Age-related differences in time-limit performance and force platform-based balance measures during one-leg stance

Full text

Age-related differences in time-limit performance and force platform-based
balance measures during one-leg stance
Rubens A. da Silva
a,b,
⇑
, Martin Bilodeau
d
, Rodolfo B. Parreira
a,b
, Denilson C. Teixeira
a,e
, César F. Amorim
c
a
Center for Health Science Research, Laboratory of Functional Evaluation and Human Motor Performance, Universidade Norte do Paraná (UNOPAR), 675 Paris Ave., CEP 86041-120,
Londrina-PR, Brazil
b
Masters Program in Rehabilitation Sciences UEL/UNOPAR, 675 Paris Ave., CEP 86041-120, Londrina-PR, Brazil
c
Faculty of Engineering, Universidade Estadual Paulista – UNESP-FEG/UNICID, Av. Doutor Ariberto Pereira da Cunha, 333, Guaratinguetá, SP 12516-410, Brazil
d
School of Rehabilitation Sciences, University of Ottawa, Élisabeth Bruyère Research Institute, 43 Bruyere St., Ottawa, ON, Canada K1N 5C8
e
Physical Education and Sport Center, Universidade Estadual de Londrina (UEL),Rod. Celso Garcia Cid. 445 Km 380, Campus Universitário Londrina - PR, 86055-900, Brazil
article info
Article history:
Received 9 November 2011
Received in revised form 9 January 2013
Accepted 9 January 2013
Keywords:
Posture
Force platform
Aging
Biomechanics
Rehabilitation
abstract
Poor posture control has been associated with an increased risk of falls and mobility disability among
older adults. This study was conducted to assess the test–retest reliability and sensitivity to group differ-
ences regarding the time-limit (T
Limit
) of one-leg standing and selected balance parameters obtained with
a force platform in older and young adults. A secondary purpose was to assess the relationship between
T
Limit
and these balance parameters. Twenty-eight healthy older adults (age: 69 ± 5 years) and thirty
young adults (age: 21 ± 4 years) participated in this study. Two one-leg stance tasks were performed:
(1) three trials of 30 s maximum and (2) one T
Limit
trial. The following balance parameters were com-
puted: center of pressure area, RMS sway amplitude, and mean velocity and mean frequency in both
the anterio-posterior and medio-lateral directions. All balance parameters obtained with the force plat-
form as well as the T
Limit
variable were sensitive to differences in balance performance between older and
young adults. The test–retest reliability of these measures was found to be acceptable (ICC: 0.40–0.85),
with better ICC scores observed for mean velocity and mean frequency in the older group. Pearson cor-
relations coefficients (r) between balance parameters and T
Limit
ranged from 0.16 to 0.54. These results
add to the current literature that can be used in the development of measurement tools for evaluating
balance in older and young adults.
Ó2013 Elsevier Ltd. All rights reserved.
1. Introduction
Poor posture control has been associated with an increased risk
of falls in older adults (Berg et al., 1992; Tinetti et al., 1988). In the
present study, posture control will be referred to as ‘‘balance’’,
which is a generic term used to describe the body’s ability to adjust
the center-of-pressure (COP) in order to maintain projection of the
center of mass (COM) within the manageable limits of the base of
support (Winter, 1995).
Several clinical and laboratory methods have been developed to
assess different dimensions of balance in order to assist clinical
decision-making with respect to interventions for balance-related
deficits, and thus fall prevention. Functional balance tests such as
Tinetti and Berg scales (Berg et al., 1992; Tinetti et al., 1988), which
use the maximum time a person can stand on one leg without sup-
port (namely here: T
Limit
) as a scale item, have been used with good
reliability to estimate a subject’s risk of falling (Godi et al., 2013).
However, as with any single domain measure (T
Limit
), critical infor-
mation about balance may not be optimal. On the other hand, COP
parameters calculated from force platform data can provide finer
information related to biomechanical and neuromuscular control
strategies for maintaining balance among different populations
(Howe et al., 2009; Lacour et al., 1997; Melzer et al., 2004; Nardone
and Schieppati, 2010).
