A comparison of barefoot versus shod running on the physiological parameters of running economy, in a submaximal incremental test, a VOtest and an 800 m performance trial

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Journal of Sports Sciences, 2013,
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A comparison of

barefoot versus shod running

on the
physiological parameters of running economy,
in
a
submaximal incremental test
, a

VO

max

test

and
an
800
m
performance trial



A.

J.
JONES


Loughborough College, Radmoor Road, Loughborough UK, LE11 3BT


Submitted
20 March 2013



The aim of this study was to
assess whether

barefoot running

(
BFR
)

improves

running

economy (
RE
)

compared to
shod running (
S
R
)

at speeds
approximate

to race pace, both on
a treadmill and overground.

Eight male participants (age 21.3
+

1.4 years; height 180.4
+

5.5 cm; weight 73.9
+

8.8 kg; m
+

sd) completed a submaximal incremental treadmill test
with, five 4 minute stages at speeds of 9, 10.5, 12, 13.5 and 15 km/h

¹
. At the end of each
stage, VO

, Heart Rate (HR)

and Blood lactate (BLa) were measured. A VO

max

treadmill
test followed where

VO

max
, Velocity at VO

max

(vVO

max
)

and HR were measured. Each
participant completed these tests, BFR and SR on separate occasions. Following laboratory
testing participants completed an 800 m performance trial on an
outdoor
athletics track,
again separatel
y in both conditions.
No significant effect was found in the incremental test
between conditions for
VO

, HR and BLa (
P

>
0.05
)
, but a trend towards lower means when
BFR

was witnessed. No significant difference was found
during the
VO

max

test for VO

max

and HR
(
P

>
0.05
)
,
however vVO

max

was significantly different (
P
= 0.021) between
conditions. Times recorded for the 800 m trial, were not significantly different
(
P

>
0.05
)

between conditions, although five participants ran faster BFR. It is concluded, overall BFR
does not have a significant effect on RE compared to SR at faster speeds. This is likely a
result of fatiguing of intrinsic foot muscles which enhance RE when BFR.
Future research
may wish to assess whether BFR training strengthens the intrinsic foot
muscles
and

delays
this premature fatigue
debilitating the BFR mechanisms which improve RE.


Keywords:

barefoot, shod, running economy, incremental, VO

max
, 800 m.


Introduction


West
on
et al
. (2000) found Kenyan
runners, despite having a lower
VO

max

than Caucasian
runners;

had
greater running economy (RE). This
research indicated RE is perhaps
more important than
VO

max
, and a
key factor in performance (Weston
et
al
., 2000; Saunders
et al
., 2004;
Gaeini
et al
., 2008). RE is defined as
‘the energy demand for a given
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velocity of submaximal running’ and
determined by measuring the steady
-
state consumption of oxygen (VO

)
(Saunders
et al
., 2004). However as
the energy cost of running is
composed of both aerobic and
anaerobic metabolism and RE
represents this energy cost; anaerobic
sources as well as aerobic (i.e. VO

)
should be measured (Conley and
Kr
ahenbuhl, 1980; Morgan and Craib
,
1992; Saunders
et al
., 2004).


Recent research has sug
gested
barefoot running (BFR) may improve
RE (
Divert
et al
., 2008; Hanson
et al
.,
2010; Perl, Daoud and Lieberman,
2012). Indeed, some Kenyan athletes
have stated they run barefoot at a
young age, perhaps explaining the
better RE in Kenyan runners found in
Weston
et al
. (2000) study. For
instance, following winning the
Olympic 800 m

and setting a new
world record, David Rudisha of Kenya
stated i
n an interview in the Express;
‘when I started it was barefoot; I didn’t
know how to use trainers on the dirt
tracks’. This raises the intriguing
question, of whether BFR enhances
performance

by improving RE.

The majority of past research has
studied the relationship between
running shoes and injury rates
(Robbins and Hanna, 1987; Hamill
and Bates, 1988; R
obbins and Waked,
1997; Richards, Magin and Callister
,
2009). Kerrigan
et al
. (2009) rep
orted
increased joint torques at the ankle,
knee and hip when running in shoes
compared to BFR, likely resultant of
the raised heel of running shoes. This
elevated heel produces a greater
collision force on impact,
supposedly
a result of individuals rear
-

foot striking
(RFS), also known as ‘shod’ running
(SR)

(Kurz and Stegiou, 2004; Divert
et al
., 2005; Lieberman
et al
., 2010;
Hanson
et al
., 2010). Greater collision
forces relate to ground reaction force
(GRF); a potential mechanism for
injury whilst run
ning in shoes (Hanson
et al
., 2010).

BFR utilises a coordination strategy
initiated at the ankle to reduce the
GRF and resulting pain from heel
-
striking, apparently achieved by

planting the fore
-
foot before bringing
the heel down (Divert
et al
., 2005;
Ku
rz and Stegiou, 2004;
Lieberman
et
al
.,
2010; Hanson
et al
., 2010).

