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Metcalfe, R. S., Babraj, J. A., Fawkner, S. G. and Vollaard, N. B. J.
(2012) Towards the minimal amount of exercise for improving
metabolic health: beneficial effects of reduced-exertion high-
intensity interval training. European Journal of Applied
Physiology, 112 (7). pp. 2767-2775. ISSN 1439-6319
Link to official URL (if available): http://dx.doi.org/10.1007/s00421-
011-2254-z
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1
Towards the minimal amount of exercise for improving metabolic health: beneficial
effects of reduced-exertion high-intensity interval training
Richard S Metcalfe1, John A Babraj2, Samantha G Fawkner1,3, Niels BJ Vollaard1 ,4
1School of Life Sciences, Heriot-Watt University, Edinburgh, UK
2School of Social and Health Sciences, University of Abertay, Dundee, UK
3School of Education, University of Edinburgh, UK
4Department for Health, University of Bath, UK
Corresponding author:
Dr Niels Vollaard
Department for Health
University of Bath
Bath, BA2 7AY, UK
N.Vollaard@bath.ac.uk
2
Abstract
High-intensity interval training (HIT) has been proposed as a time-efficient alternative to traditional
cardiorespiratory exercise training, but is very fatiguing. In this study we investigated the effects of a
reduced-exertion HIT (REHIT) exercise intervention on insulin sensitivity and aerobic capacity.
Twenty-nine healthy but sedentary young men and women were randomly assigned to the REHIT
intervention (men: n=7, women n=8) or a control group (men n=6; women n=8). Subjects assigned to
the control groups maintained their normal sedentary lifestyle, whilst subjects in the training groups
completed 3 exercise sessions per week for 6 weeks. The 10-min exercise sessions consisted of low
intensity cycling (60 Watts) and one (1st session) or two (all other sessions) brief all-
in week 1, 15 s in weeks 2-3 and 20 s in the final 3 weeks). Aerobic capacity (
2peak) and the
glucose and insulin response to a 75-g glucose load (OGTT) were determined before and 3 days after
the exercise program. Despite relatively low ratings of perceived exertion (RPE: 13±1), insulin
sensitivity significantly increased by 28% in the male training group following the REHIT intervention
(P<0.05).
2peak increased in the male training (+15%) and female training (+12%) groups
(P<0.01). In conclusion we show that a novel, feasible exercise intervention can improve metabolic
health and aerobic capacity. REHIT may offer a genuinely time-efficient alternative to HIT and
conventional cardiorespiratory exercise training for improving risk factors of T2D.
Key words: insulin sensitivity; glycaemic control; aerobic capacity; HIT
3
Introduction
The prevalence of type 2 diabetes (T2D) is increasing rapidly in the UK (Gonzalez et al. 2009) and
throughout the world (Danaei et al. 2011). T2D is associated with substantial human costs in terms of
reduced quality of life and life expectancy, and management of the symptoms and secondary
complications of T2D accounts for a considerable proportion of total public health care expenditure
(American Diabetes Association 2008). As such, finding effective and inexpensive strategies to
prevent and treat T2D should be a key objective and is indeed essential if affordable health care
systems are to remain a viable proposition.
The primary defect underlying the development of T2D is skeletal muscle insulin resistance
(DeFronzo and Tripathy 2009). The metabolic causes of insulin resistance are numerous and
complex but there is accumulating evidence that physical inactivity may be the major initiating factor
(Thyfault and Krogh-Madsen 2011), whereas regular exercise is associated with improved muscle
insulin sensitivity and thus represents an effective strategy to prevent T2D (Hawley and Gibala 2009).
