research team members were blinded
to the treatment, until after the statistical analyses.
Aerobic endurance exercise (AEE)
An AEE bout consisted of a self-selected 5-min warm-
up, followed by a 30-min treadmill (Q65 Series 90,
Quinton Instrument Co., Seattle, WA, USA) jog at 45%
to 55% HRR . RPE (Borg scale) was recorded, and HR
was measured at the end of each minute; both were av-
eraged over the 30-min exercise period.
High-intensity interval running (HIIT)
A HIIT bout consisted of a self-selected 5-min warm-up,
followed by ten rounds of a 60-s treadmill run at 85% to
95% HRR with a 60-s passive rest period. The entire exer-
cise bout lasted approximately 20 min. RPE was recorded,
and HR was measured at the end of each interval; and
an average of the ten 60-s exercise intervals was used
for statistical analysis.
Wingfield et al. Sports Medicine - Open (2016) 2:11 Page 4 of 11
High-intensity resistance training (HIRT)
Data obtained from the strength assessment were used
to determine an appropriate weight load for the HIRT
session. Exercises were performed in the following order:
leg press and bench press (York Barbell Co., York, PA,
USA), lunges, shoulder press, biceps curl, and triceps exten-
sion using free weights. Subjects performed a self-selected
warm-up prior to starting. A HIRT bout consisted of three
sets of 6RM to 8RM followed by a 20- to 30-s rest for
each exercise. There was a rest period of 2.5 min
between each exercise . The average length of HIRT
sessions was approximately 25 min. HR was measured
at the end of each set, and RPE was recorded at the end
of each exercise; the average of HR and RPE of each of
the six exercises was used in the statistical analyses.
REE and RER were analyzed using a metabolic cart and
internal software (TrueOne 2400, ParvoMedics, Inc.,
Sandy, UT, USA). Indirect assessments of oxygen uptake
) and carbon dioxide production (VCO
measured and used in the following equations to calcu-
late REE  and RER , respectively:
ÞÞ 1440 min
The gas analysis was performed via a mouthpiece and
hose immediately prior to each exercise session, for
15 min, to obtain resting measures (base). Immediately
after the conclusion of the exercise sessions, participants
were seated and reconnected to the metabolic cart for
15 min to obtain immediately post- (IP) exercise mea-
sures. The participants were then disconnected from the
cart and remained quietly seated. Measurements were
taken again during minutes 25 to 35 (30 min) and 50 to
60 (60 min).
A one-way repeated measures ANOVA was performed
to determine baseline differences in salivary estradiol
and cortisol levels. An analysis of covariance (ANCOVA)
mixed effects linear model was used to compare mean
longitudinal changes in REE and RER. Initial models in-
cluded fixed effects for nutritional treatment (CHO vs.
PRO), exercise modality (AEE vs. HIIT vs. HIRT), time
(baseline vs. IP vs. 30 min vs. 60 min), two-way and
three-way interactions, as well as baseline salivary estra-
diol level. The three-way interaction was tested first; if
non-significant, a reduced model was fit without the
three-way interaction. Multiple degree of freedom con-
trasts were then used to test for any evidence of differ-
ences between nutritional interventions or exercise
modalities over time. Only if those overall contrasts were
significant, pairwise comparisons were completed. An
ANCOVA was performed on the change in cortisol, co-
varied for baseline differences. A repeated measures
ANOVA was performed on HR and RPE differences in
modalities. SPSS version 20 (IBM; Armonk, NY, USA)
was used to perform the statistical analyses. All tests
were conducted at the 5% significance level.
There was no significant difference (p= 0.636; ES = 0.035)
between baseline estradiol concentrations for each exer-
cise session. While this pvalue was not significant, the
concentrations obtained were physiologically different be-
tween and within subjects. Concentrations spanned from
0.00 to 5.04 pg/mL between subjects, with one subject
ranging 0 to 4.70 pg/mL between testing days.
The three-way interaction for REE was non-significant
(p= 0.634), so it was removed from the model. The modal-
ity and treatment interaction was not significant (p=0.060)
(Additional file 1: Appendix 1), so main effects over time
are reported. Significant two-way interactions were found
between modality and time (p< 0.001) and time and treat-
ment (p= 0.008), indicating differential changes over time.
Significant modality differences were found between
HIIT and AEE (p< 0.001), and HIIT and HIRT (p<0.001)
over time, but not between AEE and HIRT (p=0.133).
