Increased muscular challenge in older adults during obstructed gait

Article (PDF Available)inGait & Posture 22(4):356-61 · January 2006with46 Reads
DOI: 10.1016/j.gaitpost.2004.11.012 · Source: PubMed
Abstract
Skeletal muscle strength is known to decline with age. Although lower extremity (LE) muscle strength is critical to maintaining dynamic stability, few studies have investigated lower extremity muscle challenge during activities of daily living. The purpose of this study was to investigate the effects of age and obstructed gait on relative lower extremity muscular challenge, with respect to available joint strength. Fifteen healthy young and fifteen healthy older adults were asked to walk over level ground and step over obstacles. Pre-amplified surface electrodes were used to measure bilateral muscular activation of the gluteus medius (GM), vastus lateralis (VL), and gastrocnemius (GA). Muscle activation signals were normalized to peak magnitudes collected during maximal manual muscle testing (MMT). Normalized magnitudes were analyzed during the double-support phase for gluteus medius and vastus lateralis and during the single-support phase for gastrocnemius. A two-factor ANOVA was used to test for age group effect, with repeated measure of obstacle height. In general, older adults demonstrated greater relative activation levels compared to young adults. Gluteus medius activity was significantly greater in the elderly as compared to young during periods of double-support (weight transfer). Increased obstacle height resulted in greater relative activation in all muscles, confirming the increased challenge to the musculo-skeletal system. While healthy elderly adults were able to successfully negotiate obstacles of different heights during walking, their muscular strength capacity was significantly lower than young adults, resulting in relatively higher muscular demands. The resulting potential for muscular fatigue during locomotion may place individuals at higher risk for trips and/or falls.

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Available from: Michael E Hahn
Increased muscular challenge in older adults during obstructed gait
Michael E. Hahn
1
, Heng-Ju Lee, Li-Shan Chou
*
Motion Analysis Laboratory, Department of Human Physiology, 1240 University of Oregon, Eugene, OR 97403, USA
Accepted 21 November 2004
Abstract
Skeletal muscle strength is known to decline with age. Although lower extremity (LE) muscle strength is critical to maintaining dynamic
stability, few studies have investigated lower extremity muscle challenge during activities of daily living. The purpose of this study was to
investigate the effects of age and obstructed gait on relative lower extremity muscular challenge, with respect to available joint strength.
Fifteen healthy young and fifteen healthy older adults were asked to walk over level ground and step over obstacles. Pre-amplified surface
electrodes were used to measure bilateral muscular activation of the gluteus medius (GM), vastus lateralis (VL), and gastrocnemius (GA).
Muscle activation signals were normalized to peak magnitudes collected during maximal manual muscle testing (MMT). Normalized
magnitudes were analyzed during the double-support phase for gluteus medius and vastus lateralis and during the single-support phase for
gastrocnemius. A two-factor ANOVA was used to test for age group effect, with repeated measure of obstacle height. In general, older adults
demonstrated greater relative activation levels compared to young adults. Gluteus medius activity was significantly greater in the elderly as
compared to young during periods of double-support (weight transfer). Increased obstacle height resulted in greater relative activation in all
muscles, confirming the increased challenge to the musculo-skeletal system. While healthy elderly adults were able to successfully negotiate
obstacles of different heights during walking, their muscular strength capacity was significantly lower than young adults, resulting in
relatively higher muscular demands. The resulting potential for muscular fatigue during locomotion may place individuals at higher risk for
trips and/or falls.
# 2004 Elsevier B.V. All rights reserved.
Keywords: Elderly; EMG; Joint strength; Obstacle crossing; Balance control
1. Introduction
Skeletal muscle strength is known to decline with age
[1,2]. As an intrinsic risk factor contributing to falls, lower
extremity (LE) muscle strength is a critical component in
limiting an elderly individual’s dynamic stability [3–5].It
has been reported that fallers demonstrated only 37% of the
knee extensor strength, and 10% of the ankle plantar flexor
strength exhibited by their non-falling peers [6]. Stepping
over obstacles has been shown to require greater muscle
force than level walking [7], and recent results have shown
significant associations between isometric strength and the
ability of elderly individuals to cross obstacles [8].
Involvement in a long-term lower extremity resistance
training regimen resulted in substantial strength gains
among older adults (197–285% increase), along with
significant improvement in obstructed gait function (speed
of crossing stride, increased obstacle clearance, etc.) [9].
