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Abstract

Background: Old referenced to young adults show a relative maintenance of maximal eccentric (RELM) compared to concentric muscle torque: ∼76 and ∼59%, respectively. However, it is unknown if RELM affords functional benefits in old adults. Objective: We examined if there is specificity between the two types of peak quadriceps torque (i.e., concentric and eccentric) and timed gait performance measured during level, ramp, and stair walking and if gait performance was higher in old adults with high versus low RELM. Methods: We measured peak concentric and eccentric quadriceps torque at 60 and 120°/s and timed gait at habitual and safe-fast speeds in healthy young (age 22.7 years, n = 24) and old (age 70.0 years, n = 21) adults. Results: Comparable to previous studies, RELM was 21%, but instead of the anticipated specificity, we found that concentric compared with eccentric torque was more strongly associated with gait performance than eccentric torque, independently of walking direction and age (R2 = 0.16: eccentric vs. descending gaits; R2 = 0.17: eccentric vs. ascending gaits; R2 = 0.45: concentric vs. descending gaits; R2 = 0.56: concentric vs. ascending gaits, n = 45, all p < 0.01). Furthermore, old adults (n = 10) with ∼30% greater than normal levels of RELM (n = 11) ambulated at similar velocities measured on level and inclined surfaces. Conclusion: Normal and 30% above normal levels of RELM do not seem to increase or predict healthy old adults' gait performance on level and inclined surfaces. Future work should examine if RELM is associated with a heightened performance in other measures of neuromuscular function, such as gait biomechanics, muscle activation, as well as rate and control of voluntary force development in old adults with high or low mobility.
E-Mail karger@karger.com
Clinical Section / Original Paper
Gerontology 2016;62:588–596
DOI: 10.1159/000445376
Functional Relevance of Relative
Maintenance of Maximal Eccentric
Quadriceps Torque in Healthy Old Adults
JeroenWaanders ChantalBeijersbergen AlessioMurgia TiborHortobágyi
Center for Human Movement Sciences, University Medical Center Groningen, University of Groningen,
Groningen , The Netherlands
0.45: concentric vs. descending gaits; R
2 = 0.56: concentric
vs. ascending gaits, n = 45, all p < 0.01). Furthermore, old
adults (n = 10) with 30% greater than normal levels of
RELM (n = 11) ambulated at similar velocities measured on
level and inclined surfaces. Conclusion: Normal and 30%
above normal levels of RELM do not seem to increase or pre-
dict healthy old adults’ gait performance on level and in-
clined surfaces. Future work should examine if RELM is as-
sociated with a heightened performance in other measures
of neuromuscular function, such as gait biomechanics, mus-
cle activation, as well as rate and control of voluntary force
development in old adults with high or low mobility.
© 2016 The Author(s)
Published by S. Karger AG, Basel
Introduction
There is overwhelming evidence that even healthy ag-
ing old adults exhibit muscular, neuronal, and cognitive
dysfunctions
[1–7] . One such impairment is a character-
istic and clearly recognizable decrease in the ability to
produce maximal voluntary leg muscle torque, starting as
early as 50 years of age
[1, 5, 6] . A multitude of factors
contributes to the evolution of the age-related weakness,
dynapenia
[8] , including a loss of muscle protein content
Key Words
Gait velocity · Walking · Stair locomotion · Ramp
locomotion · Muscle torque · Aging
Abstract
Background: Old referenced to young adults show a rela-
tive maintenance of maximal eccentric (RELM) compared to
concentric muscle torque: 76 and 59%, respectively.
However, it is unknown if RELM affords functional benefits
in old adults. Objective: We examined if there is specificity
between the two types of peak quadriceps torque (i.e., con-
centric and eccentric) and timed gait performance mea-
sured during level, ramp, and stair walking and if gait per-
formance was higher in old adults with high versus low
RELM. Methods: We measured peak concentric and eccen-
tric quadriceps torque at 60 and 120°/s and timed gait at
habitual and safe-fast speeds in healthy young (age 22.7
years, n = 24) and old (age 70.0 years, n = 21) adults. Results:
Comparable to previous studies, RELM was 21%, but instead
of the anticipated specificity, we found that concentric com-
pared with eccentric torque was more strongly associated
with gait performance than eccentric torque, independent-
ly of walking direction and age (R
2 = 0.16: eccentric vs. de-
scending gaits; R
2 = 0.17: eccentric vs. ascending gaits; R
2 =
Received: January 25, 2016
Accepted: March 13, 2016
Published online: April 28, 2016
Jeroen Waanders
Center for Human Movement Sciences
University Medical Center Groningen, A. Deusinglaan 1
NL–9700 AD Groningen (The Netherlands)
E-Mail j.b.waanders @ gmail.com
© 2016 The Author(s)
Published by S. Karger AG, Basel
0304–324X/16/0626–0588$39.50/0
www.karger.com/ger is article is licensed under the Creative Commons Attribution-
NonCommercial-NoDerivatives 4.0 International License (CC BY-
NC-ND) (http://www.karger.com/Services/OpenAccessLicense).
Usage and distribution for commercial purposes as well as any dis-
tribution of modi ed material requires written permission.
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Functional Relevance of RELM in Healthy
Aging
Gerontology 2016;62:588–596
DOI: 10.1159/000445376
589
or sarcopenia [9, 10] , neuronal hypoexcitability [11, 12] ,
and a reconfiguration of tendon structure that interferes
with the transmission of muscle force to the bony levers
[13, 14] . Interestingly, the magnitude of the age-related
decline in maximal voluntary quadriceps muscle torque
is not uniform across the three main types of muscle con-
traction. While maximal voluntary quadriceps muscle
torque can decline by 50% when the muscle actively
shortens [i.e., concentric (CON) contraction] or produc-
es tension at the same length (i.e., isometric contraction)
[1, 5, 6, 15] , the magnitude of decline when the quadriceps
muscle actively lengthens [i.e., eccentric (ECC) contrac-
tion] can be as small as 20%
[7, 16–18] .
