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The influence of 2 weeks of low volume high-intensity interval training on
health outcomes in adolescent boys
Running title: High-intensity interval training and health outcomes in adolescent
boys
Key words: Trainability, youth, aerobic fitness, lipid oxidation, blood pressure, BMI.
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ABSTRACT
The present study aimed to establish whether 2 weeks of high intensity interval
training would have a beneficial effect on aerobic fitness, fat oxidation, blood
pressure and body mass index (BMI) in healthy adolescent boys. Ten adolescent
boys (15.1 ± 0.3 y, 1.3 ± 0.2 years post peak height velocity) completed six sessions
of Wingate-style high-intensity interval training over a 2 week period. The first
session consisted of four sprints with training progressed to seven sprints in the final
session. High-intensity interval training had a beneficial effect on maximal O2 uptake
(mean change, 90% confidence intervals: 0.19 L·min-1, ±0.19), the O2 uptake at the
gas exchange threshold (0.09 L·min-1, ±0.13) and on the O2 cost of sub-maximal
exercise (-0.04 L·min-1, ±0.04). A beneficial effect on the contribution of lipid (0.06
g·min-1, ±0.06) and carbohydrate (-0.23 g·min-1, ±0.14) oxidation was observed
during sub-maximal exercise, but not for the maximal rate of fat oxidation (0.04
g·min-1, ±0.08). Systolic blood pressure (1 mmHg, ±4) and BMI (0.1 kg·m2, ±0.1)
were not altered following training. These data demonstrate that meaningful changes
in health outcomes are possible in healthy adolescent boys after just 6 sessions of
high-intensity interval training over a 2 week period.
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INTRODUCTION
Physical activity and aerobic fitness are independent predictors of cardio-metabolic
health in young people (Andersen et al., 2006; Ekelund et al., 2007). Consequently,
the health benefits of regular physical activity are of importance to the public health
agenda for researchers, educators and policy makers. Children and adolescents are
recommended to undertake at least 60 min of daily moderate to vigorous exercise
(Janssen & Leblanc, 2010). Studies employing objective assessment of physical
activity however, demonstrate a marked decline in physical activity from childhood
and during adolescence (Sherar, Esliger, Baxter-Jones, & Tremblay, 2007), and that
few children and adolescents meet the recommended daily dose of physical activity
(Metcalf, Voss, Hosking, Jeffery, & Wilkin, 2008; Riddoch et al., 2007). The
efficacy of alternative forms of physical activity therefore needs to be considered in
young people.
Recent adult studies have shown low volume, high-intensity interval training to offer
either similar or superior benefits to cardio-metabolic health outcomes compared to
traditional continuous exercise (Gibala, Little, Macdonald, & Hawley, 2012). For
example, just 2-6 weeks of high-intensity interval training in adults can enhance
maximal oxygen uptake (𝑉̇ O2max) (Burgomaster et al., 2008; Macpherson, Hazell,
Olver, Paterson, & Lemon, 2011; Whyte, Gill, & Cathcart, 2010), insulin-sensitivity
(Babraj et al., 2009; Whyte, et al., 2010), lipid oxidation at rest (Whyte, et al., 2010)
and during exercise (Burgomaster, et al., 2008), systolic blood pressure (Whyte, et
al., 2010) and body composition (Macpherson, et al., 2011; Whyte, et al., 2010). In
contrast, research studying the efficacy of high-intensity interval training on health
related outcomes in children and adolescents is sparse. There is evidence showing 7-
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8 weeks of high-intensity interval training improves 𝑉̇ O2max in healthy children
(Baquet et al., 2010; McManus, Cheng, Leung, Yung, & Macfarlane, 2005).
Furthermore, a recent study found 7 weeks of high-intensity interval training to
improve physical performance (20 m shuttle run test, agility, 10 m sprint) and
cardio-metabolic health (systolic blood pressure, body mass index [BMI]) outcomes
in healthy adolescents (Buchan et al., 2011). To our knowledge however, no study
has examined whether improvements in cardio-metabolic health outcomes are
possible using high-intensity interval training over a 2 week period in youth, as has
recently been demonstrated in adults (Babraj, et al., 2009; Whyte, et al., 2010).
The purpose of the present study was to test the hypothesis that 2-weeks of highintensity interval training would improve aerobic fitness (e.g. 𝑉̇ O2max) and lipid
oxidation during sub-maximal exercise, and reduce resting systolic blood pressure
and BMI in healthy male adolescents.