The
pain is allegedly lessened by the force
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during each landing, being distributed
across a greater surface area,
decreasing the amount of force the
heel receives (Freychat
et al
., 1996;
De Wit, De Clercq and Aerts, 2000;
Divert
et al
., 2005; Hanson
et al
.,
2010). Reduced GRF also lowers the
metabolic cost of running, resulting in
enhanced RE

(Kram and Taylor, 1990;
Farley and McMahon, 1992; Heise
and Martin, 2001; Saunders
et al
.,
2004).

In addition to GRF reduction; elastic
energy storage and restitution can
enhance RE. Theoretically
greater
restitution of elastic energy in the
muscles reduces the demand for
aerobic energy production
consequently decreasing the VO


demand and enhancing RE
(
Cavagna
et al
., 1964;
Saunders
et al
., 2004;

Shephard and Astrand, 2008
).
It has
been proposed BFR improves RE
through this mechanism (Divert
et al
.,
2005; Hanson
et al
., 2010).

This relates to the mentioned change
in gait. Repor
tedly more than 75% of
shod runners’ rearfoot strike, whereas
BFR often results in a forefoot strike
(FFS) (
Kurz and Stegiou, 2004;
Divert
et al
., 2005; Hanson
et al
., 2010;
Lieberman
et al
.,
2010; Perl, Daoud
and Lieberman, 2012
). These strike
types, produce slightly different mass
-
spring mechanics in the tendons,
ligaments and muscles of the lower
extremities, which store and recoil
elastic energy allowing the body’s
mass to be pushed upward and
forwards (Biewener, 2003;
Perl, D
aoud
and Lieberman, 2012
). It is reported
the FFS when BFR, uses these
structures more effectively to utilise
elastic energy

(Perl, Daoud and
Lieberman, 2012
).

One potential mechanism allowing this
is
greater elastic energy storage in the
Achilles tendon
(Perl, Daoud and
Lieberman, 2012) which recovers 35%
of the mechanical energy the body
generates each step (Ker
et al
., 1987;
Alexander, 1991). Due to controlled
dorsiflexion as the heel descends
during a FFS; the Achilles tendon is
stretched, whilst the t
riceps surae
contracts eccentrically or isometrically,
permitting more elastic energy storage
and recoil (Hof, Zandwijk and Bobbert,
2002; Perl, Daoud and Lieberman,
2012). Conversely the Achilles tendon
does not stretch at impact but
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predominantly from d
orsiflexion after
the foot is flat and the tibia passes
over the foot, when RFS resulting in
less storage and return of elastic
energy (Perl, Daoud and Lieberman,
2012).


Another possible mechanism causing
differences in RE between BFR and
SR is energy st
orage in the arch (Perl,
Daoud and Lieberman, 2012). It is
estimated 17% of the mechanical
energy generated per step, is
recovered by the elastic structures in
the longitudinal and transverse arches
of the foot (Ker
et al
., 1987); thus BFR
likely

store
s

mo
re elastic energy due
to external arch supports caused by
FFS, which is lessened by vertical
arch compression during the stance
phase when RFS (SR), limiting how
much the arch can stretch and recoil
(
Bramble and Lieberman, 2004;
Hanson
et al
., 2010;
Perl,
Daoud and
Lieberman, 2012). Furthermore due to
GRF being placed on the arch below
the ankle during SR, where it is
opposed by the downward force of the
body’s mass and force near the arch’s’
apex; the arch likely stiffens until the
foot flattens, inhibitin
g elastic storage
of energy that impact creates (Perl,
Daoud and Lieberman, 2012).


The described change in gait may not
offer the only explanation for improved
RE when
BFR. Burkett, Kohrt and
Buchbinder (1985) found BFR reduced
the oxygen cost of running when
compared to shoes and shoes with
orthotics although they were uncertain
whether this was resultant of a change
in gait, shoe mass or both. They found
running in sho
es needed 1.3% more
oxygen, compared to BFR, and
running in shoes with orthotics needed
2.4% more oxygen compared to BFR,
conceivably due to the extra weight of
orthotics. These percentages were
approximately the differences
foreseen for the additional sh
oe mass
(Frederick, 1984).


Divert
et al
.

(2008) showed 350 g
weighted socks and 350 g shoes,
elicited greater VO


values, than BFR.
Due to runners being 3% more costly
in 350 g shoes and socks, than BFR
they concluded the cost difference
was resultant of mass. However they
noted; 75% of participants had no
impact peak on ground contact when
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BFR (Divert
et al
., 2008;
Perl, Daoud
and Lieberman, 2012). This indicates
a shift from RFS to FFS, as a high
impact peak which is associated with
RFS is painful without the cushioned
heel of shoes which slows the impact
rate (Perl, Daoud and Lieberman,
2012). Hence the adopted FFS

when
BFR prevents the impact peak to
reduce pain
(Cavanagh and Lafortune,
1980; Ker
et al
., 1987;

Shorten, 1993;

Perl, Daoud and Lieberman, 2012).