Despite differences in how previous studies deter-
mined the magnitude of ECC torque maintenance (e.g.,
contraction velocity and normalization method), calcu-
lated as the relative maintenance of maximal ECC (RELM)
compared to maximal CON muscle torque in the present
study, RELM seems to be a robust phenomenon. That is,
it is present not only in healthy aging old adults but also
in aging adults with mobility disability and spasticity
[16,
19] . For example, paretic and non-paretic lower limb
muscles showed a 16 and 14% higher maintenance, re-
spectively, of relative maximal ECC versus relative CON
muscle torque in elderly stroke patients compared to
healthy age-matched controls
[19] . The underlying mech-
anisms of RELM in old muscles are still unclear, although
molecular and behavioral factors have been considered in
the form of a slowed detachment rate of active cross-
bridges and high fiber stiffness
[16] . For reasons that are
poorly understood, there is a gender effect in RELM, as a
few studies reported actually no age-related decline in
maximal voluntary ECC forces measured in females com-
pared to the decline seen in males
[7, 17] . For example,
old males were able to produce 80% of young males’ ECC
peak torque, while this amount was 110% in elderly fe-
males
[7] .
In line with the predictions of mobility disability mod-
els
[20, 21] , old adults with high versus low levels of max-
imal voluntary leg torque ambulate faster, perform ac-
tivities of daily living (ADL) more easily, and negotiate
stairs and ramps with less effort
[22, 23] . The functional
benefits of a well-maintained ability to generate maximal
voluntary torque in old age materialize through the con-
cept of relative effort, showing that old adults often exe-
cute ADLs near their maximal available abilities
[23] . It
is, therefore, a relevant but unexplored question how, if
at all, RELM translates into functional benefits and
whether such benefits differ between genders. Firstly, we
examined the effects of age and gender on peak CON and
ECC quadriceps torque as well as on a set of ADL locomo-
tor tasks (level, ascending, and descending gaits). Second-
ly, we determined the relationship between peak torque
and ADL locomotor tasks in young and old adults. Third-
ly, we examined the effects of high versus low RELM on
ADL task performance. We performed these analyses
across a spectrum of torques (ECC, CON) and tasks (lev-
el, ascending, and descending gaits) that were similar or
dissimilar with respect to the type of muscle contraction
to provide evidence for the hypothesis that the relative
maintenance of maximal quadriceps ECC torque per se
and not just maximal leg muscle torque in general affords
functional benefits in old adults.
Methods
Study Design
For this cross-sectional study, subjects reported to the labora-
tory once for measurements consisting of: (1) maximal quadriceps
strength and (2) gait performance, administered in random order.
Subjects were recruited from the surrounding communities and
shopping malls through word of mouth, flyers, and newspaper ad-
vertisements. The Medical Ethics Committee at the University
Medical Center of Groningen, Groningen, the Netherlands, ap-
proved the study protocol (No.: METc 2015/144), and each subject
signed a written informed consent form before the start of the mea-
surements, which were completed according to the Declaration of
Helsinki.
Subject Characteristics
Healthy young (n = 24) and healthy, community-dwelling old
(n = 21) adults participated in the study. Inclusion criteria were:
age 20–30 or over 65 years and being in good health. Exclusion
criteria were: joint replacement, amputation, neuromuscular im-
pairments, a history of neurological conditions (stroke, Parkin-
son’s disease, and dementia), pulmonary disease, pregnancy, dia-
betes with neuropathy in the legs, and a body mass index over 30.
In addition, subjects were cognitively healthy, physically active,
and did not have mobility disability, according to the Mini Mental
State Examination (MMSE), the Short Questionnaire to Assess
Health-Enhancing Physical Activity (SQUASH), and the Short
Physical Performance Battery (SPPB), respectively ( table1 ). Body
mass was measured to the nearest 0.1 kg on a digital weight scale
(Seca 803; Seca GmbH and Co., Hamburg, Germany), and height
was measured to the nearest 0.5 cm using a stadiometer (Seca
213).
Isokinetic Dynamometry
Maximal voluntary CON and ECC torque of the right quadri-
ceps were measured using a KinCom isokinetic dynamometer
(model AP125; Chattecx Inc., Chattanooga, Tenn., USA), reveal-
ing acceptable test-retest reliability of quadriceps torque [intra-
class correlation coefficient ranged from r = 0.74 to 0.92 (ECC
180°/s to CON 180°/s)]
[7] . The present study focused on the quad-
riceps, because this muscle group generates and absorbs much of
the power in locomotor ADL tasks
[24, 25] .
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Hortobágyi
Gerontology 2016;62:588–596
DOI: 10.1159/000445376
590
The location of the dynamometer seat and power head was set
individually for each subject. During testing, subjects sat with a hip
angle of 85° with arms folded in front of the chest and two cross-
over upper-body belts, a lap belt, and a thigh strap, minimizing
extraneous movements. The transverse axis of the joint was aligned
with the rotational axis of the dynamometer’s head, and the joint’s
anatomical zero was set at a joint position corresponding to the leg
fully extended. The mass of the lower leg was measured and the
dynamometer’s software automatically computed torques correct-
ed for leg mass. Range of motion (ROM) was set between 10 and
75° of maximal knee extension. Before testing, subjects performed
familiarization trials for both types of dynamic contraction. Sub-
jects were instructed to contract as hard and fast as possible and
were verbally encouraged during the test. Two trials were per-
formed at 60 and 120°/s for both CON and ECC conditions, with
a 3-second pause between contractions and 1 min of rest between
conditions and speeds. The order of muscle contraction type and
angular velocity was randomized between subjects.
Gait Performance
Gait performance was measured by recording the time needed
to complete 5 standardized locomotion tasks: level walking, stair
ascent, stair descent, ramp ascent, and ramp descent. Time to com-
pletion was measured with a stopwatch for stair and ramp nego-
tiation, as it is not possible to instrument an entire natural stairwell
and ramp with a 3D motion capture system. Subjects performed
each task at a habitual and at a safe-fast speed twice. For the ha-
bitual conditions, subjects were instructed to walk ‘as if you walked
to the supermarket’, and for the safe-fast speed conditions the in-
struction was to walk ‘as fast and safe as you can but do not run’.
Subjects performed one familiarization trial for each task. There
were 30 s of rest between trials and 1 min of rest between tasks.
For the level walking task, subjects walked on a well-lighted,
linoleum-surfaced laboratory floor. The start and end of the
11-meter-long walkway was marked with a pylon. Subjects acceler-
ated and decelerated over a distance of 3 m before and after a mid-
dle 5-meter portion of the walkway where they reached a steady
pace gait. During this task, a hip marker was tracked at 100 Hz with
an Optotrak motion-capture system to calculate gait speed.
For the ramp tasks, subjects walked on a 20-meter-long non-
skid, paved, and semicovered entryway to an indoor parking ga-
rage, inclined 13%. At about midway, the walking time was mea-
sured with a stopwatch over a 5-meter distance, preceded by 3 m
of acceleration and followed by 3 m of deceleration.