Mean REE significantly increased more with HIIT com-
pared to AEE from baseline to IP exercise (p<0.001),
30 min post (p= 0.002), and 60 min post (p= 0.002);
(Additional file 1: Appendix 1 and Figure 2A). Mean
REE significantly increased more with HIIT than HIRT
from baseline to IP exercise (p<0.001) but was not
significantly different at 30 min (p= 0.335) or 60 min
(p= 0.143). Mean REE significantly increased more fol-
lowing PRO compared to CHO IP (p=0.007), 30 min
(p= 0.010), and 60 min (p= 0.002) (Figure 2B).
The three-way interaction for RER was non-significant
(p= 0.161), so it was removed from the model. The
interaction between modality and treatment was not sig-
nificant (p= 0.650), so main effects were over time. Signifi-
cant two-way interactions were found between modality
Wingfield et al. Sports Medicine - Open (2016) 2:11 Page 5 of 11
and time (p< 0.001) and time and treatment (p<0.001),
indicating differential changes over time.
Significant over-time differences were found between
HIIT and AEE (p< 0.001), HIIT and HIRT (p< 0.001),
and AEE and HIRT (p= 0.002). As a result of HIIT, mean
RER increased significantly more than AEE and HIRT
from baseline to IP exercise (p< 0.001) (Additional file 1:
Appendix 2 and Figure 3A). However, mean RER signifi-
cantly decreased more at 30 (p< 0.001) and 60 min post
exercise (p= 0.002) for HIIT than AEE. Mean RER sig-
nificantly reduced more from baseline to 30 min (p=
0.017) but was not significantly different at 60 min post (p=
0.360) for HIIT when compared to HIRT. When compar-
ing HIRT and AEE, there was no significant difference
from baseline to IP exercise (p= 0.337), but mean RER
was significantly lower for HIRT to 30 (p< 0.001) and
60 min (p= 0.027). Mean RER was significantly different
over time between CHO and PRO IP exercise (p<
0.001) and was significantly lower for PRO compared
to CHO from baseline to 30 (p= 0.001) and 60 min
post (p< 0.001) (Figure 3B).
ANCOVA change scores demonstrated no significant ef-
fect of exercise modality on cortisol values (p= 0.168;
ES = 0.015) (Table 2).
HR and RPE
There was a modality effect on average HR (p< 0.001)
and RPE (p< 0.001). Compared to HIIT, AEE produced
a significantly lower mean HR (Δ=−58 bpm; p< 0.001)
and RPE (Δ=−6; p< 0.001) (Table 3). There was no
difference in HR (Δ=−3 bpm; p= 0.834) between AEE
and HIRT. Mean RPE was significantly lower for AEE
Figure 2 Energy expenditure (REE; kcal/day) as a result of A) modality and time and B) treatment and time. Values expressed as mean ±
SD. A) Asterisk indicates significant difference between AEE and HIIT (p< 0.001 to p= 0.002); Number sign indicates significant difference between
HIIT and HIRT (p< 0.001). B) Asterisk indicates significant difference between CHO and PRO (p= 0.002 to p= 0.010). REE, resting energy
expenditure (kcal/day); CHO, carbohydrate; PRO, protein; AEE, aerobic endurance exercise; HIIT, high-intensity interval run; HIRT, high-intensity
resistance training; Base, baseline measurement; IP, immediately post-exercise measurement; 30 min, 30 minutes post-exercise measurement;
60 min, 60 minutes post-exercise measurement.
Wingfield et al. Sports Medicine - Open (2016) 2:11 Page 6 of 11
compared to HIRT (Δ=−5; p< 0.001). HIIT resulted in
significantly higher mean HR (Δ= 54 bpm; p< 0.001)
and RPE (Δ=1; p= 0.001) compared to HIRT.
Previous research evaluating the effect of AEE, HIIT,
and HIRT individually on energy expenditure and en-
ergy substrate utilization have failed to provide direct
comparisons between exercise modes; as well as failing
to evaluate these effects in women. The current study is
the first to compare common exercise modalities, with
acute nutritional intake, on post-exercise REE and RER
in women. Results of the current study indicate that
HIIT produces a significantly higher REE than AEE up
Figure 3 Respiratory exchange ratio as a result of A) modality and time and B) treatment and time. Values expressed as
mean ± SD. A) Asterisk indicates significant difference between AEE and HIIT (p< 0.001 to p= 0.002); Number sign indicates significant
difference between HIIT and HIRT (p< 0.001 to p= 0.017); Section sign indicates significant difference between AEE and HIRT (p=0.001
to 0.027). B) Asterisk indicates significant difference between CHO and PRO (p< 0.001 to p= 0.001). RER, respiratory exchange ratio;
CHO, carbohydrate; PRO, protein; AEE, aerobic endurance exercise; HIIT, high-intensity interval run; HIRT, high-intensity resistance
training; Base, baseline measurement; IP, immediately post-exercise measurement; 30 min, 30 minutes post-exercise measurement;
60 min, 60 minutes post-exercise measurement.