Commonly used measures of COP displacement can be calcu-
lated in the time (e.g., velocity) and frequency (e.g., median fre-
quency) domains (Bauer et al., 2008; Corriveau et al., 2000;
Gribble and Hertel, 2004; LeClair and Riach, 1996). However, be-
cause these variables originate from biological systems, they also
have an intrinsic variability that can affect their reliability and
validity. Different studies using different experimental protocols
have documented the reliability of these variables for both healthy
young adults and older subjects (Bauer et al., 2008; Corriveau et al.,
2000; Gribble and Hertel, 2004; LeClair and Riach, 1996; Goldie
et al., 1989; Lin et al., 2008; Pinsault and Vuillerme, 2009; Santos
1050-6411/$ - see front matter Ó2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.jelekin.2013.01.008
⇑
Corresponding author at: Center for Health Science Research, Laboratory of
Functional Evaluation and Human Motor Performance, Universidade Norte do
Paraná (UNOPAR), 675 Paris Ave., CEP 86041-120, Londrina-PR, Brazil.
E-mail address: rubens@unopar.br (R.A. da Silva).
Journal of Electromyography and Kinesiology 23 (2013) 634–639
Contents lists available at SciVerse ScienceDirect
Journal of Electromyography and Kinesiology
journal homepage: www.elsevier.com/locate/jelekin

et al., 2008). These studies reported excellent reliability (>0.75) for
several balance parameters (Bauer et al., 2008; Corriveau et al.,
2000; Lin et al., 2008; Pinsault and Vuillerme, 2009; Lafond et al.,
2004) during a bipedal quiet standing task. However, maintaining
a quiet standing position using two legs is not a major challenge to
our balance control system (Cliffor, 2010). Thus, the clinical useful-
ness of data obtained under such conditions, i.e., when document-
ing balance deficits in young adults, the older or rehabilitation
patients, is limited. Few studies have investigated these balance
parameters for the one-leg stance and still fewer have determined
their reliability (Pinsault and Vuillerme, 2009), which is of concern
when these are used to determine the efficacy of a specific balance
intervention for fall prevention in older individuals. Furthermore,
some studies (Hughes et al., 1996; Holbein-Jenny et al., 2007) have
correlated the T
Limit
from functional performance with COP balance
parameters obtained in bipedal tasks only. It is likely that such an
association would be stronger for balance parameters obtained
during a one-leg stance condition, and this could have implications
for the prediction/prevention of falls (Michikawa et al., 2009).
The aims of the present study were to assess (1) the test–retest
reliabilities of T-limit and four measures of the COP, (2) the sensi-
tivities of these measures to group differences (older and young
adults), and (3) the relationships between T
Limit
and each of the
four COP measures.
2. Methods
2.1. Subjects
Twenty-eight healthy older (20 women) and 30 young adult
volunteers (16 women) participated in this study. All participants
were recruited by convenience between 2010 and 2011; older
adults from the local community who were participants in a phys-
ical exercise program for seniors at the Universidade Norte do
Paraná (enrolled for at least 1 year) and young adults from the uni-
versity community. The characteristics of the subjects are pre-
sented in Table 1. Inclusion criteria were as follows: (1) older
adults: aged over 60 years, living independently, no falls in the past
year and a cognitive status of >21 on the Mini-Mental State Exam-
ination (Hughes et al., 1996); (2) young adults: aged between 18
and 30 years and not enrolled in any physical activity program at
the time of the study. General exclusion criteria were as follows:
self-reported injuries, illnesses, musculoskeletal disorders, sys-
temic–neurological–degenerative diseases, severe labyrinthitis
and chronic diseases of the cardiovascular or respiratory system.