For the stair tasks, subjects walked up two flights of non-skid
edged indoor stairs consisting of 22 steps in total. While negotiat-
ing the stairs, subjects had to take a U-shaped turn on a 1.52 m
(depth) by 2.57 m (width) landing after the 11th step of the first
flight. Each step had a rise of 0.18 m and a depth of 0.22 m. Subjects
were instructed to adopt an alternating step strategy without skip-
ping any step and not to use handrails unless they felt they would
lose balance. Time was measured with a stopwatch at the instant
the subject’s foot came into contact with the surface of the first step
and the ground after the last stair step.
Data Analysis
The highest peak torque value from both trials was obtained
analyzing the text file exported from the dynamometer with a cus-
tomized MATLAB script (MATLAB 14b; MathWorks Inc., Natick,
Mass., USA, 2000). The CON and ECC torque values of each indi-
vidual subject were divided by the corresponding mean CON and
ECC torque values of the young adults for each speed
[7] , resulting
in a measure of age-related muscle torque maintenance for each
speed condition. Previously, the RELM magnitude was expressed
as the difference between ECC and CON torque maintenance (in
%)
[16] . In addition, we normalized the RELM magnitude by CON
torque maintenance, i.e., [(ECC – CON)/CON] × 100, to control
for CON strength levels. For example, an individual with 90% max-
imal ECC torque maintenance and 70% maximal CON torque
maintenance has a RELM magnitude of 28.6% [(90 – 70)/70 ×
100 = 28.6%]. Then, high and low RELM individuals in the old
group were identified as having a higher or lower RELM magnitude
than the mean of the group, respectively. Habitual gait task perfor-
mance was determined by computing the average of two trials and
maximal performance was the fastest trial. Time to completion dur-
ing the gait performance tasks was recorded at the closest 0.01 s.
Statistical Analyses
The main analysis was an age (young, old) by gender (male,
female) by speed (ECC120, ECC60, CON60, CON120) analysis of
variance (ANOVA) with repeated measures on speed, followed by
a Tukey’s post hoc analysis to determine the means that were dif-
ferent (p < 0.05). Independent t tests were performed to test for
significant differences between old and young adults on gait per-
formance at habitual and maximal speed, adjusted for body height.
An exploratory analysis was performed using simple linear regres-
sions to determine (non-)task-specific relationships between CON
and ECC muscle torque (predictors) and level, ascent, and descent
locomotion performance (outcomes). Therefore, average scores
for CON [e.g., (CON120 + CON60)/2] and ECC muscle torque
and for ascent [e.g., (ramp ascent + stair ascent)/2] and descent
locomotion were computed for every individual. To test for an age
effect, a dummy variable of age (young, old) was used. To test for
differences in slopes within a group, paired t tests with a pooled
standard error were used. Muscle torque was normalized for
height and mass, gait performance only for height. Lastly, indepen-
dent t tests were performed to test for significant differences be-
Table 1. Subject characteristics
Characteristics Young
(11 F, 13 M)
Old
(10 F, 11 M)
Age, years 22.7 ± 2.1 70.0 ± 3.2
Body weight, kg 68.9 ± 8.0 73.4 ± 8.4
Body height, m 1.78 ± 0.07 1.74 ± 0.06
Body mass index 21.9 ± 2.1 24.3 ± 2.3
SPPB score 11.75 ± 0.53 11.29 ± 0.78
MMSE score 29.25 ± 1.19 28.43 ± 1.36
SQUASH
Total scorea8,884 ± 3,749 10,906 ± 4.876
Light, min/week 1,395 ± 855 804 ± 667
Moderate, min/week 285 ± 228 593 ± 575
Heavy, min/week 319 ± 279 578 ± 473
Values are mean ± SD. a Total score is expressed as minutes per
week × intensity of the activity.
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Functional Relevance of RELM in Healthy
Aging
Gerontology 2016;62:588–596
DOI: 10.1159/000445376
591
tween high and low RELM individuals on gait performance at both
speeds, adjusted for body height. Fifteen out of 22 variables were
normally distributed and an additional 7 were too after log-trans-
formation. Statistical analysis was done on these log-transformed
variables, but the non-transformed data are presented in the Re-
sults section. IBM SPSS statistics v20 was used for all statistical
analyses. Statistical significance was set at p 0.05.
Results
Muscle Torque
Table 2 shows the non-normalized peak isokinetic
muscle torques produced by males and females sepa-
rately and combined and the maintenance of muscle
torque for the old compared to young adults ( fig.1 ).
There was an age (young, old) effect [F(1, 41) = 10.29,
p = 0.003, r = 0.85], speed (4 speeds) effect [F(2.23,
91.22) = 7.21, p = 0.001, r = 0.60], and age by speed in-
teraction effect [F(2.23, 91.22) = 6.75, p = 0.001, r =
0.58] on the isokinetic torque maintenance. There was
also a significant main effect of gender [F(1, 41) = 11.73,
p = 0.001, r = 0.88]; males were stronger than females.
Tukey’s post hoc analysis revealed significant (p < 0.05)
differences in old versus young for CON and ECC main-
tenance and a higher ECC versus CON muscle torque
maintenance (i.e., RELM). For males and females com-
bined, RELM was 20.6%. There was no age by gender by
speed interaction (p = 0.25); thus, RELM magnitude
was similar in old males and females. There were also
no age by gender (p = 0.27) and gender by speed (p =
0.67) interactions.
Gait Performance
Table3 shows the gait performance data. With genders
combined, young versus old adults performed faster at
the maximal speed (all p < 0.01), resulting in moderate to
strong effect sizes. Habitual gait performance was similar
in the two age groups (p > 0.05).
Muscle Torque versus Gait Performance
Table4 shows an overall (non-)task-specific relation-
ships between averaged peak muscle torque variables
(CON, ECC) and averaged gait scores based on the direc-
tion (ascent, descent, level) of locomotion. CON and ECC
muscle torque predicted only maximal but not habitual
functional performance significantly. CON was not a sig-
nificantly better predictor of level walking than ECC in
‘all’ (t = 1.67). However, CON predicted ascending gait
performance significantly better than ECC in ‘all’ (t =
3.71). Furthermore, CON predicted descending gait per-
formance better than ECC in ‘all’ (t = 2.71) and old (t =
2.67). Also, CON predicted ascending gait significantly
better in old compared to young (t = 2.23). In ‘all’ (t =
0.29) and old (t = 0.22), CON was not a significantly bet-
ter predictor of ascending compared to descending gait
performance.
