A Pilot Study to Examine the Activity of Primary Plantar Flexor Muscles

using an Electric Motorized Treadmill in Comparison to Overground

Walking

Katja Orlowski

, Dennis Wagner

, Annett l’Orteye

, Heike Ringk

Verena Kohl

and Thomas Schrader

Department of Computer Science and Media, Brandenburg University of Applied Sciences,

Magdeburger Str. 50, Brandenburg, Havel, Germany

adtisches Klinikum Brandenburg, Medical School, Brandenburg, Havel, Germany

Helios Fachklinikum Brandenburg Hohenst

ucken, Brandenburg, Havel, Germany

Keywords:

Overground Walking, Treadmill Walking, Plantar Flexor Muscles, Walking Velocity.

Abstract:

The gait during overground (OG) and treadmill (TM) walking was already investigated by different scientiﬁc

groups. Differences in the muscle activation and in the kinetics were found. The aim of the present exami-

nation was to ﬁnd conditions for a comparable or higher activation of the plantar ﬂexor muscles during TM

walking in order to give recommendations for training and rehabilitation. A pilot study with different condi-

tions (e.g. with and without inclination) was done. Furthermore, the aspect of different walking velocities in

OG and TM walking was investigated. The self selected speed was reduced during TM walking (1.1 km/h).

Regarding the muscle activation, it is recognizable that the primary plantar ﬂexor muscles react similarly. The

activation is reduced during TM walking. Based on the inclination of 1.5 %, a little larger activity during

TM walking is observed for the muscles M. gastrocnemius medialis and lateralis. Our results conﬁrm that

there are differences between OG and TM walking in the activation of the primary plantar ﬂexor muscles.

The results indicate that there is an effect of different, adjustable conditions (speed and inclination). Further

examinations are planned to ﬁnd detailed information about the different conditions and their impact on the

muscle activation.

1 INTRODUCTION

Treadmills are used in the ﬁelds of sport and rehabili-

tation due to the required space for walking/running

large distances. That is why a treadmill is often used

for the repetitive exercise of walking in rehabilitation

routines or for training aspects in order to pass

longer distance with a deﬁned speed. The applied

treadmills are mostly electric motorized treadmills.

The person, who is walking on the treadmill, is to

some extent moved by the motor which is integrated

in the treadmill. However, on the market there

are also self-powered treadmills, so called manual

treadmills. Using such a treadmill, the motion during

walking is created by the muscle strength of the

running or walking person. In spite of this offer, in

most institutions, electric motorized treadmills are

available and used for walking.

In patients with cerebral palsy (CP) the plantar ﬂexor

muscles are weakened, and gait deviations exist. CP

occurs in different types, for example, the dropped

foot (Type 1) or the equine foot (Type 2A) (Tugui

and Antonescu, 2013). The gait of patients with an

equine foot has a spasticity in the primary plantar

ﬂexors, the muscles M. gastrocnemius medialis and

lateralis and M. soleus. Furthermore, a spasticity

in the M. tibialis posterior is present. Due to that

spasticity, the plantarﬂexion cannot be executed in an

adequate way. Following the gait of these patients is

characterized by walking on the tiptoes because the

gait cycle (stride) is not initiated by the heel strike.

The different phases and subphases of the gait of CP

patients are impaired and do not proceed as described

for the physiological gait (Perry and Burnﬁeld, 2010;

Whittle, 2007). The aim of therapeutic interventions

is to strengthen these plantar ﬂexor muscles and

harmonize the gait in order to prevent secondary

diseases. For that reason, a treadmill is used in a

physiotherapeutic intervention to improve the gait of

CP patients by repetitive walking.

Orlowski K., Wagner D., l’Orteye A., Ringk H., Kohl V. and Schrader T.

A Pilot Study to Examine the Activity of Primary Plantar Flexor Muscles using an Electric Motorized Treadmill in Comparison to Overground Walking.