In fact, it is now recognised that exercise, rather than just being a useful strategy for improving health,
is actually essential for good metabolic and cardiovascular function, of which insulin action is a key
component (Thyfault and Krogh-Madsen 2011; Booth et al. 2002). W ith this in mind, the finding that
~6 out of 10 men and ~7 out of 10 women in the UK are currently not achieving the (low) minimum
recommended levels of physical activity is a major concern (Allender et al. 2008). Recommendations
for levels of physical activity place heavy emphasis on performing moderate and/or vigorous-intensity
cardiorespiratory exercise training (Garber et al. 2011), which is associated with a substantial time-
commitment. Lack of time is often cited as a barrier to being physically active (Korkiakangas et al.
2009; Reichert et al. 2007), suggesting that these guidelines may not be the ideal approach to
increase physical activity levels to improve public health.
Several recent studies have suggested that high-intensity interval training (HIT), a training model
involving a series of 30-second all-out cycling sprints (i.e. Wingate sprints) with 4 minutes of
rest/recovery between each bout, may provide a time-efficient strategy for inducing adaptations that
are similar to traditional cardiorespiratory training (Gibala et al. 2006; Burgomaster et al. 2005;
Burgomaster et al. 2008; Rakobowchuk et al. 2008; Burgomaster et al. 2007; Trilk et al. 2010).
4
Furthermore, we have recently demonstrated the beneficial effects of HIT on insulin sensitivity (Babraj
et al. 2009), a finding that has since been confirmed by others (Little et al. 2011; Richards et al. 2010;
Whyte et al. 2010). However, whilst these observations are interesting from a human physiological
perspective, their translation into physical activity recommendations for the general population is
uncertain for two reasons. Firstly, the relatively high exertion associated with HIT sessions
requires strong motivation and may be perceived as too strenuous for many sedentary individuals
(Hawley and Gibala 2009). Secondly, although a typical HIT session requires only 2-3 minutes of
actual sprint exercise, when considered as a feasible exercise session including a warm-up, recovery
intervals and cool-down, the total time commitment is more than 20 minutes, reducing the time-
efficiency (Garber et al. 2011). Thus, there is scope for further research to determine whether the
current HIT protocol can be modified to reduce levels of exertion and time-commitment while
maintaining the associated health benefits.
We (Babraj et al. 2009) and others (Whyte et al. 2010) have suggested that high levels of glycogen
depletion observed during repeated 30-second W ingate sprints may play an important role in
mediating improvements in insulin sensitivity following HIT. This hypothesis is based on evidence that
muscle glycogen availability is inversely related to muscle cell membrane GLUT4 content during
insulin stimulation (Derave et al. 2000), glycogen synthase activity (Jensen et al. 2006), the
expression of GLUT4 mRNA (Steinberg et al. 2006), and hence insulin sensitivity (Derave et al. 2000;
Jensen et al. 2006; Kawanaka et al. 2000; Laurent et al. 2000; Litherland et al. 2007; Richter et al.
2001). The upregulation of key metabolic genes initiated by the release of glycogen-bound proteins
may, at least in part, explain how glycogen depletion affects insulin-dependent muscle glucose uptake
(Steinberg et al. 2006; Graham et al. 2010). Regardless of the potential mechanisms however, if
muscle glycogen regulates insulin sensitivity then exercise protocols aiming to reduce glycogen levels
should be effective.
It has consistently been shown that a single 30-second Wingate sprint can reduce muscle glycogen
stores in the vastus lateralis by 20-30% (Esbjornsson-Liljedahl et al. 1999; Parolin et al. 1999;
Esbjornsson-Liljedahl et al. 2002; Gibala et al. 2009). What is intriguing, however, is that
glycogenolysis is only activated during the first 15 seconds of the sprint and is then strongly
attenuated during the final 15 seconds (Parolin et al. 1999). Moreover, activation of glycogenolysis is
5
inhibited in subsequent repeated sprints (Parolin et al. 1999). This suggests that the traditional HIT
protocol (4-6×30 seconds) may be unnecessarily strenuous as similar glycogen depletion may be
achieved using 1-2 sprints of shorter duration (15-20 seconds). In turn, this would make the training
sessions more time-efficient, less strenuous and more applicable to the largely sedentary general
population. Therefore, in the current study we investigated the effects of a reduced-exertion HIT
(REHIT) intervention on insulin sensitivity in previously sedentary subjects. We hypothesised that
despite reducing sprint time and number, REHIT would still be effective at improving glucose
tolerance.
