Do Fit-Flops Increase Energy Expenditure During 3 Simulated Tasks of Daily Living?

8/11/2019 Do Fit-Flops Increase Energy Expenditure During 3 Simulated Tasks of Daily Living?

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1006877BSc (Hons) Applied Sport and Exercise Science

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Module number: HS4101Research title: Do FitflopstmIncrease Energy Expenditure In Women

During 3 Simulated Activities Of Daily Living?Research Supervisor: Dr Katherine BurgessDate of hand-in: 02 May 2014Student number: 1006877Word count: 8500 (ex citations (618)

TurnItIn checked: Yes


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DO FITFLOPSTMINCREASE ENERGY

EXPENDITURE IN WOMEN DURING

3 SIMULATED ACTIVITIES OF DAILYLIVING?

Pete Gilpin


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Contents:

Acknowledgements 3

Abstract 4

Introduction 5

Project Aims 14

Methodology 15

Results 21

Discussion 24

Conclusion 30

References 32

Appendices 42


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MBTTM, Sketchers Shape-upTMand Stretch WalkerTMand the variable density sole

used in the FitFlopTMrange and to a lesser extent in the MBTTM. (Appendix 2)

The first unstable shoes were developed under the view that the combination of

contemporary cushioned footwear and the modern built environment has

diminished postural control of the lower limb by the small extrinsic muscles ofthe foot thereby exposing individuals to increased injury risk (Landry et al.

2010). Indeed, Nigg et al. 2005 used a theoretical mechanical model to show

that the smaller muscles of the foot may react faster to perturbations than the

larger muscles, providing support for the hypothesis of training them. However

it is not certain whether these observations would still hold in-vivo. Despite the

numerous studies that have subsequently examined muscle activation and EE in

unstable shoes, the findings have been variable and thus far inconclusive. In

addition, the methodological differences in their approaches have also made

comparisons challenging.

Certainly, the presence of instability and devices such as the wobbleboardTM

designed to induce it, are reported to increase electromyographic (EMG) activity

in both static and dynamic conditions, even in the well resistance trained (Wahl

and Behm 2008; Anderson et al. 2013). Muscle activation is closely associated

with force output (Hof 1984; Alkner et al. 2000), which is in turn associated withmetabolic energy rate (Hawkins and Mol 1997; Umberger et al. 2003). The

entire relationship is a more complex interaction of mechanical and bio-energetic

factors, a full explanation of which is beyond the scope of this paper.

The FitFlopis a thong-style flip-flop produced by the company of the same

name. The footwear features their proprietary microwobbleboardtechnology

which consists of a variable density sole composed of a high-density heel, low

density mid-foot and medium density forefoot (appendix 2). The variable

density sole was originally purported to create instability at the ankle joint that

is overcome through additional muscle recruitment, providing a workout while

you walk (FitFlops Ltd. 2013). Despite claims that the FitFlopTMcan increase

muscle activity, improve posture, redistribute plantar pressure, reduce both back

and joint pain and increase energy expenditure, (FlipFlopsLtd. 2013) few

experimental studies have explored all of these assertions and few firm

conclusions reached.


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Only 3 peer-reviewed studies have examined the FitFlopTM. Burgess and

Swinton, 2011 assessed the EMG activity of selected muscles of women walking

in FitFlopsTMand reported no significant increases in normalised rms-EMG

activity of the gluteus maximus (GM), biceps femoris (BF), rectus femoris or

medial gastrocnemius compared to regular thong flip-flops or barefoot walkingacross three simulated daily activities. However, the authors only examined the

larger muscles of the lower extremity and thus increased activation of smaller

leg and extrinsic postural muscles cannot be wholly excluded. Particularly given

the findings of Landry et al. 2010 who reported increased activation of the small

medial flexor digitorum longus, peroneal and anterior compartment muscles but

not the larger soleus. However, the results of Landry et al. were observed in the

MBTs shoes and during quiet standing and whether a similar effect is observed

during walking is unknown. Nevertheless, the magnitude of an increase in EE

arising from the increased activation of only these small muscle groups would

likely be small and questionable in terms of producing a meaningful impact on

energy balance.

Price et al. 2013a compared both EMG and kinematic variables during walking in

the FitFlopTMto other unstable shoes and a control and reported findings

somewhat in support of the non-significant trend toward lower EMG values in theFitFlopTMcompared to a flip-flop reported by Burgess and Swinton, 2011.

Activation of the soleus, medial gastrocnemius and BF were all reduced while in

the FitFlopTMcompared to the flip-flop, however only during mid-stance. The

tibialis anterior (TA) and peroneus longus muscle also showed reduced loading

response in the FitFlopTM. Price et al. 2013b also used a bespoke pressure insole

to examine plantar pressures of the foot during walking and reported that

compared to a Haviana flip-flop, the FitFlopTMsignificantly reduced peak pressure

in the heel (-3.6%) and the pressure time integral at the 1st

metatarsophalangeal joint (-12%), increased total contact area and redistributed

plantar pressure towards the mid-foot. Interestingly however, local plantar

pressure redistribution has been associated with increased shoe comfort (Chen

et al. 1994, Jordan et al. 1997) and increased shoe comfort has in turn been

associated with increased submaximal running economy and reduced oxygen

consumption (VO2) (-7.6%) (Burke and Papuga, 2012). These findings in

aggregate suggest that the acute effect of FitFlopsTMon EE could potentially be

one of reduced EE rather than an increase. Although clearly the exercise


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modality in Burke and Papupa, 2012 may have implications with respect to

generalisation to this study.