140
120
100
80
60
–120 –60 60
**
Angular velocity (°/s)
Young mean torque (%)
b
Young
Old
120
Table 2. Peak quadriceps muscle torques in young and old adults
Muscle
contrac-
tion
Velocity,
˚/s
Group Young
(11 F,
13 M)
Old
(10 F,
11 M)
Maintenance, %
yo ung old
ECC 120 M 176 ± 34 161 ± 32 100 ± 19 91 ± 18
F 145 ± 31 134 ± 29 100 ± 22 92 ± 20
All 162 ± 35 148 ± 33 100 ± 22 91 ± 21
60 M 176 ± 33 153 ± 28 100 ± 19 87 ± 16
F 142 ± 39 136 ± 34 100 ± 28 96 ± 24
All 160 ± 39 145 ± 31 100 ± 24 90 ± 19
CON 60 M 142 ± 32 98 ± 15 100 ± 22 69 ± 11
F 102 ± 21 86 ± 15 100 ± 21 84 ± 15
All 124 ± 34 92 ± 16 100 ± 27 75 ± 13
120 M 115 ± 31 84 ± 18 100 ± 27 73 ± 16
F93
± 20 72 ± 9 100 ± 22 78 ± 10
All 105 ± 29 78 ± 15 100 ± 27 75 ± 15
Values are mean ± SD in Nm. Maintenance: percent of
corresponding young mean value, expressing the relative
maintenance of torque in old adults.
Fig. 1. Torque-velocity relationship of the quadriceps muscle with
the data plotted as percentages of the mean of the young group (=
100%). The asterisks indicatesignificant difference from the young
group (p < 0.05). ϒ= Significant difference between ECC and CON
maintenance. Vertical bars denote SD.
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Gerontology 2016;62:588–596
DOI: 10.1159/000445376
592
Table 4. Coefficients of determination for the relationship between peak quadriceps torque and gait tasks
Speed Ascending
gait vs. CON
Descending gait
vs. ECC
Ascending
gait vs. ECC
Descending gait
vs. CON
Level walking
vs. CON
Level walking
vs. ECC
Habitual
Young adults (n = 24) 0.02 0.15 0.09 0.02 0.10 0.15
Old adults (n = 21) 0.12 0.03 0.00 0.15 0.11 0.06
All1 (n = 45) 0.00 0.00 0.01 0.04 0.04 0.02
Maximal
Young adults (n = 24) 0.31** 0.00 0.03 0.08 0.10 0.02
Old adults (n = 21) 0.39** 0.20*0.09 0.36** 0.07 0.04
All1 (n = 45) 0.56*** 0.16** 0.17** 0.45*** 0.22** 0.09*
CON and ECC, peak concentric and eccentric quadriceps muscle torques. Ascending and descending gaits comprise of respectively
stair and ramp ascent and stair and ramp descent. * p < 0.05, ** p < 0.01, *** p < 0.001. 1 Young and old adults.
Table 3. Gait performance in young and old adults
Speed Task Direction Group Young
(11 F, 13 M)
Old
(10 F, 11 M)
p valueaEffect
size ra
Habitual LevelbLevel M
F
All
1.41 ± 0.13
1.45 ± 0.16
1.43 ± 0.14
1.42 ± 0.23
1.51 ± 0.14
1.47 ± 0.19
0.18 0.20
Stair Ascent M
F
All
12.04 ± 1.31
11.41 ± 0.68
11.75 ± 1.10
11.69 ± 1.51
10.86 ± 1.03
11.30 ± 1.34
0.60 0.08
Descent M
F
All
11.28 ± 1.25
10.49 ± 1.16
10.92 ± 1.25
11.76 ± 1.66
10.66 ± 0.68
11.23 ± 1.38
0.16 0.21
Ramp Ascent M
F
All
3.28 ± 0.45
3.15 ± 0.26
3.22 ± 0.37
3.38 ± 0.48
3.33 ± 0.30
3.35 ± 0.39
0.11 0.25
Descent M
F
All
3.04 ± 0.46
2.99 ± 0.41
3.01 ± 0.43
3.26 ± 0.38
3.14 ± 0.31
3.20 ± 0.35
0.054 0.29
Maximal Level Level M
F
All
2.25 ± 0.19
2.17 ± 0.25
2.22 ± 0.22
1.96 ± 0.27
1.93 ± 0.29
1.95 ± 0.27
<0.01*0.44
Stair Ascent M
F
All
5.97 ± 0.52
6.13 ± 0.54
6.05 ± 0.52
7.67 ± 0.75
7.83 ± 1.09
7.75 ± 0.91
<0.01*0.77
Descent M
F
All
6.23 ± 0.60
6.13 ± 0.54
6.19 ± 0.76
8.01 ± 1.22
8.13 ± 0.79
8.07 ± 1.02
<0.01*0.77
Ramp Ascent M
F
All
2.10 ± 0.22
2.12 ± 0.26
2.11 ± 0.23
2.42 ± 0.48
2.42 ± 0.38
2.42 ± 0.42
<0.01*0.46
Descent M 1.89 ± 0.18 2.18 ± 0.29 <0.01*0.52
F 1.85 ± 0.27 2.23 ± 0.37
All 1.88 ± 0.22 2.20 ± 0.32
Values are mean ± SD in m/s for level walking and in s for other variables. The asterisk indicates significance.
a Based on all young vs. old adult groups. b Level walking.
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Functional Relevance of RELM in Healthy
Aging
Gerontology 2016;62:588–596
DOI: 10.1159/000445376
593
Functional Significance of RELM
Table 5 shows quadriceps muscle torque and gait
performance data of high and low RELM groups for
males and females separately. For high versus low
RELM, the magnitude of RELM was significantly high-
er in males (44.6 ± 7.5 vs. 12.0 ± 11.0%, p < 0.001) and
females (31.8 ± 25.7 vs. 1.4 ± 8.4%, p < 0.05). Thus, in a
select group of males and females, respectively, with
33 and 30% greater levels of RELM, this difference
beyond 30% of RELM produced no difference in level
and non-level gait performances. For low versus high
RELM, females performed significantly better on habit-
ual stair ascent and maximal ramp ascent performance
(both p = 0.04)
.
Discussion
We observed a lack of specificity between the type of
muscle contraction-generated peak torque of the quadri-
ceps and the type of gait tasks dominated by either CON
or ECC muscle contraction. We also found no evidence
that RELM, which was similar in males and females,
would afford functional benefits for healthy old adults’
gait performance. We discuss these findings with a per-
spective on how age affects the relationship between mus-
cle strength and locomotion performance with an em-
phasis on ECC quadriceps muscle function.
