Full text of DOI:10.1093/gerona/56.10.B443

Journal of Gerontology: BIOLOGICAL SCIENCES
Copyright 2001 by The Gerontological Society of America
2001, Vol. 56A, No. 10, B443–B448
The Interrelationship Among Muscle Mass, Strength,
and the Ability to Perform Physical Tasks of Daily
Living in Younger and Older Women
Kathleen A. Landers,1 Gary R. Hunter,1,2 Carla J. Wetzstein,1 Marcas M. Bamman,1
and Roland L. Weinsier2
Departments of 1Human Studies and 2Nutrition Sciences, University of Alabama at Birmingham.
The purpose of this study was to objectively compare the difficulty and determine the contribu-
tion of strength and muscle mass to the performance of physical tasks of daily living in a group
of younger and older women. A cross-sectional design was used. Volunteer participants were
from the community of Birmingham, AL; there were 21 older (aged 60–75 years) and 20
younger (23–34 years) healthy women in the study. Subjects were matched for height and
weight. Their testing included total and regional body composition evaluation by use of dual-
energy x-ray absorptiometry, isometric strength tests of elbow flexors and knee extensors, and in-
tegrated electromyography (IEMG) evaluation while the subjects were standing from and sitting
into a chair, and while they were carrying a small load (weight relative to strength). A two-way
analysis of variance and a two-way analysis of covariance with repeated measures, Pearson
product correlation, and first-order partial correlations were used to analyze the data. A signifi-
cant inverse correlation was observed between age and isometric strength of both the knee ex-
tensors and elbow flexors. Adjusting for upper leg lean tissue did not change the significant
inverse correlation between age and knee extensor strength. However, after an adjustment for
arm lean tissue, there was no significant correlation between elbow flexor strength and age.
Older women experienced significantly greater difficulty in standing than younger women as
measured by quadriceps normalized IEMG (i.e., IEMG during task/IEMG during maximum iso-
metric strength test). This difference persisted even after the covariate upper leg lean tissue was
added to the model. No significant difference was observed between younger and older women
for difficulty (biceps normalized IEMG) during the carry task after the covariate arm lean tissue
was added to the model. The older women in this study had less strength in the knee extensors
and experienced greater difficulty standing from a chair than the younger women, even after the
covariate upper leg lean tissue was added to the model. This suggests that other factors, in addi-
tion to loss of lean tissue, contribute to the age-related decline of muscular strength and the abil-
ity to perform tasks with the legs. In contrast, although elbow flexor strength declined, this
appeared to be largely due to decreased arm lean tissue mass.
USCLE size, strength, and the ability to perform phys-
ical tasks of daily living (PTDL) reach a peak in a per-
cle (5,8,11). Compromised task performance with age may
result from a variety of factors, including muscle weakness
and decreased muscle mass in relation to fat mass (12,13).
The relationship of muscle mass and strength to the diffi-
culty of performing daily tasks such as standing from and
sitting into a chair or carrying a box of groceries is not
known. Although muscle cross-sectional area and thus
quantity of limb lean tissue are related to strength and effort
in performing daily tasks, it is not known whether this rela-
tionship is the same in younger and older adults. A compar-
ison of the relationship between the quantity of muscle mass
and muscle function between young and old adults should
improve our understanding of the age-related decline in the
ability to perform PTDL.
M
son’s early thirties and then decline with age (1–3). This de-
cline occurs regardless of physical fitness or amount of
training (1,4). Schultz and Curnow have documented the pro-
gressive performance decrements of highly trained athletes as
they age (4). Cross-sectional studies suggest varying rates of
skeletal muscle atrophy, from 20% in the biceps brachii to
33% in the quadriceps femoris, when sedentary young (20–
35 years) and old (68–86 years) adults are compared (1,5,6).