Similarly Squadrone and Gallozzi
(2009) found SR was 1.3
-
2.8% more
costly than BFR, although shoe mass
was
not controlled, and it was found
participants when BFR switched from
RFS to FFS
, further supporting the
change in gait theory.
Recent research
by Hanson
et al
.

(2010) found BFR
was 3.8% more economical than SR,
although they did not control shoes
mass, or strike type.


Results from Divert
et al
.

(2008) give
the best support for shoe mass
affecting RE. During running the
oxygen cost, increases approximately
1% e
very 100 g of mass (Frederick,
1984); thus the 3% difference between
BFR and SR recorded in Divert
et al
.

(2008) study corresponds with the
additional 350
g of mass. Thus it is
apparent BFR

is more economical,
consequential of a reduction in mass
and chang
e in gait.


The majority of previous research,
examining BFR in comparison to SR
on RE, has been completed on a
treadmill, at moderate speeds and
hasn’t been event specific. The
speeds used in past studies examining
the effects of BFR on RE, have ranged
fr
om 10.8


13 km/h (Burkett, Kohrt
and Buchbinder, 1985; Divert
et al
.,
2004; Divert
et al
., 2008; Squadrone
and Gallozzi, 2009; Perl, Daoud and
Lieberman, 2012). Recent research by
Hanson
et al
.

(2010) studied the
effects of BFR compared to SR on a
treadmi
ll and an indoor track
(overground), at 70% of participants’
v
VO

max
. The average speed of
participants at 70% v
VO

max

in this
study was 10.7 km/h, fitting in the
range of past studies. They
recommended further study of BFR
overgr
ound, and at faster velocities
which are
approximate

to race pace
(Hanson
et al
., 2010).


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Therefore, the current study will use
three tests performed at faster speeds.
A submaximal incremental test, with
the last two stages of the test (13.5
and 15 km/h)
being faster than past
research
(Burkett, Kohrt and
Buchbinder, 1985; Divert
et al
., 2004;
Divert
et al
., 2008; Squadrone and
Gallozzi, 2009; Perl, Daoud and
Lieberman, 2012)
, will be used to
assess the effect of BFR on RE at
faster velocities.

This will b
e followed
by a VO

max

test, which
is
approximate

to
5000m race pace
, suiting Hanson
et
al
.

(2010) suggestion. For instance,
VO

max

percentages in the

5000 m

is
~96%

(Jones, 2007)
imply
ing

vVO

max

will be approximate to th
is race pace
(Fee, 2005). It’s
also noteworthy no
studies examining BFR and RE have
used a VO

max

test.


It is hypothesized both the incremental
and VO

max

test will result in better RE
when BFR compared to SR. This is
predicted, due to BFR instigating
greater storage and restitution of
elastic energy at faster velocities,
subsequent of greater pre
-
stretch
levels and reduced contact time
enhancing the stretc
h shortening
cycle, enabling less metabolic energy
to sustain body movement
(Divert
et
al
., 2004; Abernethy
et al
., 2005;
Hanson
et al
., 2010).

Finally an 800 m performance trial will
be completed, fitting the gap in
literature for event specific BFR
rese
arch. It is expected due to even
greater speed compared with the other
tests; BFR will elici
t greater benefits
on RE. Thus
t
he overall aim of the
current study is to e
xamine whether
BFR improves RE
in comparison to
SR
,

at faster speeds
approximate

to
race pace, both on a treadmill and
overground.


Method


Subjects

8 male college students participated in
the current study. All subjects were
physically active. Demographics for
participants can be found in Table 1.
Criteria for participation excluded
participants with current lower
extremity injuries, heart conditions

or
any illnesses that might be provoked
by strenuous activity such as
pulmonary, metabolic or
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cardiovascular conditions (Heyward,
2006). The study received ethical
clearance from the Loughborough
College ethics committee.


Table 1.
Demographics of
participants.



Protocol

A repeated measures design, with four
testing sessions inc
orporating six
different tests
was used. Namely a
submaximal incremental test and
VO

max

test performed on a treadmill
and an 800 m performance trial on an
outdoor

synthetic

athletics track, each
completed twice both barefoot and
shod.


Prior to testing; all participants were
subject t
o a familiaris
ation trial. During
this trial,

participants completed
appropriate documents (including
informed consent and a physical
activity readiness questionnaire), were
permitted to run barefoot on the
treadmill for familiarisation (Hanson
et
al
., 20
10), and were informed of the
protocol.
Feedback from participants
in the familiarization trial revealed the
treadmill belt generated heat after a
duration which was abrasive to the
feet. Thus during the barefoot
condition when testing, participants
wore s
ocks for protection.

Laboratory tests in the two conditions
(i.e. barefoot and shod), was
conducted on two separate occasions
in a
randomised order.

