The final phase should document, if the subjects have
adopted the behavior of the previous phase or not. For
a detailed investigation the deflection of the Rocker
Board and the muscular activity were recorded. The
EMG values were derived from both sides of the M.
peroneus longus, the M. tibialis anterior and the M.
vastus lateralis. Again, the skin preparation and the
placement of the electrodes followed the recommen-
dations of the SENIAM project (SENIAM project,
2012). The measurements of both setups had also in
common, that the test persons had to stand the whole
time without shoes on both feet. The study was su-
pervised by an experienced physiotherapist.
Table 3: Setup 2 - Test procedure.
Phase Task Duration
1 Without Intervention 60 s
2 Right Intervention 30 s
3 Left Intervention 30 s
4 Without Intervention 120 s
5 Physiotherapists Intervention 120 s
6 Without Intervention 120 s
2.4 Data Analyzes
Before starting the signal processing, the data sets
were synchronized. The first step of signal process-
ing was the application of a notch filter to EMG data
with a blocking frequency of 50 Hz. Secondly a fir
band-pass filter was applied to the data (Merletti and
Parker, 2004). Afterwards, the normalization of the
EMG data took place. Therefore the average muscu-
lar activity when staying in front of the exerciser was
calculated and used as normalization value. Subse-
quently, the absolute values of the measurement on
the exercisers were transformed into relative values
by using the normalization value. Finally, all EMG
values were presented as a percentage value of the
stance.
The next step regarding the EMG processing im-
plies the full-wave rectification of the EMG data
(Merletti and Parker, 2004). For the evaluation of
the muscular activity in the time domain different sta-
tistical parameters were calculated. For instance the
maximum and mean values for the whole signal over
a time window of 512 ms (Gu et al., 2010). These sta-
tistical parameters were evaluated within further cal-
culations. Namely, on the one hand the course of the
maximum values over time was documented. On the
other hand the mean value of the maximum voltage
values for each phase as well as for the complete pro-
cedure were calculated. Besides that, the accumulated
EMG activity (iEMG) was analyzed. Therefore, the
EMG was integrated over time. Consequently, the to-
tal accumulated activity was computed by the calcula-
tion of the area under the EMG for a chosen time pe-
riod (Robertson and Caldwell, 2004; Medved, 2000).
This calculation was performed for each phase as well
as for the complete test procedure. For a more de-
tailed investigation, the course of the iEMG over the
time was calculated and plotted.
3 RESULTS
3.1 Setup 1
Figure 2 provides an overview of the overall muscular
activity of all test persons during the complete test
procedure on each exerciser.
The complete accumulated EMG activity during
the individual test sequences of each test person were
computed. The data were normalized for each sub-
ject. Therefore, the muscle with the highest strain
during all trials of each person was identified. This
muscles represents 100 %. The values of the remain-
ing muscles of the different trials were presented in
relation to the 100 %. This data was collected for all
of the 13 subjects. Finally, the whole data was aver-
aged and visualized in figure 2.
The investigation of the EMG data had revealed,
that it is useful to distinguish between the process of
the compensation of the instability caused by the ex-
erciser and the process of the maintenance of the body
stability. The first part is mainly realized by the mus-
culature of the lower legs. However, the maintenance
of the body balance is linked to the stability of the
knee joints. Due to that, the musculature of the thigh
has to produce the major part of the performance. Ac-
cordingly, the patterns of the M. biceps femoris and
the M. vastus lateralis show for all of the three exer-
cisers a similar intensity.
On the basis of this approach, the evaluation of
the musculature of the M. tibialis anterior and the
M. soleus shows individual results for the equip-
ment. The instability caused by the different Boards
is mainly compensated by the ankle sprains. Conse-
quently, a higher intensity of the instability induces a
higher muscular activity. One assumption in the lit-
erature is, that an exerciser with a multidimensional
instability requires a higher muscles strain in compar-
ison to an exerciser with an one-dimensional insta-
bility (Grifka and Dullien, 2008). This assumption
can not be validated by the measured EMG activity in
this study. Both types of the one-dimensional Rocker
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