The decline in muscle strength appears to follow the decline
in muscle mass closely (6–9). However, some controversy ex-
ists as to whether the decline in strength is solely due to a de-
cline in (quantitative) muscle mass (1,5,6,10) or to whether
changes in muscle quality also occur, such as alterations in the
activation of motor units or contractile properties of the mus-
To our knowledge, few studies have examined objective
physiological measurements of difficulty, while the subjects
B443

B444
LANDERS ET AL.
are performing daily tasks, in young and old persons. The
physiological effort required to do tasks can be evaluated by
using integrated electromyography (IEMG; 14). The electri-
cal activity of the muscle recorded as IEMG is normalized
by dividing the IEMG recorded while the subject is per-
forming a task (or gradation of maximum strength) by the
maximum IEMG recorded from the same muscle group dur-
ing a maximum effort. Higher normalized IEMG (nIEMG)
values indicate greater muscular effort or intensity of con-
traction. When combined with a measure of lean tissue,
nIEMG during task performance can provide objective com-
parisons between the muscle function of older and younger
individuals.
tion Corporation, Madison, WI). Scans were conducted in
the adult medium mode (8 cm/s). A DXA analysis provided
fat mass percentage of total body weight, fat mass, and lean tis-
sue mass (excluding bone mineral content). Regions of in-
terest were used to separate right arm and upper right leg
from total body lean tissue mass (LTM). This procedure al-
lowed the measure of LTM of the extremity, including the
predominant muscle or muscle group used to perform the
MVICs and tasks of daily living completed in this study.
The LTM of the upper leg provided a surrogate measure of
the knee extensors. The LTM of the total arm served as the
surrogate measure for the elbow flexors because elbow flex-
ors lie in both the upper and lower arm.
Using younger and older women matched for body mass
index (BMI), this study was designed to test the following
hypotheses: (1) older women have lower strength and lean
tissue mass in the arms and legs than younger women; (2)
an age-related decline in the strength of the knee extensors
is independent of limb lean tissue mass, whereas the age-
related decline in elbow flexor strength is dependent on limb
lean tissue mass; (3) an age-related decline in the ability to
stand from a chair is independent of limb lean tissue and
strength; and (4) older and younger women have similar
muscle function for a carrying task that is proportional to
each woman’s maximal strength.
Isometric Strength Tests
Maximum isometric strength of the knee extensors and
elbow flexors was evaluated while the IEMG of the rectus
femoris and biceps brachii, respectively, were measured. A
Universal Shear Beam Load Cell-LCC 500 (Omega, Stam-
ford, CT) was used to measure force for both strength tests.
Subjects were provided with immediate force measurement
feedback by a digital transducer (Omega) and were verbally
encouraged to obtain the highest force possible.
During elbow flexion, each subject stood with a metal
harness to limit shoulder movement. The harness was sus-
pended from a strap behind the subject’s neck. It crossed the
subject’s chest and lay behind her triceps. Both arms re-
mained fixed at the sides, with the right elbow bent to a
flexion of 1.92 rad (radians) and a strap positioned over the
styloid process and attached to the force transducer.
Isometric knee extension strength was measured with the
subject sitting in a chair with the right knee extended to 1.92
and again at 2.44 rad. Hip movement was limited by secur-
ing the subject to the chair at the thighs and torso. Force
production was measured 1 in. (2.54 cm) above the malleo-
lus, where a strap was positioned and attached to the force
transducer. IEMG was recorded during each contraction at
the knee extension angles of 1.92 and 2.44 rad to normalize
data during the stand–sit task. Subjects were given three
practice trials, followed by three MVICs at each test angle.
The average of the two highest values for each angle was
used for statistical analysis.
METHODS
Subjects
Twenty-one healthy older women (60–75 years of age)
and 20 younger women (23–34 years of age) participated in
the study. Subjects were pooled from two separate research
projects that were concurrently conducted. A physician
screened potential subjects by history and physical exam.
Subjects were excluded from the study if they had evidence
of diabetes, significant renal or hepatic disease, hypothy-
roidism, or musculoskeletal problems that would hinder
participation. None of the subjects performed resistance
weight training, and none were training for improved aero-
bic fitness. Estrogen replacement therapy was not an exclu-
sion factor. Methods and procedures were approved by the
Institutional Review Board of the University of Alabama at
Birmingham. All subjects gave signed informed consent.