METHOD
Participants
Ten male 14-16 year old adolescents volunteered to take part in this study. The
participants were 15.1 ± 0.3 years old and 1.3 ± 0.2 years post estimated peak height
velocity. All participants and their parent(s)/guardian(s) provided informed assent
and consent respectively, to partake in the project, which was approved by the
institutional ethics committee. The participants were healthy, recreationally active,
and showed no contraindications to perform maximal exercise. In addition to their
weekly Physical Education classes, the participants were involved in 6.6 ± 3.0 hours
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of organised sports participation on a weekly basis (e.g. cycling, running, sailing,
cricket and swimming).
Experimental protocol
In line with related adolescent (Sperlich et al., 2011) or adult studies (Burgomaster,
et al., 2008; Gibala et al., 2006; Jacobs et al., 2013; Whyte, et al., 2010) investigating
high-intensity interval training, a control group was not employed in the current
study for two reasons: 1) changes in the outcomes variables due to growth and
maturation would be minimal over a 2 week period; 2) the participants refrained
from participating in their usual weekly organised sports activities during the study,
thus allowing the effect of the high-intensity interval training programme on the
outcome variables to be observed. All participants visited the laboratory on 10
separate occasions over a 3 week period, with at least 24 hours rest provided
between each visit. Visits 1 and 2 consisted of the pre-training outcome measures.
Subsequently, participants returned to the laboratory for six sessions of highintensity interval training (visits 3-8), before completing the post-training measures
(visits 9 and 10). For all visits the participants arrived at the laboratory in a rested
state and were requested to refrain from consuming food and caffeine for at least 2
hours prior to testing. All exercise tests were performed using a mechanically braked
cycle ergometer (Monark 827e/814e, Monark exercise AB, Sweden). The
participants were habituated to the test procedures and protocols during visits 1 and
2. This included cycling on the ergometer at a set cadence with gas exchange
measures, and attempting a number of short sprints (~ 5-10 s) in preparation for the
high-intensity interval training programme.
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Visits 1-2: Pre-training measures
On visit 1, body mass (Seca 899, GmBH & co, Germany), seated height and stature
(Harpenden Portable Stadiometer, Holtain, Wales) were measured to the nearest 0.1
kg and 0.1 cm respectively. Somatic maturity was estimated using sex specific
equations to predict age from peak height velocity to within ±1 y accuracy (Mirwald,
Baxter-Jones, Bailey, & Beunen, 2002):
Maturity Offset (years) = -9.236 + 0.0002708·Leg Length and Sitting Height
interaction -0.001663·Age and Leg Length interaction + 0.007216·Age and Sitting
Height interaction + 0.02292·Weight by Height ratio
R2 = 0.89, Standard Error of the Estimate = 0.59 years
A combined ramp and supra-maximal exercise test to exhaustion was employed to
determine 𝑉̇ O2max and the gas exchange threshold (Barker, Williams, Jones, &
Armstrong, 2011). A step-incremental test to exhaustion was undertaken whereby
power output increased at a rate of 21 W·min-1. Participants cycled at a cadence of
70 rev·min-1 and exhaustion was defined as a drop in cadence below 65 rev·min-1 for
5 consecutive seconds. Following a 15 min recovery, participants performed a supramaximal exercise bout to exhaustion at a power output corresponding to 105% of the
peak power achieved during the incremental test. The highest 15 s averaged 𝑉̇ O2
during the ramp or supra-maximal test was taken as 𝑉̇ O2max. The 𝑉̇ O2 at the gas
exchange threshold was identified as a disproportionate increase in expired carbon
dioxide (𝑉̇ CO2) relative to 𝑉̇ O2 and the ventilatory equivalents for 𝑉̇ O2 and 𝑉̇ CO2
(Wasserman, Hansen, Sue, Stringer, & Whipp, 2005).
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Participants returned to the laboratory ~ 48 hours after visit 1, for the meaurment of
blood pressure using a portable mercury sphygmomanometer (Dekamet, Accoson,
Essex, England) following 10 min of rest in the supine position. The median of three
measures was taken as the participant’s blood pressure. Subsequently, the
participants undertook a submaximal step-incremental exercise test to determine the
relationship between 𝑉̇ O2, heart rate and substrate utilisation during steady state
exercise. The exercise protocol started at 35W and increased in 3 min stages to
ensure 7-10 stages were completed prior to achieving ~ 80% of the participant’s
𝑉̇ O2max (Zakrzewski & Tolfrey, 2011). Prior to visit 2, participants were provided
with a food diary to record all the food and drink consumed during the day and were
requested to replicate this for the post-training measures. The food diaries were
assessed for total energy and macronutrient intake (CompEat Pro, Nutrition Systems,
UK).