6
Methods
Subjects
Twenty-nine sedentary but healthy young men (n=13) and women (n=16) were recruited to take part
in the study and randomly allocated to a training group or a control group. Subjects allocated to the
training group completed the full experimental protocol whilst subjects in the control group completed
the pre- and post-training assessments without an exercise intervention. Baseline characteristics for
each subject group are shown in Table 1. All participants were classified as sedentary according to
the criteria of the International Physical Activity Questionnaire (IPAQ) (Craig et al. 2003) and were
only included no to all questions in the physical activity readiness
questionnaire (PAR-Q) (Thomas et al. 1992). Further exclusion criteria included clinically significant
hypertension (>140/90 mm Hg) and a personal history of metabolic or cardiovascular disease. All
subjects were fully informed of the experimental protocol and any associated risks, both verbally and
in writing, before providing written informed consent to participate. In addition, the potentially
confounding effect of changes in diet and physical activity patterns was fully explained to all
participants and they were asked to maintain their normal lifestyle patterns throughout the study
period. The experimental protocol was approved by the Heriot-Watt University School of Life Sciences
Ethics Committee and was conducted in accordance with the Declaration of Helsinki.
Experimental Design
All subjects underwent pre- and post-intervention testing for insulin sensitivity and aerobic capacity.
Insulin sensitivity was assessed using an oral glucose tolerance test (OGTT) and aerobic capacity
was assessed using a conventional
2peak cycling test. The baseline OGTTs were performed two
weeks before training commenced and the post-intervention OGTTs were conducted 3 days after the
final training bout at the same time of day as the pre-intervention OGTT. This meant that there were
exactly 8 weeks between the pre- and post-training OGTTs which ensured that female subjects were
in the same stage of their menstrual cycle. The
2peak tests took place 1-2 days after the OGTTs.
Oral Glucose Tolerance Test (OGTT)
7
Prior to OGTTs subjects performed no moderate or vigorous intensity physical activities for three
days, and refrained from drinking alcohol for one day. Furthermore, subjects completed a 3-day food
diary before each OGTT which was analysed for total energy and macronutrient content using
commercially available dietary analysis software (Dietplan6, Forestfield Software, UK). There were no
significant differences in total energy, carbohydrate, fat or protein content over the 3 days before the
pre- and post-intervention OGTTs in any of the subject groups.
On the day of the OGTT subjects reported to the laboratory between 7:30 and 9:30 am following an
overnight fast from 10 pm the previous evening. A fasting blood sample was obtained from a forearm
antecubital vein by venepuncture using the vacutainer system. 75 g of anhydrous glucose (Fisher
Scientific, Loughborough, UK) dissolved in 100 ml of water was then orally administered and further
blood samples were taken at 60 and 120 min after glucose ingestion. Collected blood samples were
stored on ice and then centrifuged for 10 min at 1600 g to separate the plasma, which was stored at -
20°C prior to the determination of plasma glucose and insulin concentrations. Plasma glucose
concentration was determined by the glucose oxidase reaction using an automated analyser (YSI Stat
2300, Yellow Spring Instruments, Yellow Spring, OH). Plasma insulin concentration was measured
using a commercially available
All glucose and insulin assays were carried out in duplicate. Area under the curve (AUC) for plasma
glucose and insulin was calculated using the trapezoid model. Peripheral insulin sensitivity was
determined using the Cederholm index (Cederholm and Wibell 1990) which is calculated using the
formula:
ISICederholm = 75000 + (G0-G120) × 1.15 × 180 × 0.19 × BW/120 × Gmean × log (Imea n)
Where BW is body weight, G0 and G120 are plasma glucose concentration at 0 and 120 min (mmol·l-1),
and Imea n and Gmean are the mean insulin (mU·l-1) and glucose (mmol·l-1) concentrations during the
OGTT. The Cederholm Index has previously been shown to correlate well with the gold standard
insulin clamp method (Piche et al. 2007).
