Dr Cara M. Wall-Scheffler

Post-Doctoral Research Fellow

Research

Kinematics of locomotion over variable terrain

Experimental evidence has now established that longer legs produce more energetically efficient running and walking.  The fact that Australopithecines retained their relatively short legs for at least one millennia is therefore surprising, especially since population variation would likely have allowed for the selection of energetically efficient longer lower limbs.  For this reason, we are studying the possible benefits for locomotion of shorter legs, in addition to other australopithecine morphological traits such as a wider pelvis.  We are using variation among modern humans to test the relationship between anthropometrics and kinematics of locomotion over variable terrain. We are most especially interested in the excursion of the center of mass since increased excursion may lead to increased metabolic costs and has implications for the strength and development of hip-abductor muscles as well as the ability to carry loads.  Reduction of excursion can have significant evolutionary implications and might provide a reason for the retention of short legs by australopiths.

Pendular exchange of potential and kinetic energy during walking at different speeds

Walking is commonly considered to involve an energy-saving inverted pendulum system in which the body rotates over the leg during stance phase. Significant pendular exchange of energy within the swinging lower limb has also been posited.  We use a simple pendulum model of the lower limb to assess the extent of exchange between potential and kinetic energy during swing period as a function of speed. By comparing speed-related changes in energy exchange with metabolic cost of transport (COT), we can determine the importance of this potential energy-saving mechanism in determining the minimum cost of transport. We are especially interested in how a variety of anthropometric factors influence the determination of COT

Interaction between limb inertial characteristics and limb dynamics during running

It has become fairly widely appreciated that swinging the limbs back and forth during running incurs a significant metabolic cost in humans and other animals.  In part, this cost is due to overcoming the inertia of the limbs.  If limb movements are comparable, larger limb inertia should result in a higher cost of transport. In a sample of runners with particularly short or long lower limbs for their body size, we are finding evidence that limb dynamics are systematically altered to mitigate the impact of limb inertia on cost of transport.

Energetics of walking over variable terrain

The role of variable terrain is a crucial one for the evolution of walking and running strategies. Both posture while walking in addition to the level of incline may have significant impact on metabolic cost.  We are currently designing a project to investigate how posture, anthropometrics, and biomechanics interact with metabolic cost.

Ongoing Projects

Bipedalism Effects on the Energetics of Pregnancy and Lactation

With the advent of bipedalism and loss of body hair, early hominid mothers with pre-weaned infants would have been unable to remain mobile in the same manner as their ancestors; their infants would no longer be able to cling to their backs.  A childbearing female would thus have either had to carry her baby in her arms, use a tool such as a sling, or risk falling behind her tribe in the search for food or in an escape from predators.  Dating of early hominids, such as Homo erectus, indicates that long distance transport while carrying an infant would had to have occurred by 1.7 million years before the present (bp). Despite this, there is scarce evidence that infant carrying tools existed before 15,000 years bp. Modern hunter gatherers use various methods to carry their infants including slings which can be moved to different locations on the body:  front, back and side.  Nonetheless, the gap in the archaeological record leaves us without a clear understanding of when carrying or other organic tool types were possibly developed.  We therefore tested whether the energetic cost of carrying an infant in one’s arms is greater than having a tool to carry the infant.  We found that the energetic drain of carrying an infant would be such that some sort of carrying device would have to have been developed before long distance travel out of Africa was feasible. In addition, research on chimpanzees suggests the optimal walking speed of mothers might be slower than other females. We are now working to test this hypothesis in modern humans.

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