Is high-intensity interval training a time-efficient exercise strategy to improve health and fitness?

Abstract

Growing research suggests that high-intensity interval training (HIIT) is a time-efficient exercise strategy to improve cardiorespiratory and metabolic health. "All out" HIIT models such as Wingate-type exercise are particularly effective, but this type of training may not be safe, tolerable or practical for many individuals. Recent studies, however, have revealed the potential for other models of HIIT, which may be more feasible but are still time-efficient, to stimulate adaptations similar to more demanding low-volume HIIT models and high-volume endurance-type training. As little as 3 HIIT sessions per week, involving ≤10 min of intense exercise within a time commitment of ≤30 min per session, including warm-up, recovery between intervals and cool down, has been shown to improve aerobic capacity, skeletal muscle oxidative capacity, exercise tolerance and markers of disease risk after only a few weeks in both healthy individuals and people with cardiometabolic disorders. Additional research is warranted, as studies conducted have been relatively short-term, with a limited number of measurements performed on small groups of subjects. However, given that "lack of time" remains one of the most commonly cited barriers to regular exercise participation, low-volume HIIT is a time-efficient exercise strategy that warrants consideration by health practitioners and fitness professionals.

Full text

CLINICAL CORNER
Is high-intensity interval training a time-efficient exercise
strategy to improve health and fitness?
Jenna B. Gillen and Martin J. Gibala
Abstract: Growing research suggests that high-intensity interval training (HIIT) is a time-efficient exercise strategy to improve
cardiorespiratory and metabolic health. “All out” HIIT models such as Wingate-type exercise are particularly effective, but this
type of training may not be safe, tolerable or practical for many individuals. Recent studies, however, have revealed the potential
for other models of HIIT, which may be more feasible but are still time-efficient, to stimulate adaptations similar to more
demanding low-volume HIIT models and high-volume endurance-type training. As little as 3 HIIT sessions per week, involving
≤10 min of intense exercise within a time commitment of ≤30 min per session, including warm-up, recovery between intervals
and cool down, has been shown to improve aerobic capacity, skeletal muscle oxidative capacity, exercise tolerance and markers
of disease risk after only a few weeks in both healthy individuals and people with cardiometabolic disorders. Additional research
is warranted, as studies conducted have been relatively short-term, with a limited number of measurements performed on small
groups of subjects. However, given that “lack of time” remains one of the most commonly cited barriers to regular exercise
participation, low-volume HIIT is a time-efficient exercise strategy that warrants consideration by health practitioners and
fitness professionals.
Key words: interval training, exercise intensity, training adaptations.
Résumé : De plus en plus d’études suggèrent que la méthode d’entraînement par intervalle de haute intensité (« HIIT ») est
économique en matière de temps investi pour l’amélioration de la santé cardiorespiratoire et métabolique. Les approches « a
`
fond de train » comme les exercices de type Wingate sont particulièrement efficaces, mais ce mode d’entraînement n’est
peut-être pas sécuritaire, facile a
`tolérer et pratique pour bien des individus. Des études récentes révèlent le potentiel d’autres
modèles HIIT Oapparemment plus pratiques et aussi efficaces Opour susciter des adaptations similaires aux plus exigeants
modèles HIIT a
`faible volume et d’entraînement en endurance a
`haut volume. À raison d’aussi peu que trois séances HIIT par
semaine comprenant ≤ 10 min d’exercice intense dans une séance de ≤ 30 min incluant l’échauffement, la récupération entre les
intervalles et le retour au calme, on améliore la capacité aérobie, la capacité oxydative du muscle squelettique, la tolérance a
`
l’effort et les marqueurs du risque de maladie, et ce, après seulement quelques semaines tant chez des individus en bonne santé
que chez des personnes aux prises avec des troubles cardiométaboliques. Il faut réaliser d’autres études, car celles qui ont été
effectuées présentaient des résultats a
`court terme avec un nombre limité de mesures enregistrées auprès de petits groupes
de sujets. Cependant, « le manque de temps » étant l’argument généralement évoqué comme obstacle a
`la pratique régulière de
l’activité physique, un programme HIIT a
`faible volume constitue une approche efficace que devraient prendre en compte les
praticiens de la santé et les professionnels de la condition physique. [Traduit par la Rédaction]
Mots-clés : entraînement par intervalle, intensité de l’exercice, adaptations a
`l’entraînement.
