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REVIEW ARTICLE
Strategies to Improve Running Economy
Kyle R. Barnes •Andrew E. Kilding
ÓSpringer International Publishing Switzerland 2014
Abstract Running economy (RE) represents a complex
interplay of physiological and biomechanical factors that is
typically defined as the energy demand for a given velocity
of submaximal running and expressed as the submaximal
oxygen uptake (VO
2
) at a given running velocity. This
review considered a wide range of acute and chronic
interventions that have been investigated with respect to
improving economy by augmenting one or more compo-
nents of the metabolic, cardiorespiratory, biomechanical or
neuromuscular systems. Improvements in RE have tradi-
tionally been achieved through endurance training.
Endurance training in runners leads to a wide range of
physiological responses, and it is very likely that these
characteristics of running training will influence RE.
Training history and training volume have been suggested
to be important factors in improving RE, while uphill and
level-ground high-intensity interval training represent fre-
quently prescribed forms of training that may elicit further
enhancements in economy. More recently, research has
demonstrated short-term resistance and plyometric training
has resulted in enhanced RE. This improvement in RE has
been hypothesized to be a result of enhanced neuromus-
cular characteristics. Altitude acclimatization results in
both central and peripheral adaptations that improve oxy-
gen delivery and utilization, mechanisms that potentially
could improve RE. Other strategies, such as stretching
should not be discounted as a training modality in order to
prevent injuries; however, it appears that there is an opti-
mal degree of flexibility and stiffness required to maximize
RE. Several nutritional interventions have also received
attention for their effects on reducing oxygen demand
during exercise, most notably dietary nitrates and caffeine.
It is clear that a range of training and passive interventions
may improve RE, and researchers should concentrate their
investigative efforts on more fully understanding the types
and mechanisms that affect RE and the practicality and
extent to which RE can be improved outside the laboratory.
Key Points
A range of training and passive interventions such as
endurance training, high-intensity interval training,
resistance training, training at altitude, stretching and
nutritional interventions may improve running
economy.
Improvements in running economy may be made by
modifying one or more factors that influence
metabolic, biomechanical and/or neuromuscular
efficiency.
1 Introduction
The goal in competitive distance running is to run a given
distance in the least time, or at least faster than the next
best competitor. A number of physiological attributes
contribute to successful distance running performance [1,
2], including (i) both a high cardiac output and a high rate
K. R. Barnes (&)A. E. Kilding
Sports Performance Research Institute New Zealand, Auckland
University of Technology, Level 2, AUT-Millennium Campus,
17 Antares Place, Mairangi Bay, Auckland, New Zealand
e-mail: kyle.barnes@yahoo.com; barnesk@gvsu.edu
K. R. Barnes
Department of Movement Science, Grand Valley State
University, Allendale, MI, USA
123
Sports Med
DOI 10.1007/s40279-014-0246-y
of oxygen delivery to working muscles, which leads to a
large capacity for aerobic adenosine triphosphate (ATP)
regeneration [i.e., a high maximal oxygen uptake
(VO
2max
)] [3,4]; (ii) the ability to sustain a high percentage
of VO
2max
for long periods of time (i.e., fractional utili-
zation of VO
2max
, relative intensity) [5]; and (iii) the ability
to move efficiently [running economy (RE)] [6–8]. Maxi-
mal aerobic capacity and fractional utilization of VO
2max
have been widely studied as determinants of running per-
formance; however, RE has been relatively ignored until
the past decade or so despite awareness of its importance
since at least the 1970s [3].
The steady-state oxygen consumption (VO
2
) at a given
running velocity, which is often referred to as RE [8–10],
reflects the energy demand of running at a constant sub-
maximal speed. Trained runners have superior RE to les-
ser-trained or untrained runners [11–13], indicating
positive adaptations occur in response to habitual training
[14,15]. While a given athlete may be genetically pre-
disposed to having ‘good’ RE [16], various strategies can
potentially further improve an individual’s RE through
augmenting metabolic, cardiorespiratory, biomechanical
and/or neuromuscular responses and adaptations. Given RE
has been identified as a critical factor contributing to dis-
tance running performance [4,5,7,9,15,17–21], effective
legal and practical strategies to improve RE are sought
after by coaches, athletes and sports scientists. To date, a
wide range of acute and chronic interventions have been
investigated with respect to improving economy, including
various forms of resistance training [22–31], high-intensity
interval training (HIT) [32–36], altitude exposure [37–44],
stretching [45–50], as well as nutritional supplements
(Fig. 1)[51–55]. Therefore, the purpose of this narrative
review is to examine various training strategies that have
attempted to improve RE, discuss the feasibility of strate-
gies previously identified but yet to be explored in the
literature, and discuss potential areas for future research.
2 Endurance Training in Runners
A range of physiological responses occur in response to
endurance training in runners, and it is likely that the
characteristics of training influence RE. Endurance training
leads to increases in the morphology and functionality of
skeletal muscle mitochondria [10,56]. Specifically, an
increase in the oxidative muscle capacity allows trained
runners to use less oxygen per mitochondrial respiratory
chain during submaximal running [57]. Furthermore,
adaptations such as improved skeletal muscle buffer
capacity [58] and hematological changes [40,59] (i.e.,
increased red cell mass) have been observed following
various training modalities. These adaptations could also
invoke improvements in oxygen delivery and utilization
that could improve an athlete’s RE.
While training has been suggested to elicit a range of
central and peripheral adaptations that improve the meta-
bolic and cardiorespiratory efficiency of a runner [60],
many of these adaptations are largely governed by the
training load, which can be manipulated for a given athlete
by increasing the volume or intensity of running over time.
2.1 Training History
Successful endurance runners typically undergo several
years of training to enhance the physiological characteris-
tics important to determining success in distance running
events. Indeed, the number of years of running experience
and high training volumes have been suggested to be
important to RE [61,62]. Unfortunately, the few longitu-
dinal studies that have examined this question have yielded
little consensus, with findings indicating no change [63,64],
a slight increase [65], and varying degrees of reductions
(1–15 %) in submaximal VO
2
among trained and untrained
runners engaging in different combinations of years, dis-
tance, interval and uphill training [36,66–68]. For example,
in moderately trained runners, Mayhew et al. [69] found
that years of training was significantly correlated (r=0.62)
with RE. In support, Midgley et al. [70] has suggested that
the most important factor in improving RE may be the
cumulative distance a runner has run over years of training
and not short-term (several weeks to month) bouts of high
training volume per se. This may be due to continued long-
term adaptations in metabolic, biomechanical and neuro-
muscular efficiency [62,70]. Case study data from world-
class runners also suggests that RE improves over several
years of training [17,21,71–73]; however, the role played
by the interaction between training volume and consistency
of training in such improvements over several years of
training remains unclear.
Fig. 1 Schematic of strategies to improve running economy
K. R. Barnes, A. E. Kilding
123
2.2 Training Volume
The influence of training volume on RE is not well dis-
cussed in the literature, and unfortunately, no training
studies to date have examined the implications of increased
training volume while controlling for potential confound-
ing variables like training intensity. This makes it difficult
to ascertain the effects of manipulating training volume
[70]. However, in a cross-sectional investigation, Pate et al.
[74] reported that training volume was not associated with
better RE. Nevertheless, the importance of training volume
should not be downplayed, as high-volume training plays a
major role in inducing adaptations important to distance
running success [75]. Clearly, there is a need for longitu-
dinal examinations of the relationship between RE and
training history, including how subtle changes in volume,
intensity, and cumulative volume interact, before conclu-
sions about their effect on RE can be made.