Visits 3-8: High-intensity interval training programme
Training commenced 2-3 days following completion of the pre-training measures. In
line with the protocol originally described by Burgomaster et al. (2005), each
participant performed a total of six high-intensity interval training sessions over a 2
week period. The first training session included four repeated 30 s sprints (e.g.
Wingate anaerobic test), but this was progressed to include seven sprints on the final
training session. Each high-intensity interval training session was preceded by a 5
min warm-up. Participants performed unloaded cycling at 100 revolutions per
minute and were given a 5 s countdown prior to applying a resistance equivalent to
7.5% body mass (Barker & Armstrong, 2011). Participants were instructed to sprint
‘all out’ for 30 s and provided with 4 min of unloaded recovery at 70 revolutions per
8
minute between each sprint. Participants had at least 24 hours rest between each
training session and completed three sessions each week. Power output was recorded
in 1 s intervals, and used to determine peak power, mean power and fatigue index for
each sprint. Heart rate was recorded throughout each training session. Participants
received strong verbal encouragement during the training and completed this in
pairs.
Visits 9-10: Post-training measures
Post-testing measures were undertaken 2-3 days following completion of the highintensity interval training programme and followed the same procedures as outlined
for visits 1-2. The participants were provided with a copy of their food diary and
asked to replicate this prior to the substrate utilisation test.
Experimental measures
Pulmonary gas exchange and ventilation were determined at 15 s averages using a
commercially available system (Cortex Metalyzer II; Cortex Medical, Leipzig,
Germany) that was calibrated prior to each test. Heart rate was recorded using short
range radio telemetry (Polar Vantage NV, Polar Electro, Kempele, Finland).
Energy expenditure and absolute and relative contributions of fat and carbohydrate
oxidation during the sub-maximal incremental exercise test was estimated from the
mean 𝑉̇ O2 and respiratory exchange ratio (RER) over the final 30 s of each 3 min
stage using established equations (Frayn, 1983). Protein oxidation was assumed to be
negligible, and an RER >1 was taken to represent 100% carbohydrate oxidation. As
estimating lipid and carbohydrate oxidation via indirect calorimetry is valid up to ~
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85% 𝑉̇ O2max (Romijn, Coyle, Hibbert, & Wolfe, 1992), data that exceeded 80%
𝑉̇ O2max were not analysed. The maximal rate of fat oxidation and the point at which
this occurred relative to 𝑉̇ O2max (FatMax) was visually identified by two independent
investigators blinded to the participant and pre/post training measure. The visual
method was employed as it has been shown to be consistent with non-linear curve
fitting techniques (Zakrzewski & Tolfrey, 2011).
Statistical analyses
In line with recent statistical recommendations (Hopkins, Marshall, Batterham, &
Hanin, 2009), we used 90% confidence interval to calculate probabilistic magnitude
based inferences for the effect of high-intensity interval training on the outcome
variables. Using a published spreadsheet (Hopkins, 2007), the mean difference for
the outcome variable pre and post high-intensity interval training were calculated
with a 90% confidence interval to represent the uncertainty of the true effect. In the
absence of data concerning the smallest worthwhile change in the physiological
outcomes reported in the current study, Cohen’s (1988) standardised effect size (ES)
of 0.2 was employed, as recommended by Batterham and Hopkins (2006). Based on
the smallest worthwhile change, the spreadsheet calculated the probability that the
observed effect, captured using the 90% confidence interval, was either beneficial
(positive, higher, faster), trivial or harmful (negative, lower, slower). The following
probability thresholds were used to inform these decisions: <0.5%, most unlikely;
0.5-5%, very unlikely; 5-25%, unlikely; 25-75%, possibly; 75-95%, likely; 9599.5%, very likely; >99.5%, most likely (Batterham & Hopkins, 2006; Hopkins, et
al., 2009). If a ‘possibly’ effect was observed, the percentage contribution of the
majority of the distribution is provided. An effect was deemed to be trivial when the
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majority (>50%) of the 90% confidence interval lay between beneficial and harmful.