Current physical activity guidelines including those from the
Canadian Society for Exercise Physiology (CSEP) recommend
that adults should accumulate at least 150 min of moderate- to
vigorous-intensity aerobic physical activity per week to achieve
health benefits (Tremblay et al. 2011). The CSEP guidelines do not
specifically define intensity ranges; however, guidelines from
other agencies, including the American College of Sports Medi-
cine, classify moderate intensity as 64%–76% of maximal heart
rate (HR
max
) (46%–63% of maximal oxygen uptake (V
˙O
2max
)) and
vigorous intensity as 77%–95% of HR
max
(64%–90% V
˙O
2max
)(Garber
et al. 2011). While public health guidelines are based on very
strong scientific evidence, accelerometer data indicate that as
many as 85% of Canadians do not meet the minimum physical
activity recommendations (Colley et al. 2011) with “lack of time”
being one of the most commonly cited barriers to regular partic-
ipation (Trost et al. 2002). Recent evidence from relatively small,
short-term studies suggests that high-intensity interval training
(HIIT) may be as effective as traditional moderate-intensity con-
tinuous training to induce physiological remodelling, which in
turn may be associated with improved health markers, despite a
reduced time commitment.
What is HIIT?
HIIT is characterized by brief, repeated bursts of relatively in-
tense exercise separated by periods of rest or low-intensity exer-
cise. “Low-volume” HIIT refers to exercise training sessions that
are relatively brief Oconsisting of ≤10 min of intense exercise
within a training session lasting ≤30 min including warm-up,
recovery periods between intervals and cool down Osuch that
the total weekly exercise and training time commitment is re-
duced compared with current public health guidelines. One of the
most common models employed in low-volume HIIT studies is the
Wingate Test, which consists of 30 s of “all-out” cycling against a
Received 30 April 2013. Accepted 21 September 2013.
J.B. Gillen and M.J. Gibala.* Department of Kinesiology, McMaster University, 1280 Main St. West, Hamilton, ON L8S 4K1, Canada.
Corresponding author: Martin J. Gibala (e-mail: gibalam@mcmaster.ca).
*All editorial decisions for this paper were made by Michelle Porter and Terry Graham.
409
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high resistance on a specialized cycle ergometer. A typical train-
ing session consists of 4–6 repetitions interspersed by ⬃4 min of
recovery. As little as 6 sessions of this type of training over 2 weeks
robustly increases skeletal muscle oxidative capacity, as reflected
by the maximal activity and (or) protein content of various mito-
chondrial enzymes (Burgomaster et al. 2005,2006;Gibala et al.
2006), in healthy individuals who were previously sedentary or
active on a recreational basis. A 6-week program increased V
˙O
2max
and induced cardiovascular and skeletal muscle remodelling sim-
ilar to a traditional endurance training program that was modeled
on current public health guidelines, despite a ⬃90% difference in
training volume (Burgomaster et al. 2007,2008), and markedly
lowered total time commitment (Table 1). Other studies have
shown that short-term Wingate-based HIIT protocols improve in-
sulin sensitivity, measured using oral glucose tolerance tests in
young healthy men (Babraj et al. 2009;Metcalfe et al. 2011) and
overweight/obese individuals (Whyte et al. 2010), as well as using
the gold standard hyperinsulinemic euglycemic clamp method in
recreationally active men and women (Richards et al. 2010). Trapp
and colleagues (2008) also reported significant fat loss in young
women following 15 weeks of low-volume HIIT, which consisted
of 8-s all-out sprints followed by 12 s of recovery for 20 min. The
same HIIT protocol performed for 12 weeks reduced whole-body
fat mass and increased lean mass in the legs and trunk in over-
weight young men (Heydari et al. 2012b).
Modified low-volume HIIT protocols
All-out HIIT protocols are effective; however, considering the
need for specialized equipment and the extremely high level of
subject motivation, this form of training may not be safe, tolera-
ble or practical for many individuals. Recent studies have also
revealed the potential for other models of HIIT, which may be
more feasible but are nonetheless time-efficient compared with
traditional public health guidelines, to stimulate adaptations sim-
ilar to more demanding low-volume HIIT models as well as
relatively high-volume endurance-type training (Table 1). For ex-
ample, a model that we have employed consists of 10 × 1-min
cycling efforts at an intensity eliciting ⬃85%–90% of HR
max
inter-
spersed with 1 min of recovery. The protocol is still relatively
time-efficient in that a single training session consists of only
10 min of vigorous exercise within a 25-min training session in-
cluding warm-up, recovery periods between intervals and cool
down. This model has been applied in studies of young healthy
individuals (Little et al. 2010), as well as overweight/obese individ-
uals (Gillen et al. 2013), older sedentary adults who may be at
higher risk for cardiometabolic disorders (Hood et al. 2011), and
patients with coronary artery disease (CAD) (Currie et al. 2013) and
type 2 diabetes (T2D) (Little et al. 2011).