Given the claims of increased muscle activation made by the manufacturers of

unstable shoes and the similarities to balance training, most studies to datehave focused on the effect of unstable shoes on balance, kinetic, kinematic and

EMG variables during standing and walking. Several studies have demonstrated

a significant effect of rocker soled shoes on both kinematic and temporal-spatial

parameters of gait (Nigg et al. 2006; Boyer and Andriacchi 2009; Demura and

Demura 2012b; Landry et al. 2012; Forghany et al. 2014) and balance (Nigg et

al.2006; Ramstrand et al. 2010; Landry et al. 2010), attributed to the shaped

sole in the anterior-posterior direction. These findings could potentially support

a hypothesis of increased energy expenditure as alterations to an individuals

usual walking mechanics or increased muscle activity arising from the need to

overcome instability could expend more energy. Indeed, clinical studies have

reported that both pathological and imposed alterations to gait pattern increase

the energy cost of walking (Bard 1963; Waters et al. 1982; Waters et al. 1988;

Mattsson and Brostrom 1990; Kerrigan et al. 1995). However, extrapolation of

findings from these studies featuring individuals with neuromuscular or

musculoskeletal conditions might be inappropriate as these individuals maydemonstrate broad variation in, and heterogeneous distribution of, postural and

locomotor muscle activity and therefore limited co-ordination of the various body

segments required for normal gait (Rogers 1996; Vachranukunkiet and

Esquenazi 2013).

While some of the findings from balance studies are relevant in terms of a

clinical outcome, their extrapolation to an energy expenditure hypothesis casts

doubt upon the longitudinal efficacy of unstable shoes in achieving additional

calorie expenditure. Both Ramstrand et al. 2010 and Landry et al. 2010 used

MBTs in 8 and 6-week interventions respectively and reported significant

improvements in balance. If alterations to balance or gait and thus muscle

activity are responsible for increases in EE at baseline, these might be overcome

after a period of acquisition or familiarisation. Research has demonstrated that

novel tasks initially impose a greater energy cost and magnitude of muscle

activation an effect seen to diminish with practice (Lay et al. 2002; Sparrow

and Irizarry-Lopez 1987). It is therefore possible that unstable shoes might


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demonstrate an acute response that is attenuated over time. Indeed, Yap et al.

2013 reported increased EE while wearing unstable shoes during the first 5

minutes of wear, but at the end of a 40 minute familiarisation period EE was not

significantly different to a control shoe, demonstrating a clear learning effect

while in the unstable shoe even over a short period of time.

Additionally Maffiuletti et al. 2012 estimated that the contribution of wearing

MBTTMshoes to increased daily EE approximated only 40 Kcal/day, far short of

the 100Kcal net deficit suggested by Hill et al. 2003 to prevent weight gain and

thus sheds doubt upon their practical application for the purposes of energy

balance manipulation.

Electromyography studies of unstable shoes have been less conclusive in their

findings, owing to methodological differences in both their experimental and

analytical approaches. One of most obvious challenges in reconciling the

findings of all unstable shoe studies relates to different brands of unstable shoes

used in the various studies. There are different design features between

unstable shoe brands that may impact the EMG response observed.

Furthermore, different models of the same brand may elicit differential

magnitudes and directions of physiological responses. As an illustrativeexample, Buchecker et al. 2012 explored the effect of 3 different MBTTMmodels

(JamboTM, TembaTM, MahutaTM) on mean velocity of centre of pressure

displacement and noted increases of 12.5, 17.2 and 21.5% respectively

compared to a control shoe. However, significant increases in muscle activation

of the vastus lateralis was only reported for the TembaTMand MahutaTMand

increased TA, and PL were only reported for the MahutaTMmodel and no

differences for the GM or BF across all shoes. The mixed directional trends

reported by Buchecker et al. underscores the difficulty of making comparisons

between experimental findings. Analytical variability may also be a source of

contrast between study findings. Romkes et al. 2006 reported a significant

effect of unstable shoes on EMG activity of the TA and GM. However the authors

used a peculiar method of partitioning the gait cycle for analysis rather than

using the entire trace, meaning that they could identify points of the stride at

which EMG was increased, differences perhaps not seen using the entire trace.

Romkes et al. also gave instruction on walking in the footwear. It is therefore


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unclear whether the new walking pattern or the shoes were truly responsible for

the difference reported.

Unstable shoes have been less well explored within the energy expenditure

domain. As with EMG studies, the findings are inconclusive. Porcari et al. 2011

examined 3 unstable shoes (MBTTM, Sketchers Shape-UpsTM, Reebok EasytoneTM)

reporting no significant increase in EE, VO2or heart rate (HR) compared to a

control. Rating of perceived exertion showed a small but significant increase in

the EasytoneTMmodel but only at the most intense workload (1.56 m/s 5%

gradient). Gjovaag et al. 2011 had more conclusive increases in EE when

examining the effect of wearing the MBTTMduring treadmill walking at 1.6 m/s-1

with a 10% gradient but not during slower flat walking (1.24 m/s). Suggesting

that the effect of unstable shoes in the EE domain may be velocity or workload

dependant. Indeed, Van Engelen et al. 2010; Maffiuletti et al. 2012 and Koyama

et al. 2012 all used imposed walking speeds above 1.24 m/s and reported

increased oxygen consumption during flat walking in unstable shoes.