Conversely, an effect was deemed unclear when the likelihood of a beneficial and
harmful effect was >5%. Descriptive statistics were calculated using SPSS (version
19.0, Chicago, USA) and presented as mean ± SD.
RESULTS
HIT training
All participants completed the six high-intensity interval training sessions with no
adverse effects resulting in a 100% adherence to the programme. Figure 1 illustrates
the changes in peak power, mean power and the fatigue index over the initial four 30
s sprints during the first and final training session. Peak power output was
meaningfully higher in the final compared to the first high-intensity interval training
session for sprints 1 (very likely), 2 (very likely), 3 (most likely) and 4 (likely).
There were no meaningful changes in the mean power output between the highintensity interval training sessions for all sprints (unclear), but the fatigue index was
meaningfully elevated in sprints 1 (likely) and 3 (likely) during the final training
session. The participants attained a peak heart rate equivalent to ~ 90-95% maximum
during the high-intensity interval training sessions.
****Figure 1 near here****
Anthropometry, blood pressure and aerobic fitness
The effect of high-intensity interval training on the physical and aerobic fitness
variables are presented in Table 1. High-intensity interval training had no meaningful
effect on body mass or BMI (ES=0.03). Changes in systolic (ES=0.07) and diastolic
(ES=0.13) blood pressure were unclear. The high-intensity interval training
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programme had a possibly beneficial effect on 𝑉̇ O2max whether expressed in absolute
(73% beneficial, ES=0.30) or relative to body mass (71% beneficial, ES=0.30). In
addition, high-intensity interval training had a very likely beneficial effect on time to
exhaustion during the incremental cycle test (ES=3.99), which corresponded into a
beneficial effect on peak power, with four participants completing one additional
stage. Finally, high-intensity interval training had a possibly beneficial effect on the
gas exchange threshold when expressed in absolute terms (56% beneficial,
ES=0.23), but an unclear effect when expressed relative to 𝑉̇ O2max (ES=-0.05).
****Table 1 near here****
Sub-maximal substrate oxidation
The energy intake for the participants on the day of the substrate oxidation test both
pre and post high-intensity interval training was 689 ± 293 kcal, with a
macronutrient contribution of 57 ± 8% carbohydrate , 28 ± 10% fat and 15 ± 7%
protein. The steady-state physiological responses during the three initial stages of the
sub-maximal test are presented in Table 2. The high-intensity interval training
programme had a beneficial effect on sub-maximal 𝑉̇ O2 (69% beneficial, ES=-0.28),
energy expenditure (ES=-0.55), RER (ES=-0.61) and on the absolute oxidation of
lipid (ES=0.52) and carbohydrate (ES=-0.76). Consequently, there was a likely
beneficial effect on the percentage contribution of carbohydrate (pre: 72.9 ± 11.3 vs.
post: 62.7 ± 18.2%; change, 90% CL: -10.2%, ±8.4, ES=-0.62) and lipid (pre: 27.1 ±
11.3 vs. post: 37.3 ± 18.2%; change, 90% CL: 10.2%, ±8.4, ES=0.62) oxidation to
the total energy expenditure during sub-maximal exercise (Figure 2). While an
unclear effect was observed on the maximal rate of fat oxidation (pre: 0.28 ± 0.10 vs.
post: 0.32 ± 0.14 g·min-1; change 90% CL: 0.04 g·min-1, ±0.08, ES=0.34), FatMax
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was likely reduced (pre: 48.5 ± 14.3 vs. post: 39.5 ± 11.4 % 𝑉̇ O2max; change 90%
CL: -9.0, ±9.4, ES=-0.64). On average, the participants were able to complete 1.2 ±
1.5 (range -1 to 3) additional stages for the assessment of lipid metabolism following
high-intensity interval training.
****Table 2 near here****
****Figure 2 near here****
DISCUSSION
The novel findings from the current study are that 2 weeks of low volume, highintensity interval training in healthy adolescent boys: 1) had a beneficial effect on
parameters of aerobic function (e.g. 𝑉̇ O2max); 2) increased the contribution of fat
oxidation during sub-maximal steady state exercise; 3) had no effect on the maximal
rate of fat oxidation and reduced FatMax, and 4) had no effect on blood pressure or
BMI. This study therefore demonstrates for the first time that just six sessions of
high-intensity interval training over a 2 week period can have a beneficial effect on a
number of health related outcomes in adolescent boys.
