Author's School

Graduate School of Arts & Sciences

Author's Department/Program

Anthropology

Language

English (en)

Date of Award

1-1-2011

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

Herman Pontzer

Abstract

Habitual bipedal locomotion in hominins required major alterations in pelvic shape, particularly the recruiting of the minor gluteal muscles to act as abductors, stabilizing the pelvis during walking and running. However, significant disagreement has emerged regarding the effect of variation in pelvic breadth, in both extinct hominins and in modern humans, on hip abductor mechanics and locomotor energetics. The purpose of this dissertation was to test whether skeletal measures of pelvic width are correlated with relevant mechanical dimensions during locomotion, and how hip abductor mechanics may influence locomotor cost. Twenty-seven individuals participated in biomechanics testing, including kinematics, force plate and oxygen consumption trials. In addition, subject specific anatomical data was obtained through Magnetic Resonance Imaging. Using an inverse dynamics approach, joint moments, effective mechanical advantage, muscle force and active muscle volume of the hip abductors, hip extensors, knee extensors and ankle plantarflexors was determined. The results show that pelvic width: biacetabular) is poorly correlated with the moment arm of ground reaction force in the coronal plane during locomotion, and therefore, hip abductor mechanics are difficult to predict from skeletal measures alone. In addition, hip abductor moments are large during both walking and running and this muscle group contributes a substantial portion to total lower limb force production and active muscle volume. Additionally, the abductor muscle group accounts for approximately 10% of metabolic demand during locomotion. Comparisons of lower limb mechanics in males and females show few differences in effective mechanical advantage or mass-specific force production in the lower limb, although females tend to have slightly lower hip abductor effective mechanical advantage during most locomotor conditions. However, overall locomotor cost does not differ between the sexes. These results call into question the effectiveness of using pelvic skeletal dimensions to predict hip abductor mechanics in extinct hominins, and the assumption that a tradeoff exists between locomotion and parturition in females.

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Permanent URL: http://dx.doi.org/10.7936/K7K0728K

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