Additionally, it has been demonstrated that lower extremity
joint strength affects stepping speed and toe trajectory
during early swing [10].
Quantification of the neuromuscul ar challenge encoun-
tered by lower extremity muscles of healthy elderly
individuals can provide baseline information against which
strength declines or strength tra ining interventions may be
compared. It is interesting to note a lack of studies
addressing the validity of using normalized electromyo-
graphy (N-EMG) to identify age-related differences in
relative levels of muscular challenge encountered during
activities of daily living. This may be due in part to the non-
linear EMG/force relationships reported by various groups
www.elsevier.com/locate/gaitpost
Gait & Posture 22 (2005) 356–361
* Corresponding author. Tel.: +1 541 346 3391; fax: +1 541 346 2841.
E-mail address: chou@uoregon.edu (L.-S. Chou).
1
Present address: Department of Health and Human Development,
Montana State University, Bozeman, MT 59717, USA.
0966-6362/$ see front matter # 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.gaitpost.2004.11.012
[11–13]. These studies reported non-linear patterns in the
EMG/force ratio for isometric contractions, but did not test
EMG/force relationships during anisometric contractions.
One recent study demonstrated non-linear relationships
between force and EMG during anisometric contractions for
the first dorsal inter-osseus muscle [14]. Their findings
indicate that less voluntary muscular activation is needed
during eccentric contractions as compared to conce ntric
contractions to produce the same force.
Previous studies have reported that older adults adopt a
conservative strategy when crossing obstacles [15,16],as
indicated by slower crossing speed, shorter step length,
shorter obstacle–heel-strike distance [15], and reduced
anterior/posterior separation between whole body center of
mass (COM) and the center of pressure (COP) [16].The
selection of a conservative obstacle-crossing strategy may
be related to natural age-relat ed strength loss. If so, then it
follows that the relative challenges of obstacle crossing (and
other functi onal tasks) may tax the available joint strength to
a point where a person’s ability to control balance
dynamically could be seriously compromised. Quantifica-
tion of the relative challenge imposed on lower extremity
muscles would be beneficial to understanding the thresholds
of joint strength that are needed to allow adequate
negotiation of obstacles in daily life.
The purpose of this study was, therefore, to investigate
the effects of age and obstacle height on relative lower
extremity muscular challenge, with respect to available joint
strength. It was hypothesized that healthy elderly adults
would require a greater percentage of their neuromuscular
capacity (as measured by increased N-EMG values) during
level walking and while crossing an obstacle. We further
hypothesized that N-EMG levels increase as obstacle height
increases; indicating the task-specific challenge imposed on
lower extremity muscles during this functional activity.
2. Methods
Fifteen young adults (8 males/7 females; 24.5 3.6
years, 172.3 6.8 cm, 72.5 10.1 kg) and 15 elderly adults
(9 males/6 females; 72.6 5.5 years, 168.3 9.5 cm,
75.8 12.2 kg) were recruited for this study from the
University of Or egon campus and the surrounding commu-
nity, within the guidelines of the Institutional Review Board.
Inclusion criteria required that subjects had no histories of
significant head trauma, neurological disease (e.g. Parkin-
son’s, post-polio syndrome, diabetic neuropathy), visual
impairment not correctable with lenses, musculo-skeletal
impairments (e.g. amputation, joint replacement, joint
fusions, joint deformity due to rheumatoid arthritis), or
persistent symptoms of vertigo, light-headedness, unsteadi-
ness. All of the subjects were community-dwelling
individuals. Elderly subjects were noted to be active
community members, with many of them currently involved
in recreational sporting activities.
Pre-amplified surface electrodes were attached bilatera lly
over the bellies of the gluteus medius (GM), vastus lateralis
(VL), and medial head of the gastrocnemius (GA). These
muscle groups were previously shown to be substantially
challenged when stepping over obstacles [17,18]. Activation
magnitude of each muscle during gait was normalized to
values taken during maximal effort manual muscle testing
(MMT). Maximal GM activation was tested in 308 of hip
abduction, while side lying. For VL maximum, subjects
were seated with the knee in 458 of flexion. Maximal GA
activation was tested in neutral ankle position, with the
subject fixed to a table in prone position. MMT procedures
were performed by one examiner for each muscle group,
bilaterally. Subjects were verbally encour aged to ensure
maximal recruitment.