In agreement with the original description of the high-intensity interval training
programme employed in the current study (Burgomaster, et al., 2005), the adolescent
boys completed all 6 sprints with no adverse side effects and resulted in an increase
in the peak, but not mean power output, and an increase in the fatigue index, from
the first to the last training session. Interestingly, this data contrasts cross sectional
evidence showing trained children and adolescents to exhibit an elevated peak
power, mean power and reduced fatigue index compared to untrained counterparts
(McNarry, Welsman, & Jones, 2011), whereas training studies have found increases
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in peak and mean power output but not the fatigue index (Bogdanis, Ziagos,
Anastasiadis, & Maridaki, 2007; Souissi et al., 2012).
The boys achieved ~ 90-95% of their maximal heart rate during each high-intensity
interval training session which is indicative of the large aerobic energy contribution
that has been reported during exercise of this type (Bogdanis, Nevill, Boobis, &
Lakomy, 1996; Hebestreit, Mimura, & Bar-Or, 1993). In the presence of this aerobic
stimulus, recent studies on healthy adults have shown that 𝑉̇ O2max (Burgomaster, et
al., 2008; Burgomaster, et al., 2005; McKay, Paterson, & Kowalchuk, 2009) or the
gas exchange threshold (McKay, et al., 2009) is not improved after ~10-14 days of
high-intensity interval training, but is after ~ 20-24 days. Our study extends this
evidence base, as a possibly beneficial effect on 𝑉̇ O2max (~ 5% increase) and 𝑉̇ O2 at
the gas exchange threshold (~ 5% increase) was observed after just 14 days of highintensity interval training in healthy adolescent boys. While this magnitude of the
improvement in 𝑉̇ O2max following 2-weeks of high-intensity interval training is only
marginally greater than the day to day reproducibility of measuring 𝑉̇ O2max in youth
(~ 4%, Welsman, Bywater, Farr, Welford, & Armstrong, 2005), this is either greater
(Williams, Armstrong, & Powell, 2000) or similar (Baquet, et al., 2010) to studies
using a running high-intensity interval training programme over 7-8 weeks in 8-11
year old boys. In contrast, using an 8 week high-intensity interval training protocol
consisting of seven 30 s maximal sprints at a power output corresponding to 𝑉̇ O2max,
McManus et al. (2005) reported a ~ 11% and 18% improvement in 𝑉̇ O2max and the
gas exchange threshold, respectively. Therefore, while the improvement in 𝑉̇ O2max
and the gas exchange threshold in the current study after just 2 weeks of highintensity interval training is in line with traditional aerobic endurance programmes
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lasting ~ 8-12 weeks in youth (Armstrong & Barker, 2011; Baquet, van Praagh, &
Berthoin, 2003), further improvements may be possible using Wingate-based highintensity interval training over a longer time frame.
Interestingly, we observed a reduction in the O2 cost to perform sub-maximal
exercise, and thus a reduction in energy expenditure, in the present study which has
not been identified in adult studies employing high-intensity interval training over a
2-4 week period (Burgomaster, et al., 2005; Gibala, et al., 2006; McKay, et al.,
2009). This finding is surprising as longer training interventions are typically
required to improve this parameter of aerobic function in adults (Jones & Carter,
2000), and previous high-intensity interval training and traditional aerobic endurance
training programmes in youth that improve 𝑉̇ O2max do not impact exercise economy
(Baquet et al., 2002; Rowland & Boyajian, 1995). While our finding of a reduced O2
cost of exercise following high-intensity interval training warrants further
investigation, coupled with the increase in 𝑉̇ O2max one would predict an improved
exercise tolerance, which was observed in the incremental test to exhaustion in the
current study. This is in agreement with a recent study on adolescent soccer players
where 5 weeks of high-intensity interval training improved both 𝑉̇ O2max and 1000 m
running performance (Sperlich, et al., 2011).
Unfortunately, we cannot provide mechanistic insight into the improvements in
aerobic function (𝑉̇ O2max, gas exchange threshold and exercise economy) in the
current study. However, a recent study on untrained adults employing a similar 2
week high-intensity interval training programme to current study observed
improvements in 𝑉̇ O2max and exercise performance alongside an increase in muscle
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oxidative capacity (cytochrome c oxidase activity) and muscle O2 extraction (Jacobs,
et al., 2013). Interestingly, changes in ‘central’ factors such as maximal cardiac
output, total haemoglobin and blood plasma volume were unaffected by 6 session of
high-intensity interval training (Jacobs, et al., 2013), suggesting ‘peripheral’
adaptations may be responsible for the findings in the current study. This notion is
corroborated by other adult work showing markers of mitochondrial biogenesis and
muscle buffering capacity to be enhanced following a short programme of highintensity interval training (Gibala, et al., 2012).