Electrode and Goniometer Placement
Design
As a way to measure IEMG, bipolar silver–silver chloride
(Ag–Ag/Cl) 2mm in diameter, electromyography surface
electrodes (Rochester Electro-Medical, Inc., Tampa, FL)
were placed one electrode width apart in a longitudinal line
with the quadriceps, and over the biceps muscle according
to standard procedures (15). The right ear lobe was used for
placement of the ground wire. All leads had an impedance
of less than 10 k ꢀ. The knee joint angle was measured by
using an electronic goniometer (ELGON). The goniometer
was secured to the lateral aspect of the right leg with the
axis of rotation at the knee joint and with the goniometer
arms extending an equal distance above and below the knee,
and aligned to the lateral malleolus and greater trochanter.
A manual goniometer was used to measure and maintain el-
bow joint position at 1.92 rad during all elbow flexion tests.
All subjects were evaluated between the hours of 7 am
and 10 am after an overnight fast. Subjects were evaluated
one time for the following: (1) body composition by dual-
energy x-ray absorptiometry (DXA) scan; (2) maximum
voluntary isometric contraction (MVIC) of the right el-
bow flexors and right knee extensors; (3) nIEMG of the
right rectus femoris while standing from and sitting into a
chair; and (4) nIEMG of the right biceps while carrying a
weighted box and walking on a treadmill. The nIEMG was
used to objectively observe electrical activity of the muscle.
DXA
A DXA total body scan was performed on each subject
(Lunar Model DPX-L, software version 1.5g, Lunar Radia-

MUSCLE MASS, STRENGTH, AND THE ABILITY TO PERFORM
B445
Electromyography–ELGON and Computer Interface
At each collection point, the raw electromyography
(EMG) signal was recorded over a 6-second time period,
sampled at a rate of 100 Hz, and processed through a Grass
Polygraph D.C. Amplifier (Quincy, MA), integrated with a
time constant of 100 ms. The IEMG, along with the EL-
GON analog data, was stored in a Gateway 2000 4DX-66
Computer System LabVIEW program (Windows 3.1, Na-
tional Instruments, Austin, TX).
pendent t tests were used to compare mean observations be-
tween groups. Relationships among limb LTM, strength,
and age were analyzed by using Pearson product moment
correlations and first-order partial correlations. Differences
between groups for the stand–sit task were analyzed with a
two-way analysis of variance (ANOVA) with repeated mea-
sures and a two-way analysis of covariance (ANCOVA)
with repeated measures, with limb LTM and knee extensor
strength as covariates. Young–old was the fixed factor and
joint position was the repeated measure. Differences be-
tween groups for the carry task were also analyzed with re-
peated measures two-way ANOVA and two-way AN-
COVA, with lower arm mass, limb LTM, and carried
weight as covariates. Young–old was the fixed factor and
time was the repeated measure. The general linear models
procedure of SPSS (SPSS, Inc., Chicago, IL) was used with
the statistical significance determined at p ꢂ .05.
Standing Test
With arms folded across the chest, each subject stood
from and sat into a standardized chair with a seat height of
44 cm and a firm seating surface (50 cm wide). The chair
was centered side to side on a platform so that foot place-
ment was flat, 11 cm apart, and 2 cm from the front edge of
the platform. The procedure began and ended with subject
knee angle positioned at 1.4 rad to horizontal. Women un-
able to maintain a 1.4 rad knee flexion and foot contact with
the force platform had an appropriate number of boards
placed under their feet to raise them to the proper height.
Subjects were instructed when to stand and sit. Velocity was
controlled by viewing the angular joint position of the knee
as recorded on a computer monitor. Angle change upon
standing and sitting resulted in the vertical displacement of
a screen cursor, allowing the subjects to match a preset rate
of ascent and descent. IEMG data were collected over 6 sec-
onds during standing (1.92 and 2.44 rad) and sitting (2.44
and 1.92 rad). Several practice trials were administered be-
fore testing. Three tests were conducted, with the test most
closely matching the predetermined velocity used for analy-
sis. Test–retest reliability in our lab for the two trials most
closely matching the predetermined velocity was R ꢁ .87.
IEMG at 1.92 and 2.44 rad during standing and sitting was
normalized by dividing by the IEMG recorded during
MVICs at knee extension angles of 1.92 and 2.44 rad, re-
spectively.
