Normalizing Lower-Extremity Strength Data for Children Without Disability Using Allometric Scaling
Abstract
Wren TA, Engsberg JR. Normalizing lower-extremity strength data for children without disability using allometric scaling.
Objectives
To evaluate existing approaches for normalizing lower-extremity strength data and to develop normalization equations using allometric scaling in children without disabilities.
Design
Cross-sectional study evaluating traditional mass normalization and allometry as methods of adjusting lower-extremity muscle torques for the influence of body mass.
Setting
Motion analysis laboratory.
Participants
Thirty-nine children without disability (age range, 4−17y).
Interventions
Not applicable.
Main Outcome Measures
Maximum torque generated during hip abduction and adduction, knee extension and flexion, and ankle dorsiflexion and plantarflexion.
Results
Linear regressions of torque/mass1.0 versus body mass and age produced slopes that differed significantly from zero (P<.001) for all muscle groups except the ankle plantarflexors versus body mass (P=.28). Regressions for torque/body mass index also produced slopes that differed significantly from zero (P<.001). Regressions of torque/(mass × height) produced slopes that differed from zero in some cases but not others. Allometric scaling exponents (exponent b) differed significantly from the theoretical value of 1.0 for all muscle groups except the ankle plantarflexors (1.32; 95% confidence interval, 0.98−1.67). Linear regressions performed using torque/massb produced slopes that did not differ significantly from zero for all muscle groups (P≥.10). Regressions performed using torque/mass1.6 for the hip and knee and torque/mass1.4 for the ankle also produced slopes that did not differ significantly from zero.
Conclusions
Traditional mass normalization does not effectively adjust for the influence of body mass. Allometric scaling performed using torque/mass1.6 for the hip and knee or torque/mass1.4 for the ankle provides more appropriate normalization.
aChildren’s Orthopaedic Center, Children’s Hospital Los Angeles, Los Angeles, CA
bDepartments of Orthopaedics, Radiology, and Biomedical Engineering, University of Southern California, Los Angeles, CA
cHuman Performance Laboratory, Barnes-Jewish Hospital, St. Louis, MO
dDepartment of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, MO.
Reprint requests to Tishya A. Wren, PhD, 4650 Sunset Blvd #69, Los Angeles, CA 90027
Supported by the National Institute for Neurological Disorders and Stroke, National Institutes of Health (grant no. R01 NS35830).
No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated.
ABSTRACT