Studies in adults have shown that 2 weeks of high-intensity interval training
increases the capacity for lipid oxidation both at the muscle and whole body level
during sub-maximal exercise (Burgomaster, et al., 2008). This finding not only has
implications for performance, possibly through sparing muscle glycogen utilisation
(Burgomaster, et al., 2008), but also health, as a reduced capacity to oxidise lipid has
been implicated in the storage of intramuscular lipids (Kim, Hickner, Cortright,
Dohm, & Houmard, 2000) and body fat (Pagliassotti, Gayles, & Hill, 1997), and in
the development of insulin resistance (Corpeleijn, Saris, & Blaak, 2009). In the
current study we found high-intensity interval training to have a likely beneficial
effect on lipid oxidation (absolute and relative contribution) during sub-maximal
exercise, and a concomitant reduction in carbohydrate oxidation. Surprisingly, the
increase in lipid oxidation following high-intensity interval training did not translate
into an increase in the maximal rate of fat oxidation, which occurred at a lower
percentage of 𝑉̇ O2max post-training. However, on average the participants were able
to complete an additional 1.2 ± 1.5 stages during the sub-maximal test, indicating an
increased capacity to oxidise fat at higher power outputs following high-intensity
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interval training. While we are not aware of a previous study exploring the effect of
high-intensity interval training on lipid oxidation in healthy youth, our data agree
with a study showing sub-maximal lipid oxidation to be increased following 4 weeks
of aerobic endurance training in healthy children (Duncan & Howley, 1998).
Interestingly, studies on obese children have shown 2 months of continuous highintensity exercise training to reduce lipid oxidation (Brandou et al., 2005), whereas
training at an intensity corresponding to the maximal rate of fat oxidation increased
submaximal lipid oxidation and FatMax (Brandou, Dumortier, Garandeau, Mercier,
& Brun, 2003), suggesting high-intensity interval training may not be beneficial for
increasing lipid oxidation in obese youth.
Buchan et al. (2011) have recently demonstrated that after 7 weeks of high-intensity
interval training, both systolic blood pressure and BMI are reduced in healthy
adolescents. Although similar benefits have been reported in sedentary,
overweight/obese men following 2 weeks of high-intensity interval training (Whyte,
et al., 2010), we found no meaningful changes in blood pressure or BMI following 2
weeks of high-intensity interval training. This suggests that a longer programme of
high-intensity interval training may be needed to improve these outcomes, at least in
healthy, normal weight and normotensive youths. This conclusion is supported by a
recent review which concluded that a minimum of 12 weeks of high-intensity
interval training may be needed to reduce BMI and systolic blood pressure in adults
(Kessler, Sisson, & Short, 2012).
A limitation of the current study is the lack of a control group that would provide
comparative data for adolescents not undertaking the high-intensity interval training
17
programme. However, the lack of a control group is consistent with previous
adolescent (Sperlich, et al., 2011) or adult (Burgomaster, et al., 2008; Gibala, et al.,
2006; Jacobs, et al., 2013; Whyte, et al., 2010) high-intensity interval training
studies. Furthermore, we also did not compare the efficacy of high-intensity interval
training to moderate intensity exercise, which would enable a direct comparison
against current physical activity recommendations. Finally, we were unable to
determine the substrate oxidation under fasting conditions, but controlled for this by
having each participant monitor and replicate their diet on the day of the submaximal
substrate oxidation test.
CONCLUSIONS
The present study presents novel data showing that meaningful changes in health
outcomes are possible after just 6 sessions of high-intensity interval training,
equivalent to 16 min 30 s of high-intensity exercise, over a 2 week period.
