INTRODUCTION
Lifestyle-induced chronic diseases significantly
alter the quality of life of sufferers. In many cases,
the disease itself can be potentially avoided or
successfully managed with appropriate lifestyle
modifications.1 Diseases such as type II diabetes,
atherosclerotic cardiovascular disease and the metabolic
syndrome are closely related and often stem
from the same preventable risk factors. Therapy for
most chronic diseases involves exercise training to
slow or reverse disease progression. Despite the
known benefits of regular moderate-intensity exercise
in regulating risk factors in chronic disease, the
majority of patients are still physically inactive.2
Rehabilitation for cardiac patients prior to the
1950s comprised abstention from all forms of
physical activity. This was thought to diminish the
cardiac load and assist in the reparative process of
the healing myocardial scar.3 Levine and Lown4
appear to be the first to document challenging the
idea of complete immobilisation by introducing the
then controversial ‘armchair treatment’ where
patients were encouraged to sit in an armchair as
much as possible during hospitalisation postmyocardial
infarction. When the weight of evidence
suggesting the benefits of light-to-moderate activity
in patients with chronic disease became irrefutable,
exercise guidelines were created for this population.5
Interval training appears to have been first
studied in cardiac rehabilitation in 1972, when
patients were asked to cycle at high workloads for
60 s with a 30 s rest between intervals. Using the
intervals, the patients were able to exercise for at
least twice as long as what they were able to do
when cycling continuously.6 In 1977, a study on
healthy participants examined the effects of a
10-week programme which included a combination
of interval and moderate continuous training.
Interestingly, the authors found a linear increase in
augmenting maximal oxygen uptake (VO2max)
over 10 weeks, contrary to the study’s hypothesis
that VO2 would plateau over time.7 In 1979, it was
suggested that high-intensity exercise was required
to provoke the necessary training adaptations
needed to improve exercise capacity in patients
with recent myocardial infarctions.8 One of the
first studies to investigate intense exercise in
patients with cardiovascular disease found that if
the exercise is intense and prolonged enough, then
it can instigate a reduction in myocardial ischaemia.9
These findings were revolutionary, as they
were established before widespread percutaneous
coronary interventions were performed. From
there, differing study protocols in the 1980 s and
1990 s in cardiac patients led to conflicting findings
that appear to have decreased the interest in this
approach.10–12 Forty years after the first reported
use of interval training in cardiac patients, the
interest in high-intensity interval training (HIIT) in
higher risk patients has now led to a number of
studies in this area.