Table 2 Change in cortisol (μg/dL) as a result of modality
(mean ± SD)
Modality Base Post Δ
AEE 0.39 ± 0.31 0.39 ± 0.33 0.00 ± 0.22
HIIT 0.44 ± 0.40 0.59 ± 0.50 0.15 ± 0.23
HIRT 0.35 ± 0.18 0.40 ± 0.20 0.05 ± 0.14
AEE, aerobic endurance exercise; HIIT, high-intensity interval run; HIRT, high-intensity
resistance training; Base, baseline measurement; Post, post-exercise measurement;
Table 3 Average HR and RPE during the duration of each
modality (Mean ± SD)
HR (bpm) RPE
AEE 126 ± 7* 10 ± 1*
HIIT 184 ± 29
16 ± 1
HIRT 129 ± 17 15 ± 1
AEE, aerobic endurance exercise; HIIT, high-intensity interval run; HIRT,
high-intensity resistance training; HR, heart rate (bpm); RPE, rating of perceiv ed
exertion (Borg scale).
Indicates significant difference between AEE and HIIT (p< 0.0001).
Indicates significant difference between HIIT and HIRT (p< 0.0001
to p= 0.001).
Indicates significant difference between AEE and HIRT (p< 0.0001).
Wingfield et al. Sports Medicine - Open (2016) 2:11 Page 7 of 11
to 60 min post exercise and a significantly higher post-
exercise REE than HIRT IP exercise; while AEE and
HIRT produced similar post-exercise REE responses.
HIIT and HIRT both also stimulated greater fat utilization
(via a lower RER) when compared to AEE. In the current
study, ingesting PRO prior to exercise produced an increased
post-exercise resting energy expenditure, compared to CHO
consumption. PRO ingestion also resulted in significantly
augmented fat utilization 30 and 60 min post exercise.
As hypothesized, a single bout of HIIT produced a sig-
nificantly higher post-exercise REE than AEE through
60 min post exercise (Δ= 189.2 kcal/day). Similar to the
current study, higher post-exercise net EE with high-
intensity short-duration cycling (75% VO
to shorter and longer durations at a low intensity (50%
) has been found in men , indicating that exer-
cise intensity affects the magnitude and duration of
excess post-exercise oxygen consumption (EPOC). HIIT’s
metabolic inefficiency has been contributed to rapid
changes in skeletal muscle oxidative capacity due to the
high level of muscle fiber recruitment, particularly in
type II fibers . In contrast to the current study,
bouts of 60 s of work with 60 s rest, at 90% VO
have been found to have the same total net EE as 20-
min bouts at 70% VO
. Perhaps the difference in
exercise intensities for the two sessions was not sub-
stantial enough to elicit significant differences, such as
those found in the current study. Additionally, it is un-
clear if differences between exercise intensities were
controlled for . Subjects in the present study com-
pleted 30 min, instead of 20 min, of AEE in order to
closely match EE during HIIT (determined during pilot
testing; unpublished data).
In contrast to our hypothesis, when compared to HIIT,
REE from HIRT was significantly lower from baseline to
IP exercise (Δ=−169.3 kcal/day), with no differences at
30 and 60 min post exercise. Additionally, there was no
difference between AEE and HIRT (Δ= 19.8 kcal/day).
Research that has examined REE differences between
AEE or HIIT and HIRT is limited. However, single bouts
of resistance training and running performed at the
same intensity have both resulted in elevated REE up to
10 h post exercise . Contrary to the current study,
total body circuit weight training (three sets of 15 repeti-
tions at 65% 1RM) has been shown to elicit a higher post-
exercise REE in women than a treadmill run matched for
aerobic energy cost . The current study also matched
EE demands of AEE and HIRT during pilot testing, with
HIRT being slightly lower, yet at a higher intensity than
that of Braun et al. . Post-exercise REE data from the
current study eludes to exercise intensity, instead of dur-
ation, as the primary determinant of EPOC variance,
similar to several studies [4-6]. Collectively, it seems as if
HIIT is the most time-effective exercise modality for in-
creasing EE in women.