2.3 High-Intensity Interval Training (HIT)
Studies that have incorporated flat overground HIT into the
training programs of distance runners have reported equiv-
ocal results in relation to improving RE (Table 1). Jones and
Carter [76] suggested that runners are typically most eco-
nomical at the running velocities at which they habitually
train; however, no training study to date has investigated the
specificity of training velocity on RE. HIT at 93–120 %
velocity at VO
2max
(vVO
2max
)[32,35,36,77–79] and con-
tinuous running at velocity at the onset of blood lactate
accumulation (vOBLA) [32,33,36,77] have both been
shown to improve RE by *1–7 % (Table 1). Other studies
using similar training intensities have reported no significant
improvement [35,77,80,81]. Morgan et al. [82] suggested
that the type of run training exerts a negligible effect on
improving RE, based on the observation that several studies
reported no differences in changes in RE despite the runners
engaging in different interval training programs.
Whereas VO
2max
has been shown to increase signifi-
cantly during the transition between the off-season and pre-
competitive period, during which training intensity is
increased [17,64,83,84], the same studies reported either
a significant improvement [17,84] or no change [64,83]in
RE. Franch et al. [35] compared interval training at 94, 106
and 132 % vVO
2max
and found that RE significantly
improved in the 94 and 106 % groups, but not in the group
that trained at 132 % vVO
2max
. This suggests that very
high-intensity running is not effective in improving RE,
possibly because of a loss of running form at very high
running velocities, or an inability to complete a sufficient
training volume to elicit a training effect [70].
Biomechanical changes could improve exercise effi-
ciency following HIT. However, Lake and Cavanagh [85]
investigated the effects of 6 weeks of HIT on various
biomechanical variables in a group of moderately trained
runners and found no relationship between changes in
performance, VO
2max
, RE and biomechanical variables.
The authors concluded that improvements in performance
following HIT were more likely to be caused by physio-
logical rather than biomechanical factors.
2.3.1 Uphill Interval Training
Uphill running represents a frequently prescribed form of
HIT in periodized training programs for distance runners.
For example, a survey of teams competing in a collegiate
cross-country national championship race verified its
widespread use as a training method and revealed that
faster team times were correlated with inclusion of uphill
training [86]. Moreover, references to its potential effec-
tiveness as a movement-specific form of resistance training
have appeared in several reviews [10,70,87]; however,
only anecdotal reports and limited research investigations
[77,88,89] exist concerning the physiological responses
and potential improvements in performance to such train-
ing. Unlike other modes of resistance training, where a
transfer of learning would need to occur to improve RE,
uphill running is movement specific and the mechanisms
for improving RE are likely to directly affect one or more
of the metabolic, biomechanical and neuromuscular
systems.
2.4 Summary
It appears that further research is required to establish the
relative efficacy of HIT for improving the RE of long-
distance runners and to establish whether improvements in
RE can be derived from uphill and flat interval training
through variations in the frequency, duration, volume and
periodization of training.
3 Resistance Training
3.1 Heavy and Strength-Endurance Resistance
Training
Understandably, running makes up a significant proportion
of a runners training. However, other forms of training are
undertaken to bring about specific physiological adapta-
tions that could directly or indirectly (i.e., reduce injury
risk) improve performance. A common training method
often utilized by distance runners is resistance training.
Various forms of resistance training can be adopted, and
several have been shown to improve RE in recreational
[29,90,91], moderately trained [22,23,28,92–95], and
Strategies to Improve Running Economy
123
Table 1 Comparison of effects on running economy and performance following adaptation to various high-intensity interval training interventions
References Subjects Volume Frequency and duration Control Results (%)
Running
economy
Performance (distance)
Interval training
Sjodin et al. [36] 8 highly trained
male runners
20 min at vOBLA (vOBLA =85 % vVO
2max
) 1 day/week for 14 weeks No control :2.8 n/a
Yoshida et al. [81] 6 recreational
female runners
20 min at vOBLA (vOBLA =91 % vVO
2max
) 6 days/week for 8 weeks Endurance
training
:2.8 n/a
Franch et al. [35] 12 recreational male
runners
Continuous at 94 % vVO
2max
3 days/week for 6 weeks No control :3.1 :94 (time to exhaustion
at 87 % VO
2max
)
12 recreational male
runners
4–6 94 min at 106 % vVO
2max
3 days/week for 6 weeks No control :3.0 :67 (time to exhaustion
at 87 % VO
2max
)
12 recreational male
runners
30–40 915 s at 132 % vVO
2max
3 days/week for 6 weeks No control :0.9 :65 (time to exhaustion
at 87 % VO
2max
)
Billat et al. [32] 8 highly trained
male runners
4 weeks: 5 93 min at 100 % vVO
2max
;2920 min
vOBLA (vOBLA =85 % vVO
2max
)
4 weeks: 3 9(5 93 min at 100 % vVO
2max
); 2 920
min vOBLA (vOBLA =85 % vVO
2max
)
2 days/week for
4 weeks ?4 days/week for
4 weeks
No control :6.1
:7.7 $(time to exhaustion at
MAS)
Slawinski et al.
[79]
6 moderately
trained runners
29vD50 intervals; 3 9continuous at 60–70 %
vVO
2max
(vD50 =93 % vVO
2max
)
2 days/week for 8 weeks No control :3.6 :17.3 (time to
exhaustion at
17 km h
-1
)
Laffite et al. [78] 7 moderately
trained male
runners
29vD50 intervals (vD50 =93 % vVO
2max
) 2 days/week for 8 weeks No control :5.4 n/a
Smith et al. [181] 18 moderately
trained runners
692 min vVO
2max
?19continuous at 60 %
vVO
2max
2 days/week for 4 weeks Endurance
training
:3.3 :2.8 (3-km)
:2.3 (5-km)
18 moderately
trained runners
592.5 min vVO
2max
?19continuous at 70 %
vVO
2max
2 days/week for 4 weeks Endurance
training $:1.0 (3-km)
$(5-km)
Denadai et al. [33] 9 moderately
trained male
runners
4960 % t
lim
at 95 % vVO
2max
;2920 min vOBLA 2 days/week for 4 weeks No control :2.6 $(1,500-m)
:1.5 (5-km)
8 moderately
trained male
runners
5960 % t
lim
at 100 % vVO
2max
;2920 min vOBLA 2 days/week for 4 weeks No control :6.7 :2.0 (1,500-m)
:1.4 (5-km)
Enoksen et al. [34] 10 highly trained
male runners
13 % of total training volume at 82–92 % HR
max
1 day/week for 10 weeks No control :4.1 n/a
9 highly trained
male runners
33 % of total training volume at 82–92 % HR
max
3 days/week for 10 weeks No control :2.6 n/a
K. R. Barnes, A. E. Kilding
123
highly trained runners [26,96] (Table 2). To date, resis-
tance training interventions have been designed specifically
to increase muscular strength, power, muscular endurance,
and/or promote neural adaptations. For the purposes of this
review, and in keeping with use of resistance methods in
the literature (Table 2), the term ‘resistance training’ will
refer to any training that uses a resistance to the force of
muscular contraction at a low velocity, while ‘heavy
resistance training’ will refer to those studies that utilize
loads \6 repetition maximum (RM) (1–6 RM), and
‘strength-endurance resistance training’ will refer to stud-
ies utilizing loads C6 RM.