Subjects were informed about the experimental protocol and the
potential risks of the study and gave written consent before their
participation. The protocol and the consent form had been previ-
ously approved by the local Ethics committee (##PP/0114/09).
2.2. Procedures
Two approximately 2-h sessions separated by a maximum of
2 weeks were required. The same investigator performed the pro-
cedures and tasks with all participants in the same laboratory envi-
ronment to ensure uniformity. To assess reliability, all subjects
performed the same experimental protocol after a 2-week interval.
2.3. Tasks
Each participant was allowed to practice the one-leg stance be-
fore testing and, since only one leg was being tested, the subjects
were free to choose which leg they preferred to stand on. The par-
ticipants performed two tasks: (1) three 30-s trials of the one-leg
stance on a force platform (Gil et al., 2011), with a rest period of
approximately 30 s between trial. The mean of these three trials
for each balance measure was retained to assess: (i) the sensitivity
of the balance parameters for discriminating between groups (ses-
sion one only) and (ii) the test–retest reliability between the mea-
sures across two sessions. This approach was used because
averaging the balance parameters values across three trials im-
proves reliability (Bauer et al., 2008).
After 5 min of rest from task one a second task, consisting of a
one legged-stance maintained until loss of balance (T
Limit
), was
performed. The T
Limit
criterion in the present study was defined
as the maximum time it took until a subject suddenly abandoned
the posture due to loss of balance, i.e., when the lifted foot touched
either the force platform or the floor. This task was used to assess
the relationship between T
Limit
of one-leg standing and selected
balance parameters from the force platform.
During all trials in both tasks, the participants were instructed
to stand on one leg (see Fig. 1 for illustration) under the following
standardized conditions: barefoot, eyes opened and looking at a
target (cross) placed on a wall at eye level 2 m away, arms at their
sides or parallel to their trunk. To prevent falls or injuries during all
testing, an investigator stood close to each participant.
Table 1
Characteristics of Subjects.
Older (n= 28) Young adults (n= 30)
Age (yrs) 69 (5) 21 (4)
Height (m) 1.56 (7.8) 1.69 (6.9)
Weight (kg) 64.2 (8.8) 65.6 (13.4)
BMI (kg/m
2
) 27 (4) 23 (4)
Cognitive status
a
27 (2) /
Note: Mean values with standard deviation (SD). BMI: Body Mass Index.
a
Mini-Mental State Examination (normal range based in a cutoff >21). Fig. 1. Subject’s position on a BIOMEC400 force platform (EMG System do Brasil, SP
Ltda.).
R.A. da Silva et al. /Journal of Electromyography and Kinesiology 23 (2013) 634–639 635

2.4. Computation of COP-based balance parameters
The vertical ground reaction force data from the force platform
(BIOMEC400, EMG System do Brasil, Ltda., SP) were sampled at
100 Hz. All force signals were filtered with a 35-Hz low-pass sec-
ond-order Butterworth filter and converted into COP data using
proper software, which was compiled with MATLAB routines
(The Mathworks, Natick, MA). Stabilographic analysis of COP data
led to the calculation of the four main balance parameters: (1)
95% confidence ellipse area of COP (A-COP in cm
2
), (2) Root Mean
Square (RMS) amplitude of COP sway (RMS in cm), and (3) mean
velocity (MVeloc in cm/s) and (4) mean frequency (MF in Hz) of
COP for both antero-posterior (A/P) and medio-lateral (M/L) direc-
tions. For both tasks, these balance parameters were calculated for
the total duration of the trial for each subject.
2.5. Statistical analysis
All statistical analyses were performed with NCSS statistical
software (version 6.0 for Windows) with an alpha level of 0.05.
All variables were normally distributed, as verified with the Shap-
iro–Wilk test. Student unpaired t-test was used to assess between-
group (older vs. young adults) differences in T
Limit
and in four COP
variables in order to determine the sensitivity of these measures
for discriminating of balance between the two groups. Pearson’s
correlation coefficients were used to assess the relationship be-
tween four balance parameters (A-COP, RMS, MVeloc, MF) and
the T
Limit
computed in task two.