Subjects were then asked to walk at a self-selected pace
during level and obstructed gait trials. Level walking trials
were performed first, followed by obstacle crossing trials. A
single obstacle consisting of two upright standards and a
light-weight crossbar was set to four height conditions;
2.5%, 5%, 10%, and 15% body height (BH). The relative
difficulty of stepping over obstacles was thus normalized to
individual body height, accounting for variation within the
sample. This obstacle crossing protocol has been accepted
previously [19–21]. Obstacle heights were randomized with
three trials collected for each condition. The leading limb
was defined as the first limb to cross the obstacle. Crossing
stride was defined as the trailing limb heel-strike before the
obstacle to heel-strike of the sam e limb after crossing the
obstacle.
For all MMT and gait trials, raw EMG signals were
collected at 960 Hz using the MA-300
TM
system (Motion
Lab Systems, Inc., Baton Rouge, LA), band-pass filtered
(20–350 Hz), full wave rectified, and passed through a linear
envelope at 10 Hz for final interpretation. Filtered signals
from the gait trials were then normalized to the MMT signal
maximum for each muscle to indicate relative activation
levels. In this way, the relative activation values were
recorded as a percentage of the maximum activation
available to each individual muscle (N-EMG). Fig. 1
demonstrates the data-processing steps leading from full-
wave rectified EMG to smo othed EMG data (time-normal-
ized to 100% crossing stride). The mean value (within-trial)
for each support phase in the gait cycle (double-support and
single-support) was calculated for the leading and trailing
limb.
Initial statistical assessment required screening of out-
liers usin g inter-quartile range. If a case was found to be
more than three times the inter-quartile range away from the
median, that case was removed from further analysis. Mean
N-EMG values were analyzed for the effects of age
group and obstacle height (two- factor ANOVA with
repeated measures of obstacle height). Significance level
was set at a = 0.05 for all tests. Statistical analyses were
conducted with SYSTAT (Version 9, SPSS Inc., Chicago,
IL).
M.E. Hahn et al. / Gait & Posture 22 (2005) 356–361 357
3. Results
Initial screening indicated that eight data points were
outside reasonable variability (3 inter-quartile ranges). Of
the 2700 total data points in the analysis (6 variables 30
subjects 5 conditions 3 trials), the outlying data
accounted for only 0.3% of the total data collected. Removal
of these data from the analysis was, therefore, felt to be
justified.
All subjects were able to complete the required measures
of MMT and gait analysis trials. No incidents of tripping
were observed. The testing session typically required 2 h for
completion. Subjects did not indicate discomfort during any
of the testing conditions, nor did they express any sense of
fatigue at the end of the testing session.
No significant age group differences were found for any
of the temporal-distance parameters (Table 1). As obstacle
height increased so did stride time ( p < 0.001) and stride
length (p = 0.005). Gait velocity was found to decrease
linearly with increased obstacle height (p < 0.001). Since
the gait velocity showed no significant difference between
age groups (p = 0.182), it was not entered as a covariate in
the analysis of following N-EMG values.
Healthy elderly adults showed greater relative
activation levels in the leading and trailing limbs, compared
to young adults (Table 2). During double-support, weight
transfer and acceptance occurs laterally as well as anteriorly.
In this phase, the GM of the healthy elderly was activated
up to an average of 46% of their maximum capacity,
compared to 23% in the young for all testing conditions.
Similarly, the VL of the healthy elderly was activated up to
an average of 35% of their capacity in double-support
phase, compared to 25% in the young. Maintenance of
dynamic stability and forward progression is required
during the single-support phase of gait. During single-
support, healthy elderly GA activity reached 45% of MMT
M.E. Hahn et al. / Gait & Posture 22 (2005) 356–361358
Fig. 1. Representative level walking condition showing vertical ground reaction force patterns from consecutive foot strikes, rectified EMG activation of the
GM, and smoothed GM activation (after normalization to MMT). The time scale of the normalized EMG patterns is with respect to the crossing stride. Support
and swing phases of gait are indicated: DS double-support, SS single-support, SW swing. F
z
represents the vertical ground reaction force.
Table 1
Temporal-distance variables compared between groups and across the obstacle heights: group mean (S.D.)