Participants
were advised to refrain from exercise
and consume a high carbohydrate
meal 24 hours prior to testing, and
also

to

consume
no caffeine 4 hours
before testing (Jones, Vanhatalo and
Doust, 2009). Upon arrival
demographics were measure
d

with a
He
avy duty analogue scale (SECA,
Birmingham, United Kingdom) for
weight and a portable height measure
(SECA, Birmingham, United Kingdom)
for height.


Gender

Age

Height
(cm)

Mass
(kg)





Male
(n=8)

21.3
+

1.4

180.4
+

5.5

73.9
+

8.8

(Mean
+

Standard deviation)

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All laboratory testing was condu
cted
on a motorised treadmill (H
p cosmos,
Traunstein, Germany). Testing beg
an
with a 5 minute warm
-
up on the
treadmill, at a self
-
selected pace
dictated by participants
(
Jones,
Vanhatalo and Doust, 2009;
Hanson
et
al
., 2010). The speed of this was
recorded for each participant, so the
same pace could be used in the
opposite condition ensuring
consistency.
Following this, a 5 minute
warm
-
up was allocated t
o inhibit
elevated baseline O


consumption
(Biener, 2007) and t
o ensure
restoration of VO


values to normal
values
(Ozyener
et al
., 2001)
.



An incremental test was then
conducted with 4 minute stages at
speeds of 9, 10.5, 12, 13.5 and 15
(
km.h


¹);
a protocol suitable for
eliciting lactate threshold and

the
o
nset of Blood Lactate Accumulation
(OBLA) (Jones, Vanhatalo and Doust,
2009).
These speeds are
appropriate

for ‘students who keep fit but do not
take part in competitive sports’ (Jones,
Vanhatalo and Doust, 2009); suiting
the characteristics of participant
s.
To
simulate the energy costs of outdoor
running, the treadmill was set at a
grade of 1% (Jones
et al
., 1996).

In the final minute of each stage;
expired air was collected via tubing
connected to Douglas bags (Hans
Rudolph, Shawnee, United States),
whic
h was later measured to
determine VO

. Participants expired
through a breathing apparatus
connected to the tubing, which was
attached to a frame, with high
-
flow,
low resistance valves allowing gas to
be collected into the Douglas bags.

H
eart rate (HR) was
also recorded
using a heart rate monitor (Polar
Electro, Warwick, England) strapped
around participant chests calibrated to
a watch (Polar Electro, Warwick,
England).


Following collection, participants were
asked to briefly dismount the treadmill
so bloo
d lactate (BLa) could be
measured. Blood was drawn from a
finger prick made using a lancet
(Accu
-
Chek, Sussex, United
Kingdom), and was measured using a
Lactate Pro measuring device with test
strips (Lactate Pro, Carlton, Australia).
Participants then
reco
mmenced the
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test, where the speed was increased
to the next stage.


Upon completion of the test,
participants had ~20 minute
s

recovery
(Thevenet
et al
., 2008; Ingham
et al
.,
2013). The
VO

max

test followed with
an initial velocity of 10 km.h

¹,
increased by 1
km.h

¹
every two
minutes until volitional exhaustion
(
Bosquet
et al
., 2007). Participants
were asked to indicate when they
could only continue for further two
minutes. During this time
VO

max

was
measured
, again using the Douglas
bags
and HR was recorded in the
same
manner as previously
described
.

Once both tests were complete
d

the
expired air collected in the Douglas
bags was analysed. The fraction of
expired Oxygen and Carbon Dioxide
were measured using a Gas analyser
(Servomex, Crow
borough, United
Kingdom). The volume of expired gas
collected was then measured using a
Dry gas meter (Harvard apparatus,
Kent, United Kingdom).

Figures
collected from these processes were
recorded on a data collection sheet.

Following this the Douglas bag
s were
emptied using a vacuum. Th
e
recorded

data was then entered into
Expired Air Software to calculate VO


and
VO

max
.

Participants returned to complete both
tests in the opposite condition
>

48
hours later to permit slow component
recovery

(McArdle, Katch and Katch,
2007
). On average; participants had 6
days between trials (6.1
+

4.4 days; m
+

sd).

Following laboratory testing;
participants completed an 800 m
performance trial
, on an
outdoor
synthetic
athletics track
.
All
participants completed a warm
-
up
consisting of a 10 minute self
-
paced
jog, 2 x 50 m strides and a continuous
high
-
intensity 200 m run, which is
suggested to produce optimal 800 m
performance (Ingham
et al
., 2013).
This
was

followed
by

a 25 minute
seate
d rest, with 2 x 50 m strides in
the last 5 minutes, before completing
the trial (Ingham
et al
., 2013).
Participants were then instructed to
complete the 800 m performance trial
at optimal effort.

Times were
measured to the nearest 0.1 (Bosquet
et al
., 20
07). Again
48 hours recovery
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10


0
50
100
150
200
250
9
10.5
12
13.5
15
Heart Rate (bpm)

Speed (km/h)

Shod
Barefoot
Figure 2
. Mean
HR

v
alues for the five
increments for

barefoot and shod
running.
Bars denote mean values, and error bars
show standard deviations.