DOI: 10.5220/0006498600330038

In Proceedings of the 5th International Congress on Sport Sciences Research and Technology Support (icSPORTS 2017), pages 33-38

ISBN: 978-989-758-269-1

Oliveira et al. (2016) investigated the muscle

activation during overground (OG) and treadmill

(TM) walking. Their results conﬁrm that there are

differences in the muscle activation in both scenarios

(Oliveira et al., 2016). The M. soleus showed a larger

activation in terms of a higher peak and a larger

integral during overground walking. In contrast to

the activation of the M. soleus, the M. gastrocnemius

medialis is more activated in the treadmill setting.

The M. gastrocnemius lateralis reacted neither as the

M. soleus nor as the M. gastrocnemius medialis. This

muscle has a larger peak for the treadmill setting, but

a larger integral for the overground setting. Van der

Krogt et al. (2015) found differences in the kinetics

of children with CP in OG and TM walking (van der

Krogt et al., 2015).

During sport training sessions treadmills are used

for warmups, cooldowns, running independetly from

the weather conditions or for ﬁtness aspects. Indeed,

strengthing the muscles of the lower limbs is not

the primary focus of the athletes. Nevertheless, the

question of muscle activation during walking on the

treadmill with different conditions (e.g. velocity

and inclination) is also interesting to sportsmen and

coaches. That’s why the current pilot study focuses

on the difference between overground and treamill

walking with the main focus on muscle activity of

primary plantar ﬂexor muscles. In addition, the

difference of walking velocity during OG and TM

walking is considered.

Due to these two main topics two hypotheses are

investigated. The ﬁrst belongs to the muscle activity

during TM walking in comparison to OG walking. It

is assumed that the muscles are less activated during

TM walking than during OG walking due to the

motorization of the TM. The second hypothesis refers

to the comfortable walking speed in both walking

scenarios. It is assumed that during TM walking the

person chooses a lower comfortable walking speed

than in OG walking.

Regardless of the aspects that have to be considered

by using treadmills in therapeutic settings, there

are different, important issues for athletes. Conse-

quently, an examination with healthy subjects was

performed to prove the assumption that the plantar

ﬂexor muscles are less activated during TM walking.

Furthermore, the aim of the conducted examination

was to ﬁnd conditions for a comparable or even

higher activation of the muscles during treadmill

walking.

2 METHODS AND MATERIALS

Different tests were done to prepare the pilot study

and to ﬁnd out which TM settings (speed and incli-

nations) are recommendable. The literature describes

a reduced velocity on the TM for runners (Arsenault

et al., 1986; Nymark et al., 2005; Kong et al., 2012;

Marsh et al., 2006). During own tests, this fact was

also noticed for the walking on a TM. Due to the mo-

torization, the comfortable, self-selected speed dur-

ing TM walking is perceived differently. For that rea-

son, an additional investigation was done with 21 sub-

jects (14 f, 7 m, age: 28.9 (± 9.1) years) to quantify

the speed difference of both settings. First, the self-

selected speed for each subject was determined by the

OG setting based on four 20m walking trials. The

mean velocity was calculated. Subsequently, the com-

fortable speed during TM walking was determined in

two trials starting once with a continuous increase of

speed from a slow velocity (0.5 km/h) and once with a

continuous decrease of speed from a fast velocity (7.0

km/h). The order was applied in a randomized way.

The gait of 23 young and healthy subjects (8 male, 15

female, age: 25.6 (± 5.4) years, height: 170 (± 10)

cm, weight: 69.0 (± 13.0) kg) was examined. The

activation of the muscles M. soleus (SO), M. gastroc-

nemius medialis (GM) and lateralis (GL), the primary

plantar ﬂexor muscles, was registered using EMG-

sensors with an 8-channel measuring device of biosig-

nalplux (Plux Wireless Biosignals S.A., Lisbon, Por-

tugal). In order to guarantee a stride-based analysis of

the muscle activation, the gait was additionally cap-

tured using two 3D-accelerometers. These sensors

were ﬁxed on each heel in order to detect the heel

strike as the initial event of the gait cycle.