3.1.1 Mechanisms of Improvement Following Heavy
or Strength-Endurance Resistance Training
Resistance training may improve RE through several
mechanisms. Kyrolainen et al. [97] proposed that resis-
tance training may improve RE through improved lower
limb coordination and co-activation of muscles, thereby
increasing leg stiffness and decreasing stance phase contact
times, allowing a faster transition from the braking to the
propulsive phase through elastic recoil [24,97–101].
Heavy resistance training may primarily cause hypertrophy
of type IIA and IIB (fast twitch) fibers, but also type I (slow
twitch) fibers [102,103], resulting in less motor unit acti-
vation to produce a given force [104]. Unfortunately,
increases in body mass are an undesirable side effect to
increases in muscle strength from resistance training that
could be counter-productive to distance running perfor-
mance. However, increased muscular strength might pri-
marily come from neural adaptations without observable
muscle hypertrophy [105] since most studies reported little
or no changes in body mass, fat free mass, percentage body
fat or girth measurements following heavy resistance
training. Sale [100] states that heavy resistance training
induces changes in the nervous system which allow an
athlete to increase the activation of the working muscles,
thus producing a greater net force with each stride. An
increase in strength following heavy resistance training as a
result of increased motor unit recruitment and motor unit
synchronization may improve mechanical efficiency and
motor recruitment patterns [100,106]. Greater muscular
strength following heavy or strength-endurance resistance
training has previously been shown to delay muscular
fatigue, resulting in a smaller increase in oxygen con-
sumption (decreased RE) at any given speed during sus-
tained endurance exercise [107]. It is well documented that
initial performance gains following heavy resistance
training are a result of neuromuscular adaptations rather
than within muscle adaptations (e.g., hypertrophy) [100,
106]. Several studies [22,28,29,96] have reported con-
comitant improvements in RE and maximal strength
Table 1 continued
References Subjects Volume Frequency and duration Control Results (%)
Running
economy
Performance (distance)
Barnes et al. [77] 5 moderately
trained runners
12–24 98–12 s 120 % vVO
2max
(uphill) in addition to
endurance training
2 days/week for 6 weeks No control :2.4 :2.1 (5-km)
5 moderately
trained runners
8–16 930–45 s 110 % vVO
2max
(uphill) in addition to
endurance training
2 days/week for 6 weeks No control :0.6 :2.0 (5-km)
5 moderately
trained runners
5–9 92–2.5 min 100 % vVO
2max
(uphill) in addition to
endurance training
2 days/week for 6 weeks No control ;1.2 :2.0 (5-km)
4 moderately
trained runners
4–7 94–5 min 90 % vVO
2max
(uphill) in addition to
endurance training
2 days/week for 6 weeks No control ;2.4 :2.1 (5-km)
3 moderately
trained runners
1–3 910–25 min 80 % vVO
2max
(uphill) in addition to
endurance training
2 days/week for 6 weeks No control ;3.2 :2.2 (5-km)
Highly trained national/international level and VO
2max
[65 ml kg
-1
min
-1
,moderately trained weekly running volume [30 km week
-1
,recreational weekly running volume \30
km week
-1
,HR
max
maximal heart rate, MAS maximal aerobic speed, n/a indicates not measured, t
lim
time limit, vD50 velocity midway between vLT and vVO
2max
,vLT velocity at the lactate
threshold, VO
2max
maximal aerobic capacity, vOBLA velocity at the onset of blood lactate accumulation, vVO
2max
velocity at VO
2max
,:indicates increase, $indicates no change, ;indicates
decrease
Strategies to Improve Running Economy
123
following heavy resistance training, indicating positive
neuromuscular adaptations. Other studies [26,93,95,101,
108] have demonstrated that the combination of strength-
endurance resistance training and endurance training
improves running performance and enhances RE in mod-
erately and highly trained runners (Table 2). Regardless of
whether strength gains occur at the muscular level, neural
level, or both, the available evidence suggests if a more
efficient recruitment pattern is induced, decreases in oxy-
gen consumption at a given speed are likely to occur [11,
67]; however, more research is necessary to support these
assertions.
Improved RE may also be due to increases in strength
that cause positive changes in mechanical aspects of run-
ning style (i.e., improved biomechanical efficiency) [23],
thus allowing a runner to do less work at a given running
speed. A number of biomechanical variables have been
identified that relate to RE, thereby providing support for
the hypothesis that mechanical aspects of running style
have an influence on RE [109]. Another possible expla-
nation for improved RE following heavy resistance training
could involve muscle fiber-type conversion from less effi-
cient fast twitch fibers (type IIB) to more efficient oxidative
fibers (type IIA and type I), though existing data in athletes
are conflicting [102,103,110,111]. For example, Staron
et al. [102,103,110] found a concomitant decrease in
submaximal VO
2
and decrease in type IIB fibers, with a
simultaneous increase in type IIA fibers following a heavy-
resistance low-velocity lower body resistance training
program in untrained men [102] and women [102,103,
110]. Conversely, Coyle et al. [111] reported that VO
2
remained unchanged for the same absolute submaximal
intensity throughout a detraining period, despite a large
shift from type IIA to IIB fibers when studying seven
endurance-trained subjects 12, 21, 56 and 84 days after
cessation of training, suggesting that muscle fiber conver-
sion has little or no impact on RE.
3.1.2 Heavy Versus Strength-Endurance Resistance
Training
Several studies have attempted to determine which form
of concurrent endurance and resistance training might be
the most effective at improving running performance in
highly trained runners. Sedano et al. [26] prescribed 18
well-trained male runners with 12 weeks of either heavy
resistance training or strength-endurance resistance train-
ing in addition to their normal running training. The
heavy-resistance group elicited substantially greater
improvements in RE (5 vs. 1.6 %) and 3-km run perfor-
mance (1.2 % vs. no change) compared with the strength-
endurance resistance training group [26]. Similarly, Ber-
ryman et al. [93] found that 8 weeks of strength-
endurance resistance training (purely concentric semi-
squats on a guided squat rack allowing only vertical
movements) improved RE by 4 % in 17 moderately
trained male runners. The improvement in economy,
along with a substantial increase in peak power, resulted
in a (mean) 4.3 % improvement in 3-km running time,
without an increase in VO
2max
, with gains attributed to
changes in neuromuscular characteristics [93]. Taipale
et al. [29] also reported significant improvements in RE
(mean 8 %) and vVO
2max
(mean 10 %) along with
improvements in neuromuscular performance (1 RM
maximal strength and electromyographic (EMG) vastus
lateralis activity) after 8 weeks of heavy resistance
training in recreation runners. However, heavy resistance
training was performed in addition to a significant
increase in endurance training volume; therefore, the
improvements in RE may be related to the increased
volume of training rather than the resistance training itself
since the subjects in this study were recreational runners
[29]. The only study [23] to examine any form of resis-
tance training in females found that 10 weeks of strength-
endurance resistance training combined with endurance
training significantly improved RE (4 %) without any
changes in VO
2max
.