Obstacle
height
None 2.5% 5% 10% 15% p-Values
a
Young Elderly Young Elderly Young Elderly Young Elderly Young Elderly
Gait
velocity
(m/s)
1.363
(0.169)
1.295
(0.097)
1.331
(0.161)
1.268
(0.148)
1.317
(0.147)
1.237
(0.141)
1.253
(0.155)
1.169
(0.183)
1.195
(0.140)
1.120
(0.219)
P
h
< 0.001,
P
g
= 0.182
Stride
time
(s)
1.032
(0.072)
1.008
(0.118)
1.098
(0.086)
1.071
(0.163)
1.118
(0.082)
1.097
(0.166)
1.185
(0.117)
1.140
(0.196)
1.244
(0.121)
1.200
(0.221)
P
h
< 0.001,
P
g
= 0.544
Stride
length
(cm)
140.0
(13.84)
135.4
(11.69)
145.4
(14.49)
139.8
(14.62)
146.6
(13.84)
139.4
(13.32)
147.4
(14.72)
140.0
(20.68)
147.7
(13.84)
139.5
(22.82)
P
h
= 0.005,
P
g
= 0.265
a
P
h
represents height effect. P
g
represents group effect.
maximum for all testing conditions, while the young
required 36% of their capacity.
For the trailing limb, there was a significant age effect on
the normalized activation levels of the GM (p = 0.003;
Fig. 2), but not the VL (p = 0.053) or the GA (p = 0.360). In
the leading limb, significant age effects were found for the
GM (p < 0.001) and VL (p = 0.042), but not for the GA
(p = 0.154). Increased obstacle height resulted in an
increased relative activation of all muscles of both the
leading and trailing limb (p 0.018). Results of the
ANOVA revealed no significant interactions between the
factors of group and obstacle height.
4. Discussion
As elderly adults cross obstacles, they encounter
essentially the same mechanical challenges as young adults
of similar stature (assuming similar gait velocities). As there
were no significant differences in gait velocity between the
two groups (p = 0.182), it can be assumed that the
mechanical challenges encountered by the joints were
similar for the young and elderly adults. Considering that the
maximum available strength has been shown to be lower in
elderly adults [1,2], it follows that the elderly will use a
greater percentage of their neuromuscular capacity to
successfully ambulate and safely cross over obstacles.
Results from this study revealed that there were age-
dependent increases in the percentage of muscular capacity
used to cross obstacles. Specifically, the gluteus medius and
the vastus lateralis were activated to a significantly greater
percentage of maximum capacity in the elderly. Further-
more, as obstacle height increased, the relative act ivation
increased for each muscle tested, indicating substantial
challenge encountered by the neuromuscular system in
maintaining balance during the dynamic task of stepping
over obstacles. These findings are supported by joint
strength data further compiled from the two subject groups
(see Fig. 3). Isometric strength testing on a KinCom
dynamometer (Rehab World, Hixson, TN) revealed a
significant age-related reduction of strength (nor malized
to individual body weight) during HA, KE and APF (one-
tailed t-test; p < 0.001, 0.001, and 0.002, respectively).
It was unexpected that walking speed would reveal no
significant group differences. However, walking speeds of
older adults in the present study compare favorably with
those reported by McFadyen and Prince [22], and the young
adult group demonstrated speeds comparable to those
reported by Chen et al. [15]. Inter-laboratory variation might
M.E. Hahn et al. / Gait & Posture 22 (2005) 356–361 359
Table 2
Normalized EMG activation percentages during double-support phases for GM and VL, single-support phases for GA: group mean (S.D.)