Importantly, Maffiuletti et als findings were observed in obese women and

research has previously reported reduced balance control in obese individuals

that could potentially exaggerate the physiological effect of the unstable shoe

(Berrigan et al. 2006; Berrigan 2008). Indeed, Browning and Kram, 2005

reported that obese women incur a greater energy cost of walking compared to

healthy controls over speeds of 0.75-1.75 m/s and that the slope of their

workload-oxygen uptake curve is steeper than healthy controls, meaning that

each increase in workload is that much more taxing than for the controls.

A potential confounding variable present in some EE studies is that the mass of

the unstable shoe used has ranged between 36% and 85% greater than the

control shoe (Van Engelen et al. 2010; Gjovaag et al. 2011; Maffiuletti et al.

2012; Koyama et al. 2012; Demura and Demura 2012). It is therefore unclear

whether the increase in EE observed in these studies was due to the shoe design

features or its additional mass. Increasing the mass of footwear is reported to

increase the relative additional mechanical work performed as a function of

maximal foot speed (Nigg et al. 2000). However, both Santos et al. 2012 and

Forghany et al. 2014, controlled for the increased mass of a rocker bottom

versus a regular athletic trainer and reported no significant differences in themetabolic cost of walking on a treadmill at a pace 10% above free walking speed


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or at free walking speed respectively. Additionally, Abe et al. 2004 reported no

significant difference in the oxygen cost of walking with a load applied to each

ankle at any walking speed in the range of 0.66 and 2 m/s between a control

condition and either a 1 and 1.5kg condition. However, other others have

reported findings to the contrary (Frederick et al. 1984).

Another difference that may explain conflicting results within the literature is the

use of self-selected vs imposed walking speeds. Some authors (Gjovaag et al.

2011; Hansen and Wang 2011; Maffiuletti et al. 2012; Forghany et al. 2014; Yap

et al. 2013) have elected to use the natural walking speed of the participants

while others (Van Engelen et al. 2010; Gjovaag et al. 2011 Porcari et al. 2011;

Koyama et al. 2012; Demura and Demura 2012) have imposed a walking speed

pre-selected by the authors. The study by Maffiuletti et al. 2012 is the only

study out of 5 that elected to use a self-selected pace and also reported

increased EE while walking in the unstable shoe. 3 of 5 studies using an

imposed walking speed reported increased oxygen uptake or increased EE while

walking in an unstable shoe. Ralston 1958 first identified the energy-speed

relationship in normal healthy subjects and concluded that the natural walking

speed of an individual reflects the speed that induces the lowest metabolic cost.

This speed was determined to be 1.23 m/s in a group of healthy adult males andfemales, slower than the imposed speeds of the aforementioned studies. Holt et

al. 1995 added to these findings and concluded that in addition to metabolic

cost, stability of the head and joint actions is also optimised at the preferred

walking speed, suggesting the higher speeds induce greater instability in gait. It

has also been shown in a group of healthy students that speeds greater than the

optimum or natural walking speed display less consistency in gait characteristics

(Sekiya et al. 1997). This greater variability in kinematic variables may be

further exaggerated at higher speeds while wearing an unstable shoe, thus

inducing a greater energy cost. Notably, in Sekiya et als study the preferred

speed for women was also 1.230.17 m/s. The greater frequency of significant

differences found in studies using an imposed walking speed may be related to

greater variability of gait and instability during gait of the imposed walking

speed. In contrast, Bertram, 2005 reported that a speed constraint might not

impact metabolic cost as much as step length or frequency constraint.


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An additional limitation of using imposed walking speeds and in contrast to

Sekiya et al. 1997 and Ralston, 1958, is that the self-selected walking speed is

reportedly different between men and women, with men typically displaying a

higher speed (Waters et al 1988). Therefore, studies that have used mixed sex

groups (Van Engelen et al. 2010; Gjovaag et al. 2011; Maffiuletti et al. 2012;Koyama et al. 2012) may have subjected the women to a higher walking speed

than their preference, which given the linear walking-speed/oxygen-uptake

relationship (Menier and Pugh 1968) would increase EE in addition to potentially

inducing the aforementioned variability in gait.

Hansen and Wang 2011 constructed their own rocker bottom shoes from a pair

of converse high-tops and reported reduced oxygen cost as a function of

reduced shoe radius. However, each reduction in shoe radius was significantly

associated with a reduction in oxygen cost relative to a flat shoe condition only.

Unfortunately not only is it difficult to extrapolate findings from this study since

the shoes were bespoke, the sole thickness on the flat shoe was much greater

(7.62 cm) than the control shoe used in other studies and not characteristic of

commercially available footwear, a fact which may have misrepresented the

physiological response against which the unstable shoes were compared and

limits the generalisation of findings in practical application.

Conceivably, sole thickness could also have an impact on EE; Ramanthan et al.