To assess the test–retest reliability across the two sessions in
task one, ICCs
(2,1)
and SEM were calculated as described in Shrout
and Fleiss (Shrout and Fleiss, 1979), based on two-way ANOVAs,
which allowed a contrast between the within-subject variability
and the between-subject variability. To classify the ICCs, we used
Fleiss’ Classification, where an ICC below 0.4 was considered as
‘‘poor’’ reliability, between 0.40 and 0.75 as ‘‘fair to good’’ reliabil-
ity and above 0.75 as ‘‘excellent’’ reliability (Fleiss, 1997).
3. Results
3.1. Reliability assessment
The reliability of T
Limit
was excellent with an ICC of 0.87 for old-
er and 0.75 for young adults across two sessions. The ICC scores of
older and young adult volunteers varied between the four balance
parameters, ranging from 0.40 to 0.85 (SEM: 0.08–6.66); i.e., show-
ing fair to excellent reliability (Table 2). Mean velocity was the
most reliable measure, followed by the MF parameter, especially
in older group, showing excellent ICC values (>0.80) and lower
SEM values in both directions. Excellent reliability was observed
for sway area of COP in young adults only (Table 2), whereas the
RMS parameter presented the poorest reliability across both
groups.
Table 2
Test–retest reliability results COP-based balance parameters (task one).
Variables Older (n= 20) Young adults (n= 30)
ICC SEM SEM (%) ICC SEM SEM (%)
A-COP (cm
2
) 0.60 6.66 41 0.83 1.30 20
RMS A/P (cm) 0.51 1.98 35 0.55 0.59 16
RMS M/L (cm) 0.40 1.82 33 0.60 0.43 14
MF A/P (Hz) 0.82 0.09 13 0.68 0.13 22
MF M/L (Hz) 0.72 0.08 10 0.70 0.10 11
MVeloc A/P (cm/s) 0.85 0.90 22 0.72 0.33 14
MVeloc M/L (cm/s) 0.82 1.3 17 0.75 0.25 10
ICC: intra-class correlation coefficient; SEM: standard error of measurement
(absolute error); SEM (%): standard error of measurement relative to the grand
mean.
0,00
2,00
4,00
6,00
8,00
10,00
A/P M/L
RMS (cm)
p =0.006 p = 0.000
0,00
5,00
10,00
15,00
20,00
25,00
30,00
A-COP (cm
2
)
p = 0.000
0,00
0,20
0,40
0,60
0,80
1,00
A/P
MF (Hz)
p = 0.000 p = 0.000
0,00
1,00
2,00
3,00
4,00
5,00
6,00
7,00
A/P M/L
MVeloc (cm/s)
p = 0.000 p = 0.000
*
*
*
**
*
*
Directions of movement Directions of movement
Older
Young adults
M/L
Fig. 2. Balance parameters (95% ellipse A-COP and RMS, MF, MVeloc in A/P and M/L directions of movement) values (error bars correspond to standard deviations) from the
BIOMEC400 force platform.
⁄
Significant differences (P< 0.05 from Student’s t-test) were found between elderly and young adults for all balance parameters.
636 R.A. da Silva et al. /Journal of Electromyography and Kinesiology 23 (2013) 634–639

3.2. Age-related differences on COP parameters and T
Limit
The comparison between older and young adults using session
one data is depicted in Fig. 2. All selected COP balance parameters
proved to be sensitive to differences between the two groups
(P< 0.05) for this specific one-leg stance task. Greater COP values
were observed for the older than the young adults.
The older adults showed significantly shorter T
Limit
values than
the younger subjects for the T
Limit
task (Table 3), ranging from 6 to
74 s (mean: 25 ± 15 s), whereas values for young adults ranged be-
tween 30 and 350 s (mean: 162 ± 113 s).
