ShambrookP, etal. BMJ Open Sport Exerc Med 2018;4:e000470. doi:10.1136/bmjsem-2018-000470
as no studies measured glucose regulation at both time
points, and few studies evaluated insulin sensitivity 36–48
hours after the final exercise bout. Regardless, the find-
ings might suggest that aerobic exercise needs to be
completed at least every second day, with data from Davey
and colleagues reporting insulin sensitivity was increased
24 hours after the final session but had returned to near
normal levels after 5 days.47 This of course might be
dependent on the mode and/or intensity of exercise.
While no change was reported for glycaemic regulation
following continuous exercise at ~75%
24 hours or 14 days following the final exercise bout,48
significant improvements were reported 24 hours and
14 days after the final supramaximal intensity interval
training exercise bout.26 It is possible that the inherent
differences of exercise intensity and session duration are
significant contributing factors to changes in glycaemic
control and regulation. Along with the broad variations
in exercise intensity noted, the duration of each exercise
session also ranged from 30 min to 90 min. Longer dura-
tion exercise provides the opportunity for an increased
number of muscle contractions, and thus possibly greater
energy requirements, which might lead to greater glucose
The evidence presented in this review is of low-to-mod-
erate quality largely due to randomisation methods not
clearly outlined, or difficulties in blinding participants
and assessors. Additionally, wide variations in the exercise
interventions employed in terms of frequency, intensity,
time and type contributed to substantial levels of hetero-
geneity. Despite the growing interest in high-intensity
interval training, only four studies have implemented this
type of intervention for at least 6 weeks with the purpose
of improving metabolic health in people without meta-
bolic health dysfunction.26 32 44 45 Interval training is an
area of exercise prescription that guidelines have not
yet adequately considered and presents an opportunity
for new investigation. The lack of consistent outcome
measures also meant that only 16 of 56 RCT studies
were able to be included in some of the meta-analyses.
Opportunities exist for future research to use a more stan-
dardised approach to determine how best to accumulate
exercise in multiple bouts throughout a day to improve
or prevent the decline of metabolic function among indi-
viduals without known metabolic dysfunction. However,
this requires broad agreement on individual components
of the exercise prescription; frequency, intensity, time
It is uncertain whether exercise accumulated throughout
a day is as, or more, effective than single-bout exercise to
reduce the risk of developing metabolic disease in insuf-
ficiently active, young to middle-aged adults. However,
based on the findings from a single study, it might not be
worse. This review supports the general observation that
glycaemic control (as measured by HbA1c) improves with
at least 30 min of continuous exercise, even among adults
with glycaemic control below the diagnostic threshold
for T2DM. It is not clear whether exercise training
programmes provide additive effects on glycaemic regu-
lation, as outcomes are only regularly measured up to 48
hours after the final exercise bout. Regular single bouts
of exercise, whether of moderate-intensity or high-inten-
sity, have a clear benefit for regulating glucose for up to
48 hours after the final exercise bout, despite potentially
inducing different degrees of glycaemic control.
Acknowledgements The authors would like to thank Paul Xanthos who provided
technical support for the project.
Contributors PS, MIK, NT, BAG: contributed to the development of the research
questions, study design and literature search strategy. PS: conducted the literature
search. PS, MIK, NT, BAG: reviewed articles and performed study selection. PS, BG:
performed methodological quality assessment and data extraction. PS, MIK, NT,
BAG: contributed to data interpretation. PS: drafted the manuscript. MIK, NT, BAG:
provided critical review. All authors read and approved the nal manuscript.
Funding PS was supported by an Australian Government Research Training
Program Scholarship. The authors have not declared any other grant from any
funding agency in the public, commercial or not-for-prot sectors.
Competing interests None declared.
Patient consent Not required.
Provenance and peer review Not commissioned; internally peer reviewed.
Open access This is an open access article distributed in accordance with the
Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which
permits others to distribute, remix, adapt, build upon this work non-commercially,
and license their derivative works on different terms, provided the original work is
properly cited, appropriate credit is given, any changes made indicated, and the
use is non-commercial. See: http:// creativecommons. org/ licenses/ by- nc/ 4. 0/
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