Limb/muscle Age group Obstacle height (% BH)
Level 2.5 5.0 10.0 15.0 Effect
Tr. GM Elderly 38.03 (13.65) 39.41 (11.34) 43.54 (16.21) 48.48 (19.13) 49.05 (14.26)
a,b
Young 21.91 (12.64) 22.94 (12.76) 23.83 (12.15) 25.73 (12.90) 28.44 (14.44)
Ld. GM Elderly 40.24 (19.13) 45.13 (31.35) 53.26 (35.33) 50.44 (30.67) 52.76 (29.86)
a,b
Young 19.74 (11.81) 20.67 (9.06) 21.42 (10.35) 22.45 (8.95) 25.28 (10.73)
Tr. VL Elderly 35.56 (18.95) 34.00 (14.94) 33.72 (15.31) 34.70 (14.73) 35.46 (15.12)
b
Young 22.28 (12.16) 25.35 (13.16) 25.83 (13.05) 26.13 (13.08) 27.61 (11.69)
Ld. VL Elderly 28.89 (13.05) 35.96 (20.50) 33.90 (15.33) 37.84 (17.52) 39.00 (15.81)
a,b
Young 20.39 (12.84) 24.05 (13.30) 24.46 (14.37) 25.27 (14.38) 25.36 (12.06)
Tr. GA Elderly 40.93 (18.80) 51.47 (34.32) 46.01 (25.42) 47.40 (21.54) 51.41 (30.73)
b
Young 31.48 (13.57) 32.55 (15.14) 33.08 (14.48) 34.23 (15.78) 39.10 (14.88)
Ld. GA Elderly 38.40 (14.15) 45.31 (35.06) 39.11 (18.57) 40.38 (18.86) 48.42 (33.00)
b
Young 35.50 (13.10) 35.88 (12.80) 39.57 (14.39) 40.12 (15.06) 41.18 (16.59)
Tr.: trailing limb; Ld.: leading limb.
a
Significant age group effect (p < 0.05).
b
Significant obstacle height effect (p < 0.05).
Fig. 2. Normalized EMG activation percentages of the GM during double-
support phases of the crossing stride. Elderly adults required significantly
greater percentages of their capacity during level walking and obstacle
crossing tasks. Activation levels increased linearly as obstacle height
increased.
be used to explain the relative equalizing of gait velocities
between the two age groups. Another explanation for the
non-significant velocity differences might be the relatively
vigorous activity level of our older adult sample. The fact
that their gait velocities were not significantly lower than
younger adults may indicate that they represent a more able-
bodied section of the broader elderly population. It is quite
possible that a sample of less active elderly individuals
would demonstrate significantly slower walking speeds.
Age-related increases in relative activation of the gluteus
medius occurred during the weight acceptance and transfer
phase of gait, indicating the critical role played by hip
abductors in maintaining medio-lateral (M-L) stability as the
center of mass shifts rapidly between each foot. The timing
of EMG activation peaks was in agreement with previous
work [23,24]. Magnitudes of our N-EMG data were also in
agreement with Dubo and colleagues’ [24] values for the VL
(25% and 35% for young and elderly adults, respectively),
however, our GA magnitudes (36% and 45% for young
and elderly adults, respectively) were noticeably lower than
Dubo’s (63%). As we measured activation of the medial
head and Dubo measured activation of the lateral head (or
triceps surae), there may be some inherent discrepancy in the
two sets of data. Further comparisons with Dubo’s results are
difficult to make because of the broad age range of their
sample (8–72 years).
It was recently reported that elderly adults with balance
disorders displayed greater ranges of motion and higher
velocities in M-L motion of the center of mass while
stepping over obstacles [20]. Increases in M-L COM motion
would certainly increase the demand on hip abductors
during weight transfer. Recent results showed that healthy
elderly adults demonstrate slightly greater displacements
and velocities in the frontal plane (as compared to young
adults), however, these differences were not significant [16].
This indicates that while healthy elderly adults may not
allow critically greater M-L COM motion, they may be
showing the effects of increased challenge in the task of
balance control, indicated by higher demand on the
neuromuscular capacity of the hip abductors.
One potential limitation of this study is the variable
nature of MMT collection. Although the same examiner
performed MMT on each subject, no simultaneous
measurement was made of the force applied by the
examiner, removing the possibility for quantifying variation
during MMT testing. However, it was noted that EMG
signals consistently leveled off during maximal contrac-
tions, indicating that maximum effort was being made by the
subjects. A second potential limitation exists in elderly
subjects having more adipose tissue over the GM muscle
tissue. Care was taken to accurately place the GM electrode
and its ability to pick up GM muscle activation was
rigorously checked prior to MMT and dynamic trials.
Normalizing EMG signals from adipose-rich tissue should
be similar to signals from other tissue, as sub-maximal
signal magnitudes are simply divided into the signal
maximum. The strength of normalization is the ability to
report data with respect to present condition.
The N-EMG data presented in this study may be used to
quantify the level of challenge on the neuromuscular system
when interpreted in light of available joint strength.
Although surface EMG has been known to exhibit high
variability, it appears that with careful normalization to
maximal voluntary activation levels, these proportional
values provide a reasonable representation of the control
system’s response to the challenge posed by daily activities.