0
10
20
30
40
50
60
9
10.5
12
13.5
15
VO


(ml.kg.min)

Speed (km/h
)

Shod
Barefoot
Figure 1
. Mean VO


v
al略猠for t桥 fiv攠
i湣牥n敮t猠 f潲

扡ref潯t 慮d 獨sd
r畮湩湧. B慲猠摥湯t攠m敡渠v慬略
猬 慮搠
敲e潲 扡r猠獨sw 獴慮摡rd 摥vi慴楯湳n

was provided, before returning to
complete the trial in the opposite
condition.


Statistical Analyses


Statistical analyses were performed
using the Statistical Package for the
Social Sciences, version 20 (SPSS
Inc., Chicago,
United States). Less
than 50 subjects (
n
= 8) were used in
the current study; thus a Shapiro
-
Wilk
normality test, was used to evaluate
whether data met parametric
assumptions (
>
0.05). All variables
other than
VO

max

were normally
distributed. For the incre
mental test a
Two Way Analysis of Variance was
used

to establish the amount of
variance due to BFR or SR for each
variable
.

Paired samples t
-
tests were
performed for data collected in the
performance trial and for HR and
vVO

max

collected in the VO

max

test
,
to determine if any effects were
significant
. For the
VO

max
data
, a
Wilcoxon
matched pairs

test was used
as a non
-
parametric alternative.

Data
was considered

statistically

significan
ce at an alpha

level of

P
=
<
0.05 for all analyses.


Results

Mean

values for the five speeds in the
incremental test for barefoot and shod
running, are reported in Figure 1(VO

),
Figure 2 (HR) and Figure 3 (BLa).


There was no significant effect
between running barefoot and shod at
the five speeds in the incremental test,
on measures of VO


(
F
=
(1, 7
)

1.028
,
P
= 0.344),

HR (
F
=
(1, 7
)

1.198
,
P
= 0.310)

and BLa (
F
=
(1, 7
)

4.785,
P
= 0.065).
















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0
2
4
6
8
10
12
9
10.5
12
13.5
15
Blood lactate (mmol)

Speed (km/h)

Shod
Barefoot
Figure 3
. Mean
BLa

v
alues for the five
increments for

barefoot and shod
running. Bars denote mean values, and
error bars show standard deviations.

0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
Shod
Barefoot
VO₂
max
(ml.kg.min)

Condition

Figure 4
. Mean
VO

max

for the

VO

浡m

test
for

barefoot and shod
running. Bars denote
mean values, and error bars show
standard deviations.

0
2
4
6
8
10
12
14
16
18
20
22
Shod
Barefoot
vVO

max

(km/h)

Condition

Figure 5
. Mean
v
V
O

max

for the

VO

max

test for

barefoot and shod
running. Bars
denote mean values, and error bars show
standard deviations.

2.00
2.05
2.10
2.15
2.20
2.25
2.30
2.35
2.40
1
2
3
4
5
6
7
8
Time (minutes.seconds)

Participant

Shod
Barefoot
Figure 6
.
Time taken for participants
to complete the 800 m time trial when
running shod and barefoot.












Mean values for the
VO

max

test for
both conditions, are presented in
Figure 4 (VO

max
) and Figure 5
(
v
VO

max
).

There was no significant difference
between both conditions on measures
for VO

max

(
P
= 0.483) and HR (
t
(7)
=
0.000,
P
= 1.000) in the VO

max

test.
However
v
VO

max

was significantly
different (
t
(7)

=
-
2.966,
P
= 0.021)
between both conditions.















Time taken for each participant to
complete the 800 m time trial when
running shod and barefoot is shown in
Figure 6.

Times recorded for the 800 m trial,
were not significantly different (
t
(7)
=
1.231,
P
= 0.258) between running
barefoot and shod.








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12


Discussion

In the current study; faster speeds
approximate

to race pace, were used
to assess whether

BFR is more
economical than SR.

There was a
trend towards lower means for VO


during the first four phases of the
incremental test when BFR compared
to SR. This indicates reduced oxygen
consumption to perform the same
workload which enhances RE
(Thomas, Fernhall and Grant, 1999;
Saunders
et al
.,
2004; McArdle, Katch
and Katch, 2007) and correlates with
reduced VO


values and enhanced
RE witnessed in past research when
BFR (Burkett, Kohrt and Buchbinder,
1985; Divert
et al
., 2008; Hanson
et
al
., 2011).