Specifically, beneficial effects were observed on parameters of aerobic function and
lipid oxidation, but not for blood pressure and BMI. These findings therefore build
upon recent evidence showing that either a single bout of high-intensity exercise
(Burns, Oo, & Tran, 2012) or 7-8 weeks of low volume high-intensity interval
training (Buchan, et al., 2011; McManus, et al., 2005) have a beneficial effect on
health outcomes in youth. Given that children appear to prefer moderate intensity
exercise interspersed with bouts of high-intensity sprints compared to moderate
intensity exercise alone (Crisp, Fournier, Licari, Braham, & Guelfi, 2012), and that
the majority of young people fail to achieve current physical activity
recommendations, further work is needed to address the feasibility and efficacy of
18
using low volume high-intensity interval training to improve health outcomes in
youth.
ACKNOWLEDGEMENTS
We thank the staff and participants at Sidmouth Community College and the staff at
Sidmouth Leisure Centre for their participation in this project.
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23
Table 1. The effect of 2-weeks of high-intensity interval training on physical, blood
pressure and aerobic fitness outcomes
Variable
Pre-training
Post-training
Effect,
±90% CI
0.2, ±0.4
Inference
Body mass
66.3 ± 11.9
66.5 ± 11.6
Trivial
(kg)
BMI
21.5 ± 2.6
21.6 ± 2.4
0.1, ±0.1
Trivial
(kg·m2)
SBP
115 ± 10
116 ± 12
1, ±4
Unclear
(mmHg)
DBP
65 ± 10
67 ± 15
2, ±6
Unclear
(mmHg)
3.49 ± 0.60
3.68 ± 0.53
0.19, ±0.19 Possibly beneficial
𝑉̇ O2max
-1
(L·min )
53.5 ± 8.3
56.2 ± 8.2
2.7, ±2.9
Possibly beneficial
𝑉̇ O2max
-1
-1
(mL·kg ·min )
TTE
11.0 ± 0.7
11.9 ± 0.5
0.9, ±0.7
Very likely
(min)
beneficial
Peak power
253 ± 39
259 ± 34
6, ±13
Possibly beneficial
(W)
GET
1.86 ± 0.34
1.95 ± 0.35
0.09, ±0.13 Possibly beneficial
-1
(L·min )
GET
53 ± 6
53 ± 7
0, ±2
Unclear
̇
(%𝑉 O2max)
Pre- and post-training data are expressed as mean ± SD. BMI, body mass index;
SBP, systolic blood pressure; DBP, diastolic blood pressure; TTE, time to
exhaustion; GET, gas exchange threshold.
Effect, represents the magnitude of the change by subtracting post-training from pretraining. 90% confidence interval (CI), represents the uncertainty of the observed
effect.
Inference, represents the probabilistic inference that the magnitude of the observed
effect is different from the smallest worthwhile change using Cohen’s standardized
effect of 0.2 (see methods for details).
24
Table 2. The effect of high-intensity interval training on the steady-state
physiological responses during the initial three stages during the sub-maximal
exercise test
Variable
Pre-training
Post-training
Possibly beneficial
35.8 ± 4.4
Effect,
±90% CI
-0.04,
±0.04
-3.3, ±2.37
𝑉̇ O2
(L·min-1)
𝑉̇ O2
(%𝑉̇ O2)
Heart rate
(beats·min-1)
RER
1.34 ± 0.12
1.30 ± 0.14
39.1 ± 5.3
Inference
116 ± 10
111 ± 5
-4, ±7
Unclear
0.91 ± 0.04
0.88 ± 0.06
Likely beneficial
-0.03,
Likely beneficial
±0.03
EE
6.86 ± 0.56
6.48 ± 0.68
-0.37,
Very likely
(kcal·min-1)
±0.18
beneficial
Fat oxidation
0.21 ± 0.07
0.26 ± 0.12
0.06,
Likely beneficial
(g·min-1)
±0.06
CHO oxidation
1.27 ± 0.22
1.04 ± 0.33
-0.23,
Very likely
-1
(g·min )
±0.14
beneficial
Pre- and post-training data are expressed as mean ± SD. RER. Respiratory exchange
ratio; EE, energy expenditure; CHO, carbohydrate.
See table 1 for a description of the statistical outcomes.
25
FIGURE CAPTIONS
Figure 1. Changes in peak power (A), mean power (B) and the fatigue index (C) over
the sprints 1-4 in the first (open bars) and last (closed bars) high-intensity interval
training session. Where * denotes a meaningful difference between the bout. See the
text for details.
Figure 2. Changes in the percentage contribution of carbohydrate (closed bars) and
lipid (open bars) to total energy expenditure during sub-maximal exercise pre and
post high-intensity interval training. See text for details.