Combined acute PRO feedings with exercise resulted
in a significantly higher REE for PRO than for CHO up
to 60 min post exercise (Δ= 59.3 kcal/day). This is similar
to previous findings [13,14] that demonstrate greater post-
exercise REE and fat oxidation following a pre-exercise
meal or snack with higher PRO content. The increase in
post-exercise REE with PRO ingestion can be contributed
to PRO’s thermic effect of food, which is higher and more
prolonged than that of CHO and fat . In women,
higher PRO diets have elicited an increased effect on diet-
induced EE, in comparison to a lower PRO diet [28,29],
which may be explained by amino acid absorption and
disposal costs . Consuming an additional 100 kcal of
PRO prior to exercise, as done in the current study, may
increase EE up to an hour after exercise.
Exercise intensity has previously been shown to be a
driving factor for energy substrate utilization during and
after exercise. Immediately after HIIT, RER was signifi-
cantly increased compared to AEE, indicating a higher
utilization of CHO during and immediately after exer-
cise. Within 25 min afterward, RER was significantly
lower than AEE (p< 0.001), demonstrating higher fat
utilization, which was maintained up to 60 min post.
Similar to the current study, previous studies have
reported a significantly lower RER post exercise with
repeated bouts of moderate intensity cycling, compared
to a single bout  and a lower RER with a lower vs.
higher intensity cycle bout (50% and 70% VO
through 3 h post exercise, indicating increased fat
utilization . Previous data demonstrates differing ex-
ercise intensity can augment post-exercise REE and fat
oxidation, but intervals do not produce differences com-
pared to continuous exercise if total EE, duration, and
intensity between the two remain the same throughout
the exercise bout. In contrast to the current study, exer-
cise bouts at 45% and 65% VO
resulted in similar
RER values when EE of exercise was matched .
Although diets were kept constant, residual effects of
pre-exercise meals could cause similar RER values, since
a fasting period of only 2 h was implemented prior to
During the post-exercise period, oxygen consumption
is elevated for a period of time as a result of homeostasis
disruption caused by exercise. Physiological changes,
such as those in cellular ion concentrations, tissue tem-
peratures, and metabolite and hormone levels, take place
into recovery, disabling oxygen consumption to lower
back to resting levels . This process of EPOC is
related to exercise duration and intensity and can be
Wingfield et al. Sports Medicine - Open (2016) 2:11 Page 8 of 11
influenced by sex-based hormones (estrogen) and
macronutrient availability, among other things .
CHO is the primary fuel used during moderate- to high-
intensity exercise; but post exercise, the body shifts from
CHO to lipid energy sources, which lowers RER .
The current study demonstrates the fuel shift within
25 min post exercise, indicating greater post-exercise fat
utilization with HIIT. When comparing HIIT and HIRT,
RER was significantly higher IP, significantly lower at
30 min, but similar 60 min after exercise. RER was lower
for HIRT than AEE at 30 (p< 0.001) and 60 min post ex-
ercise (p= 0.027). Little research has compared RER be-
tween aerobic and resistance training, but investigations
that have been done present conflicting results. In con-
trast to this study, no post-exercise differences in RER
were found between a 60-min circuit weight training
bout (four sets of ten repetitions, 70% 1RM) and a cyc-
ling bout (70% VO
) in men . Similar to the
current study, a lower RER was demonstrated 22 h after
HIRT compared to more traditional resistance training
(four sets of 8 to 12 repetitions, 1- to 2-min rest) . In
relation to sex, no differences were reported in post-
circuit weight training RER between men and women
. It is important to examine the menstrual cycle due
to the effects estrogen may have on energy substrate
utilization, as the mid-luteal phase is characterized by
high estrogen levels, which can enhance lipid utilization
with exercise in women [19,33].
In the present study, no differences were found in RER
between CHO and PRO IP exercise; but supporting our
hypothesis, RER was significantly decreased for PRO
compared to CHO at 30 min (Δ= 0.036; p= 0.001) and
60 min post exercise (Δ= 0.052; p< 0.001). Similarly,
higher fat oxidation has been reported with a low CHO
diet compared to a moderate CHO diet at 1 h post exer-
cise . Substrate oxidation can be influenced by sub-
strate availability from dietary intake and physical activity.
While this study only evaluated acute feedings, low CHO
diets have been shown to decrease circulating insulin
levels, which promotes fatty acid utilization in skeletal
muscle , perhaps supporting the lower RER for PRO
ingestion in the current study.