Reduction in mean HR when BFR
(Figure 2)

was l
ikely responsible for
th
e

decrease in VO


during the first
four phases. For instance, myocardial
VO


which constitutes a significant
portion of overall VO


is mediated by
HR (Saunders
et al
., 2004). Reduction
in myocardial VO


is resultant of
decreased HR
and increased stroke
volume (Bailey and Pate, 1991;
Saunders
et al
., 2004). Although
stroke volume was not measured; the
reduction in mean HR values when
BFR indicates reduced myocardial and
consequently overall VO

, which
improves RE (Bailey and Pate, 199
1;
Saunders
et al
., 2004).
This is
consistent with Hanson
et al
., (2010)
who found a decrease in heart rate
and overall VO


when BFR compared
to SR.

However, unlike past research
(
Hanson
et al
., 2010; Perl, Daoud and
Lieberman, 2012);

no significant effect
was found between the conditions for
VO


or HR
, meaning the
improvements when BFR were
unsubstantial in enhancing RE.
Furthermore mean data for VO


during
the last stage (15 km/h) showed SR
had a lower mean VO


than BFR
(Figure 1). P
erhaps the faster speeds
used in this study compared to past
research (
Hanson
et al
., 2010; Perl,
Daoud and Lieberman, 2012)

caused
fatigue

which debilitated

the
anatomical structures that allow BFR
to benefit RE.

Although it is beyond
the scope of this st
udy to definitively
prove

due to only measuring
physiological variables
;
it is
conceivable, the fatigued anatomical
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13


structures
related to a

change to a
FFS

when participants ran barefoot.
For instance, all participants reported
contracting blisters on
their forefoot
whilst BFR during the familiarisation
trial. As participants prior to the study
likely utilised a rearfoot strike when SR
(
Perl, Daoud and Lieberman, 2012);
a
lack of adaptation to a FFS when BFR
probably caused blisters on the
forefoot (Squ
adrone and Gallozzi,
2009). This shift to a FFS when BFR,
is supported by past research

(Kurz
and Stegiou, 2004;
Divert
et al
., 2005;
Lieberman
et al.,
2010; Hanson
et al
.,
2010).

U
tilising

a FFS when BFR
, reduces

GRF (Kurz

and Stegiou, 2004;
Saunders
et
al
., 2004; Divert
et al
.,
2005; Lieberman
et al
., 2010; Hanson
et al
., 2010). This
mechanism
improves shock attenuation
by
reducing the shock on impact (Shorten
and Winslow, 1992; Hamill, Derrick
and Holt, 1995; Derrick, Hamill, and
Caldwell, 1998; Derric
k, DeReu and
McLean, 2002; Mercer
et al
., 2003).
As utilising a FFS reduces GRF and
enhances shock attenuation through
muscle contractions and energy
absorbing capabilities of anatomical
structures (Valiant, 1990); when these
structures are fatigued their
ability to
reduce shock are decreased (Mercer
et al
., 2003).

It is suggested these structures
became fatigued by the
last stage of
the incremental test

when BFR,

reducing shock attenuation and
increasing th
e metabolic cost of
running,
consequently
causing
the
higher mean VO


value (Kram and
Taylor, 1990; Farley and McMahon,
1992; Heise and Martin, 2001;
Saunders
et al
., 2004). Specifically,

this could be a result of

fatiguing of
the
intrinsic foot muscles which allow
flexibility for shock absorption and
at
tenuation of forces (
Lynn, Padilla
and Tsang, 2012).
Research shows
individuals who wear shoes with arch
support, have weaker intrinsic foot
muscles, than those who are
accustomed to BFR (Bruggemann
et
al
., 2005). Due

to participants in the
current study b
eing habituated to
running in shoes; their intrinsic foot
muscles were likely weaker requiring a
higher muscle cost to stabilize the
arch, resulting in quicker fatigue
(Bruggemann
et al
., 2005; Perl, Daoud
and Lieberman).
Furthermore, as
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14


these foot muscle
s are responsible for
elastic energy storage in the arch;
fatiguing of these will reduce RE
(Perl,
Daoud and Lieberman, 2012;
Lynn,
Padilla and Tsang, 2012
). The higher
VO


during the last stage
confirms

this
as a decrease in elastic energy
utilisation; increases the submaximal
VO


demand

(Cavagna
et al
., 1964;
Saunders
et al
., 2004).


Mean BLa values
supports
commencement of fatigue occurring
during the latter stages when BFR.
The
onset of blood lactate
(OBLA)
occurs when BLa increases above a
baseline of 4 mmol (McArdle, Katch
and Katch, 2007; Baechle and Earle,
2009).
Results showed

a mean BLa
value of 3.9 mmol when SR at the end
of the third stage of the incremental
test, compared to a mean value of 3.
3
mmol when BFR (Figure 3). It is
speculated when SR, BLa generally
reaches OBLA sooner considering the
mean value was 0.1 mmol away from
the proposed OBLA baseline, during
the third stage. Mean values indicated
OBLA when BFR mostly occurred
during the fou
rth stage.

