Download Muscle Stiffness As A Cause For Sarcopenia: A Pilot Study

Muscle Stiffness As A Cause For Sarcopenia: A Pilot Study
Jamie E. Hibbert, Erica A. Bell, Josh M. Leonardis, Paul DeVita, Zachary J. Domire
Department of Kinesiology, East Carolina University, Greenville, North Carolina
Introduction
Methods
Sarcopenia is the degeneration of muscle mass and strength with age.
It is a significant predictor of mortality and is associated with decreased
independence in older adults. A novel possible cause for sarcopenia is
a decreased response to mechanical stimuli caused by increased
muscle stiffness. It has been shown that older adults do not respond to
exercise as well as their young counterparts. One possible explanation
for this attenuated response is decreased mechanotransduction into the
myocytes due to stiffening of the extracellular matrix with the aging
process; thus muscle cells will experience less strain and therefore less
mechanical signaling for any given force applied. If muscle stiffness
does decrease response to exercise, it would be expected that there is
an inverse relationship between strength and muscle stiffness.
Muscle Stiffness vs. Age
Data on muscle stiffness and strength were collected for 11 healthy
women (age 70-80). Stiffness measurements were taken of the Vastus
Lateralis using the Aixplorer ultrasound elastography system
(SuperSonic Imagine, Aix-en-Provence, France). Stiffness was
determined by selecting a region of interest 50% of the distance
between the greater trochanter and lateral joint line of the knee and
calculating the mean shear modulus from this region. Strength was
measured on a HUMAC isokinetic dynamometer (CSMI Medical
Solutions, Stoughton, MA). Subjects then performed 5 repetitions of
maximal isokinetic knee extension at 60 degrees per second and
strength was calculated as the overall peak torques.
Figure 5. The Relationship between muscle stiffness and age
Elastography
Knee joint compression forces at baseline (solid), 6 months (dashed)
and 12 months (dotted). First and second maximum forces reduced 18%
and 24% (α, p<0.05) at 6 months but were unchanged at 12 months.
Conclusion
Elastography fills in information about the tissue properties of the
muscles being stretched that simple goniometry cannot. Elastography
was developed in 1991 for the purpose of detecting non-uniform areas
in tissue. Elastography uses an imaging technique to measure wave
motion through a tissue and calculate tissue material properties based
on the mechanics of wave propagation. Elastography has been
applied to study muscle in a variety of different conditions. For
example, MR elastography has been used to examine changes in
material properties of muscle associated with aging. For more
information on elastography please visit this webpage:
Figure 3. Experimental Setup.
Results
λ
Figure 1: Ultrasound elastography
uses a focused ultrasound pulse to
induce tissue deformation and
measure the resulting wave using
standard B-mode imaging. This
figure shows the propagation of
ultrasound pulse from the
transducer head into the muscle
and the propagation of the resulting
shear wave. The shear modulus of
the muscle is calculated as µ =
f2.λ2.ρ where f- frequency, λwavelength, and ρ- tissue density.
A trend exists for a moderate relationship between strength and muscle
stiffness. The lack of a relationship between strength and age is likely
explained by the small sample size and that most subjects fell within a
relatively narrow age range. Additional subjects, with particular
emphasis on subjects over 75, are currently being recruited to improve
statistical power. Future research will be focused on ways to modulate
muscle stiffness and examine the effect that has on response to
mechanical stimuli.
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Muscle Stiffness vs. Strength
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Figure 2: The colored box
above is the area receiving the
pulsed ultrasound. The color
variation within the box
indicates areas of differing
stiffness. The circle in the
middle of the box, or Q-box, is
the area that the stiffness
measurement will be taken
from. On the right side of the
screen the mean stiffness is
indicated, as well as the min
and max stiffness and the
standard deviation within the
Q-box.
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Figure 4. The Relationship between muscle stiffness and Quadriceps
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