Lisa Powers

Graduate Student and Teaching Assistant, Department of Zoology

 

Contact Information

Lisa Powers
Department of Zoology
University of Wisconsin – Madison
363 Birge Hall, 430 Lincoln Drive
Madison, WI 53706, U.S.A.
e-mail: lpowers2@wisc.edu

Effects of Arm Swing on the Energetic Cost of Human Walking

My research focuses on the role of the upper limbs in human walking. When early hominins made the transition from quadrupedal to bipedal locomotion, how did energetic cost constrain the evolution of upper limb morphology? Do inertial properties of the free-swinging upper limb help minimize the energetic cost of human locomotion, or are they simply “extra baggage” that must be transported?

A particular inertial property of interest is the natural pendular period (NPP). NPP is the period at which a given pendulum requires the least amount of energy to maintain its swing. For a compound pendulum such as a limb, this period is determined by the limb’s mass, center of mass and moment of inertia. Previous research in the field of locomotor biomechanics and energetics has indicated that mass distribution along the limbs of quadruped mammals results in very similar pendular periods for forelimbs and hindlimbs, despite great differences in limb length, mass, and morphology. It is hypothesized that forelimb and hindlimb NPPs converge on all quadrupeds because it is the most energy efficient arrangement. It is also known that humans swing their upper limbs in phase with lower limbs during locomotion. This suggests that hominid upper and lower limbs should retain similar NPPs in order to maximize locomotor economy, but this would require that upper limbs be especially massive at their distal ends in order to have NPPs equivalent to the much longer, more massive lower limbs.

It remains unclear whether the theoretical minimization of mechanical work from similar upper and lower limb NPPs would result in a significant reduction in locomotor cost, or if the mass of the arms alone is primarily responsible for locomotor costs associated with the upper limbs. I am currently engaged in experimental research that compares energetic cost (via measurement of volume of oxygen consumption) on human subjects with mass added to simulate various pairings of upper and lower limb NPPs to gain insight into these questions.

 

Courses Taught

Teaching Assistantships in the Department of Zoology:

Zoology 101: Introduction to Animal Biology Lecture (discussion)
Fall 2005-Spring 2006.

In this introductory zoology course, I lead students through in-depth discussion and review of the previous week’s lecture material on the topics of evolution, ecology, animal behavior, cell biology, genetics, physiology and major organ systems of animals. Topics are investigated from multiple perspectives to help beginning biology students become familiar with sometimes difficult concepts.

Zoology 102: Introduction to Animal Biology Laboratory
Fall 2005-Spring 2006.

In this hands-on introductory zoology course, I introduce students to the systematics, phylogenetics, and diversity of the animal kingdom, with emphasis placed on the relationship between animal form and function. I typically begin labs with video footage of representatives of a given phylum interacting with their natural environments, followed by dissections interspersed with discussions that encourage students to relate anatomy to ecology. Throughout the semester, students are lead through modules that introduce them to the scientific process and scientific writing, culminating in a student-designed experiment and research paper.

Zoology 430: Comparative Anatomy of Vertebrates (laboratory)
Fall 2006.

In this upper-level course, I lead students through laboratory dissection of vertebrate animals, primarily cats (Felis) and sharks (Squalus). This is a very challenging class, in which students are familiarized with the skeletal, muscular, circulatory and nervous systems at a high-level of detail.  Course Webpage

Previous Experience

Combined Bachelor’s in Biology and Anthropology – Loyola University Chicago, 2003.
Self-designed degree focusing on evolutionary processes in the fields of biology and anthropology.

Research Assistant/Intern – Mammals Division, Field Museum of Natural History, Chicago, IL – January 2003 to January 2004.
Assisted in preparation and cataloguing of incoming specimens from recent field work expeditions for installation in skin, skeleton and fluid-preserved research collections. Aided in fieldwork for small mammals biogeography research conducted in the Markagunt and Wasatch Plateaus of Utah.

 

Previous Research Projects

Phylogenetic analysis of SAMD9 – 2004.
Investigated the evolutionary history of a 4700bp gene of unknown function that has been duplicated in some mammalian species with Dr. James Thomas at Emory University’s Department of Human Genetics.

Study of ecologic factors associated with Oliveros virus prevalence in Bolomys obscurus -2004.
Performed statistical analyses to search for viral infection trends associated with geographic distribution, age, sex, and interspecific competition of rodent host populations at the Special Pathogens Branch at Centers for Disease Control and Prevention with Dr. James Mills.