Our peak quadriceps data are in line with previous re-
ports in that old compared to young adults overall gener-
Table 5. Differences in quadriceps muscle torque and gait performance between high and low RELM subgroups
Peak
torque
RELM Group High RELM
(5 F, 5 M)
Low RELM
(5 F, 6 M)
p value Effect size
r
CON M
F
84 ± 14
79 ± 15
96 ± 17
80 ± 8
0.25
0.83
0.38
0.08
ECC M
F
167 ± 27
151 ± 35
148 ± 30
119 ± 17
0.27
0.11
0.37
0.54
Magnitude M
F
44.6 ± 7.5
31.8 ± 25.7
12.0 ± 11.0
1.4 ± 8.4
<0.001*
0.04*
0.88
0.66
Speed Task Direction
Habitual Level Level M
F
1.46 ± 0.20
1.48 ± 0.12
1.38 ± 0.27
1.55 ± 0.16
0.99
0.43
0.00
0.28
Stair Ascent M
F
11.78 ± 1.62
11.54 ± 0.68
11.59 ± 1.55
10.18 ± 0.88
0.73
0.04*
0.12
0.66
Descent M
F
12.00 ± 1.88
11.00 ± 0.45
11.46 ± 1.50
10.31 ± 0.74
0.93
0.15
0.03
0.50
Ramp Ascent M
F
3.34 ± 0.48
3.46 ± 0.37
3.42 ± 0.53
3.19 ± 0.10
0.73
0.16
0.12
0.54
Descent M
F
3.26 ± 0.46
3.28 ± 0.28
3.26 ± 0.31
2.99 ± 0.30
0.84
0.21
0.07
0.44
Maximal Level Level M
F
1.99 ± 0.37
1.84 ± 0.30
1.92 ± 0.01
2.03 ± 0.27
0.70
0.29
0.13
0.37
Stair Ascent M
F
7.63 ± 0.78
8.46 ± 1.20
7.71 ± 0.80
7.20 ± 0.50
0.63
0.06
0.17
0.61
Descent M 8.00 ± 1.53 8.03 ± 0.91 0.96 0.02
F 8.38 ± 0.93 7.88 ± 0.64 0.31 0.36
Ramp Ascent M 2.47 ± 0.64 2.37 ± 0.24 0.81 0.08
F 2.65 ± 0.38 2.19 ± 0.23 0.04*0.65
Descent M 2.17 ± 0.37 2.18 ± 0.21 0.56 0.20
F 2.40 ± 0.29 2.05 ± 0.39 0.18 0.47
Values are mean ± SD in m/s for level walking, in Nm for peak torque, in % for RELM magnitude, and in s
for stair and ramp tasks. The asterisk indicates significance.
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ated 17.3% lower peak quadriceps torques during ECC
and CON contraction
[1, 5–7, 15, 18] ( fig.1 ; table2 ). Spe-
cifically, healthy old versus young adults produced 25%
lower CON and 9.5% lower peak ECC quadriceps torque
(both p < 0.05). Such reductions in maximal torque gen-
eration are in line with the evolution of age-related dy-
napenic weakness, most likely caused by a loss of muscle
proteins
[9, 10] , neuronal hypoexcitability [11, 12] , and
an increase in tendon compliance impeding force trans-
mission to the body levers
[13, 14] . Our data also agree
with previously published data with respect to the ratio
between ECC and CON peak torques. In the quadriceps,
the 1.4 (young males and females) and 1.7 (old males and
females) ratios are numerically identical with some previ-
ously published ECC-to-CON torque ratios
[1, 7, 15, 18] .
The overall pattern of the peak torque and the ratio data
provide a sound basis for the examination of RELM and
whether or not there is specificity between the type of
peak torque and the type of functional task with respect
to the nature of muscle contraction and if age affects this
specificity.
Young compared to old adults ambulated 17.0% fast-
er in the 5 functional tasks when tested at the safe-fast
speed (p < 0.01) but not at the habitual speed (difference:
1.2%). Age-related declines in habitual level walking
speed are well documented
[22] , but there are also stud-
ies reporting a lack of age effect on gait speed
[26] . Most
likely, our old adults represent a highly healthy cohort
suggested by the 1.47 m/s habitual level walking speed.
Indeed, a previous review reported a 17% slower mean
habitual level walking speed of 1.22 m/s measured at
baseline of 42 intervention studies in nearly 2,500 healthy
old adults
[27] , and other reviews also reported slower
values, 1.15
[26] and 1.30 m/s [28] , as ‘standards’ for ha-
bitual level walking speed in healthy old adults. The 1.95
m/s fast walking speed is also substantially higher than
the 1.44 m/s reported in 766 similarly healthy old adults
[27] , or the 1.50 m/s [26] , and slightly higher than the
1.90 m/s
[28] ; the latter two speeds were reported as
‘standard’. The use of a curved measurement path and
the lack of lead-in as in the Timed Up and Go and the
SPPB tests produce slower gait speeds, but neither meth-
od was used in the present study. A comparison of our
walking speeds measured on inclined surfaces with other
studies is not possible because the measurement param-
eters vary widely across studies
[29–32] . It seems desir-
able to compile normative data on stair and ramp gaits
in old adults because such locomotion tasks may be even
more sensitive to subtle and subclinical musculoskeletal
dysfunctions, due to the high relative effort and joint
torques
[24, 30, 33] . Stair and ramp gaits may also predict
future mobility disability more accurately than level
walking in apparently healthily aging old adults.
We observed a lack of specificity between the type of
muscle contraction-generated peak torques of the quad-
riceps and the type of gait tasks dominated by either CON
or ECC muscle contraction. The expected specificity be-
tween muscle contraction type and functional perfor-
mance in the locomotion tasks is conceptually well found-
ed based on muscle mechanics
[16, 34, 35] , muscle activa-
tion
[16, 36, 37] , and metabolic cost [16, 36] . Previous
studies also implied but never explicitly examined such
specificity
[7, 16] . Specificity is also expected because the
positive and negative knee joint powers, as measured by
inverse dynamics, are significantly higher during ascent
and descent gaits compared to level walking
[24, 29, 33] .
Determining whether the associations between leg
strength and gait performance are task-specific is impor-
tant because dynapenia is the primary risk factor for mo-
bility disability
[8] , implying that mobility disability could
be more accurately predicted when peak leg muscle
strength is measured in a manner that is specific than
when it is not specific to a functional task.