2011 reported increases in the average amplitude of EMG signals during both

flat standing and 0-20foot inversion in response to a wearing a shoe with a

5cm sole thickness compared to a standard shoe. It is possible that these

increases in EMG in response to sole thickness are also manifested as increases

in EE and thereby misrepresented the control condition in Hansen and Wangs

experiment, although no study to my knowledge has confirmed this notion

directly and Ramanthan et al. 2011 did not examine EMG of walking in flat sole

shoes. It should also be noted that the adaption created soles in the unstable

shoe condition with a uniform compliance unlike both the MBTTMand the

FitFlopTM, which feature variable densities of sole construction.

Despite the evidence in support of wobble-board training for improving balance

and reducing injury (Holm et al. 2004; Waddington and Adams 2004; Emery et

al. 2005), some unstable shoes have made exaggerated claims. In 2011 Reebok


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Inc. was ordered by the United States Federal Trade Commission (USFTC) to pay

25 million dollars to settle fines relating to the sale of their EasytoneTMmodel

after their claims that it improved muscle tone and increase energy expenditure

were found to be unsatisfactory and not supported by quality scientific research

(USFTC 2011). David Vladeck, USFTC director of consumer protectioncommented - The FTC wants national advertisers to understand that they must

exercise some responsibility and ensure that their claims for fitness gear are

supported by sound science. The not insignificant fines levelled by the USFTC

on these two companies highlights the necessity for all products that make such

claims to be evaluated by independent research in the interests of both the

consumer and clinicians who may wish to prescribe their use. It is therefore the

intention of this study to assess the energy expenditure claims attached to the

FitFlopTM model of footwear.


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Experimental Protocol

Footwear

The footwear models used in this study were the Fit-Flop Walkstar, a cheaper

control flip-flop and the participants own shoes (figure 1a & 1b).

Figure 1a Figure 1bFitFlop Walkstar Control Flip-Flop

Thong style footwear has previously been reported to elicit an effect on gait

characteristics (Finnis and Walton 2008; Shroyer 2009; Shroyer and Weimar

2010; Zhang et al. 2013) effects that are likely to also be manifested while

wearing the FitFlopTMand could potentially influence the oxygen cost of walking.

It is therefore necessary to compare the FitFlopTMto regular thong footwear in

order to determine the true effect of the variable density sole. The participants

own shoe condition (POS) is meant as a functional comparison as an individual is

expected to replace their normal footwear with unstable footwear. All footwear

masses were also recorded using table top digital scales (Salter UK).

Measurement of Energy Expenditure

Energy expenditure was determined by use of breath-by-breath open circuit

indirect calorimetry, whereby VO2and carbon dioxide production (CO2) are

measured to establish metabolic EE during exercise (Weir 1949). Oxygen

exchange is one of the most widely accepted and reliable methods of assessing

dynamic EE (McArdle et al. 1991; Branson and Johannigman 2004).


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The indirect calorimeter used in this study was the Cosmed K4 b2 portable

metabolic system (COSMED s.r.l. Rome, Italy). The K4b2is a portable gas

analyser unit that has been reported on extensively in the literature with respect

to its reliability and validity (MacLauchlan et al 2001; Pinnington et al. 2001;

Littlewood et al. 2002; Miaolo et al. 2003; Duffield et al. 2004; Schrack et al.2010) and use in research (Brown et al. 2001; Duffield et al. 2004; Castaga et

al. 2007; Herkmans et al. 2012). The K4b2was dry gas calibrated with known

reference gases (16% O2, 5% Co2,79% Nitrogen) (Cosmed s.r.l Rome, Italy)

and volume calibrated with a 3 litre calibration syringe (Cosmed). The unit was

used according to the manufacturers handbook.

Standard Meal

Participants were instructed to maintain 2-hour gap between their previous

whole meal and attending the testing session as described by Maffiuetti et al.

2012. Participants were however, permitted to consume a snack restricted to a

standard caloric value of approx. 200-250 kcal during the interval. A list of

snacks/foods that meet this calorie value was included in the participant

recruitment email and a web link to an online calorie counter was also provided

(http://www.myfitnesspal.com/food/calorie-chart-nutrition-facts). This measure

was taken to attempt to control for the thermic effect of food that mightinfluence within-subject measurements over the duration of the testing session.

Randomisation

Randomisation of the activities and shoe conditions was performed to minimise

any potential ordering effects. Participants selected from hidden options to

determine the order of the walking activities and then for the shoe order in each

activity.

Self-Selected Walking Speed

The walking speed for each activity was participant determined in order to allow

for individual variation in height, body mass, age and aerobic capacity which can

influence the self-selected walking speed (SSWS) and gait. Additionally,

imposing a speed that is too fast may induce compensatory gait strategies while

wearing the FitFlopTMand flip-flops that might not be representative of their

normal use (Holt et al. 1995; Sekiya et al. 1997). Additionally, thong style

footwear is generally not conducive to safe and effective movement at speeds


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greater than free walking speed. Prior to testing any of the shoe conditions, the

participants were instructed to walk on a motor driven treadmill at 0% incline in

the FitFlopsTMat a speed reflective of their norm for 5 minutes to establish the

SSWS. The process was repeated at a 10% incline and both speeds were noted

and kept constant across all shoe conditions for each activity, as walking speeddirectly influences oxygen uptake (Ralston 1958). The FitFlopTMwas used as the

reference speed as it was expected that it would produce the slowest SSWS due

to its greater mass and the impact of a truncated stride length; an effect that

thong style flip-flops have been shown to elicit on the gait cycle (Finnis and

Walton 2008; Shroyer and Weimar 2010; Zhang et al. 2013).