O2peak Test
Peak oxygen uptake capacity (
2peak) was determined using a graded cycling test to volitional
exhaustion on a mechanically braked cycle ergometer (Ergomedic 874e, Monark, Vansbro, Sweden).
8
Subjects cycled at 60 W for one minute after which -1 until
the pedal cadence could no longer be maintained at 60 rpm. Participants respired through a rubber
mouthpiece which was connected to an online gas analysis system (Sensor-Medics, Bilthoven, the
Netherlands). Respiratory volume, flow and levels of expired O2 and CO2 were measured and
2
was averaged over 10 second periods.
2peak was taken as the highest 10 second value achieved
during the test. In all tests two or more of the following criteria were met: a plateau in
2 despite
increasing intensity, RER > 1.15, heart rate within 10 beats of age-predicted maximum, and/or
volitional exhaustion.
Training Protocol
Subjects allocated to the training group completed three exercise sessions per week for 6 weeks,
completing 18 sessions overall. All exercise sessions lasted 10 minutes in total, including a warm up
and cool down, which meant a total training time of 30 minutes per week. Each training session
consisted of low intensity cycling (60 W atts) and one (1st session) or two (all other sessions) all-out
cycling sprints. Just before each sprint, resistance was removed, subjects increased the pedal
cadence to their maximal speed, a braking force equivalent to 7.5% of body weight was then applied
to the ergometer, and participants sprinted against the braking force for a designated time period. The
duration of the sprints increased from 10 seconds in week 1, to 15 seconds in weeks 2 and 3, and 20
seconds in the final 3 weeks. A full schematic of the training protocol is shown in Figure 1. Training
sessions were fully supervised and verbal encouragement was given during each sprint. A rat ing of
perceived exertion (RPE) was collected using the 15-point Borg scale (Borg 1970) at the end of the
first session, and subsequently at the end of each training week, immediately following the completion
of the 10-minute training session.
Statistical Analysis
All data are presented as mean ± SEM. Data were analysed using the commercially available SPSS
statistics package (PASW Statistics, version 17.0). Three-way mixed-model ANOVAs (gender [male,
female] × group [REHIT, control] × time [pre, post]) were performed to test the effects of the REHIT
intervention. For variables with significant gender × time interactions, males and females were
analysed separately using 2-way mixed model ANOVAs (group × time). Comparisons in RPE data
9
between men and women were made using an independent sample t-test. Significance was accepted
at P<0.05.
10
Results
No significant differences existed between the REHIT and control groups at baseline (Tables 1-2).
There were no changes in weight or BMI following the REHIT training program in any of the groups
(Table 2). Ten out of fifteen training group participants completed all 18 training sessions (100%
adherence), with a mean adherence to the REHIT training program of 97% for all subjects combined.
2peak
For
2peak there were significant main effects of gender (P<0.001) and time (P<0.01), and a
significant interaction effect for group × time (P<0.01): following REHIT
2peak was increased by
15% in men and by 12% in women with no significant gender difference in this effect
2peak was expressed in l·min-1 or ml·kg-1min-1.
Glucose and insulin responses to the OGTT
Effects of the REHIT intervention on glucose and insulin responses to an oral glucose load are shown
in Figure 2, with glucose and insulin AUCs shown in Table 2. As we observed a significant interaction
effect for gender × time for glucose AUC (P<0.05), results for male and female subjects were
analysed separately using a two-way mixed-model ANOVA (group × time). No significant effects were
observed for men. A significant main effect for time for women (P<0.05) indicated that post-
intervention values for glucose AUC were increased, but there was no significant difference between
the female REHIT and control groups. No significant changes in insulin AUC were observed (Table 2).