In the OG setting the subjects passed six trials of a

40 m straightforward distance. They were asked to

choose their comfortable walking speed during OG

walking which was registered for each trial. Based

on the noticed walking speed of the six OG trials the

mean value was determined. Following the OG set-

ting, each subject passed two walking trials on the

TM, one without inclination (TM1) and another with

an inclination of 1.5 % (TM2) following the recom-

mendations of the literature (Jones and Doust, 1996;

Heck et al., 1985; Vanhelst et al., 2009). Each of the

TM trials has nearly the same length as all OG trials

together to guarantee the almost the same amount of

gait cycle in both settings are registered. Furthermore,

a 1 km/h reduced speed was chosen for the TM tri-

als based on the literature (Kong et al., 2012; Marsh

et al., 2006) and own examinations (see results be-

low). A randomization of the testing order could not

be performed due to the adjustment of the TM speed

Figure 1: The mean EMG curve and marked the four calculated parameters: peak height (x and y), peak width and the integral.

which results from the OG setting.

Data Processing

Based on the detection of the gait cycle the stride-

based activity of the muscles can be determined,

and the mean EMG signal can be calculated after an

appropriate ﬁltering, rectiﬁcation of the signal and

the calculation of the envelope curve by using the

root mean square (RMS) (Pfeifer et al., 2003). A

ﬁnite impulse response (FIR) bandpass ﬁlter 1000

order with a frequency bandwidth of 20 - 300 Hz

was used for ﬁltering the raw EMG signals (Criswell,

2011; Miller et al., 2012; Mitchell et al., 2015).

Data Analysis

Four parameters were calculated for each set-

ting (OG, TM1 and TM2) as visualized in ﬁgure 1.

The peak height as the maximum of the average EMG

signal in terms of the temporal occurrence (in percent

of the gait cycle) and the amplitude (peak height in

mV). In addition to the peak height, the peak width

and the integral under the curve (EMG signal) was

calculated. For calculating the peak width and the

integral, two points have to be detected in the mean

EMG curve. These two points, the integral start and

end point, are located on the EMG curve at 50 % of

the peak height (detected maximum of the EMG), see

ﬁgure 1.

These parameters were analyzed descriptively and

regarding signiﬁcant differences. For the descriptive

analysis, the mean value of the OG and TM muscle

activity from all trials and all subjects, the mean

difference between OG and TM (OG vs. TM1,

OG vs. TM2) as well as the percentual quotient

between OG and TM walking (TM1 or TM2) was

calculated. Concerning the parameter peak height, a

value smaller than 100 % indicates a lower activation

of the plantar ﬂexor muscles during TM walking.

The whole analysis (preprocessing, heel strike

detection, calculation of mean EMG curve and

parameters, statistical analysis) was done in MAT-

LAB (TheMathworks Inc., Natick, MA, USA).

The calculated parameters were tested for normal

distribution by using the Kolmogorow-Smirnov test.

Paired students t-tests were used for parameters with

normal distribution (Atkinson and Nevill, 1998).

The level of signiﬁcance was set to α = 0.05 for the

above-mentioned statistical tests.

3 RESULTS

The results of the preliminary walking speed inves-

tigations are presented in detail with a bar chart in

ﬁgure 2 as well as using a boxplot for summarizing

the data of all subjects (ﬁgure 3). The mean speed for

each subject in each setting is depicted in the bar chart

(see ﬁgure 2). Furthermore, the diagram included the

difference of the mean speed (OG and TM) as a red

graph. Variations around 1 km/h are recognizable.

The overall mean is 1.1 km/h with a standard devia-

tion of 0.6 km/h. The differences in walking speed of

both scenarios are clearly visible in the boxplot (see

ﬁgure 3). The presented median values of the OG and

TM walking show signiﬁcant difference. Noticeable

is the shape of the boxplots which varies clearly.