Physiologically, OBLA is considered
the point of celluar hypoxia in the
contracting muscles resultant of a
limited rate of oxidative
phosphorylation and increased
reliance on the glycolytic system which
produces hydrogen (Wasserman,
1984;

McArdl
e, Katch and Katch,
2007; Eston and Reilly, 2009
).
The
build
-
up of hydrogen in the skeletal
muscles
subsequently

causes fatigue
(Gladden, 2001; Saunders
et al
.,
2004; Plowman and Smith, 2008;
Gaeini
et al
., 2008).


Although OBLA was reached sooner
when
SR; it is suggested when OBLA
occurred during the fourth stage when
BFR, the associated fatigue was more
debilitating to the weaker intrinsic foot
muscles
, thus

reducing RE
(Bruggemann
et al
., 2005; Perl, Daoud
and Lieberman).

This explains the
conflict wi
th past research which has
shown significant improvements in RE
when BFR (
Divert
et al
., 2008; Hanson
et al
., 2010; Perl, Daoud and
Lieberman, 2012)
. For instance;

the
slower speeds in these studies
unlikely elicited hydrogen build
-
up
,
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15


which allowed BFR me
chanisms to
improve RE.

Based on this concept, it would
suggest further reduction in RE when
BFR during the

VO

max

test due to the
greater
intensity

causing more severe
fatigue of the intrinsic foot muscles
(Wasserman, 1984;

Xu and Rhodes,
1999;
McArdle,
Katch and Katch,
2007; Eston and Reilly, 2009
).


As a
result, i
t would be expected
due to
ineffective

voluntary neuromuscular
function of the intrinsic foot muscles
when BFR;

vVO

max

would be reduced
(
Ha¨kkinen
,

1994;

Paavolainen
et al
.,
1999).

Though

there was
approximately a 1 km/h improvement
for mean vVO

max

(Figure 5) when
BFR, indicating improved RE;
this
finding can be
applied

to support the
concept of fatiguing structures.

It has been suggested athletes will
begin exercise with elevated
baseline
O


consumption, following prior
activity (Biener, 2007). The elevated
VO


at the beginning of exercise
allows more initial work to be
performed aerobically, which spares
anaerobic sources and minimizes the
accumulation of waste products which
crea
te fatigue (Bishop, 2003; Biener,
2007). As the incremental test was
performed prior to the VO

max

test

it is
speculated, participants
entered the
VO

max

test with an elevated
baseline
O


consumption

decelerating

the
onset of fatigue of the intrinsic foot
muscles, allowing BFR to yield greater
benefits on RE for longer.

The increase velocity supports this.
Reduction in time for the structures of
the foot to fatigue would allow longer
utilisation of elastic energ
y, which
contributes to propulsion (Aruin and
Prilutskii, 1985; Aura and Komi, 1986;
Saunders
et al
., 2004).
This accounts
for the incre
ase velocity achieved
when BFR
and favours the theory;

a
change in gait to a FFS when BFR
causes

greater elastic energy
utilisation
,

improving
RE (Saunders
et
al
., 2004; Perl, Daoud and Lieberman,
2012)
.

Mean values for VO

max

further
confirm this

notion of enhanced RE
during the VO

max

test, grounded in a
suggested paradigm between RE and
VO

max
. The paradigm suggests;
maximal work capacity of an athlete
determines the VO


attained during
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the VO

max

test, meaning whenever
athletes have similar peak work rates,
RE will be inversely related to VO

max
(Noakes, 1998; McCann and
Higginson, 2008). In literal terms; the
greater

the RE, the lower the VO


achieved at peak work rate (i.e. peak
running speed) (McCann and
Higginson, 2008). Thus, as BFR
produced a lower mean VO

max

value
than SR (Figure 4); the reduced
VO

max

at the peak work rate indicates
improved RE, most likely ac
hieved by
the change in gait.

D
uring the 800 m performance trial;
five participants ran quicker when
BFR
, perhaps indicating further
improvements in RE

(Figure 6). This
again

supports t
he greater elastic
energy utilis
ation concept, as at higher
speeds, elastic recoil yields greater
energy and accounts for most of the
work (Taylor, 1994; Cavagna and
Kaneko, 1977; Saunders
et al
., 2004;
Hanson
et al
., 2010).
However no
significant difference was found
between the condit
ions

T
he lack of
significant effect again
relates

to fatigue of the intrinsic foot
muscles debilitating the benefits of
BFR.

At race paces; past research
conflicts on whether alterations in

running kinematics associated with
fatigue, reduces RE
(Ellio
t
t an
d
Robert, 1980; Nicol, Komi and
Marconnet, 1991; Kryöläinen
et al
.,
2000). Nicol, Komi and Marconnet
(1991) and Kryöläinen et al. (2000)
found reduced RE was not associated
with changes in running mechanics
when in a fatigued state, following a
marathon. However due to the
marathon, being mainly aerobic
(Coyle, 2007); t
hese findings are
limited when considering the 800 m
requires significant contributions from
both the aerobic and anaerobic
system (Thomas
et al
., 2005).