RESULTS
Characteristics of the study population are shown in Ta-
ble 1. Weight, height, BMI, and percentage of body fat were
not significantly different between the younger and older
women; however, overall LTM was significantly higher in
the younger women (38.5 vs 35.5 kg, p ꢁ .028). Table 1
also provides regional body composition measurements of
upper leg (knee extensors), total arm and upper arm (pri-
mary location of elbow flexors), and strength measures for
the right side of the body. The older women had 15% and
14% less LTM in the legs and arms, respectively, and 23%
and 10% less strength for the knee extensors and elbow
flexors compared with the younger women (p ꢃ .05).
Significant inverse correlations (Table 2) were observed
between age and MVIC for knee extension (r ꢁ ꢄ.524, p ꢃ
.01) and elbow flexion (r ꢁ ꢄ.354, p ꢃ .05). Upper leg
LTM was significantly related to maximum knee extension
(r ꢁ .464, p ꢃ .01), whereas upper and total arm LTM were
significantly related to MVIC for elbow flexion (r ꢁ .514,
p ꢃ .01; r ꢁ .561, p ꢃ .01). After upper leg LTM was ad-
justed for, a significant inverse correlation remained be-
tween age and maximum knee extension (partial, R ꢁ
ꢄ.338, p ꢃ .05). After upper arm or total arm LTM was ad-
Weight-Loaded Walking Test
Subjects walked on a treadmill for 4 minutes at 2 miles/h
while carrying a simulated box of groceries with the right
arm. The box was filled with sand equivalent to a weight
that was 30% of the subject’s elbow flexion MVIC. A metal
harness was suspended from behind the neck to prevent
shoulder movement and to maintain position of the right
arm. Elbow flexion was maintained at 1.92 rad with the use
of a manual goniometer. IEMG data at the biceps brachii
were recorded for a 6-second time period at 00:10, 2:00, and
at 3:45 from the beginning of the test. IEMG was normal-
ized by dividing the results of the carry test by the IEMG
obtained during elbow flexion MVIC.
Lower arm mass had to be accounted for as it contributed
to the load being carried at 1.92 rad elbow flexion. Because
the younger women possessed significantly greater lower
arm mass than the older women, lower arm mass was in-
cluded as a covariate during the carry task.
Table 1. Subject Characteristics
Young
Old
Parameter
(n ꢁ 20)
(n ꢁ 21)
p Value
Demographics
Weight (kg)
Height (cm)
Body mass index (kg/m2)
% Fat mass (% total weight)
65.3 ꢅ 8.7
163.9 ꢅ 7.7
24.2 ꢅ 2.0
34.2 ꢅ 5.1
62.3 ꢅ 9.0
163.6 ꢅ 5.4
23.5 ꢅ 3.0
35.8 ꢅ 7.1
35.5 ꢅ 3.4
.279
.894
.343
.413
.028
Fat free, bone free, lean tissue (kg) 38.5 ꢅ 4.6
Regional body composition measures
Upper arm lean mass (kg)
Total arm lean mass (kg)
Lower arm mass (kg)
1.64 ꢅ 0.23
2.35 ꢅ 0.36
4.73 ꢅ 0.48
1.09 ꢅ 0.33
1.47 ꢅ 0.26
2.02 ꢅ 0.37 ꢃ.001
4.02 ꢅ 0.42 ꢃ.001
.006
Upper leg lean (kg)
0.91 ꢅ 0.15
.023
Strength measures
Elbow Flexion 1.92 radian (N)
Knee Extension 1.92 radian (N)
178 ꢅ 26.5
433 ꢅ 118.0
160 ꢅ 47.0
330 ꢅ 65.0
.026
.001
Analysis of Data
The means and standard deviations for all quantitative
data were calculated for both groups (young and old). Inde-
Note: Subject characteristics are mean ꢅ standard deviation.

B446
LANDERS ET AL.
Table 2. Correlations of Strength, Age, and LTM of the Upper Leg
and Arm
significantly different between groups. No interaction be-
tween knee joint angle and group on nIEMG was observed;
however, the group effect still remained significant (p ꢁ
.004). In the same ANCOVA model, a significant group ef-
fect remained (p ꢁ .014) when both the covariates of upper
leg LTM and knee extensor strength were included.