Only two balance-related variables were significantly associ-
ated with T
Limit
: A/P MF correlated moderately with T
Limit
in both
groups; whereas A-COP correlated with T
Limit
only in the older
group (Table 3). Other than A-COP, correlation values were not
shown to be systematically higher for one group than the other
across balance parameters.
4. Discussion
The test–retest reliability of the three measures (T
Limit
, MF and
MVeloc) was found to be acceptable for evaluating balance in older
and young adults during one-leg stance test. Also, all four balance
parameters obtained with the force platform as well as the time-
limit variable were sensitive enough to discriminate the balance
between older and young adults. Both MF and MVeloc balance
parameters showed an association with T
Limit
. These results add
to the literature concerning the development of measurement
tools for evaluating balance deficits in older adults, especially dur-
ing a challenging task.
4.1. Reliability assessment
To the authors’ knowledge and based on a brief recent literature
search concerning the reliability of COP measures (Goldie et al.,
1989), the reliability of balance parameters computed during a
one-leg stance test in both older and young individuals has not
been reported. Despite differences in experimental protocol and
statistical models of reliability measurements, our results are in
agreement with other studies (Bauer et al., 2008; Corriveau et al.,
2000; Lin et al., 2008; Pinsault and Vuillerme, 2009). Balance
parameters can present quite diverse levels of reliability. Our re-
sults indicated that mean velocity (MVeloc) was the most reliable
balance parameter (ICC = 0.72–0.85; SEM = 0.2–1.3) across groups
(older and younger) and for both directions (A/P and M/L), which
is consistent with results from previous studies of older adults dur-
ing bipedal quiet standing (Lin et al., 2008; Lafond et al., 2004).
Furthermore, our results pointed out the excellent reliability of
mean frequency (MF) in the A/P direction, especially for the older
group, suggesting that this parameter, in addition to being associ-
ated with the T
Limit
variable, also presents stability over time under
this experimental condition. This suggests that this parameter, as
well as MVeloc, could be used with relevance for clinical deci-
sion-making concerning the effects of a rehabilitation program
over the course of several days for improving balance in older
adults. Interestingly, ICC scores for MF and MVeloc were slightly
higher for the older adults, as also observed by Lin et al. (2008)
during a bipedal task. This may be related, at least in part, to a
higher variation of measures across older individuals, which in
turn contributes to higher ICC scores (Portney and Watkins, 2000).
4.2. Age-related differences
It is well known that aging is associated with neuro-musculo-
skeletal alterations and decreased physiological functions, which
in turn can lead to problems such as muscular weakness and lack
of mobility, as well as other sensory-motor deficits and a conse-
quent loss of balance and falls (Orr, 2010; Piirtola and Era, 2006).
In the present study, the performance of the older adults was
worse in both tasks (30-s balance trials and T
Limit
). These results
agree with previous studies conducted with older adults (Corri-
veau et al., 2000; Pinsault and Vuillerme, 2009; Lafond et al.,
2004). In contrast to these previous studies, which assessed
healthy community-dwelling older adults using double-leg stance
tasks, the present study included a more challenging balance-con-
trol task, which may be more predictive of balance problems and,
consequently, a better indicator of falls (Hurvitz et al., 2000).
Typical measurements used to evaluate balance and fall risk in
older adults (Berg et al., 1992; Tinetti et al., 1988; Lord et al., 2001;
Persad et al., 2010; Rubenstein, 2006) include the time necessary
for carrying out functional tasks, such as getting up from a chair,
circling a cone and returning, maintaining a one-legged stance, or
walking a distance of 10 m as fast as possible (Persad et al.,
2010; Mancini and Horak, 2010; Fregly et al., 1973). As expected,
age-related differences were found in the present study regarding
T
Limit
during the one-leg stance trial (which was not stopped at
30 s), suggesting a possible balance deficit in the older adults that
could be associated with poor lower-limb muscular endurance
(Shrout and Fleiss, 1979). The mean T
Limit
in this study corresponds
to earlier results reported for older (Mancini and Horak, 2010), as
well as for young adults (Fregly et al., 1973).
