DIFFERENCES IN JOINT TORQUES DURING WALKING DUE TO STANDARDIZED VS. SUBJECT-SPECIFIC SEGMENTAL INERTIAL
PARAMETERS, MAGNITUDE OF OBESITY, AND WALKING SPEED.
Ann Marie Tullock, Patrick M. Rider, John D. Willson, Zachary J. Domire, Jessica B. Van Meter, Paul DeVita
Department of Kinesiology, East Carolina University, Greenville, North Carolina
Introduction
Methods
Inverse dynamics are the standard analytical technique used to
calculate joint torques during a variety of movements including
locomotion. Inverse dynamics typically uses experimentally observed,
subject-specific body kinematics and ground reaction forces but
standardized body segment inertial parameters (BSIPs) that distribute
masses to each segment based on a single set of relative weightings for
all participants. Based on the observations that hip joint torques during
the stance phase of walking are meaningfully affected by BSIP values
(2), that obese vs. lean have altered mass distributions, and that faster
walking speeds have larger segmental accelerations, we expect that
joint torque predictions would be more accurate when based on subjectspecific BSIPs particularly in obese individuals. We hypothesize that the
magnitude of the differences between joint torques derived with
standard vs. subject-specific BSIPs will be directly related to the
magnitude of obesity and to walking speed.
20 adults (44 yrs) with BMI values between 18 and 44 kg/m2 participated
after providing written informed consent. Dual x-ray absorptiometry
(DXA) was used to define subject-specific pelvis, thigh, shank, and foot
segments along with subject-specific BSIP values. Hip and knee joint
torques were calculated using both standard (from Dempster) and
subject-specific BSIPs while walking at 1.53, 1.70, and 2.06 m/s.
Differences between maximum hip and knee extensor torques and
extensor angular impulses from the two analyses were regressed onto
BMI.
Visual 3D Locomotion
Videos
Visual 3D Locomotion Videos
Custom Segment
Masses
Dual X-Ray Absorptiometry
Dual x-ray absorptiometry (DXA) is currently considered the most
accurate method of measuring body composition. DXA is able to define
bone mineral density, lean tissue mass, and adipose tissue mass using
a lower does of radiation than the traditional MRI and greater accuracy
than anthropometric measurements. Programmed settings typically
calculate these values for trunk, arm, and leg segments. For this study,
custom segments were defined using guidelines from Browning, et al
(1). These segments allowed for the calculation of pelvis, thigh, shank,
and foot masses.
Comparison of %Body Mass between Standard Segment Masses and
Custom Segment Masses
Standard Segment Masses
(from Dempster)
Results
All results showed significant, positive, curvilinear relationships between
the differences in torques and angular impulses and BMI and the
strength of the relationships increased with walking speed (table 1). The
magnitude of the differences became substantially larger as BMI
increased, particularly at values over 30 kg/m2 at which point differences
reached 10% of the maximum hip torque values.
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
These data suggest the use of subject-specific BSIPs for obese
individuals, derived through either measurement-based techniques or
from population-based regression equations would be beneficial for
predicting lower extremity joint torques during walking.
References
Browning, R.C., Baker, E. A., Herron, J.S., Kram, R. Effects of obesity and sex on
the energetic cost and preferred speed of walking. Journal of Applied Physiology
100: 390-398, 2006.
Rao G, Amarantini D, Berton E, Favier D. Influence of body segments’ parameters
estimation models on inverse dynamics solutions during gait. Journal of
Biomechanics 39: 1531–1536, 2006.
Table 1. Coefficients of determination from regression analysis between differences in
joint torques predicted with standardized vs. subject-specific BSIPs and BMI at three
walking speeds.
Hip Angular Impulse
Customized Body Segment Parameters
Standard Body Segment
Parameters
Knee Torque