Max. Knee Extension
Max. Elbow Flexion
Adj. for
Upper
Adj. for Adj. for
Upper Total
Unadjusted
Leg LT
Unadjusted Arm LT Arm LT
A repeated measures ANOVA was used to evaluate dif-
ferences in nIEMG of the elbow flexors between groups
during the carry task (absolute means are presented in Table
3). Overall, the change in nIEMG across time was signifi-
cant at p ꢁ .021. The group effect was also significant (p ꢁ
.019), with the younger women averaging a higher nIEMG
value. This same repeated measures model was performed
again with the covariates of carried weight, lower arm mass,
and total arm lean tissue. No significant differences in nIEMG
were found between groups when these covariates were
added to the model (Table 3).
Age
ꢄ0.524*
0.464**
ꢄ0.338**
ꢄ0.354** ꢄ0.231 ꢄ0.154
Upper leg LT
Upper arm LT
Total arm LT
0.514*
0.561*
Notes: LT ꢁ lean tissue; LTM ꢁ LT mass.
*p ꢃ .01; **p ꢃ .05.
justed for, there was no longer a significant relationship be-
tween maximum elbow flexion and age (Table 2).
A repeated measures ANOVA was used to compare
nIEMG at knee joint angles of 1.92 and 2.44 rad in the
younger and older women during standing and sitting. The
group effect was significant at p ꢃ .01. Figure 1 repre-
sents the means of this repeated measures ANOVA. Older
women used a higher percentage of maximum IEMG than
younger women at all standing and sitting joint positions.
Overall, the nIEMG changed significantly across all subject
knee joint angles, but there was no joint angle by group in-
teraction. Repeated measures ANCOVA means (covariates
upper leg lean tissue and knee extensor strength) are shown
in Table 3. With upper leg lean tissue as a covariate, there
was no overall change in the nIEMG as a result of change in
knee angle, and the nIEMG at each joint angle remained
DISCUSSION
These cross-sectional data indicate that, compared with
younger women, older women have reduced strength and
increased difficulty in doing daily tasks. After either leg or
arm LTM was adjusted for, these differences persisted in
the legs but not in the arms. These results suggest that age-
related reductions in muscle mass are responsible for most
of the loss of function in the arms, but additional factors ap-
pear to contribute to the loss of function in the legs.
Age, Knee Extensor Strength, and Upper Leg
Lean Tissue
Several factors may contribute to the age-related decline
in knee extensor strength: poor nutrition; pain; decreased
flexibility and range of motion; or atrophy of type II muscle
fibers (12,13,16). Because the older women in this study
were healthy and free of joint pain, the most plausible ex-
planation for these results may be a disproportionate atro-
phy of type II muscle fibers. Preferential decline of type II
fiber cross-sectional area in leg muscle is a consistent find-
ing in cross-sectional studies of age, strength, and muscle
mass (17–20).
Type I muscle fibers are the primary fiber used for main-
tenance of posture and slow, low-intensity movements.
Changes in muscle fiber type that occur with aging may be
related to changes in the functional demands of muscle over
long periods of time (21). A slowing of leg movements with
age, caused by decreased activity and therefore a predomi-
nance of low-threshold tonic activation of leg muscles, may
contribute to the reinnervation of type II fibers by type I
motor neurons. Because several studies suggest that type II
muscle fibers are characteristically capable of generating
more force than type I muscle fibers of similar cross-sec-
tional area (18,22,23), a change in the size of type II muscle
fibers would decrease the strength-to-cross-sectional area
ratio.
Age-related changes in fiber architecture may also inter-
fere with the development of maximum force. Lexell and
Taylor (17) have found structural abnormalities in the fiber
size and shape in approximately one third of all fascicles of
vastus lateralis muscle in older individuals (69–74 years of
age) whereas these abnormalities were rarely seen in the
Figure 1. Two-way repeated measures analysis of variance of the
percentage of maximum knee extension IEMG (nIEMG) at mea-
sured knee angles during the stand–sit task; p ꢃ .01 represents the
overall significant difference between young and old across different
knee joint angles. Data are means ꢅ SEM.