There is a moderate association between leg strength
and habitual gait speed in healthy old adults
[22, 28] , but
our data revealed a weak or no association between these
two variables ( table 4 ). Perhaps our very healthy old
adults performed the gait tasks at the habitual speed at a
low relative effort so that the joint torques generated and
required in these gait tasks were much lower than the pre-
viously reported 80% of the available maximum in stair
ascent and descent, minimizing the dependence on peak
quadriceps torques
[23] . When subjects executed the gait
tasks at the safe-fast speed, quadriceps peak torque cor-
related significantly with gait speed in all six conditions
( table4 , bottom row, R
2 range = 0.09–0.56, all p < 0.05).
These associations were characterized by a lack of speci-
ficity between type of peak torque (ECC, CON) and type
of gait (ascent, descent). The consistently higher task- and
non-task-specific associations between gait performance
and CON but not ECC peak quadriceps torque assign a
putative role to CON effort in these gait tasks. To illus-
trate this, the association between ascending gait speed
and CON torque was 3.5 times stronger (R
2 = 0.56) than
the association between descending gait speed and ECC
torque (R
2 = 0.16). Even for the non-specific comparison,
the association between descending gait speed and CON
peak torque was 2.6 times stronger (R
2 = 0.45) than the
association between ascending gait speed and ECC torque
(R
2 = 0.17) ( table4 ). One interpretation is that low CON
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Functional Relevance of RELM in Healthy
Aging
Gerontology 2016;62:588–596
DOI: 10.1159/000445376
595
peak quadriceps torque can be a limiting factor in old
adults’ fast gait performance on an incline. The much
lower associations in the comparisons that involve ECC
versus CON quadriceps peak torque, in both young and
old adults ( table4 ), may also suggest less reliance on the
quadriceps and perhaps shifting effort to ankle and hip
muscles
[33, 38] and the different use of the trailing leg in
ascent and descent gaits
[39] . A movement coordination-
related factor, i.e., using a forefoot landing strategy, could
also minimize the correlations between peak quadriceps
ECC torque and descending gait performance by subjects
shifting the reliance from the knee extensors to the plan-
tar flexors. A different neural strategy to control balance
during ascent and descent could also contribute to these
lower associations. For example, muscle coactivity of the
knee flexors and extensors is 2.0 and 1.4 times greater in
old versus young adults during stair descent and ascent,
respectively
[23] . An increase in coactivity possibly serves
as a functional mechanism to maintain limb and joint
stiffness
[40] , as old adults have less functional ‘reserve’
to compensate for sudden unexpected perturbations, es-
pecially during demanding and hazardous ADLs like stair
and ramp negotiation. These speculations require confir-
mations.
Over the past 3 decades, numerous studies reported
on the phenomenon of RELM
[7, 15, 16, 19] . There are
striking examples for the age-related sparing of peak vol-
untary ECC muscle torque, as in one study, where old
adults actually produced numerically almost identical
ECC plantarflexion
[17] vis-à-vis the 30–50% lower peak
isometric or CON torques
[15] . In the present study, the
difference in peak CON quadriceps torque between
young and old adults was 25%, whereas the difference in
ECC torque was 9.5%, documenting RELM in the pres-
ent sample qualitatively to about the same extent as re-
ported previously
[7, 15, 16] , based on the computation
of RELM
[16] (discussed extensively in our data analysis
section).
For the first time, we examined whether or not RELM
affords functional benefits when old adults walk on level
and inclined surfaces. To amplify any potential effects of
RELM, we created subgroups of healthy old males and
females with 33 and 30% greater levels of RELM than
other subgroups of the same age, accompanied by large
effect sizes of r = 0.88 and 0.66 ( table5 ). Against the hy-
pothesis, after careful examination of table 5 (absolute
torques and RELM), high RELM and higher ECC muscle
function, in particular for the women, did not translate
into higher gait speed measured on level and inclined sur-
faces between these subgroups of healthy old adults. In
women, even the high versus low RELM group performed
significantly worse on habitual ascending stairs and fast
ascending a ramp (both p = 0.04). The previously dis-
cussed lack of specificity between the type of peak quad-
riceps torque and type of gait task foreshadowed the ab-
sence of RELM effect on locomotor function, but the near
nil effect of RELM on performance in descending gaits
(effect size range: 0.02–0.50) is rather unexpected ( ta-
ble5 ). Considering that improving ECC leg muscle func-
tion by various forms of ECC training resulted in im-
proved gait speed
[41, 42] , balance [41] , and fall risk [41,
43] , it is as reasonable to expect that high ECC function
as quantified in the present study, especially through the
high RELM subgroup, would provide an agreement with
improved functional outcomes reported in interventions
studies.
One reason for a lack of RELM effect on gait function
could be that even though the RELM subgroups differed
in RELM itself, subjects in the subgroups were similar in
peak ECC and CON quadriceps torque ( table5 ). Perhaps
larger sample sizes would have allowed us to detect the
expected effects of RELM on gait function ( table5 ). Even
though quadriceps strength has been promoted as a key
contributor to locomotion, the recent concept of biome-
chanical plasticity in old adults’ gait
[22, 44] shifted atten-
tion to the observation of a preferential reduction in ankle
plantarflexion function even in healthy old adults, an out-
come we did not measure in the present study.
In conclusion, the present study confirmed previous
findings of RELM, but found no evidence for specificity
in the associations between the type of muscle contrac-
tion (ECC, CON) and the type of gait task (descent, as-
cent), and also found no evidence that normal and 30%
above normal levels of RELM would increase or predict
healthy old adults’ gait performance on level and inclined
surfaces. Future work should examine if RELM is associ-
ated with a heightened performance in other measures of
neuromuscular function such as gait biomechanics, mus-
cle activation, as well as rate and control of voluntary
force development in old adults with high or low mobil-
ity.
Disclosure Statement
The authors declare no conflicts of interest.
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Hortobágyi
Gerontology 2016;62:588–596
DOI: 10.1159/000445376
596
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... First, eccentric knee extensor and plantarflexor functions are relatively well maintained in older age. Indeed, older adults exhibit a relative maintenance of maximal voluntary eccentric strength (0%-30% loss) compared with isometric (20%-40% loss) and, in particular, concentric (30%-50% loss) strength for both muscle groups (23)(24)(25)(26). Second, based on peak joint moments, the relative demand on hip and knee extensors and ankle plantarflexors to perform negative work during level and downhill walking is lower than that on the plantarflexors to perform positive work during level and uphill walking (18). ...