As previously mentioned; the
anaerobic contribution, causes fatigue
of the skeletal muscles (Gladden
,
2001; Saunders
et al
., 2004; Plowman
and Smith, 2008; Gaeini
et al
., 2008;
Hanon and Thomas, 2011).
It is
probable, in the same

manner

as
su
ggested in the incremental test;
a
naerobic contribution caused fatigue
of the intrinsic foot muscles
limiting

the

biomechanical mechanisms of BFR.



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Additionally fatigue may have been
caused sooner in some participants
due to an ineffective pacing strategy
(Thomas
et al
., 2005
;

Hanon and
Thomas, 2011) which is a potential
limitation of this study. Fast
-
start
pacing strategies for example,
possess the potential to cause
premature fatigue in the muscles due
to disturbances in muscle pH,
inhibiting aerobic capacity
(Jubrias
et
al
.,

2003;

Hanon and Thomas, 2011
).
This could result in some participants
experiencing fatigue sooner, which
would debilitate mechanisms of BFR
quicker,
reducing the

time with the
benefits of BFR.

Another limitation of this study was the
different shoes worn
by participants.
This is limiting as difference in mass
could distally increases the aerobic
demand of running (Myers and
Steudel, 1985; Jones
et al
., 1986;
Saunders
et al
., 2004). Past research
has shown an increase in VO

,
ranging from 4.5
-

14% per kilog
ram of
load carried on the feet (Martin, 1985;
Myers and Steudel, 1985; Jones
et al
.,
1986). Thus, caution should be taken
when drawing on an overall
percentage of VO


improvement for all
participants. For example, difference
in shoe mass between participa
nts will
cause variation in VO


values when
SR meaning when BFR; the reduction
in VO


in participants may not be
proportionate. Nevertheless, each
participant wore their own same shoes
during testing, preventing variation on
an individual basis.

Furthermor
e, m
ost research
measuring RE has used non
-
competitive running speeds, and has
not included the oxygen demand of
overcoming environmental factors and
surface (Saunders
et al
., 2004;
McCann and Higginson, 2008).
Although these restrictions are rational
for

achieving repeatable measures of
RE (McCann and Higginson, 2008);
the current study has partly deviated
from these restrictions, to attempt to
understand the application of BFR in a
performance scenario. For instance
the 800 m performance trial was
comple
ted at competitive running
speed, and was performed
overground. Although this may
not be
a reliable measure of RE;

when
combined with fin
dings in the
laboratory testing,

this has allowed
application of the mechanisms of BFR
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18


in a performance scenario which
is
highly relevant to Sports Science.

In conclusion, BFR does not seem to
significantly improve RE when
compared to SR at faster speeds
closer to race pace, as hypothesized.
It is

probable due to
the
anaerobic
contribution at faster speeds; weak
intrinsic foot muscles of participants
fatigued

(
Bruggemann
et al
., 2005)
preventing their mechanism to
significantly improve RE when BFR.
Although this conflicts with past
research (
Divert
et al
., 2008; Hanso
n
et al
., 2010; P
erl, Daoud and
Lieberman, 2012); the slower speeds
used in these studies, unlikely elicited
an anaerobic reaction preventing
fatigue debilitating the BFR
mechanisms which improve RE.
Indeed the
VO

max

test in present
study likely had a delayed anaerobic
response due to an
elevated baseline
O


consumption

caused by the
incremental test. As a result fatiguing
of BFR mechanisms was preventing
allowing enhanced RE.
Thus it is
concluded;
though BFR ho
lds
me
chanisms which benefit RE,
at
faster speeds
which require anaerobic
energy
these mechanisms are
debilitated.

It is apparent from these
findings;

BFR
does not instantly enhance RE as
previously alluded to (
Divert
et al
.,
2008; Hanson
et al
., 2010; P
erl,
Da
oud and Lieberman, 2012)
.
Perhaps BFR training, could
strengthen the intrinsic muscles of the
foot (Williams, Green and Wurzinger,
2012) reducing
susceptibility to
fatigue, and allowing the BFR
mechanisms to have a more positive
effect on RE. Indeed, Utz
-
Meager,
Nulty and Holt (2011) found adaptation
in running biomechanics following a 2
week BFR training plan. Due to a
dearth of research in this area; future
studies

may wish to examine the effect
of BFR training programmes on
performance.

Additionally future research may
consider

comparing BFR with running
in athletic spikes overground. Spikes
have been found to produce a larger
vertical impact force and loading rat
e,
similar to BFR (Dickinson
et al
., 1985;
De Wit
et al
., 1996; De Wit
et al
.,
2000; Logan
et al
., 2010). Due to
causing similar biomechanics to BFR;
spikes may provide similar benefits
Journal of Sports Sciences, 2013,
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and perhaps would be a more suitable
option because of foot protection
. Also
spikes may provide support of the arch
similar to SR, preventing fatigue
of
intrinsic foot muscles
(
Bruggemann
et
al
., 2005). This would allow for better
utilisation of elastic energy
, and thus
enhance RE

(Logan
et al
., 2010).



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