MUSCLE MASS, STRENGTH, AND THE ABILITY TO PERFORM
B447
Table 3. nIEMG Values for Stand–Sit and Carry Tasks
Adj. for LT of
Adj. for Upper Leg LT &
Knee Extensor Strength**
Unadjusted*
the Upper Leg*
Older
Younger
Older
Younger
Older
Younger
Parameter
(n ꢁ 21)
(n ꢁ 18)
(n ꢁ 21)
(n ꢁ 18)
(n ꢁ 21)
(n ꢁ 18)
Knee Joint Angle†
Stand 1.92 radian
Stand 2.44 radian
Sit 2.44 radian
51.4 ꢅ 33
45.3 ꢅ 14
21.3 ꢅ 11
38.9 ꢅ 17
29.9 ꢅ 18
23.2 ꢅ 13
14.6 ꢅ 06
24.6 ꢅ 15
52.2
44.7
21.8
41.1
29.0
23.9
14.1
22.1
51.1
43.7
20.8
39.6
30.4
25.2
15.2
23.8
Sit 1.92 radian
Unadjusted**
Adj. for LT of the Total Arm, LAM, and Carry Weight
Older
(n ꢁ 21)
Younger
(n ꢁ 20)
Older
(n ꢁ 21)
Younger
(n ꢁ 20)
Carry Time‡
10 s
2 min
4 min
44.1 ꢅ 11
45.8 ꢅ 14
47.4 ꢅ 17
51.0 ꢅ 23
54.9 ꢅ 17
64.0 ꢅ 19
45.7
47.7
49.0
49.2
53.0
62.0
Notes: No significant interaction occurred for any repeated measures analyses; nIEMG values are expressed as percent of maximum IEMG; repeated measures
analysis of variance and analysis of covariance are means ꢅ standard deviation. IEMG ꢁ integrated electromyography; nIEMG ꢁ normalized IEMG; LT ꢁ lean tis-
sue; LAM ꢁ lower arm mass.
†The p value represents an overall significant difference between young and old across different knee joint angles.
‡The p value represents an overall significant difference between young and old across time.
*p ꢃ .01; **p ꢃ .05.
vastus lateralis of younger individuals (19–35 years of age).
The abnormalities were suggested to be the result of negli-
gible neural stimulation (24). Structural abnormalities that
occur with age and affect force production may be more
easily recognized in pennate versus fusiform muscle. Pen-
nate muscles (e.g., knee extensors) are composed of fibers
that lie at an angle to the longitudinal axis of the muscle.
This fiber arrangement allows for increased force produc-
tion. This is in contrast to fusiform muscle (e.g., biceps
brachii), in which all muscle fibers run parallel to the longi-
tudinal axis of the muscle. The result of age-related changes
in neural stimulation possibly affecting the size and shape
of muscle fibers may, therefore, have a more pronounced
effect on force production by the knee extensors compared
with elbow flexors.
and older women in this study were of similar height and
weight, so all women were moving a similar mass during
this task. Though total mass was similar, the older women
did have significantly less total LTM (p ꢃ .05) than younger
women. As expected, older women experienced greater
difficulty (increased nIEMG) during standing and sitting.
These data suggest that the initial phase of rising from a
chair requires the greatest effort from both young and old
women, but with the older group using a significantly
greater percentage of maximum muscular activity (51.4 vs
29.9). These results suggest a diminished reserve capacity
of strength in the older women and are in agreement with
previous nIEMG values obtained from similar research (2).
Alexander and colleagues (25) did not record muscle elec-
trical activity but did find that older subjects spent a greater
percentage of time in the first phase of rising from a chair
than did a younger group. Although the healthy older
women in this current study successfully completed the
task, the results from nIEMG suggest that they were stress-
ing their knee extensors to a greater extent than the younger
women.
The age-related decline in the ability to carry objects with
the arms seemed to be primarily a function of muscle size
and strength. Interestingly, similar results with the triceps
brachii muscle were seen in nIEMG data collected by
Wheeler and colleagues (2). When younger and older per-
sons spontaneously used their arms to assist their standing
from a seated position, peak nIEMG activity as well as aver-
age nIEMG activity were not statistically different between
the two groups.