Short-term studies employing continuous glucose monitoring
have shown that the modified 10 × 1-min model reduced 24-h
blood glucose concentration in people with T2D when measured
immediately after a single bout (Gillen et al. 2012) as well as 72 h
following a 2-week training intervention (Little et al. 2011). Mean
ratings of perceived exertion measured in the latter study were
⬃7 on a 10-point scale, suggesting the stimulus was manageable
for subjects. Another recent study found that 10 × 1-min HIIT
performed 2 times per week for 12 weeks improved arterial endo-
thelial function (assessed by flow mediated dilation) and V
˙O
2max
in patients with CAD to the same extent as performing ⬃40 min of
continuous cycling at 60% peak power output per session (Currie
et al. 2013). In addition, Boutcher (2011) recently reviewed poten-
tial mechanisms that may mediate changes in body composition
following HIIT, one of which has been speculated to include re-
peated, transient elevations in postexercise oxygen consumption
over the course of training (Hazell et al. 2012). While the findings
from these small pilot projects are intriguing, large scale investi-
gations with appropriate participant screening and monitoring
are clearly warranted, including randomized clinical trials to
directly compare low-volume HIIT versus traditional endur-
ance training in a comprehensive manner, especially in those
with, or at risk for, cardiometabolic disorders.
How low can you go?
A modified Wingate-based HIIT protocol that consisted of 4 ×
10 s all out sprints induced improvements in aerobic and anaero-
bic performance that were comparable toa4×30-s protocol
(Hazell et al. 2010). Another study by Metcalfe et al. (2011) showed
that a protocol consisting of 2 × 20-s all-out sprints, included
within a 10-min bout of primarily low-intensity cycling, improved
V
˙O
2max
after 6 weeks of training (18 total sessions). Interestingly,
while V
˙O
2max
improved in both men and women, insulin sensitiv-
ity measured using oral glucose tolerance tests was only improved
in men (Metcalfe et al. 2011). These findings suggest that provided
exercise is performed using an all-out effort, it may be possible to
confer benefits using protocols that are even more time-efficient
than employed in previous Wingate-based HIIT studies. There is
insufficient evidence at present to make sweeping recommenda-
tions, however, and as alluded to earlier, the effort required with
this type of training and need for specialized equipment may
make it impractical for many individuals. When it comes to low-
volume HIIT protocols, there may be a trade-off between relative
work intensity and the time required to stimulate adaptations,
and this remains a fruitful area of future investigation.
Conclusion and recommendations
While far from definitive, growing evidence suggests that train-
ing using brief repeated bursts of relatively intense exercise can
be an effective strategy to improve fitness and health. Most of the
low-volume HIIT studies have employed a cycling model but other
models of traditional whole-body exercise are also likely to be
effective, e.g., climbing stairs, brisk uphill walking or running.
One recent study found that subjects who trained using 1 set of 8 ×
20 s of a single exercise (burpees, jumping jacks, mountain climb-
ers, or squat thrusts) interspersed by 10 s of rest per session,
4 times per week for 4 weeks increased V
˙O
2max
to the same extent
as a group who performed 30 min of traditional endurance train-
ing per session (McRae et al. 2012). It is possible that the very
intense nature of HIIT stimulates rapid changes, whereas adapta-
tions induced by traditional endurance training may occur more
slowly. As with the initiation of any new exercise program, it is
important to undergo proper screening procedures, which in-
cludes completion of an evidence-based screening form such as
the Physical Activity Readiness Questionnaire Plus as well as
medical clearance especially for those who may be at risk for or
afflicted by chronic diseases such as diabetes or cardiovascular
disease (Warburton et al. 2011). It may also be prudent to include a
preconditioning phase of training consisting of more traditional
moderate-intensity aerobic exercise prior to initiating HIIT (e.g.,
20–30 min per session, a few times per week for several weeks), as
it has been shown that a baseline level of fitness is a cardiopro-
tectant and reduces the risks associated with exercise-induced
ischemic events (Thompson et al. 2007). One recent study reported
that HIIT was perceived to be more enjoyable compared with
moderate-intensity continuous exercise training, at least in young
active men (Bartlett et al. 2011), but relatively little is known re-
garding the feasibility of implementing HIIT into individual exer-
cise prescriptions outside of a laboratory setting. It is also
important to note that it may be favourable to include variety in
one’s exercise program in terms of type, intensity and duration
rather than training with only 1 form of exercise. Additional work
is clearly warranted to comprehensively evaluate the long-term
health benefits associated with low-volume HIIT in comparison
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Table 1. Summary of adaptations following 2, 6 and 12–15 weeks of low-volume high-intensity interval training (HIIT).