Participant Preparation

Participants visited the University on a single occasion for testing which typically

lasted 2.5-3 hours. Participants stretched stature height and body mass were

recorded using a stadiometer and digital scales! Individuals were self-fitted with

a thoracic belt HR monitor (Polar T31), wetted to ensure proper function.

Participants were instructed on proper placement if they were unfamiliar! A

harness for the portable unit and battery was then placed on the participant. A

netted head strap (Hans Rudolph, Kansas city, MO) was used to secure the

facemask (Hans Rudolph, Kansas city, MO) ensuring complete coverage of the

nose and mouth. Improper seals were checked for by obstructing the flow

meter and asking the participant to blow gently. Any small gaps not rectifiable

by the use of a smaller mask were filled with VaselineTM. Participants were

rested in a standing position for 5 minutes to establish baseline reference

measurements of EErate VO2, VE, HR and RER according to the advice of Levine,

2005 to obtain baseline values in the posture of reference i.e. that which the

participant shall adopt during the task. The participants received a 10-minutebreak between activity conditions to allow them to recover and for physiological

variables to return to baseline values. A bladed fan was placed on a low setting

at 2 meters distance directly in front of the participant during the treadmill tasks

to replicate the airflow experienced during the cones task, which may cool the

participant and potentially alter measurements. Ambient room temperature was

maintained at 25 1C throughout intra-individual trials and was 25.2 0.85C

across separate testing sessions. Between shoe trials in each activity,

participants rested in seated position for 2 minutes and then stood until their

VO2, VE, HR, RER and EErate returned to resting levels as per the methodology


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of Porcari et al. 2011 in to control for carry over effects between trails that

would compromise their independence. In the interest of hygiene, the facemask

and flow meter were sterilised between uses with different individuals and the

HR monitor and footwear were cleaned with antibacterial wipes.

Simulated Activities of Daily Living

The activity protocols were selected to simulate the physiological demands of

common daily living tasks. The rationale being that the FitFlopTMis supposed to

replace an individuals normal footwear to provide a calorie burning boost to

activities regular daily living. The American time use survey 2011 (US Bureau of

Labour Statistics) indicates that the most common non-sedentary activities of

daily living for women are: household activities, purchasing goods and services,

and leisure. These activities would likely involve some quantity of walking in

able-bodied individuals.

A flat and 10% inclined treadmill task have been selected to replicate walking

over flat and uphill conditions. The 10% incline was selected to provide a

greater exercise stimulus in line with the work of Gjovaag et al. 2011 and Porcari

et al. 2011. A slalom style cones task (appendix 8) is designed to be

reminiscent of weaving between people and in a busy shop or street and will

allow us to investigate whether the recruitment patterns of this direction change

task influence the EE response in the three shoe types differentially to the other

tasks. In both treadmill tasks, participants were instructed to walk at the

previously determined speed and corresponding grade for at least 3 minutes

until a steady exercise state was attained, defined according to Donald et al.

1955, as a plateau of VO2with respect to time, with no meaningful deviation or

persistent trend for one minute. Participants then continued for 2 minutes atthe steady state. All participants achieved steady state within 4 minutes thus

participants walked for between 5-6 minutes in each shoe condition and task.

In the direction change protocol, participants were instructed to walk a pre-

designated path around a set of cones and to maintain a constant volitional pace

until a steady state was achieved as for the treadmill tasks. The course was

measured using a rolling line marker (Silverline), and was determined to be

18.50m in distance. Participants walked for 5-6 minutes as with the treadmill

protocol. The whole number and fraction of laps of the course completed during


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the 2 minute steady state period were recorded in order to calculate walking

speed based on distance travelled. Walking speeds were analysed for significant

differences across shoe conditions, as speed could not be controlled in this

activity condition.

Dependant Variables

The main dependant variable of interest in this study is total energy expenditure

(EEtotal). This was calculated in real-time from expired gas fractions of O2and

CO2by the K4b2software and using the Weir equation, which corrects for protein

metabolism (Weir 1949; for a more recent re-appraisal see Mansell and

Macdonald 1990). The initial value of EEtotal from the beginning of the 2-

minute SS period was subtracted from the final value of EEtotal from the end of

the 2-minute SS period to yield EEtotal for the task. The respiratory exchange

ratio (RER) is the ratio of VCO2& VO2and gives an indication of substrate

utilisation for use in EE calculations. HR was monitored as an indicator of

relative intensity and for normal physiological response.