... In partial agreement with previous studies, we observed a relative maintenance of maximal voluntary eccentric versus concentric muscle function for the knee extensors (23,26) but not the plantarflexors (24). Porter et al. (24) also observed relative eccentric strength maintenance for the plantarflexors, but their sample included females only and older females tend to show a greater eccentric strength maintenance than older males (23,25). ...
... Notably, older patients can improve their walking speed (36,37), fall risk (36), and balance (36) after eccentric muscle training. However, we previously (26) observed relatively weak associations between self-selected speed during downhill walking or stair decent and eccentric knee extensor strength in healthy older adults. As we elaborate below, our walking data provide important functional context for associations between the type of muscle action and walking condition, with implications for the prescription of targeted, musclespecific exercise interventions for older adults. ...
Article
Full-text available
Introduction: Advanced age brings a distal-to-proximal redistribution of positive joint work during walking that is relevant to walking performance and economy. It is unclear whether negative joint work is similarly redistributed in old age. Negative work can affect positive work through elastic energy return in gait. We determined the effects of age, walking speed, and grade on positive and negative joint work in young and older adults. Methods: Bilateral ground reaction force and marker data were collected from healthy young (age = 22.5 yr, n = 18) and older (age = 76.0 yr, n = 22) adults walking on a split-belt instrumented treadmill at 1.1, 1.4, and 1.7 m·s at each of three grades (0%, 10%, and -10%). Subjects also performed maximal voluntary eccentric, isometric, and concentric contractions for the knee extensors (120°·s, 90°·s, and 0°·s) and plantarflexors (90°·s, 30°·s, and 0°·s). Results: Compared with young adults, older adults exhibited a distal-to-proximal redistribution of positive leg joint work during level (P < 0.001) and uphill (P < 0.001) walking, with larger differences at faster walking speeds. However, the distribution of negative joint work was unaffected by age during level (P = 0.150) and downhill (P = 0.350) walking. Finally, the age-related loss of maximal voluntary knee extensor (P < 0.001) and plantarflexor (P = 0.001) strength was smaller during an eccentric contraction versus concentric contraction for the knee extensors (P < 0.001) but not for the plantarflexors (P = 0.320). Conclusion: The distal-to-proximal redistribution of positive joint work during level and uphill walking is absent for negative joint work during level and downhill walking. Exercise prescription should focus on improving ankle muscle function while preserving knee muscle function in older adults trying to maintain their independence.
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Habitual walking speed predicts many clinical conditions later in life, but it declines with age. However, which particular exercise intervention can minimize the age-related gait speed loss is unclear. Our objective was to determine the effects of strength, power, coordination, and multimodal exercise training on healthy old adults' habitual and fast gait speed. We performed a computerized systematic literature search in PubMed and Web of Knowledge from January 1984 up to December 2014. Search terms included 'Resistance training', 'power training', 'coordination training', 'multimodal training', and 'gait speed (outcome term). Inclusion criteria were articles available in full text, publication period over past 30 years, human species, journal articles, clinical trials, randomized controlled trials, English as publication language, and subject age ≥65 years. The methodological quality of all eligible intervention studies was assessed using the Physiotherapy Evidence Database (PEDro) scale. We computed weighted average standardized mean differences of the intervention-induced adaptations in gait speed using a random-effects model and tested for overall and individual intervention effects relative to no-exercise controls. A total of 42 studies (mean PEDro score of 5.0 ± 1.2) were included in the analyses (2495 healthy old adults; age 74.2 years [64.4-82.7]; body mass 69.9 ± 4.9 kg, height 1.64 ± 0.05 m, body mass index 26.4 ± 1.9 kg/m(2), and gait speed 1.22 ± 0.18 m/s). The search identified only one power training study, therefore the subsequent analyses focused only on the effects of resistance, coordination, and multimodal training on gait speed. The three types of intervention improved gait speed in the three experimental groups combined (n = 1297) by 0.10 m/s (±0.12) or 8.4 % (±9.7), with a large effect size (ES) of 0.84. Resistance (24 studies; n = 613; 0.11 m/s; 9.3 %; ES: 0.84), coordination (eight studies, n = 198; 0.09 m/s; 7.6 %; ES: 0.76), and multimodal training (19 studies; n = 486; 0.09 m/s; 8.4 %, ES: 0.86) increased gait speed statistically and similarly. Commonly used exercise interventions can functionally and clinically increase habitual and fast gait speed and help slow the loss of gait speed or delay its onset.
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Weakness predisposes seniors to a fourfold increase in functional limitations. The potential for age-related degradation in nervous system function to contribute to weakness and physical disability has garnered much interest of late. In this study, we tested the hypothesis that weaker seniors have impairments in voluntary (neural) activation and increased indices of GABAergic inhibition of the motor cortex, assessed using transcranial magnetic stimulation. Young adults (N = 46; 21.2±0.5 years) and seniors (N = 42; 70.7±0.9 years) had their wrist flexion strength quantified along with voluntary activation capacity (by comparing voluntary and electrically evoked forces). Single-pulse transcranial magnetic stimulation was used to measure motor-evoked potential amplitude and silent period duration during isometric contractions at 15% and 30% of maximum strength. Paired-pulse transcranial magnetic stimulation was used to measure intracortical facilitation and short-interval and long-interval intracortical inhibition. The primary analysis compared seniors to young adults. The secondary analysis compared stronger seniors (top two tertiles) to weaker seniors (bottom tertile) based on strength relative to body weight. The most novel findings were that weaker seniors exhibited: (i) a 20% deficit in voluntary activation; (ii) ~20% smaller motor-evoked potentials during the 30% contraction task; and (iii) nearly twofold higher levels of long-interval intracortical inhibition under resting conditions. These findings indicate that weaker seniors exhibit significant impairments in voluntary activation, and that this impairment may be mechanistically associated with increased GABAergic inhibition of the motor cortex. © The Author 2015. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
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Muscle mass, strength, and power are known determinants of mobility in older adults but there is limited knowledge on the influence of muscle architecture or tendon properties on mobility. The purpose of this study was to examine the relationship between mobility and plantarflexor muscle-tendon properties in healthy older adults. A total of 52 subjects (age 70-81 years) were measured for 6-minute walk test (6MWT), timed "up and go"-test (TUG), isometric plantarflexion strength, Achilles tendon stiffness, triceps surae muscle architecture, lower extremity lean mass, isometric leg extension strength, and leg extension power. Partial correlations and multivariate regression models adjusted for sex, age, body mass, and height were used to examine the relationship between mobility (6MWT and TUG) and lower limb muscle-tendon properties. Multivariate regression models revealed that Achilles tendon stiffness (p = .020), plantarflexion strength (p = .022), and medial gastrocnemius fascicle length (p = .046) were independently associated with 6MWT. Plantarflexion strength (p = .037) and soleus fascicle length (p = .031) were independently associated with TUG. Plantarflexor muscle-tendon properties were associated with mobility in older adults independent of lower extremity lean mass, leg extension strength, or power. Plantarflexion strength was a stronger predictor of mobility than leg extension strength or power. The novel finding of this study was that muscle architecture and tendon properties explained interindividual differences in mobility. This study highlights the importance of the plantarflexors for mobility in older adults and provides understanding of possible mechanisms of age-related decline in mobility. © The Author 2015. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
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Functional testing is particularly useful in the clinic and for making research translatable; however, finding measures relevant across ages and different conditions can be difficult. A systematic review was conducted to investigate timed stair tests as an objective measure of functional abilities and musculoskeletal integrity. Data were analyzed for their ability to differentiate between controls and patient groups and between different patient groups. Literature was reviewed using the Medline, CINAHL, and PubMed databases until February 2012. Data were grouped according to methodology, ages, and medical conditions. Time per step was calculated to allow comparison between studies. Eighty-eight studies were included in this review. Methodologies varied considerably with stair ascent, stair descent, or a combination of the two being used across a wide range of ages and medical conditions. Times increased with age for ascent, descent, and combined and for a variety of medical problems. Timed stair tests appear to be sensitive to medical conditions but further data are required to obtain normative values for this test. We suggest that timed stair tests should follow a more standardized methodology using a combination of ascent and descent and asking participants to complete the stairs as quickly and safely as possible.