Take out, factors regulating balance are multifaceted (i.e., the
integration of different systems) and this could explain the weak
(>0.16) to moderate (<0.54) correlations between T
Limit
and bal-
ance COP parameters. Our correlation results supplement those of
previous studies (Hughes et al., 1996; Lindmark et al., 1999; Tang
Table 3
Relationship between COP-based balance parameters and time-limit.
Variables Older (n= 28) Young adults (n= 30)
Mean ± SD Pearson r(pvalue) Mean ± SD Pearson r(pvalue)
T
Limit
from task two (s)
a
25 (15) / 162 (113) / (0.000)
A-COP (cm
2
) 18.5 (8.6) 0.47 (0.002)
*
8.1 (2.2) 0.20 (0.690)
RMS A/P (cm) 6.45 (1.5) 0.20 (0.315) 4.26 (1) 0.30 (0.104)
RMS M/L (cm) 6.98 (2.1) 0.16 (0.419) 4.21 (0.7) 0.26 (0.239)
MF A/P (Hz) 0.91 (0.2) 0.46 (0.013)
*
0.43 (0.1) 0.54 (0.002)⁄
MF M/L (Hz) 0.88 (0.2) 0.32 (0.094) 0.54 (0.1) 0.31 (0.090)
MVeloc A/P (cm/s) 3.95 (0.8) 0.18 (0.353) 2.29 (0.5) 0.20 (0.373)
MVeloc M/L (cm/s) 3.98 (0.6) 0.24 (0.235) 2.28 (0.4) 0.20 (0.367)
Mean values with standard deviation (SD). rPearson’s: Correlation Coefficients between balance parameters and time-limit (T
Limit
) of test one-leg stance trial.
a
Significant differences between older and young adults for T
Limit
variable (P< 0 .05).
*
Significant correlations (P< 0 .05).
R.A. da Silva et al. /Journal of Electromyography and Kinesiology 23 (2013) 634–639 637

et al., 1998) that correlated different balance parameters with the
time taken during different bipedal functional balance tests. The
results of this study identified two balance parameters (MF and
A-COP) from the force platform data that were found to be associ-
ated with a unipodal balance deficit by the T
Limit
in older adults.
Compared with previous studies, the relationships we documented
have to do with a task that has greater fall-related relevance in old-
er adults (Hughes et al., 1996), and could thus have implications for
both the prevention and rehabilitation of balance problems in older
adults. Nevertheless, a dysfunction in an individual’s ability to
maintain or restore a state of balance implies a deficit in postural
control (Pollock et al., 2000). Any cognitive, proprioceptive (sensory
and motor), muscular strength or motor coordination impairment
could result in postural control deficits, and clinical balance assess-
ment tools, such as the T
Limit
variable or COP parameters, can pro-
vide some information on a variety of dimensions of postural
control deficits (Hughes et al., 1996; Michikawa et al., 2009; Hurvitz
et al., 2000, 2000; Mancini and Horak, 2010; Pollock et al., 2000).
Functional tests can measure balance deficit indirectly through
the recorded time-limit of physical performance (i.e., one aspect
of physical condition or muscular capacity of individual), while
COP parameters from a force platform can directly analyze balance
deficits related to proprioception and postural adjustments (feed-
back and feedfoward) of the neuromuscular system (Winter,
1995; Lacour et al., 1997; Lafond et al., 2004; Hughes et al., 1996;
Holbein-Jenny et al., 2007; Pollock et al., 2000). This is further sup-
ported by a recent study (Nguyen et al., 2012) suggesting that clin-
ical functional tests such as time-limit to stand one leg and
laboratory-based measures from COP parameters may capture dif-
ferent aspects of balance and likely complement each other.