Furthermore, the magnitude of demand/capacity ratio
presented here appears more reasonable than joint moment
percentages reported by Bus et al. [25]. Their results
indicated that several activities of daily living required
greater than 100% of the available tor que production in a
joint (per maximal voluntary contraction, using a dynam-
ometer). The reason for these high values may arise from the
necessary assumptions made in joint torque measurement
and estimation techniques [25]. Further study is certainly
necessary to resolve discrepancies between measured
dynamometric torque and estimated joint moments. Addi-
tionally, comparison between these studies suggests that
further research is necessary to compare N-EMG values
calculated using MMT with those which may be calculated
from normalizing to maximal dynamometric contractions.
As EMG is a direct measure of muscle activation, perhaps its
use is more reliable for representing musculo-skeletal
challenge than methods relying on dynamometric joint
torque and joint moment estimation techniques, which
require many assumptions to be met [26].
The results of this study indicate that healthy elderly
adults do require greater percentages of their neuromuscular
capacity during level walking and obstacle crossing tasks
than young adults. Specifically, the gluteus medius was
significantly challenged when the older adults stepped over
obstacles. Bus et al. [25] reported significantly greater hip
abductor moments in active elderly adults during stair
ascent, stair descent and level walking, compared to young
M.E. Hahn et al. / Gait & Posture 22 (2005) 356–361360
Fig. 3. A comparison of isometric maximal joint strengths between the
young and older adult groups (normalized to body weight). Older adults
demonstrated significantly lower strength values for each of the joint
motions tested (
*
p 0.002).
adults. Our results support their suggestion that hip
abductors should be considered in the functional assessment
of elderly adults, and targeted as a critical component of
resistance strength training in the older adult population.
As ste pping over a higher obstacle poses a greater
challenge to dynamic balance control, it may be inferred that
decreased lower extremity muscle strength places the elderly
population at greater risk for falls. These findings are in
agreement with recent work by Lamoureux et al. [8],
showing strong association between lower extremity
isometric strength and elderly individuals’ ability to
negotiate obstacles. Combined with the addi tional findings
of Lamoureux et al. [9], the present results add emphasis to
the need for muscle strengthening as a preventative
intervention, thereby providing improved function in the
ambulatory tasks of daily living.
In conclusion, the N-EMG data reported in this study
were used to quantify the level of muscular challenge
imposed on an individual in relation to their strength
capacity. While healthy elderly adults were able to
successfully negotiate obstacles of different heights during
walking, their muscular strength capacity was significantly
lower than young adults, resulting in higher relative
muscular demands. Higher demands placed on lower
extremity muscles while stepping over obstacles may
increase the likelihood of muscle fatigue during daily
ambulation, thus placing elderly individuals at higher risk
for trips and/or falls. These findings provide further
justification for including lower extremity resistance
training in the list of preventative interventions for the
elderly com munity.
Acknowledgements
This work was supported by the Oregon Medical
Research Foundation, National Institutes of Health (AG
022204-01; HD 042039-01A1) and the International Society
of Biomechanics Dissertation Matching Grant. We grate-
fully acknowledge the contributions of Mar isa Hastie and
Sentaro Koshida in data collection and analysis for this
project.
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M.E. Hahn et al. / Gait & Posture 22 (2005) 356–361 361
    • "The choice of the obstacle height was based on the following considerations. This task was used in our earlier studies of obstacle crossing [5,17,18] and the same high obstacle height on older subjects has been used in previous researches [2,3] to reflect typical high height encountered in everyday life. The obstacle location was chosen in any distance by each subject. "
    [Show abstract] [Hide abstract] ABSTRACT: Background To evaluate if multi-muscle synergies are comprised of flexible combinations of a small number of postural muscles to stabilize the center of pressure (COP) shift during preparation to making a step in the elderly (self-paced level stepping vs. obstacle crossing stepping).Methods Electromyography (EMG) signals of leg and trunk muscles were recorded. Linear combination of integrated indices of muscle activity (M-modes) and their relationship to changes in the COP shift in the anterior-posterior (AP) direction were first determined. Uncontrolled manifold (UCM) analysis was performed to determine the extent to which variance of the M-modes acted to produce a consistent change in the COP displacement.ResultsThe elderly were capable of stabilizing the COPAP coordinate based on co-varied involvement of the M-modes. The synergy index (¿V) changes in the elderly emerged later (100 ms prior to t0) and its magnitude was smaller as compared to that reported in younger persons.Conclusions Our study reveals that aging is associated with a preserved ability to explore the flexibility of the M-mode compositions but a decrease ability to use multi-M-mode synergies following a predictable perturbation.
