Skeletal muscle ﬁber-type-speciﬁc changes in markers of
capillary and mitochondrial content after low-volume
interval training in overweight women
, Joshua P. Nederveen
, Jenna B. Gillen
, Sophie Joanisse
, Gianni Parise
Mark A. Tarnopolsky
& Martin J. Gibala
1 Department of Kinesiology, McMaster University, Hamilton, ON, Canada
2 Pediatrics and Medicine, McMaster University, Hamilton, ON, Canada
angiogenesis, capillarization, COXIV, high-
intensity interval exercise, oxidative capacity.
Martin J. Gibala, Department of Kinesiology,
Ivor Wynne Centre, Rm 219, McMaster
University, 1280 Main St. West, Hamilton,
ON L8S 4K1, Canada.
Tel: 905-525-9140 ext. 23591
This project was supported by Natural
Sciences and Engineering Research Council
(NSERC) operating grants to MJG and GP.
Received: 14 October 2017; Revised: 29
December 2017; Accepted: 3 January 2018
Physiol Rep, 6 (5), 2018, e13597,
High-intensity interval training (HIIT) enhances skeletal muscle oxygen deliv-
ery and utilization but data are limited regarding ﬁber-speciﬁc adaptations in
humans. We examined the effect of 18 sessions of HIIT (10 9 60-sec cycling
intervals at ~90% HR
, interspersed by 60-sec of recovery) over 6 weeks on
markers of microvascular density and oxidative capacity in type I and II ﬁbers
in healthy but sedentary young women (Age: 26 Æ 7 years; BMI:
30 Æ 4kgÁm
: 2.16 Æ 0.45 LÁm
). Immunohistochemical analyses
of muscle cross sections revealed a training-induced increase in capillary con-
tacts per ﬁber in type I ﬁbers (PRE: 4.38 Æ 0.37 vs. POST: 5.17 Æ 0.80; main
effect, P < 0.05) and type II ﬁbers (PRE: 4.24 Æ 0.55 vs. POST: 4.92 Æ 0.54;
main effect, P < 0.05). The capillary-to-ﬁber ratio also increased after training
in type I ﬁbers (PRE: 1.53 Æ 1.44 vs. POST: 1.88 Æ 0.38; main effect,
P < 0.05) and type II ﬁbers (PRE: 1.45 Æ 0.19 vs. POST: 1.76 Æ 0.27; main
effect, P < 0.05). Muscle oxidative capacity as reﬂected by the protein content
of cytochrome oxidase IV also increased after training in type I ﬁbers (PRE:
3500 Æ 858 vs. POST: 4442 Æ 1377 arbitrary units; main effect, P < 0.01)
and type II ﬁbers (PRE: 2632 Æ 629 vs. POST: 3863 Æ 1307 arbitrary units;
main effect, P < 0.01). We conclude that short-term HIIT in previously inac-
tive women similarly increases markers of capillary density and mitochondrial
content in type I and type II ﬁbers.
Interval training is characterized by intermittent periods
of relatively intense exercise and recovery within a single
exercise session. The method can be broadly classiﬁed
into two categories: high-intensity interval training (HIIT)
involves intense but submaximal efforts that elicit ≥80%
of maximal heart rate (HR
), whereas sprint-interval
training (SIT) refers to “supramaximal” efforts performed
in an all-out manner or at an intensity that elicits ≥100%
of peak aerobic capacity (VO
) (Weston et al. 2014).
SIT and HIIT can elicit physiological adaptations compa-
rable to or even superior than moderate-intensity
continuous training (MICT), including indices of skeletal
muscle oxygen delivery (Cocks et al. 2013) and utilization
(Burgomaster et al. 2008; Little et al. 2010), despite
reduced total exercise volume and time commitment.
Limited data are available regarding potential muscle
ﬁber-type-speciﬁc responses to interval training in
humans and most have employed SIT interventions.
Scribbans et al. (2014) showed that 6 weeks of SIT, using
a protocol that involved 8 9 20-sec cycling efforts at a
workload equivalent to ~170% VO
with 10-sec recov-
ery, increased oxidative capacity in type I and type II
ﬁbers as reﬂected by the protein content of succinate
dehydrogenase (SDH) (Scribbans et al. 2014). Cocks et al.
ª 2018 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of
The Physiological Society and the American Physiological Society.
This is an open access article under the terms of the Creative Commons Attribution License,
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2018 | Vol. 6 | Iss. 5 | e13597
Physiological Reports ISSN 2051-817X