Human bipedal locomotion is characterized by a habitual heel-strike (HS) plantigrade gait, yet the significance of walking foot-posture is not well understood. To date, researchers have not fully investigated the costs of non-heel-strike (NHS) walking. Therefore, we examined walking speed, walk-to-run transition speed, estimated locomotor costs (lower limb muscle volume activated during walking), impact transient (rapid increase in ground force at touchdown) and effective limb length (ELL) in subjects (n=14) who walked at self-selected speeds using HS and NHS gaits. HS walking increases ELL compared with NHS walking since the center of pressure translates anteriorly from heel touchdown to toe-off. NHS gaits led to decreased absolutewalking speeds (P=0.012) and walk-to-run transition speeds (P=0.0025), and increased estimated locomotor energy costs (P<0.0001) compared with HS gaits. These differences lost significance after using the dynamic similarity hypothesis to account for the effects of foot landing posture on ELL. Thus, reduced locomotor costs and increased maximum walking speeds in HS gaits are linked to the increased ELL compared with NHS gaits. However, HS walking significantly increases impact transient values at all speeds (P<0.0001). These trade-offs may be key to understanding the functional benefits of HS walking. Given the current debate over the locomotor mechanics of early hominins and the range of foot landing postures used by nonhuman apes, we suggest the consistent use of HS gaits provides key locomotor advantages to striding bipeds and may have appeared early in hominin evolution.

Adolescents living in the inner-city of Pretoria have their own special challenges that they must face everyday. These challenges entails a poverty context, communities of violence, difficult family circumstances and a developmental phase in which they struggle with their own identity. The focus of this research is to listen to the stories of adolescents that have not being listened to before, concerning HIV/AIDS and their experiences regarding care. These young people is infected and/or affected by HIV/AIDS. The researcher does this research in the Narrative therapeutical paradigm, listening Practical Theologically to the stories of young people infected and/or affected by HIV/AIDS regarding care. Other stories about adolescents and care will also be listened to. The research process is social-constructionally structured. The researcher is searching for a holistic understanding of care from the perspective of young people. Discourses about adolescents, about care, about the inner city and about AIDS will be discussed. Two separate groups of young people participated in the research. The researcher also listened to voices of the Sediba Hope AIDS Care Center about care and about young people. Reflection groups were used, consisting of teenagers and people from the academic community. The researcher used the method of reflection and self reflection throughout the research. Care is described after there were listened to the stories of the young people. The role of an African world-view is described as a resource to understand care holistically. The researcher spent time to reflect on the theological implications of the stories of young people and about the role they must play in the church and in the community. Different care narratives are described as an outcome of the research. Other outcomes are also named and reflected upon. / Thesis (PhD (Practical Theology))--University of Pretoria, 2006. / Practical Theology / unrestricted