A significant interaction effect for gender × time was also observed for insulin sensitivity (P<0.01), so
male and female subjects were analysed separately. Following REHIT, insulin sensitivity significantly
improved by 28% in male subjects (P<0.05), but not in female subjects (Figure 3).
Rate of Perceived Exertion
RPE data over the course of the REHIT training program is shown in Figure 4. On the whole, despite
the incorporation of brief but intense sprints, the training sessions were well tolerated by all of the
participants. Mean RPE values peaked at the end of session 12 (week 4; 2x20 s), corresponding to
a women respectively (Figure
11
4A). None of the participants gave an RPE score higher than 15. When mean RPE values over the
whole training program were calculated, female participants found the training program significantly
harder than male participants (Figure 4B).
12
Discussion
In the present study we show that a 6-week novel exercise intervention consisting of very brief,
manageable sessions is associated with improved insulin sensitivity in sedentary young men, and
improved aerobic capacity in men and women. The beneficial effects occurred independently of
changes in body mass and may represent a chronic training adaptation since post-training
measurements were taken 3 days after the final exercise bout. Importantly, the improvements were
observed despite the low time commitment (totalling 30 minutes per week) and low required effort:
RPE peaked at an average of 14 ) in week 4 which is comparable with RPE scores
reported with prolonged cycling at 50-75%
2max (Borg 1982). This study extends the previous
literature showing the beneficial effects of HIT (Burgomaster et al. 2007; Babraj et al. 2009; Richards
et al. 2010; W hyte et al. 2010; Rakobowchuk et al. 2008; Trilk et al. 2010) by showing that the sprint
number and duration can be substantially reduced whilst still maintaining positive effects.
Based on current knowledge, when considering the health effects of exercise solely from a
physiological perspective it is fair to state that more (within reason) is better. In other words, to
optimise the metabolic, cardiovascular and psychological benefits that exercise can offer, people
should be encouraged to perform a large volume (at least 30 minutes per day) of both moderate and
vigorous intensity cardiorespiratory exercise on most days of the week, as well as sessions focused
on strength and flexibility 2-3 times per week (Garber et al. 2011). However, whilst these guidelines
may be effective in people who adhere to them, they remain largely ineffective at a societal level
(Allender et al. 2008), partly because they fail to sufficiently consider the key barriers which prevent
people from performing regular . For exercise prescriptions to have a
beneficial effect for society there must be a balance between providing adequate health benefits and
helping to generate motivation to perform exercise by overcoming key barriers. One possible
alternative strategy could be to define the minimum volume of exercise required to improve health
indices with the aim of increasing exercise adherence. To date, the training program utilised in the
current study represents the smallest volume of exercise (when considered per session) that has
been shown to induce positive effects on health.
13
Insulin sensitivity was increased by 28% in men following REHIT. The magnitude of this change is
comparable with responses to 2 weeks of classic HIT in recreationally active men and women (Babraj
et al. 2009; Richards et al. 2010) and in obese men (Whyte et al. 2010). Our results suggest that
repeated glycogen depletion might be a key determinant of improved insulin sensitivity following HIT,
at least in young lean sedentary male subjects. However, as we did not determine glycogen depletion
during the REHIT training sessions this is only speculative, and further studies are required to
elucidate the mechanisms by which REHIT improves insulin sensitivity.
The improvements in insulin sensitivity after REHIT appear to be gender-specific as mean insulin
sensitivity was not improved in the female subjects after the training program. This is in contrast to a
previous study which did not observe gender differences in the improvements in insulin sensitivity in
12 recreationally active subjects after 2 weeks of classic HIT (Richards et al. 2010). No other study
has investigated the effects of HIT on insulin sensitivity in women. Following a traditional aerobic
exercise intervention in a large cohort, insulin sensitivity improved to a greater degree in men when
compared with women but (similar to our study) the female participants had a higher baseline level of
insulin sensitivity which may have impacted on the subsequent training response (Boule et al. 2005).