Protocol Time/session 2 wk 6 wk 12–15 wk
Wingate HIIT (four to six
30-s sprints; 4-min
recovery)
⬃20 min 1V
˙O
2max
(Whyte et al. 2010;Hazell et al. 2010;
Astorino et al. 2012)
1V
˙O
2max
(Burgomaster et al. 2007,2008;Astorino
et al. 2012)
1250, 750 kJ and 5 km TT performance
(Burgomaster et al. 2005;Gibala et al. 2006;
Hazell et al. 2010)
1250 kJ TT performance (Burgomaster et al. 2007)
1Wingate PPO and MPO (Burgomaster et al. 2005;
Whyte et al. 2010;Hazell et al. 2010)
1Wingate PPO and MPO (Burgomaster et al. 2008)
1Resting muscle glycogen content (Burgomaster
et al. 2005)
1Resting muscle glycogen content and 2glycogen
utilization during exercise (Burgomaster et al. 2008)
1Maximal activity of CS and COX (Burgomaster et al.
2005,2006;Gibala et al. 2006)
1Maximal activity of CS and ␤-HAD (Burgomaster
et al. 2008)
1COXII and COXIV protein content (Gibala et al.
2006)
1GLUT4, PDH and COXIV protein content
(Burgomaster et al. 2007,2008)
1IS (Cederholm Index and GIR) (Babraj et al. 2009;
Richards et al. 2010)
1Whole-body fat oxidation and 2CHO oxidation
during exercise (Burgomaster et al. 2008)
2OGTT glucose and insulin AUC (Babraj et al.
2009;Richards et al. 2010)
1Peripheral arterial compliance (Rakobowchuck
et al. 2008)
1Resting fat oxidation 24 h post-training (Whyte
et al. 2010)
1Endothelial function (Rakobowchuck et al. 2008)
2SBP 24-h post-training (Whyte et al. 2010)
Modified HIIT (10×1min
sprints at ⬃90% HR
max
;
1 min recovery)
20 min 150 and 750 kJ TT performance (Little et al. 2010)1V
˙O
2max
(Gillen et al. 2013)1V
˙O
2max
in CAD patients (Currie et al.
2013)
1W
max
in T2D patients (Little et al. 2011)1W
max
(Gillen et al. 2013)
1Maximal activity of CS and COX (Little et al.
2010,2011;Hood et al. 2011)
1Maximal activity of CS and ␤-HAD (Gillen et al.
2013)
1COXIV and GLUT4 protein content (Little et al.
2010,2011;Hood et al. 2011)
1GLUT4 protein content (Gillen et al. 2013)
2Fasting [insulin] (Hood et al. 2011)2Whole-body and abdominal fat mass (Gillen et al.
2013)
1Endothelial function in CAD patients
(Currie et al. 2013)
1IS (HOMA) (Hood et al. 2011)1Leg and gynoid fat-free mass (Gillen et al. 2013)
1Glycemic control in T2D patients (Little et al. 2011)
10×6sall-out sprints;
60 s recovery (2 wk)
10 min 110 km TT performance (Jakeman et al. 2012)1V
˙O
2max
(Metcalfe et al. 2011)
10 min at 60 W with two
20 s all out sprints (6 wk)
1IS (Cederholm Index) in males only (Metcalfe
et al. 2011)
8 s sprint at 120 rpm;
12 s recovery at 40 rpm.
Workload ⬃90% HR
max
20 min 1V
˙O
2max
(Trapp et al. 2008;Heydari
et al. 2012b)
2Whole-body abdominal and trunk fat
mass (Trapp et al. 2008;Heydari et al.
2012b)
1Whole-body leg and trunk fat free
mass (Trapp et al. 2008)
1Resting fat oxidation (Trapp et al. 2008)
2Fasting [insulin] and insulin resistance
(HOMA-IR) (Trapp et al. 2008)
2Arterial stiffness, systolic and
diastolic BP (Heydari et al. 2012a)
Note: Training adaptations were measured ≥72 h following the last training session unless otherwise specified. Most studies were conducted in recreationally active or sedentary healthy men and women, except
for those in overweight men and women (Whyte et al. 2010;Trapp et al. 2008;Heydari et al. 2012a,2012b;Gillen et al. 2012), patients with type 2 diabetes (T2D) (Little et al. 2011), patients with coronary artery disease
(CAD) (Currie et al. 2013) or triathletes (Jakeman et al. 2012). V
˙O
2max
, maximal oxygen uptake; TT, time trial; PPO, peak power output; MPO, mean power output; CS, citrate synthase; COX, cytochrome c oxidase; ␤-HAD,
beta hydroxydehydrogenase; GLUT4, glucose transporter 4; PDH, pyruvate dehydrogenase; IS, insulin sensitivity; GIR, glucose infusion rate; CHO, carbohydrate; OGTT, oral glucose tolerance test; AUC, area under the
curve; SBP, systolic blood pressure; HR
max
, maximal heart rate; W
max
, maximal workload in watts; HOMA, Homeostasis Model of Assessment; BP, blood pressure.
Gillen and Gibala 411
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with traditional exercise training guidelines, and clarify the rela-
tive importance of exercise intensity versus duration for improv-
ing cardiorespiratory and metabolic fitness.
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