Chronic dietary manipulations have an impact on sub-
strate utilization. Based on 3-day diet logs, participants
consumed on average 48.8% CHO, 16.8% PRO, and
34.2% fat daily. Although intakes were within the
Acceptable Macronutrient Distribution Ranges for
Americans, average baseline PRO intake was 1.3 g∙kg
higher than the Recommended
Dietary Allowance) . Interestingly, while average PRO
intake was relatively high, an additional acute feeding of
25 g of PRO significantly augmented REE in the current
study, perhaps supporting the suggestion that higher pro-
tein needs (1.63 g∙kg
) may be necessary for women
to maintain nitrogen balance . While the importance
of chronic dietary manipulations is apparent, the current
study supports the benefit of acute PRO feedings on EE,
in healthy women eating within dietary guidelines. Acute
pre-exercise feedings have positively influenced fat oxida-
tion, in comparison to a fasted state that blunted fat oxi-
dation . Future long-term studies identifying the acute
effects on weight loss and body composition improve-
ments in women would be valuable.
A limitation in the current study was the use of indirect
calorimetry to measure REE and RER, rather than whole
body direct calorimetry, which is considered the gold
standard. Also, excluding the acute PRO and CHO sup-
plementation, no dietary modifications were made, which
could have a potential effect on the acute RER measure-
ment. However, because no modifications were made, the
study results may be more practical for a woman who only
wants to change her pre-workout nutrition rather than
her whole diet. In addition, since this was an acute inter-
vention, and post-exercise measurements were only
conducted for 60 min, it is difficult to predict longer
term EE and energy substrate utilization. Specifically,
EE calculations extrapolate our 60-min findings to a 24-h
period (using Weir et al.  equation), potentially ele-
vating the actual caloric differences (i.e. approximately
800 kcal). Future research should focus on determining
the effects of chronic exercise and nutrition modifica-
tions in women using whole body calorimetry.
This study indicates that HIIT elicited the largest increase
in post-exercise REE, as well as augmented RER, com-
pared to AEE and HIRT. Immediately post exercise, there
was a heightened caloric effect from the HIIT bout stimu-
lating approximately 800 kcal/day more than HIRT and
AEE. Beginning around 30 min post exercise, HIIT and
HIRT both had a higher fat utilization than AEE; at
60 min post, HIIT and HIRT resulted in similar energy
substrate utilization in comparison to each other. In
combination with varying exercise modalities, PRO intake
elevated post-exercise REE and fat oxidation to a greater
extent than CHO. PRO ingestion prior to exercise may
help further maximize the caloric effect, with an additional
approximately 90 kcal/day expended compared to CHO.
Around 30 min post exercise, PRO increased fat utilization
compared to CHO. Collectively, these findings suggest a
potential benefit of integrating HIIT and pre-exercise PRO
intake into exercise routines. Specifically in women, this
strategy may have positive implications on their health,
weight, and body composition.
Wingfield et al. Sports Medicine - Open (2016) 2:11 Page 9 of 11
Additional file 1: Appendix 1. REE (kcal/day) for each modality and
time (mean ± SD). Appendix 2. RER for each modality, treatment, and
time (mean ± SD).
The authors declare that they have no competing interests.
HWL assisted with study design, carried out data collection, and drafted
manuscript; ASR conceived study design, carried out statistical analysis, and
drafted manuscript; EJR and ETT carried out data collection, reviewed
results, and manuscript draft; MAW assisted with study design and statistical
analysis; ACH assisted with biochemical analyses; EDR contributed to study
design and reviewed results and manuscript draft. All authors read and
approved the final manuscript.
This study was supported by the National Strength and Conditioning Association
Foundation. CHO and PRO were blinded and donated by Dymatize Nutrition
(Farmers Branch, TX, USA). ASR and MW declare that they were supported by the
National Center for Advancing Translational Sciences, National Institutes of Health,
through Grants 1KL2TR001109 and 1UL1TR001111. The content is solely the
responsibility of the authors and does not necessarily represent the official views
of the NIH.
Department of Exercise and Sport Science, University of North Carolina, 209
Fetzer Hall, CB #8700, Chapel Hill, NC 27599-8700, USA.
Nutrition - Gillings School of Global Public Health, University of North
Carolina, Chapel Hill, NC, USA.
Departments of Medicine and Biostatistics,
University of North Carolina, Chapel Hill, NC, USA.
Received: 27 July 2014 Accepted: 9 February 2015
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