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This essay begins by proposing that muscle weakness of old age from sarcopenia is due in large part to reduced capillary density in the muscles, as documented in 9 reports of aged persons and animals. Capillary density (CD) is determined by local levels of various angiogenic factors, which also decline in muscles with aging, as reported in 7 studies of old persons and animals. There are also numerous reports of reduced CD in the aged brain and other studies showing reduced CD in the kidney and heart of aged animals. Thus a waning angiogenesis throughout the body may be a natural occurrence in later years and may account significantly for the lesser ailments (physical and cognitive) of elderly people. Old age is regarded here as a deficiency state which may be corrected by therapeutic angiogenesis, much as a hormonal deficiency can be relieved by the appropriate hormone therapy. Such therapy could employ recombinant angiogenic factors which are now commercially available. Copyright © 2015 Elsevier B.V. All rights reserved.
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Advancing age is the focus of recent studies on familial and sporadic Alzheimer's disease (AD) suggesting a prolonged preclinical phase several decades before the onset of dementia symptoms. Influencing some age-related conditions, such as frailty, may have an impact on the prevention of late-life cognitive disorders. Frailty reflects a nonspecific state of vulnerability and a multisystem physiological change with increased risk for adverse health outcomes in older age. In this systematic review, frailty indexes based on a deficit accumulation model were associated with late life cognitive impairment and decline, incident dementia and AD. Physical frailty constructs were associated with late-life cognitive impairment and decline, incident AD and mild cognitive impairment, vascular dementia, non-AD dementias, and AD pathology in older persons with and without dementia, so also proposing cognitive frailty as a new clinical condition with coexisting physical frailty and cognitive impairment in nondemented older subjects. Considering both physical frailty and cognitive impairment as a single complex phenotype may be central in the prevention of dementia and its subtypes with secondary preventive trials on cognitive frail older subjects. The mechanisms underlying the cognitive-frailty link are multifactorial and vascular, inflammatory, nutritional, and metabolic influences may be of major relevance. There is a critical need for randomized controlled trials of intervention investigating the role of nutrition and/or physical exercise on cognitive frail subjects with the progression to dementia as primary outcome. These preventive trials and larger longitudinal population-based studies targeting cognitive outcomes could be useful in further understanding the cognitive-frailty interplay in older age.
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Aging is associated with increased risk of reduced mobility. However, data on muscle components in relation to subjective and objective indicators of disability is limited. Data were from 2,725 participants (43% men) aged 74.8±4.7 years from the AGES-Reykjavik Study. At baseline, maximal isometric thigh strength (dynamometer chair), and midthigh muscle area and muscle fat infiltration were assessed with computed tomography. Usual 6 m gait speed and mobility disability were assessed at baseline and after 5.2±0.3 years. Incident mobility disability was defined as having much difficulty or unable to walk 500 m or climb-up 10 steps. A decrease of ≥0.1 m/s in gait speed was considered clinically relevant. Greater strength and area were protective for mobility disability risk and gait speed decline. After adjustment for other muscle components, greater strength was independently associated with lower mobility disability risk in women odds ratios (OR) 0.78 (95% CI 0.62, 0.99), and lower decline in gait speed risk among both men OR 0.64 (0.54, 0.76), and women OR 0.72 (0.62, 0.82). Larger muscle area was independently associated with lower mobility disability risk in women OR 0.67 (0.52, 0.87) and lower decline in gait speed risk in men OR 0.74 (0.61, 0.91). Greater muscle strength and area were independently associated with 15-30% decreased risk of mobility disability in women and gait speed decline in men. Among women, greater muscle strength was also associated with lower risk of gait speed decline. Interventions aimed at maintaining muscle strength and area in old age might delay functional decline. Published by Oxford University Press on behalf of the Gerontological Society of America 2015.
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We have previously reported that elderly compared to young women executed downward stepping with substantially greater leg stiffness. Because antagonist muscle coactivity increases joint stiffness we hypothesized that increased leg stiffness in aging is associated with increased muscle coactivity. We also explored the possibility that the magnitude of the preparatory muscle activity preceding impact also differed between young and old subjects. Young (n=11, 20. 8 yr) and old (n=12, 69 yr) women performed downward stepping from a platform set at 20% body height. The leg was modeled as a simple mass-spring system. From video and ground reaction force data leg stiffness was computed as the ratio of force under the foot and the linear shortening of the limb. EMG activity of the vastus lateralis, biceps femoris, gastrocnemius lateralis, and tibialis anterior were recorded with a telemetric system. Elders compared to young subjects had 64% greater leg stiffness during downward stepping. Muscle activity over a 200-ms period preceding touch down was 136% greater in elderly than in young subjects. Biceps femoris and tibialis anterior coactivity during ground contact was 120% greater in the elders. Muscle pre- and coactivity, respectively, accounted for about 50% of the variance in leg stiffness. In conclusion, elderly people elevate muscle pre- and coactivity during downward stepping to stiffen the leg in compensation for impaired neuromotor functions.