The available data involving athletes suggest RE can
be improved with simultaneous resistance and endurance
training, with no chronic deleterious effect on VO
2max
or
running performance [10]. Examination of the acute
effects of resistance and endurance training sequence on
RE shows that running performance is impaired to a
greater degree the day following the resistance training
then run sequence compared with the run then resistance
training sequence [112]. The combination of improved
biomechanical efficiency along with greater motor unit
recruitment and muscle coordination may allow for a
reduction in relative workload, thereby reducing oxygen
consumption [113]. Most of the studies discussed here
showed improvements in RE in 10 weeks or less; how-
ever, more studies are needed to determine if improve-
ments can be made in shorter periods or what the time
course of changes in RE are. Most studies demonstrating
improvement in RE following resistance training cite
enhancements in neuromuscular characteristics as the
mechanism for improvement; however, most studies only
make indirect measures of neuromuscular activity.
Therefore, more direct measures such as EMG analysis
may allow researchers to identify if a transfer of learning
from resistance training to running performance occurs.
Additionally, each of these studies employed different
modes of resistance training; therefore, more research is
required to determine which mode of resistance training
might be most effective at improving RE and performance
in well-trained athletes.
K. R. Barnes, A. E. Kilding
123
Table 2 Comparison of effects on running economy and performance following adaptation to various resistance training, plyometric and explosive resistance training interventions
References Subjects Volume Frequency and
duration
Control Results (%)
Running
economy
Performance
(distance)
Resistance training
Johnston et al. [23] 12 moderately trained
female runners
2–3 sets of 6–20 RM in addition to
endurance training
3 days/week for
10 weeks
Endurance running :4 n/a
Millet et al. [96] 15 highly trained male
triathletes
3–5 sets of 3–5 RM in addition to endurance
training
2 days/week for
14 weeks
Endurance training (swim,
cycle, run)
:5.6–7 :2.6 (3-km)
Storen et al. [28] 17 moderately trained
male/female runners
4 sets of 4 RM in addition to endurance
training
8 weeks Endurance running :5:21.3 (time to
exhaustion at MAS)
Guglielmo et al. [22] 7 moderately trained
runners
3–5 sets of 6 RM in addition to endurance
training
2 days/week for
4 weeks
No control :6.2 n/a
Taipale et al. [29] 18 recreational male
runners
2–3 sets of 4–15 RM in addition to endurance
training
2 days/week for
8 weeks
Circuit ?endurance running :8:10
Ferrauti et al. [182] 22 recreational male/
female runners
4 sets of 3–5 RM or 3 sets of 20–25 RM in
addition to endurance training
2 days/week for
8 weeks
Endurance training $n/a
Mikkola et al. [183] 11 moderately trained
male runners
3 sets of 4–6 RM in addition to endurance
training
2 days/week for
8 weeks
No control $n/a
6 moderately trained male
runners
3 sets of 40–50 reps in addition to endurance
training
2 days/week for
8 weeks
No control $n/a
Berryman et al. [93] 17 moderately trained
male runners
3–6 sets of 8 reps in addition to endurance
training
1 day/week for
8 weeks
Endurance running :4:4.3 (3-km)
Cheng et al. [101] 24 recreational male
runners
10 sets of 60 s whole body vibration semi
squats
3 days/week for
8 weeks
Placebo resistance
training ?endurance
training
:7.8 n/a
Francesca et al. [95] 16 moderately trained
male runners
4 sets of 3–4 at 85–90 % 1 RM in addition to
endurance training
2 days/week for
6 weeks
Endurance training :6.2 n/a
16 moderately trained
male runners
3 sets of 10 reps at 70 % 1 RM in addition to
endurance training
2 days/week for
6 weeks
Endurance training $n/a
Albracht and
Arampatzis [94]
26 recreational male
runners
5 sets of 4 reps in addition to endurance
training
4 days/week for
14 weeks
Endurance running :4 n/a
Barnes et al. [92] 13 moderately trained
male runners
1–4 sets of 4–12 RM in addition to endurance
training
2 days/week for
10–13 weeks
No control :1.7 $0.1 (8-km)
9 moderately trained
female runners
1–4 sets of 4–12 RM in addition to endurance
training
2 days/week for
10–13 weeks
No control :3.4 :1.4 (6-km)
Sedano et al. [26] 12 highly trained male
runners
3 sets of 7–10 reps in addition to endurance
training
2 days/week for
12 weeks
Circuit ?endurance running :5:1.2 (3-km)
12 highly trained male
runners
3 sets of 20 reps in addition to endurance
training
2 days/week for
12 weeks
Circuit ?endurance running :1.6 $(3-km)
Taipale et al. [91] 18 recreational male
runners
2–3 sets of 4–6 reps in addition to endurance
training
1–2 days/week
for 8 weeks
Endurance training $n/a
Strategies to Improve Running Economy
123
Table 2 continued
References Subjects Volume Frequency and
duration
Control Results (%)
Running
economy
Performance
(distance)
Plyometric/explosive resistance training
Paavolainen et al.
[24]
22 moderately trained
male runners
15–90 min/session in addition to endurance
training
9 weeks Endurance running and
circuit training
:
24.4–33.8
:3.1 (5-km)
Spurrs et al. [27] 17 moderately trained
male runners
2–3 sets of 8–15 reps in addition to endurance
training
2–3 days/week
for 6 weeks
Endurance running :5.7 :2.7 (3-km)
Turner et al. [31] 18 recreational male/
female runners
1 set of 5–25 reps in addition to endurance
training
3 days/week for
6 weeks
Endurance running :2–3 n/a
Saunders et al. [25] 15 highly trained male
runners
30 min/session in addition to endurance
training
3 days/week for
9 weeks
Endurance running :4 n/a
Mikkola et al. [120] 25 moderately trained
male/female runners
30–60 min session in addition to endurance
training
3 days/week for
8 weeks
Endurance running :3$(peak running
speed)
Guglielmo et al. [22] 9 moderately trained
runners
3–5 sets of 12 RM in addition to endurance
training
2 days/week for
4 weeks
No control :1.9 n/a
Taipale et al. [29] 17 recreational male
runners
2–3 sets of 5–10 reps in addition to endurance
training
2 days/week for 8
weeks
Circuit ?endurance running :4:6
Berryman et al. [93] 16 moderately trained
male runners
3–6 sets of 8 reps in addition to endurance
training
1 day/week for
8 weeks
Endurance running :7:5.1 (3-km)
Mikkola et al. [183] 10 moderately trained
male runners
3 sets of 6 reps in addition to endurance
training
2 days/week for
8 weeks
No control $n/a
Barnes et al. [92] 10 moderately trained
male runners
1–3 sets of 6–12 reps in addition to endurance
training
2 days/week for
10–13 weeks
No control :0.2 $0.8 (8-km)
10 moderately trained
female runners
1–3 sets of 6–12 reps in addition to endurance
training
2 days/week for
10–13 weeks
No control :1.0 :1.1 (6-km)
Taipale et al. [91] 17 recreational male
runners
2–3 sets of 5–10 reps in addition to endurance
training
1–2 days/week
for 8 weeks
Endurance training $n/a
16 recreational male
runners
2–3 sets of 4–10 reps in addition to endurance
training
1–2 days/week
for 8 weeks
Endurance training $n/a
Barnes et al. [121] 11 moderately trained
male runners
1 set of 6 910-s strides with weighted vest Acute Endurance training :6.0 :2.9 (peak running
speed)
Highly trained national/international level and VO
2max
[65 ml kg
-1
min
-1
,moderately trained weekly running volume [30 km week
-1
,recreational weekly running volume
\30 km week
-1
,MAS maximal aerobic speed, n/a indicates not measured, reps repetitions, RM repetition maximum, VO
2max
maximal aerobic capacity, :indicates increase, $indicates no
change
K. R. Barnes, A. E. Kilding
123
3.2 Plyometrics and Explosive Resistance Training
The concept of movement specificity suggests that the type
of resistance training used by runners should closely sim-
ulate the movement that will be performed during training
and competition [114]. Plyometrics and explosive resis-
tance training are specific forms of strength training that
aim to enhance the ability of muscles to generate power by
exaggerating the stretch shortening cycle (SSC), using
explosive exercises such as jumping, hopping and bound-
ing [31].