The gender differences in the change in insulin sensitivity in response to our REHIT intervention may
in part be caused by the low statistical power of our study, with only 8 female subjects performing the
REHIT intervention. However, it can be speculated that differences in metabolic perturbations during
the brief high-intensity cycle sprints may contribute to the observed gender difference, as women
have been shown to break down up to 50% less glycogen during a single Wingate sprint
(Esbjornsson-Liljedahl et al. 2002; Esbjornsson-Liljedahl et al. 1999). From this perspective, it would
be interesting to determine whether the extent of muscle glycogen breakdown during a REHIT training
bout correlates with changes in GLUT4 protein content, insulin-stimulated canonical signalling protein
content and activation, glycogen synthase activity, and insulin sensitivity following the training
program. Alternatively, it could be that our small sample included several non-responders. Previous
studies have comprehensively demonstrated that following a period of exercise training part of the
population will not adapt for specific parameters (non-responders), and for insulin sensitivity this has
been shown to be the case for up to 40% of the population (Boule et al. 2005; Vollaard et al. 2009;
Bouchard and Rankinen 2001). Therefore, further studies with larger sample sizes will be needed to
14
confirm or refute our initial observations. Furthermore, the post-intervention OGTT was scheduled
three days following the final exercise session, and we cannot rule out that insulin sensitivity was
improved in female subjects at an earlier time-point. Finally, although we did not measure power
output during the sprints, we observed that some of the female volunteers struggled with the transition
from 60 W to the all-out sprints, and were unable to substantially increase their pedal frequency, and
thus their power output during the sprints. This may have increased the aerobic contribution to energy
supply and reduced glycogen depletion. For sedentary women substituting the 60 W cycling with
unloaded pedalling may make the sprints more effective.
Aerobic capacity increased by 15% and 12% in men and women respectively after the REHIT
intervention, an important observation since a high aerobic capacity is associated with a lower risk of
cardiometabolic disease (Church et al. 2005; Wei et al. 1999). Interestingly, since women improved
their aerobic capacity but not their insulin sensitivity, it appears that there is a dissociation between
changes in aerobic capacity and changes in insulin sensitivity.
Average RPE values reported on immediate completion of the REHIT training sessions were
comparable with RPE values obtained during prolonged moderate intensity cardiorespiratory exercise
at 50-75%
2max (Borg 1982). However, there are limitations to the use of the RPE scale in the
current study, as the RPE scale is designed for use during (or immediately following) continuous
exercise at a constant intensity and may not be a valid measure of exertion during interval based
exercises, especially when values are given retrospective of the most intense exercise, as was the
case in this study. RPE values obtained in this manner may underestimate exertion during the sprints;
indeed, other studies where RPE has been obtained following a 20 second all out sprint have
reported higher values of ~16-18 (Baker et al. 2001; Gearhart et al. 2005). However, we were
interested in gaining an exertion measure to characterise our entire training intervention and our
subjects were asked to consider the whole 10 minute exercise session when giving their ratings.
Whether the effort required to perform REHIT sessions would deter individuals from performing this
type of intervention is a question to be answered in future studies.
In conclusion, in this study we have shown that a very brief and feasible exercise intervention is
associated with improvements in metabolic health and aerobic capacity. Our findings suggest that this
15
REHIT protocol may offer a genuinely time-efficient alternative to HIT and conventional
cardiorespiratory exercise training for improving risk factors of T2D.
Acknowledgements
We would like to thank John Fox for technical assistance, and Paul Aikman, Ben Ashcroft, Barnaby
Barber, Sarah Dunnett, Mahmoud Gholoum, Liam Harper, Andrew Hebson, Adam Reed, Keith
Simpson and Alison Thomson for assistance with testing and the training sessions. The study was
funded by Heriot-Watt University.
Conflict of interest
The authors declare that they have no conflict of interest.