The examination of the muscle activity during OG

and TM walking dedicates the four parameters: maxi-

Figure 2: The registered mean velocity for both settings (overground in dark grey and treadmill in light gray) and each of the

21 subjects is given as bar chart. The difference between both settings is presented as red curve. In addition, the values are

given below the chart and the mean and median velocity is stated.

mum peak (height, the amplitude in mV and temporal

occurrence in percent), the peak width and the integral

(the area under the curve). The determined values are

presented in the following tables 1 - 3. Comparing all

the values for the three examined muscles, it is recog-

nizable that the primary plantar ﬂexor muscles react

similarly and a reduced activation during TM walk-

ing exist.

The TM gait without inclination causes a lower activ-

ity of all three muscles in comparison to the OG walk-

ing. The calculated difference for the parameter peak

height (amplitude in mV) with negative values as well

as the quotient with values smaller than 100 % con-

ﬁrm that fact quantitatively (GM: 83.9 %, GL: 75.5 %,

SO: 68.9 %). Based on the used inclination of 1.5 %,

a little larger activity during TM walking (TM2) is

observed for the muscles GM and GL (GM: 91.3 %,

GL: 79.6 %), but a similar or even larger activation

could not be achieved with the chosen inclination.

The determined parameter peak width is always

smaller for the OG walking resulting in negative dif-

ference and percentual values above 100 % (see ta-

ble 1 - 3). The chosen inclination shows an effect to

the parameter peak width. The value determined for

the TM2 scenario is smaller than that calculated for

the TM1 scenario (GM: 113.6 % vs. 105.4 %, GL:

145.8 % vs. 125.6 %, SO: 148.4 % vs. 129.3 %).

Considering the parameter integral under the curve

(under the peak) the difference is always negative, and

the quotient is smaller than 100 %, but no uniform

behavior can be registered. The muscles GL and SO

show a reduced activation during the TM2 scenario

(with the 1.5 % inclination) compared to TM1 setting

(without inclination) (GL: 99.9 % vs. 95.7 %; SO:

96.4 % vs. 86.4 %), while the integral of the muscle

GM increases (GM: 94.0 % vs. 96.3 %).

All the parameters and the found differences are fur-

ther investigated using t-test regarding signiﬁcant dif-

ferences. As marked in the tables below the differ-

ences are signiﬁcant. The calculated correlation co-

efﬁcient also conﬁrms this signiﬁcant difference with

values smaller than 0.5 showing no good agreement.

Additionally, the temporal occurrence of the maxi-

mum peak was determined and considered in the in-

vestigation. This parameter shows no signiﬁcant dif-

ference between the compared settings (p > 0.05)

with moderate to high correlation coefﬁcient (r =

[0.66, 0.92]) for the small differences between the

mean of OG and TM setting ranging from -0.77 to

0.45 % (see mean difference of the parameter peak

occurence in tables 1 - 3).

Figure 3: Boxplots of the walking speed during the two

walking scenarios (overground and treadmill) with a higher

median walking speed for the overground setting.

4 DISCUSSION AND

CONCLUSION

The velocity examination shows that the motorization

of the treadmill affects the perception of self selected

comfortable walking speed. On average, the walking

speed on the TM is reduced by approximate 1 km/h

Table 1: Parameters of the OG walking compared to the TM walking (TM1 and TM2) of the muscle M. gastrocnemius

medialis (GM). * stands for p<0.01 and ** for p<0.05.

GM Parameter mean OG mean TM mean difference mean quotient (%)

OG vs. TM1 Peak occurence (%) 38.00 37.30 -0.70 98.21

peak height (mV) 4722.93 3963.36 -759.57* 83.92

peak width (%) 23.18 26.33 3.15* 113.59

integral (UA) 84305.29 79261.56 -5043.73** 94.02

OG vs. TM2 Peak occurence (%) 38.00 37.88 -0.12 99.63

peak height (mV) 4722.93 4312.86 -410.07* 91.32

peak width (%) 23.18 24.42 1.24 105.36

integral (UA) 84305.29 81169.29 -3136.00** 96.28

Table 2: Parameters of the OG walking compared to the TM walking (TM1 and TM2) of the muscle M. gastrocnemius lateralis

(GL). * stands for p<0.01.