Data Analysis

All raw physiological data for each trial was exported from the K4b2 software to

Microsoft Excel to calculate the mean values of EEtotal, EErate, VO2, VE, HR andRER for the final 2 minute period of each individual and trial. This data were

then transferred to SPSS 21.0 (IBM) for further analysis. For each variable

Shapiro-Wilks analysis was used to confirm assumptions of normality, as it is

better suited to smaller sample sizes (Shapiro and Wilks 1965). The main

effects of the shoes and tasks were analysed using a one-way analysis of

variance for repeated measures (ANOVA). However, because the study design

violates the assumption of independence, the assumption of sphericity or the

assumption that the variances of the difference between combinations of shoe

conditions are not significantly different was tested using a Mauchlys W test,

with a non-significant output (p=>0.05) affirming the assumption. If sphericity

could not be assumed, a greenhouse geiser correction of the degrees of freedom

was performed. Post-hoc Bonferroni corrected t-tests were conducted to

investigate further any significant differences elucidated by the ANOVA, as the

probability of witnessing a statistically significant event is increased with

numerous test conditions or comparisons (Bland and Altman 1995). Significance

levels were set to 0.05 for both analyses. EErate, VO2, VE, HR and RERhave


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also been analysed and reported in keeping with previous EE studies of unstable

shoes, which have typically also reported these values.


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Results

The results of the physiological responses to the 3 walking tasks in each shoe

type are presented in table 2.

Table 2

Physiological responses to walking tasks in each shoe type. Data are means and

standard deviation in parenthesis.

* = main effects, Significant main effect (p


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The ANOVA revealed a main effect of shoe type for RER (F= 5.732, (2), effect

size (partial eta2) = 0.417, (p


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Discussion

This study is the first to examine the influence of FitFlopsTMon energy

expenditure and the findings indicate that total energy expenditure during three

simulated activities of daily living is not significantly altered while wearing the

FitFlop

TM

compared to either a regular flip-flop or an individuals own normalfootwear.

While there is little comparative data for energy expenditure while wearing

FitFlopsTMthis study extends the EMG study of FitFlopsTMby Burgess and

Swinton, 2011 into the energy expenditure domain using similar simulated tasks

of daily living. The findings of a non-significant trend toward reduced

physiological responses while wearing the FitFlopsTM compared to the flip-flops is

congruous with the authors findings of a trend towards reduced EMG activity

while wearing the FitFlopsTMcompared to a cheap thong style flip-flop. The

finding of no significant alteration in EEtotal, EErate, VE, HR or VO2is consistent

with previous research that reported no increase in EE while walking in an

unstable shoe (Porcari et al. 2011, Elkjaer et al. 2011; Santos et al. 2012;

Forghany et al. 2012). The findings are however in contrast with (Van Engelen

et al. 2010; Gjovaag et al. 2011; Hansen and Wang 2011; Maffiuletti et al.

2012; Koyama et al. 2012; Fukuchi et al 2013). RER however, did display asignificant increase during the incline-walking task but while wearing the flip-

flops as opposed to the unstable FitFlopTM.

Only one study (Maffiuletti et al. 2012) has reported RER as being significantly

reduced while wearing an unstable shoe but this observation was only made

during quiet standing and no significant difference were noted during walking.

Only one other study (Gjovaag et al. 2011) has reported RER but these authors

reported an increase of +0.02 (p


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The values obtained for VO2in the flat task while wearing unstable shoes are

similar to those reported by Gjovaag et al. 2011, lower than that reported by

Porcari et al. 2011 and Demura and Demura, 2012 (14.2 and 14.94 ml/kg/min).

The latter study featured men only, which, given that women typically display

lower VO2uptake values than men (Astrand 1952; Drinkwater 1973; Sparling1980), likely explains this finding. The VO2values were also lower than

Maffiuletti et al. 2012 (16.4 ml/kg/min) which is possibly due their sample being

formed of obese women who reportedly display elevated metabolic responses to

walking exercise compared to healthy weight women (Browning and Kram

2005). Notably, the values presented here are higher than those reported by

Hansen and Wang, 2010 in a group of mixed gender subjects, a difference

possibly related to the improved rollover characteristics of the ankle afforded by

the reduced shoe radii of their bespoke shoe (Adamczyk et al. 2006).

The current study used a cheap thong style flip-flop as the control shoe for this

experiment. The difference in shoe mass between the unstable shoe and the

control shoe was greater than the +36 to +85% range reported by other studies

that reported increases in EE (Gjovaag et al 2011; Maffiuletti et al 2012;

Demura and Demura 2012; Koyama et al 2012). However, in spite of this

increased mass, the FitFlopTM

did not significantly increase EE compared to theflip-flop. This finding is in contrast with previous studies that have reported an

increase in EE while walking in an unstable shoe (Van Engelen et al. 2010;

Gjovaag et al 2011; Maffiuletti et al 2012; Demura and Demura 2012; Koyama

et al 2012). A key difference between the latter studies and this current project

is the shoe design, the FitFlop used in this study uses a variable density sole

which is quite different to the rocker sole of the MBTTMand shape up used by

these authors.

A salient finding of this study is that EE and indeed no physiological parameter

demonstrated a significant difference between the FitFlopTMand the POS.

Despite the fact that the POS was on average 48% heavier, this significant

(p


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work performed (Nigg et al. 2000). Indeed, no significant increase in the

metabolic cost of flat walking due to footwear mass was reported by Jones et al.