3.2.1 Mechanisms of Improvement Following Plyometric
or Explosive Resistance Training
Plyometric training has the potential to increase the stiff-
ness of the muscle-tendon system, which allows the body
to store and utilize elastic energy more efficiently, resulting
in decreased ground contact time and reduced energy
expenditure [27,109,115–117]. Paavolainen et al. [24]
indicated that 9 weeks of explosive resistance training
improved 5-km run performance (mean 3.1 %) and RE
(mean 8.1 %) with no changes in VO
2max
in 22 moderately
trained male runners. Furthermore, significant improve-
ments in velocity over a 20-m sprint (mean 3.4 %), dis-
tance jumped (mean 4.6 %), along with a concurrent
decrease in stance phase contact times were observed [24].
These variables are thought to represent indirect measures
of the neuromuscular system’s ability to repeatedly pro-
duce rapid force during intense exercise, and the capability
to store and utilize elastic energy [24,98,99]. The authors
suggested that the improved performance was a result of
enhanced neuromuscular characteristics and biomechanical
efficiency that were transferred into improved muscle
power and RE [24].
The importance of the neuromuscular characteristics in
determining RE and thereby running performance has also
been pointed out previously [27,118]. Dalleau et al. [118]
showed that the energy demand during running is signifi-
cantly related to the stiffness of the propulsive leg. Simi-
larly, Spurrs et al. [27] demonstrated 6 weeks of
plyometric training significantly improved RE, muscle-
tendon stiffness, maximal isometric force, rate of force
development, jump height, five jump distance and 3-km
time trial performance. Plyometric training consisted of
2–3 sessions per week of various unloaded jumps, bounds,
and hops. Several other studies (Table 2) have provided
support that simultaneous plyometric or explosive resis-
tance training and endurance training improves RE in
recreational [29,31,91], moderately trained [22,24,27,
92,93,119,120], and highly trained runners [25]. Saunders
et al. [25] examined the effects of 9 weeks of plyometric
training on RE in highly trained runners using loaded and
unloaded exercises 3 times per week. The subjects were
tested for RE at 14, 16 and 18 km h
-1
at weeks 5 and 9;
however, significant improvements were only found at
week 9 for the 18 km h
-1
test. Other studies have shown
improvements in RE after 8 weeks of plyometric training in
moderately trained runners with no change in VO
2max
,[93,
120], with the former study showing a (mean) 7 %
improvement in RE and (mean) 5.1 % in 3-km run per-
formance. Proposed explanations for the improvements
include increased lower limb stiffness and elastic energy
return, enhanced muscle strength and power, or enhanced
running mechanics. Recent evidence has also suggested RE
can be improved (mean 6.0 %) acutely following a series
of warm-up strides with a weighted vest, and this was
consistent with improved lower limb stiffness [121].
Turner et al. [31], however, reported no change in four
indirect measures of the ability of the muscles to store and
return elastic energy despite a (mean) 3 % improvement in
RE following 6 weeks of plyometric training in recrea-
tional runners. These findings suggest that either more
direct measures of potential mechanisms that could
improve RE need to be made in future research or other
factors are yet to be elucidated as potential mechanisms for
enhancing RE following plyometric training.
3.3 Resistance Training Versus Plyometric
or Explosive Resistance Training
Paavolainen et al. [24] stated that explosive training,
mimicking the eccentric phase of running, is most likely to
improve the use of stored elastic energy and motor unit
synchronization which increases the ability of the lower-
limb joints to act more stiffly on ground contact. Moreover,
Millet et al. [96] stated that explosive-strength training
leads to different muscular adaptations than does typical
heavy weight training; for example, a greater increase in
the rate of activation of the motor units. The available data
(Table 2), however, suggest that of the six studies [22,29,
91–93] that included a resistance training and plyometric or
explosive resistance training group, four [22,29,91,92]
demonstrated greater improvements in RE following tra-
ditional resistance training, while one [91] showed no
changes in economy in either type of training.
According to Guglielmo et al. [22] when comparing
heavy resistance training to explosive resistance training
performed on the same equipment, heavy weight training
seems to be the more effective mode of training to improve
RE. Similarly, Barnes et al. [108] and Sedano et al. [26]
have found that a heavy resistance training program was
superior to a low-resistance high-speed weight training
program at improving RE. Paton and Hopkins [122] came
to the same conclusion when reviewing the effects of high-
intensity training on performance and physiology in
Strategies to Improve Running Economy
123
endurance athletes. This is assuming that each of these
studies’ resistance training programs were matched for
volume load and the subjects in each group were matched
for training history and ability level.
3.4 Summary
It is reasonable to assume that there are individual
responses to various modes of resistance training. How-
ever, until more data are collected to describe subject or
training characteristics that may identify responders and
non-responders to these different modes of resistance
training, the current data suggest that traditional resistance
training may be superior to plyometric training, but any
type of resistance may have a positive effect on RE [114].
While the exact mechanisms responsible for the
improved RE following plyometric or explosive resistance
training are unclear, the findings to date indicate that
improved neuromuscular function likely plays a role in the
enhancement in RE and performance. However, this pre-
mise is based on indirect measures of neuromuscular
function and elastic energy return such as contact times and
vertical jump height. Enhancements in strength and power
development during isolated tasks (e.g., vertical and for-
ward jumps) may reflect neuromuscular adaptations, but
this has not been confirmed by more direct measurements
of muscle recruitment, such as EMG activity. Thus it is not
possible to infer that these adaptations translate into more
efficient muscle recruitment patterns during running or that
they are responsible for the enhanced RE following plyo-
metric training. Alternatively, changes in running style that
result in more efficient gait patterns, kinematics and
kinetics may also improve the economy of runners fol-
lowing plyometric or explosive resistance training. How-
ever, the majority of research into kinetics and kinematics
of running has been descriptive and changes in biome-
chanical efficiency may be a result of improved neuro-
muscular efficiency. Finally, significant improvements in
work economy found in cross-country skiers [113,123–
125] and cyclist [126,127] performing movement specific
modes of resistance training may provide evidence that
these forms of training may be most beneficial to
improving RE and performance; therefore, future studies
should examine movement-specific forms of resistance
training such as hill running, hypergravity running or
running through sand.
4 Altitude Exposure
Interventions to improve RE besides endurance and resis-
tance training are constantly sought after by athletes, coa-
ches and sports scientists; however, there is a paucity of
data regarding environmental strategies. Training at alti-
tude offers one potential strategy. Despite altitude exposure
being reasonably well-researched over the past few dec-
ades, there is still limited data in regard to improving RE;
other strategies such as training in heat, cold or humid
environments are yet to be examined.