Age, Elbow Flexor Strength, and Arm Lean Tissue
Age was significantly related to elbow flexor strength be-
fore but not after an adjustment for total arm LTM. This
finding suggests that the age-related decline in elbow flexor
strength was primarily a function of reduced LTM of the
arm. The extent of muscle and strength decline with age is
probably influenced by use of the muscle. Because both
sedentary younger and older women perform relatively
modest work with the arms, it is possible that the majority
of the age-related decline in physical activity of this group
occurs in the legs. Thus, as an individual ages, relative arm
activity may be maintained to a greater extent than leg ac-
tivity, leading to greater inactivity-induced type II muscle
fiber atrophy in the leg versus arm muscles.
The data recorded in this current study suggest that other
factors may influence the ability of older women to stand
from and sit into a chair (Table 3). Balance, flexibility, and
muscular endurance may contribute to the ability of older
Physical Tasks of Daily Living
The knee extensors were the primary leg muscles used in
the performance of the standardized stand–sit task. Younger

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LANDERS ET AL.
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17. Lexell J, Taylor C. Variability in muscle fibre areas in whole human
quadriceps muscle: effects of increasing age. J Anat. 1991;174:239–249.
18. Grimby G, Danneskiold-Samsoe B, Hvid K, Saltin B. Morphology and
enzymatic capacity in arm and leg muscles in 78–81 year-old men and
women. Acta Physiol Scand. 1982;115:125–134.
Conclusions
The older women in this study were not as strong as the
younger women, and they experienced greater difficulty
standing from and sitting into a chair than did the younger
group. The relative strength difference between younger
and older women was greater in the leg than in the arm de-
spite an almost identical difference in arm and leg lean tis-
sue. The difference in arm strength between groups ap-
peared to be largely due to the difference in arm LTM,
whereas the difference in upper leg strength between groups
was only partly accounted for by upper leg LTM. Though
the tasks used in this study did not test similar capacities of
leg and arm function, these results indicate that muscle
strength and perhaps function is reduced more in the legs
than in the arms of older women. Interventions designed to
reduce the age-related decline in muscle function should in-
clude whole body strengthening exercises with particular
emphasis on the legs.
Acknowledgments
This research was supported by the National Institutes of Health under
Grants R01 DK49779 and R01 DK51684 and by the Ralph L. Smith Foun-
dation.
19. Stalberg E, Borges O, Ericsson M, et al. The quadriceps femoris mus-
cle in 20–70 year-old subjects: relationship between knee extension
torque, electrophysiological parameters, and muscle fiber characteris-
tics. Muscle Nerve. 1989;12:382–389.
20. Lexell J, Taylor C, Sjostrom M. What is the cause of the ageing atro-
phy? Total number, size and proportion of different fiber types studied
in whole vastus lateralis muscle from 15- to 83-year-old men. J Neurol
Sci. 1988;84:275–294.
21. Larsson L. Morphological and functional characteristics of the ageing
skeletal muscle in man. Acta Physiol Scand. 1978;S457:4–28.
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type distribution in man. Acta Physiol Scand. 1978;103:47–51.
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age. J Nutr. 1997;127:1011S–1013S.
25. Alexander NB, Schultz AB, Warwick DN. Rising from a chair: effects
of age and functional ability on performance biomechanics. J Gerontol
Med Sci. 1991;46:M91–M98.
26. Cress ME, Buchner DM, Questad KA, Esselman PC, de Lateur BJ,
Schwartz RS. Continuous-scale physical functional performance in
healthy older adults: a validation study. Arch Phys Med Rehabil. 1996;
77:1243–1250.
We thank the graduate students who assisted with data collection; Wil-
liam Vaughn for his help with DXA analysis; Robert Petri for his expertise
with EMG data collection and analysis; and we especially thank the volun-
teers who contributed their time and energy to participating in this study.
Address correspondence to Gary R Hunter, PhD, Department of Hu-
man Studies, University of Alabama, Birmingham, AL 35294. E-mail:
ghunter@uab.edu
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Received February 15, 2001
Accepted May 17, 2001
Decision Editor: John Faulkner, PhD