1986 at a speed of 1.11 m/s, but was reported at two higher speeds (1.55 and

2.02 m/s). In contrast, Abe et al. 2004, reported no significant difference in the

oxygen cost of walking at any speed in the range 0.66-2 m/s with a 1kg or1.5kg load applied to both ankles compared to no load. It is therefore possible

that the finding of no difference in EE between the FitFlopsTMand the POS is

either due to the slower walking speed in this study, the difference in mass not

being great enough to impose an additional metabolic cost or an interaction of

both factors. This finding is in direct contrast to the only other study that has

used the participants own shoes as a control and the authors reported a 10.7%

increase while wearing the unstable shoe (MBTTM) compared to the participants

own shoe (Van Engelen et al. 2010). The authors however, did not weigh the

participants shoe and only estimated to be lighter than the MBTTM. The finding

holds important implications for the practical use of FitFlopsTMunder the premise

of increasing EE. The expectation is that an individual would wear the FitFlopTM

in place of their normal footwear and it is likely that most of their use while

walking would be performed at the preferred walking speed. Particularly since

thong style footwear is generally not conducive to very fast walking or running.

Any significant effect of the increased mass of the POS on EE may also havebeen obscured by the greater variability in mass of the POS.

This study utilised a self-selected walking speed in each walking condition.

The mean walking speed selected by the participants for the flat walking task

was 1.07 m/s, which is within the range of slow to fast walking speeds used by

Koyama et al. 2012 (0.83-1.94 m/s) but greater than the self-selected walking

speed reported by Yap et al. 2013 (0.91 m/s). However, it is slower than the

SWSS reported by Hansen and Wang 2011 (1.12 m/s), Gjovaag et al. 2011

(1.24 m/s), Maffiuletti et al. 2012 (1.36 m/s) and the imposed walking speeds

used in the studies undertaken by Van Engelen et al. 2010 (1.25 m/s) Porcari et

al. 2011 (1.34, 1.56 m/s) and Gjovaag et al. 2011 (1.60 m/s).

The walking speed in the incline task (0.93 m/s) was slower than that selected

for the flat walking task and similar to that used in the cones task (0.94 m/s).

Other studies that have used an inclination (Gjovaag et al. 2011; Porcari et al.

2011) have used a higher walking speed (1.6 and 1.56 m/s) than during their


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flat walking task although this speed was imposed on the participant and not

self-selected. The slower speed selected by participants in the current study is

likely a function of the footwear type used in this study as other researchers

have used unstable shoes that feature a more conventional closed shoe design

(Zhang et al. 2013). Research has shown that the natural walking speed of anindividual is equal to their metabolic optimum, meaning that a person will always

select the walking speed that incurs the lowest metabolic cost (Ralston 1958;

Holt et al. 1995). More importantly, self-selected pace has been shown to

demonstrate the least number of variable errors or greater spatial consistency

of gait characteristics than an imposed speed above free-walking speed and

thereby optimises gait performance, energy efficiency and attentional demand

(Zarrugh et al 1974; Holt et al. 1995; Sekiya et al. 1997). By limiting the

amount of kinematic and temporal-spatial variability by using a self-selected

speed we were able to achieve greater control of the experiment such that any

variability in EE as a result of alterations to gait characteristics could be

attributed to the footwear.

A possible shortcoming of the methodology in this current study is that the

authors used the self-selected walking speed obtained in a five-minute trial of

the flat and incline-walking tasks while wearing the FitFlopsTM

and this speed wasused for all shoes. It is possible, particularly given that some participants

reported that the FitFlopTMwas more comfortable and fit better than the flip-flop,

that the shoe type may have influenced the natural or optimal walking speed.

Thong footwear reduces the stride length and increases cadence while walking

(Shroyer 2009; Shroyer and Weimar 2010; Zhang et al. 2013), an effect

possibly accentuated while wearing the flip-flop compared to the FitFlopTMdue to

the poorer fit.

The level of inclination used in this study was the same as that of Gjovaag et al.

2011 who found a significant effect of unstable shoes on oxygen uptake at a

10% grade and a fast walking speed. The findings of this study however, are in

contrast with that of Gjovaag et al. in that no increase in EE was observed at

this grade. The contrast in findings may be related to the slower self-selected

walking speed used by the authors of the current study (0.93 0.10 m/s)

compared to the faster walking speed imposed on the participants by Gjovaag et

al. (1.6 m/s). A possible explanation might be that the fast walking on a 10%


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grade in the unstable shoe was a novel and challenging task for the participants

that imposed additional task and environmental constraints, altering kinematics

and imposing a greater metabolic cost (Sparrow 1983; Newell 1986; Sparrow

and Irizarry-Lopez 1987; Lay et al. 2002). Indeed, both step and stride length

were also significantly reduced during this condition, increasing cadencecompared to a regular athletic trainer (Gjovaag et al. 2011).

The direction change task used in this study was modelled on that described by

Burgess and Swinton 2011. However, as the dimensions of the course layout

used by these authors was not described and because the participants of this

study completed repeated laps of the course as opposed to one lap, a

comparison with the walking speeds used in this current study is not possible.

It has been reported that footwear comfort may influence the metabolic cost of

movement (Burke and Papuga 2012). Although the authors of this present

study did not record subjective ratings of comfort, level of exertion or gait

characteristics, some participants did state that the FitFlopTMwas more

comfortable and easier to walk with compared to the flip-flop. Price et al. 2013

reported reduced plantar pressure in the heel and 1stmetaphalangeal joint and

pressure redistribution towards the midfoot while wearing the FitFlopsTM.

Reduced plantar pressure of the medial forefoot and redistribution of pressure

towards the midfoot is reportedly associated with increased comfort (Chen et al.