Many athletes undertake some form of altitude training
to gain small improvements in physiology and perfor-
mance. Results from a recent meta-analysis indicate
*1–4 % performance enhancements following various
protocols using natural and artificial altitude exposure in
highly and moderately trained athletes [128]. Improve-
ments in performance have been primarily attributed to
increased hematological parameters leading to an increase
in maximal aerobic capacity [40,129–131]; however,
hypoxia-induced enhancements in muscle buffering
capacity [58] and RE [42,43] have also been suggested.
4.1 Altitude Versus Sea-level Natives
Several descriptive, cross-sectional and intervention stud-
ies have been conducted in an attempt to highlight differ-
ences in RE between altitude natives and individuals
residing at sea level with equivocal results. While reporting
the physiological characteristics of Kenyan runners living
and training at altitude and the Scandinavian runners at sea
level, Saltin et al. [132] found that Kenyan runners had
5–15 % lower VO
2
at submaximal running speeds ranging
from 10 to 16 km h
-1
and did not accumulate lactate
during running until near peak training intensities. Simi-
larly, Weston et al. [133] reported Kenyan runners had
better economy and higher resistance to fatigue while
running at the same percentage of VO
2max
than Caucasian
runners. Differences in RE that do exist between various
ethnic groups could be related to differences in body mass
and mass distribution. Therefore, in running, it has been
shown that allometric scaling body mass to the power of
0.67 or 0.75 (e.g., ml kg
-0.67
min
-1
or ml kg
-0.75
min
-1
)
may be more appropriate when comparing RE between
individuals with varying body mass [19,134–144].
One study [145] examining changes in physiological
and performance parameters following 46 weeks of train-
ing at 2,210 m altitude in sea-level and altitude natives
suggested that changes in former sea-level residents may
require longer periods at altitude to achieve similar changes
in altitude natives. Sea-level natives had significantly
poorer RE (mean ?6.6 %), lower VO
2max
(mean -5.9 %)
and slower 1.5-mile run time (mean ?5.4 %) compared
with altitude natives following similar training at altitude.
Similarly, Lundby et al. [146] reported that there were no
significant changes in RE of sea-level natives after 8 weeks
of exposure to 4,100 m compared with altitude natives who
had a (mean) 15 % lower submaximal VO
2
than sea-level
K. R. Barnes, A. E. Kilding
123
residents, consistent with the observations of others [132,
133,147–149].
4.2 Adaptations to Different Hypoxic Environments
In sea-level natives, several studies [37–44,150,151] have
demonstrated improvements (2–7 %) in RE following
different types, ascents and durations of altitude exposure
(Table 3). Conversely, an equivocal number of studies
have demonstrated that submaximal VO
2
at sea level
remains largely unchanged following exposure to different
hypoxic environments (Table 3)[129,131,146,152–155].
4.2.1 Blood Parameters
Mechanisms that have been suggested to explain the dis-
crepancy in improvements in economy after altitude
exposure have been related to differences in changes in
hemoglobin mass and concentration, following hypoxic
exposure. While the dosing of hypoxia for the enhancement
of the total hemoglobin mass is currently well defined, this
does not apply to RE. About 400 h of hypoxia corre-
sponding to an altitude [2,100 m seems to be necessary to
increase total hemoglobin mass [43]. In a study by Burt-
scher et al. [37], the duration of hypoxic exposure was only
30 h during one 5-week period, which unsurprisingly was
insufficient to significantly increase total hemoglobin mass,
but was adequate for the improvement of RE. The authors
did report small increases in hemoglobin concentration and
hematocrit, which were closely related to the improvement
in RE. An increase in hematocrit results in a linear increase
of the oxygen carrying capacity and an exponential
increase in blood viscosity [37]. Because blood viscosity is
not highly dependent on hematocrit at high cardiac outputs
[37], the enhanced oxygen carrying capacity could con-
tribute to the improved RE and performance after hypoxia
by reducing the amount of oxygen required for higher heart
rates (HRs) and ventilation. Levine and Stray-Gundersen
[40] reported that moderately trained runners living at
moderate altitude (2,500 m) and training at low altitude
(1,250 m) increased red cell mass (9 %) as well as
improved VO
2max
(mean 5 %) and RE (2–5 %) after return
to sea level.
4.2.2 Cardiorespiratory Adaptations
The findings from a number of studies suggests that
enhancements in RE following hypoxic exposure may be
the result of decreased cardiorespiratory costs [decreased
minute ventilation (V
E
), lower HR] [39,43,156], a shift
toward a greater glycolytic involvement in ATP regenera-
tion [156], greater carbohydrate utilization during oxidative
phosphorylation [58,157], increased ability of the
excitation and contraction processes to perform work at
lower energy costs [156,158], and/or acclimatization-
induced transformation of muscle fiber types [156]. One
study examining the effects of *46 nights at 2,860 m
simulated altitude on RE and performance prior to the
competitive track season found altitude improved RE by
1.0–5.2 %, increased hemoglobin mass by (mean) 4.9 %,
and decreased submaximal HR by (mean) 3.1 % [43]. The
authors suggest plausible mechanisms for improved RE
include a decrease in the ATP cost of muscle contraction,
or a decrease in the cardiorespiratory cost of O
2
transport.
Another recent study demonstrated that 11–14 h a day for
17–24 days of normobaric hypoxia (2,500–3,500 m)
improved RE by (mean) 7 % [44]. The authors suggested
that changes in substrate utilization and lower cardiore-
spiratory costs contributed to the improved RE, which is
supported by the increased submaximal respiratory
exchange ratio (RER) and the decreased V
E
and HR values
within the experimental groups. More recently, it was
demonstrated that 3 h per day for 2 weeks of intermittent
exposure to normobaric hypoxia (equivalent of 4,500 m)
improved RE by (mean) 2.6 % (14 km h
-1
) and (mean)
2.9 % (16 km h
-1
). The improved RE was accompanied
by a decreased HR (mean 3.3 and 3.9 % at 14 and
16 km h
-1
, respectively) and a trend towards improved
3,000-m run time (mean 1.3 %) [39].
The findings from other studies indicate that a small
shift in substrate metabolism towards an increase in car-
bohydrate use and lower cardiorespiratory costs, such as
decreased V
E
and HR contributed to the improved RE after
a period of altitude exposure [37,44]. Both studies reported
an improvement in RE (mean 2.3 % [37] and 7.7 % [44])
with an accompanying shift towards carbohydrate metab-
olism. The former study reported that two 5-week periods
of intermittent hypoxia (3,200–5,500 m) 3 days per week
for 2 h each day improved RE only during the first 5-week
period of intermittent hypoxia when compared with train-
ing alone. Although RE continuously improved during the
13-week study period, no further changes occurred after the
first 5-week period. These findings suggest that the first
5-week intermittent hypoxia exposure was responsible for
the initial improvement in RE and the run training during
the following 8 weeks was responsible for maintaining the
enhancements in economy. These results emphasize the
importance of the training phase on the effectiveness of
altitude exposure on RE.
4.2.3 Metabolic Efficiency
Results from other studies [42,158] suggest the physio-
logical mechanisms eliciting an improved RE in highly
trained runners after hypoxic exposure appear unrelated to
decreased ventilation or a substantial shift in substrate use.