GL Parameter mean OG mean TM mean difference mean quotient (%)

OG vs. TM1 Peak occurence (%) 40.52 40.52 0.00 99.96

peak height (mV) 3470.75 2621.18 -849.57* 75.52

peak width (%) 20.14 29.36 9.22* 145.80

integral (UA) 54551.43 54472.49 -78.93 99.86

OG vs. TM2 Peak occurence (%) 40.52 40.97 0.45 101.08

peak height (mV) 3470.75 2763.14 -707.61* 79.61

peak width (%) 20.14 25.29 5.16* 125.60

integral (UA) 54551.43 52228.61 -2322.81 95.74

Table 3: Parameters of the OG walking compared to the TM walking (TM1 and TM2) of the muscle M. soleus (SO). * stands

for p<0.01.

SO Parameter mean OG mean TM mean difference mean quotient (%)

OG vs. TM1 Peak occurence (%) 41.61 41.56 -0.09 99.76

peak height (mV) 2575.85 1773.51 -802.34* 68.85

peak width (%) 20.22 30.00 9.78* 148.39

integral (UA) 39982.37 38522.78 -1459.59 96.35

OG vs. TM2 Peak occurence (%) 41.61 41.74 0.13 100.32

peak height (mV) 2575.85 1720.35 -855.50* 66.79

peak width (%) 20.22 26.13 5.91* 129.25

integral (UA) 39982.37 34550.92 -5431.45* 86.42

compared to the walking velocity in the OG setting.

The literature shows similar results, but partly not in

these dimensions. In walking scenario, Arsenault et

al. (Arsenault et al., 1986) and Marsh et al. (Marsh

et al., 2006) found a difference in speed of 0.3 km/h

or 1.4 km/h, respectively. Oliveira et al. (Oliveira

et al., 2016) and Kong et al. (Kong et al., 2012) inves-

tigated running scenarios and registered differences in

the self-selected and comfortable running velocity of

0.4 km/h or 4.2 km/h.

Considering the muscle activation during walking, the

results of our investigations conﬁrm that there are dif-

ferences between OG and TM walking. The consid-

ered hypothesis that the primary plantar ﬂexor mus-

cles are less activated during TM walking than in OG

walking can be veriﬁed with the present results con-

sidering the parameter peak height. Referring the pa-

rameter peak occurence no difference in the temporal

appearance of the maximum activation of the plantar

ﬂexor muscles could be found in the investigated sam-

ple. At the moment, the effect represented by the pos-

itive difference between the settings (OG vs. TM1,

OG vs. TM2) of the parameter peak width resulting

in a percentual quotient larger than 100 % cannot be

interpreted. Compared to the OG walking the activa-

tion curve shows a broader but ﬂatter course for the

TM walking. That means that the muscle is earlier

and longer activated during the gait cycle. The reason

for that phenomenon is currently unknown.

The statements published by Oliveira et al. can only

be partially conﬁrmed (Oliveira et al., 2016). The au-

thors found a higher activation of the SO and a lower

activation of the GM and GL during OG walking.

Compared to our approach Oliveira et al. (Oliveira

et al., 2016) examined the muscle activation while

overground and treadmill running. In contrast, our

ﬁndings show a higher activation for all primary plan-

tar ﬂexor muscles during OG walking.

The determined parameters of the muscle activation

indicate that there is an effect of different, adjustable

conditions (speed and inclination). Using the recom-

mended inclination of 1.5 %, a little higher activation

of the primary plantar ﬂexor muscles is recognizable.

With the exception of SO showing a decrease, an in-

crease in muscle activation of 4 to 7 % was observed.

However, the temporal occurrence of the maximum

activation of the muscles is not inﬂuenced by these

conditions.

In future, examinations are planned to ﬁnd detailed

information about the different conditions and their

impact on the muscle activation in order to ﬁnd rec-

ommendations for therapeutic interventions or train-

ing programs. For achieving the goal, these facts are

important to know.

Furthermore, investigations with CP patiens should

be conducted in order to ﬁnd the impact of the con-

ditions to the gait and the muscle activation of these

patients. Depending on the CP-type the setting and

the detection of gait initiation have to be changed.

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