    Full-text · Article · Feb 2015
    • "According to our results regarding the EMG measurements , higher obstacles induced minimal, nonsignificant increase in the EMG amplitude of the calf muscles during stance or swing phase. In a previous study, comparing the EMG of elderly and young people during obstacle crossing it was observed that increased obstacle height induces higher muscle activation (Hahn et al., 2005). Nonetheless, for the young population, this increase was marginal and probably not significant, which is in accordance with our findings. "
    [Show abstract] [Hide abstract] ABSTRACT: The aim of this study was to investigate the effect of fatigue on electromyographic (EMG) parameters of healthy young adults during obstacle crossing of two different heights. Twelve un-trained male adults (23 ± 5 years of age) were fatigued running on a treadmill with increasing speed and inclination and walked over an obstacle with a height set at 10% and 20% of each indi-vidual's lower limb length. Maximal plantar flexor torque and EMG of the medial gastrocnemius, soleus, and tibialis anterior muscles of the trailing limb were assessed during obstacle cross-ing. Data were captured before, immediately after and 5 minutes after a fatigue session. Fatigue induced significant reduction on the plantar flexor torque output immediately after and 5 minutes after exhaustion. After fatigue gait speed was not affected, the minimum distance between the obstacle and the trailing or leading foot remained unchanged, and the trailing foot contacted the ground closer to the obstacle immediately after fatigue. Regarding the EMG, medial gastrocnemius became after fatigue more active during swing phase when increasing the obstacle height, whereas this was not the case before or 5 minutes after fatigue. No other significant difference was observed for any of the examined muscles. It is concluded that the assessed fatigue protocol induced only minimal changes in the EMG activity of the examined muscles during obstacle crossing. Therefore, it is suggested that the neuromuscular system of healthy young individuals is able to respond to the decreased force capacity after fatigue during obstacle crossing of heights up to the 20% of the limb length.
    Full-text · Article · Dec 2014
    • "According to Hahn et al. (2005) older adults had increased hip (gluteus medius) and thigh (VL) muscles activation during motor dual task gait (stepping over obstacles). Thus, considering that the maximum strength has been shown to be lower in older adults, it follows that the older women used greater percentage of their neuromuscular capacity during apprehensive gait, which resulting potential for muscular fatigue during locomotion may place individuals at higher risk for falls (Hahn et al., 2005). Further, recent study demonstrated that greater hip stabilizerTable 2 Two way repeated measures ANOVA results on the effect of group (older and younger adults groups) and condition (normal gait and apprehensive gait) and interaction between group and condition on thigh and shank EMG activation.Table 4 Two way repeated measures ANOVA results on the effect of group (older and younger adults groups) and condition (normal gait and apprehensive gait) and interaction between group and condition on thigh and shank muscles cocontraction. "
    [Show abstract] [Hide abstract] ABSTRACT: Objective: Investigate the influence of apprehensive gait on activation and cocontraction of lower limb muscles of younger and older female adults. Methods: Data of 17 younger (21.47 ± 2.06 yr) and 18 older women (65.33 ± 3.14 yr) were considered for this study. Participants walked on the treadmill at two different conditions: normal gait and apprehensive gait. The surface electromyographic signals (EMG) were recorded during both conditions on: rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF), tibialis anterior (TA), gas-trocnemius lateralis (GL), and soleus (SO). Results: Apprehensive gait promoted greater activation of thigh muscles than normal gait (F = 5.34 and p = 0.007, for significant main effect of condition; RF, p = 0.002; VM, p < 0.001; VL, p = 0.003; and BF, p = 0.001). Older adults had greater cocontraction of knee and ankle stabilizer muscles than younger women (F = 4.05 and p = 0.019, for significant main effect of groups; VM/BF, p = 0.010; TA/GL, p = 0.007; and TA/SO, p = 0.002). Conclusion: Apprehensive gait promoted greater activation of thigh muscles and older adults had greater cocontraction of knee and ankle stabilizer muscles. Thus, apprehensive gait may leads to increased percentage of neuromuscular capacity, which is associated with greater cocontraction and contribute to the onset of fatigue and increased risk of falling in older people.
    Full-text · Article · Jun 2013
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