16
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19
Table 1 Subject Characteristics
Training
Control
Male (n=7)
Female (n=8)
Male (n=6)
Female (n=8)
Age (y)
26±3
24±3
19±1
21±1
Height (m)
1.74±0.02
1.62±0.02
1.78±0.03
1.65±0.03
Weight (kg)
73.7±6.0
59.7±2.7
80.5±6.6
60.8±5.3
SBP (mm Hg)
126±4
118±3
126±4
120±4
DBP (mm Hg)
74±3
74±3
71±3
73±3
SBP: systolic blood pressure; DBP diastolic blood pressure
Data shown are mean ± SEM
Table 2 Effects of REHIT on BMI, 2peak, and glucose and insulin AUC
Male
Female
REHIT (n=7)
Control (n=6)
REHIT (n=8)
Control (n=8)
Pre
Post
Pre
Post
Pre
Post
Pre
Post
BMI (kg·m-2)
24.4±1.9
24.0±1.7
25.2±1.6
25.3±1.6
22.7±1.1
22.8±1.3
22.3±1.4
22.3±1.4
2-1·min-1)
36.3±2.2
41.6±1.5 *
38.0±2.7
38.0±2.3
32.5±1.5
36.4±1.3 *
32.9±2.1
31.6±2.1
Glucose AUC (mmol·min·l-1)
789±65
695±53
762±41
801±55
671±67
712±76 ^
748±108
850±93 ^
Insulin AUC (mU·min·l-1)
11713±1829
7147±1152
8728±1914
9944±2089
7399±1393
8599±1728
6734±1427
7970±1477
O2
2peak is shown for n=6 due to
technical problems during the pre-training tests.
Data shown are mean ± SEM
*: P<0.01 for the group × time interaction effect
^: P<0.05 for the main effect of time in women
20
Figure 1 REHIT training protocol
Time (Min)
0 - 1 1 - 2 2 - 3 3 - 4 4 - 5 5 - 6 6 - 7 7 - 8 8 - 9 9 -10
Training
Sessions
15:00 5:10
2 - 3 3:00 3:10 6:50 7:00
4 - 9 3:00 3:15 6:45 7:00
10 -18 3:00 3:20 6:40 7:00
Low intensity warm up Sprints and low intensity recovery Low intensity cool down
= High intensity sprints
21
Figure 2 Effects of REHIT on glucose (A-B) and insulin (C-D) responses to an OGTT in men (A-C)
and women (B-D). Solid dots: REHIT group, open dots: control group; dotted lines: pre, solid lines:
post.
4
5
6
7
8
9
10
060 120
Plasma glucose (mmol·l-1)
Time (min)
REHIT pre
REHIT post
Control pre
Control post
A
4
5
6
7
8
9
10
060 120
Plasma glucose (mmol·l-1)
Time (min)
B
0
25
50
75
100
125
150
175
060 120
Plasma insulin (mU·l-1)
Time (min)
C
0
25
50
75
100
125
150
175
060 120
Plasma insulin (mU·l-1)
Time (min)
D
22
Figure 3 Effects of REHIT on insulin sensitivity (Cederholm Index) in (A) men and (B) women.
* P<0.05 for the group × time interaction effect
40
50
60
70
80
pre post
Insulin sensitivity
(mg·l2·mmol-1·mU-1·min-1
)
REHIT
Control
A
*
40
50
60
70
80
pre post
Insulin sensitivity
(mg·l2·mmol-1·mU-1·min-1
)
REHIT
Control
B
23
Figure 4 Rate of perceived exertion for REHIT training sessions (A) and gender differences in the
mean RPE score over the REHIT training intervention (B).
* P<0.05 men vs. women
6
8
10
12
14
16
18
20
1
3
6
9
12
15
18
Rate of Perceived Exertion
(RPE)
Training Session
Males
Females
6
8
10
12
14
16
18
20
Males (n=7)
Females (n=8)
Rate of Perceived Exertion
(RPE)
*
A B