Strategies to Improve Running Economy
123
Table 3 Comparison of effects on running economy and performance following adaptation to hypoxia experienced in studies with various protocols of natural and artificial altitude
References Subjects Altitude type
a
Intervention Control Results (%)
Running
economy
Performance (distance)
Telford et al. [154] 18 highly trained male runners Natural altitude, LHTH 4 weeks at 1,700–2,000 m, 24 h/day LLTL $:2 (3.2-km)
Levine and Stray-
Gundersen [40]
26 moderately trained male/
female runners
Natural altitude, LHTL 4 weeks at 2,500 m, 16–20 h/day LLTL :4.8 :1.4 (5-km)
26 moderately trained male/
female runners
Natural altitude, LHTH 4 weeks at 2,500 m, 24 h/day LLTL :2.8 $(5-km)
Bailey et al. [150] 23 moderately trained male/
female runners
Natural altitude, LHTH 4 weeks at 1,500–2,000 m, 24 h/day LLTL $n/a
Stray-Gundersen et al.
[131]
22 highly trained male/female
runners
Natural altitude, LHTH 27 days at 2,500 m, 24 h/day No
control $:1.1 (3-km)
Katayama et al. [38] 12 highly trained male runners Simulated altitude,
LHTL
3 days/week for 3 weeks at 4,500 m, 90 min/day LLTL :3.3 :1 (3-km)
Julian et al. [152] 14 highly trained male/female
runners
Simulated altitude,
LHTL
5 days/week for 4 weeks at 3,600–5,000 m,
70 min/day
LLTL $$(3-km)
Katayama et al. [39] 15 highly trained male runners Simulated altitude,
LHTL
14 days at 4,500 m, 3 h/day LLTL :2.9 :1.3 (3-km)
Saunders et al. [42] 10 highly trained male runners Artificial altitude,
LHTL
5 days/week for 4 weeks at 2,000–3,100 m,
9–12 h/day
LLTL :3.3 n/a
10 highly trained male runners Natural altitude, LHTL 5 days/week for 4 weeks at 2,000–3,100 m,
9–12 h/day
LLTL $n/a
Schmitt et al. [44] 11 moderately trained male
runners
Natural altitude, LHTL 17–24 days at 2,500–3,500 m, 11–14 h/day LLTL :7.0 n/a
Lundby et al. [146] 24 highly trained male/female
runners
Natural altitude, LHTH 4 week at 2,500–2,850 m, 24 h/day No
control $n/a
Neya et al. [41] 16 highly trained male runners Artificial altitude,
LHTL
29 days at 3,000 m, 11 h/day LLTL :5.5 n/a
15 highly trained male runners Artificial altitude,
LHTH
29 days at 3,000 m, 11 h/day LLTL $n/a
Truijens et al. [155] 10 moderately trained male/
female runners
Artificial altitude,
LHTL
5 days/week for 4,000–5,500 m, 3 h/day LLTL $n/a
Saunders et al. [43] 18 highly trained runners Artificial altitude,
LHTL
46 days at 2,860 m, 9 h/day LLTL :3.2 :1.9 (1,500-m)
Burtscher et al. [37] 11 moderately trained male/
female runners
Artificial altitude,
LHTL
3 days/week for 2 95 weeks at 3,200–5,500 m,
2 h/day
LLTL :2.3 :31 (time to exhaustion
at MAS)
K. R. Barnes, A. E. Kilding
123
Therefore, it is possible that the main mechanisms
responsible for improved RE at sea level after a period of
altitude exposure are either an increase in the ATP pro-
duction per mole of oxygen used and/or a decrease in the
ATP cost of muscle contraction; however, currently, there
is no direct evidence to support these claims. Katayama
et al. [38,159] have demonstrated on two occasions that
intermittent hypoxic exposure improves RE in highly
trained runners without changes in ventilation, suggesting
other mechanisms may be responsible for the changes in
economy. The first study reported that simulated hypoxic
exposure using intermittent hypobaria of 4,500 m 3 h per
day for 14 consecutive days improved RE by (mean) 2.6 %
(14 km h
-1
) and (mean) 3.3 % (16 km h
-1
), improved
3,000-m run time by 1 % and time to exhaustion on the
treadmill by 2.7 % [38]. Another recent study demon-
strated that 20 days of live high (simulated altitude
2,000–3,100 m) train low improved RE (mean 3.3 %) in
the absence of any changes in V
E
, RER, HR or hemoglobin
mass [42]. There was also no evidence of an increase in
lactate concentration after the live-high train-low inter-
vention, suggesting that the lower aerobic demand of
running was not attributable to an increased anaerobic
energy contribution. Green et al. [156] suggested a reduced
energy requirement of one or more processes involved in
excitation and contraction of the working muscles could be
a result of a reduction in by-product accumulation, such as
adenosine diphosphate (ADP), inorganic phosphate or H
?
that occurs after altitude acclimatization. Such changes
increase the amount of free energy released from ATP
hydrolysis and depress the need to maintain hydrolysis
rates at pre-acclimatized levels [60].
4.2.4 Muscle Fiber Type
It has been shown that the type I muscle fibers are consider-
ably more efficient than type II muscle fibers. Acclimatiza-
tion-induced transformation of fiber types could conceivably
underlie changes in neuromuscular efficiency and subse-
quently RE; however, this is yet to be studied in runners.
4.3 Other Environmental Strategies
Several other environmental strategies have been previ-
ously identified as feasible strategies to improve RE, such
as training in the heat [6,10,160] or cold and altering
training surface [161], but have yet to be examined in the
literature.
4.4 Summary
The literature indicates that altitude exposure for runners
has no detrimental effects on RE and that there is good
Table 3 continued
References Subjects Altitude type
a
Intervention Control Results (%)
Running
economy
Performance (distance)
Robertson et al. [153] 8 highly trained male/female
runners
Artificial altitude,
LHTL ?TH
3 weeks at 3,000 m, 14 h/day ?4 days/week
training at 2,200 m
No
control $:1.1 (3-km)
9 highly trained male/female
runners
Artificial altitude,
LLTH
4 days/week for 3 weeks training at 2,200 m No
control $$(3-km)
16 highly trained male/female
runners
Artificial altitude,
LHTL
3 weeks training at 3,000 m, 14 h/day LLTL $:1.9 (3-km)
Highly trained national/international level and VO
2max
[65 ml kg
-1
min
-1
,moderately trained weekly running volume [30 km week
-1
,LHTH live high train low, LHTL live high train low,
LLTH live low train high, LLTL live low train low, MAS maximal aerobic speed, n/a indicates not measured, TH train high, VO
2max
maximal aerobic capacity, :indicates increase, $indicates
no change
a
See Bonetti and Hopkins [128] for definitions of natural and artificial altitude, sea-level, low, moderate and high altitude
Strategies to Improve Running Economy
123
evidence to suggest that it may lead to worthwhile
improvements in RE at sea level. Altitude acclimatization
results in both central and peripheral adaptations that
improve oxygen delivery and utilization and enhance
metabolic efficiency; mechanisms that could potentially
explain the changes in RE. Many of the studies that did not
find an improvement in RE (Table 3) after altitude expo-
sure were performed close to the competition season,
which emphasizes the importance of timing and training
phase on the effectiveness of altitude exposure on RE.