4.3. Study limitations
The overall results of this study cannot necessarily be general-
ized to all older adults because of the limited size of our sample
(n= 28), which likely does not represent the heterogeneity of bal-
ance status of all older individuals. Another limitation is that there
was no comparison between sexes because we used a convenience
sample that was not matched for sex. Also, EMG complementary
analysis of muscular pattern during unipodal balance test would
be relevant to help in interpretation of results from relationship
between T
Limit
and balance COP parameters.
5. Conclusion
The test–retest reliability of the balance measures was found to
be acceptable, with better ICC scores observed for MVeloc and MF
in the older group. All four balance parameters obtained with the
force platform as well as the T
Limit
were sensitive enough to dis-
criminate older from young adults in a one-leg stance task. Our re-
sults suggest that the two parameters, showing an association with
T
Limit
, MF and MVeloc, are likely more optimal in the context of
clinical decision-making concerning the effects of a rehabilitation
program for improving balance in older adults.
Conflict of interest
None declared.
Acknowledgements
Rubens A. da Silva, research grant recipient from the National
Foundation for the Development of Private Higher Education
(FUNADESP, Brazil). We gratefully acknowledge the assistance of
Letícia L. Medonça, Jéssica A. Ghizoni and Bruna De Longhi (Phys-
iotherapist students at University) for the recruitment of subjects
and data collection.
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Rubens da Silva received a B.Sc. degree in Physio-
therapy in 2000 (at Universidade Tuiuti do Parana,
Brazil) and a Master and Ph.D. degree in Biomedical
Sciences (Rehabilitation) in 2003 and 2008, respec-
tively from the University of Montreal. He was a
postdoctoral fellow at the Elisabeth Bruyere Research
Institute affiliated to Ottawa University from 2008. He
is a Titular professor at the University of North of
Parana (UNOPAR, Brazil) since 2009. He is the coor-
dinator of Laboratory of functional evaluation and
human motor performance at the Center for Health
Science Research of UNOPAR. His current research
interests include the study of balance postural control,
aging, muscle fatigue, low back pain, trunk muscles and exercises on area reha-
bilitation.
Martin Bilodeau received a B.Sc. degree in Physio-
therapy in 1988 and a Ph.D. degree in Biomedical
Sciences (Rehabilitation) in 1993 from the University
of Montreal and was a postdoctoral fellow at the
Cleveland Clinic Foundation from 1993 to 1995. He
was assistant and associate professor at the University
of Iowa from 1996 until 2004. He joined the School of
Rehabilitation Sciences, Faculty of Health Sciences at
the University of Ottawa in 2004, and is a full pro-
fessor. His current research interests include the study
of neuromuscular fatigue, aging, mobility, rehabilita-
tion and stroke.
Rodolfo B. Parreira received his master’s degree in
Rehabilitation Science and the bachelor degree from
The Universidade Norte do Paraná (UNOPAR). His
research has focused on postural strategies distur-
bance and muscle fatigue. His is a clinical physical
therapist at Londrina city (Parana, Brazil).
Denilson de Castro Teixeira is Graduated in Physical
Education. His received his master’s degree in Human
Movement Pedagogy from the University of São Paulo
– USP and your Ph.D in Health Science from 2009 by
the Universidade Estadual de Londrina (UEL). He is
full professor in University of Northern Paraná -
UNOPAR and UEL. He is teaching in the master’s
program of Physical Activity in Health Promotion
(UNOPAR). His area of research interest is physical
exercise and health promotion for older people.
César F. Amorim was born in São Paulo, Brazil.
Graduated in Eletronics Engineering from University
of Vale do Paraíba-UNIVAP in 1992. He received his
Ph.D. in Biomedical Engineering from University of
Vale do Paraiba – São Paulo, Brazil. He is professor of
Biomedical Engineering Department and Physical
Therapy master course. His areas of research interests
are signal processing applied to biomedical signals,
detection, processing and interpretation of surface
EMG.
R.A. da Silva et al. /Journal of Electromyography and Kinesiology 23 (2013) 634–639 639