1994). It is therefore likely that the increased comfort reported by participants

in this study is explained by these findings. Indeed, during the process of this

study FitFlop Ltd. and many of its footwear models including the Walkstar

featured in this study received the American Podiatric Medical Associations Seal

of Acceptance, awarded to products that promote good foot health. An

interesting and poignant extension of Chen et als findings is that increased shoe

comfort has been associated with reduced oxygen uptake during submaximal

running (Burke and Papuga 2012). The findings of Burke and Papuga might

explain the trends towards a lower physiological response while wearing the

FitFlopsTMcompared to the flip-flops. Additionally it has been reported that

plantar pressures are higher while wearing flip flops compared to athletic

trainers (Carl and Barrett 2008).


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One might speculate about flip-flop influenced alterations in gait during the

incline condition. During uphill walking, the foot maintains a dorsiflexed position

upon heel contact, initiated in the mid-swing phase (Leroux et al. 1999).

Shroyer and Weimar, 2010 previously reported increased dorsiflexion and a

toe-gripping strategy while wearing flip-flops, which when considered inconjunction with the anecdotal reports of greater comfort and the better fit of

the FitFlopsTM, may help explain the trend towards increased physiological

responses while walking in the flip-flops compared to the FitFlopsTMpossibly

arising from increased TA activation (Shroyer 2009). However, while Burgess

and Swinton 2011 did not observe significant difference while wearing the flip-

flop compared to the FitFlopsTM, the authors did not use an inclined walking task

as in this study.

One of the major strengths of this study is that we used three different exercise

stimuli to test the influence of the FitFlopsTMon EE. Some studies (Hansen and

Wang 2011; Koyama et al. 2012; Maffiuletti et al. 2012; Demura and Demura

2012) have only assessed EE of an unstable shoe in a flat treadmill condition,

limiting the applicability of their findings to this exercise modality only.

LimitationsRegrettably this study did not examine the physiological responses of while

standing.

Generalisation of findings from this study is limited to healthy young females 20-

31 years old. Effects of the variable density sole construction may be more

pronounced in a group of less active or older individuals with reduced

proprioceptive ability or weaker balance control strategies (Fujiwara et al. 2007).

Additionally, Nigg et al. 2010 identified differences in male and female ankle

joint moments while walking in unstable shoes which further limits the ability to

generalise findings from this study to males.


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Recommendations for future research

It has been reported that the metabolic cost of walking on the treadmill is higher

compared to flat over ground walking (Dasilva et al.2007; Berryman et al.

2013). The physiological responses of wearing unstable footwear during the

treadmill tasks may not reflect the metabolic cost of the same activity on a hard

flat surface. This is a limitation of the present study and has potential

implications for the applications of these findings to free living conditions.

Indeed some of the other surfaces encountered in daily life; grass, carpet, may

impose different demands not captured by the tasks used in the current study.

A future project may wish to explore the differences in walking on flat and

treadmill conditions in unstable shoes.

Recently FitFlop Ltd. has incorporated their microwobbleboardTMtechnology into

a range of footwear for men. Men and women are reported to employ different

gait strategies when walking in unstable shoes (Nigg et al.2010) a future

project may wish to evaluate the EE response of men while walking in this new

range of footwear.

No data has been gathered regarding the effect of wearing unstable shoes in

free-living humans. The findings of finely controlled laboratory studies are often

not replicable in free-living conditions suggesting they have limited ecological

validity (Brewer 2000). Therefore a future project may wish to undertake this

using the doubly labelled water method.

Given the reports of increased comfort and the findings of Price et al. 2013

regarding plantar pressure redistribution, a future area of examination might be

to explore the kinetic and kinematic variables in the context of mitigating injury.

The thicker sole may provide additional cushioning, dissipation of ground

reaction forces and possibly better arch support, factors associated with foot

pain and injury according to the American College of Foot and Ankle Surgeons

2006.


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Conclusion

The term microwobbleboard has associations with balance training and infers

increased muscle activation and energy expenditure that is associated with

unstable surface training (Wahl and Behm 2008; Anderson 2013). This

association is unjustified given the findings of this present study, which hasdemonstrated no increase in energy expenditure associated with use of the

FitFlopsTMcompared to an individuals own footwear. The practical implication is

that manipulation of energy balance cannot be achieved by replacing ones own

footwear with FitFlopsTM. Furthermore, the general trend towards reduced

physiological responses while wearing the flip-flops compared to the FitFlopsTM

indicates that a cheap, widely available flip-flop may be more effective than the

FitFlopsTMat achieving a greater metabolic response. However, given that no

significant differences were noted between the flip-flop and the POS, the

practical applicability of using any type of footwear to increase the energy

expenditure of daily living appears to be limited.


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Appendices

Appendix 1 43

Energy Expenditure Studies

Appendix 2 45Unstable shoes

Appendix 3 46Recruitment Email

Appendix 4 48Recruitment Poster

Appendix 5 49Participant Information Sheet

Appendix 6 52Physical activity readiness questionnaire

Appendix 7 54Informed Consent Form

Appendix 8 55Layout Of Cones Walking Course

Appendix 9 56Data collection sheet

Do Fit-Flops Increase Energy Expenditure During 3 Simulated Tasks of Daily Living?

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