5 Flexibility and Stretching
5.1 Flexibility
There appears to be equivocal results in regard to the
effects of stretching or flexibility on RE. Some researchers
have identified an inverse relationship between flexibility
and RE; that is, less flexibility is associated with better RE
[45,46,48,49,162]. Gleim et al. [46] tested 100 male and
female subjects over a range of speeds from 3 to 12 km h
-1
and found that those who exhibited less flexibility in a
battery of 11 trunk and lower limb flexibility tests were
most economical. These results suggest that the inflexi-
bility of the lower limbs and trunk musculature as well as
limited range of motion around the joints of the lower body
allow for greater elastic energy storage and use in the
muscles and tendons during the running gait [46,49].
Specifically, it was suggested that inflexibility in the
transverse and frontal planes of the trunk and hip regions of
the body may stabilize the pelvis at the time of foot impact
with the ground, reducing excessive range of motion and
metabolically expensive stabilizing muscular activity [46].
Furthermore, research has demonstrated that runners with
tighter or stiffer musculotendonous structures store more
elastic energy in their lower limbs, resulting in a lower VO
2
at submaximal running velocities [45,46,49,163].
In contrast, other research fails to support the existence
of an inverse relationship, countering that flexibility is an
essential component of distance running performance [47,
164–166]. Godges et al. [47] found improved RE at 40, 60
and 80 % VO
2max
in response to static stretching proce-
dures in seven moderately trained athletic male college
students when flexibility increased. They reported a
reduced aerobic demand of running at all speeds when hip
flexion and extension were increased [47]. Improved hip
flexibility, myofascial balance, and pelvic symmetry due to
stretching are thought to enhance neuromuscular balance
and contraction, thus leading to a lower submaximal VO
2
and improved RE. These results corroborate general beliefs
that improved flexibility is desirable for optimal running
performance.
5.2 Stretching
Conflicting results among stretching studies may be asso-
ciated with limitations in methodological design. Several
studies [46,47,166] did not employ an adequate treadmill
accommodation period; therefore, improvements in RE
may have been associated with familiarization with tread-
mill running [45]. Furthermore, subjects were not described
as runners of any caliber in several studies [46,47,164,
166]. Therefore, a lack of familiarity with treadmill run-
ning mechanics may have made economy measures invalid
in these studies. Additionally, some studies [46,162,164]
have combined male and female results in the analyses;
because females are generally more flexible [162] and less
economical than males [19], the true association between
economy and flexibility may be difficult to discern if sexes
are not studied separately. Finally, a recent systematic
review concluded that an acute bout of stretching may
improve RE, but regular stretching prior to running over
time has no effect on economy [167].
5.3 Summary
Overall these findings suggest that an increase in the
stiffness of lower body musculotendinous structures
appears to improve RE. However, stretching should not
be discounted as a training modality, because stretching
exercises are commonly prescribed for runners to facili-
tate injury prevention and maximize stride length [10,
168].
6 Nutritional Interventions
Beyond the typical endurance athlete preparation, which
features large amounts of aerobic training, HIT, resistance
and/or plyometric training, and various environmental
exposures during a periodized season [169], several nutri-
tional interventions have received attention for their effects
on reducing oxygen demand during exercise, most notably
dietary nitrates.
6.1 Dietary Nitrates
Nitric oxide (NO) is an important physiological signaling
molecule that can modulate skeletal muscle function
through its role in the regulation of blood flow, muscle
contractility, glucose and calcium homeostasis, and mito-
chondrial respiration and biogenesis [53]. It is now known
that tissue concentrations of nitrate (NO
3-
) and nitrite
(NO
2-
) can be increased by dietary means. Green leafy
vegetables such as lettuce, spinach, rocket, celery and
beetroot are particularly rich in nitrate. Therefore dietary
K. R. Barnes, A. E. Kilding
123
nitrate supplementation represents a practical method to
increase circulating plasma nitrite and thus nitric oxide to
lower the oxygen demand of submaximal exercise (i.e.,
enhances metabolic efficiency and subsequently RE) and
potentially enhance running performance [53,170–176].
The physiological mechanisms responsible for the reduced
oxygen demand following nitrate supplementation could
result from two different mechanisms. First, a lower ATP
cost of muscle contraction for the same force production
(i.e., improved muscle contractile efficiency via sarco-
plasmic reticulum calcium handling or actin-myosin
interaction), or second, a lower oxygen consumption for
the same rate of oxidative ATP resynthesis (i.e., enhanced
mitochondrial efficiency via improved oxidative phos-
phorylation) [53,170,171].
While only one study to date has demonstrated an
improved RE [54] following nitrate supplementation, a
reduced oxygen demand and improved work efficiency
has been reported for several other types of exercise,
including cycling [175–178], walking [54], and knee
extension exercise [174,179]. Larsen et al. [176] reported
that 3 days of sodium nitrate supplementation increased
plasma nitrite and reduced the oxygen demand of sub-
maximal cycling exercise. These findings were corrobo-
rated in a study by Bailey et al. [175] in which nitrate was
administered in the form of beetroot juice. The reduction
in VO
2
after nitrate supplementation was of the order of
5 % in the studies of Larsen et al. [176] and Bailey et al.
[175], in which supplementation was continued for 3–6
days. A similar reduction in steady-state VO
2
has been
reported following acute nitrate supplementation. Van-
hatalo et al. [178] reported a significant reduction in
steady-state VO
2
just 2.5 h following beetroot juice
ingestion.
6.2 Other Nutritional Interventions
There is a paucity of data examining the effects of other
dietary interventions on RE. One investigation found
4 weeks of oral Echinacea supplementation had a trivial
enhancement (mean 1.7 %) on RE [55]. However, the
margin of improvement was well within the normal
variation in RE (typical error of 2.4 % [180]) and could
have occurred by chance. Results from a study examin-
ing caffeine ingestion in cross-country runners suggest
that the ingestion of caffeine at 7 mg kg
-1
of body
weight prior to submaximal running might provide a
modest ergogenic effect via improved respiratory effi-
ciency and a psychological lift [52]. Combined creatine
and glycerol ingestion has been shown to be an effective
means in reducing thermal and cardiovascular strain
during exercise in the heat, without negatively impacting
on RE [51].
6.3 Summary
Although dietary nitrate appears to be a promising ergo-
genic aid, additional research is required to determine the
scope of its effects on well-trained distance runners and
across different competition events. Future research should
also examine the efficacy of using other nutritional inter-
ventions to enhance RE.
7 Conclusions and Future Directions
A variety of training strategies have been adopted in an
attempt to improve RE by modifying one or more factors
that influence metabolic, biomechanical and/or neuromus-
cular efficiency. The most common strategies used are
resistance training, plyometric training and explosive
resistance training. Each of these modes of ancillary
training have been reported to improve RE in recreational,
moderately trained, and highly trained runners through
primarily neuromuscular mechanisms. Results from HIT
studies are unclear, but the best results to improve RE
appear to occur when training at near maximal or supra-
maximal intensities on flat or uphill terrain. Adaptations to
living and training at natural and artificial altitude have
been primarily attributed to increased hematological
parameters that improve RE. There appears to be equivocal
results regarding the effects of stretching or flexibility on
RE. Ingestion of dietary nitrate, especially in the form of
beetroot juice, also appears to hold promise as a natural
means to improve RE. From a practical standpoint, it is
clear that training and passive interventions affect RE, and
researchers should concentrate their investigative efforts on
more fully understanding the types and mechanisms which
affect RE and the practicality and extent to which RE can
be improved outside the laboratory.
Acknowledgments No sources of funding were used to assist in the
preparation of this review. The authors have no conflicts of interest
that are directly relevant to the content of this review.
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