Research

The Effects of Limb Length on the Energetic Cost of Human Running

Karen Steudel-Numbers, Cara Wall-Scheffler, Marcie Myers, and Tim Weaver

We are nearing completion of a study in which we find that longer lower limbs reduce the cost of human running to an extent similar to that for human walking. Thus short limbed hominins, such as Neanderthals and, particularly, Australopithecus, would have been at a disadvantage in both walking and running.

The Effects of Body Proportions on Thermoregulation: An Experimental Assessment of Allen’s Rule

Mike Tilkens, Cara Wall-Scheffler, Tim Weaver, and Karen Steudel-Numbers

We have found that longer limbed subjects have higher resting metabolic rates, confirming the widely held expectation of Allen’s Rule, that short limbs reduce the metabolic cost of maintaining body temperature, while long limbs result in greater heat dissipation. The shorter limbs of Neandertals, despite being energetically disadvantageous while walking, would indeed have been advantageous for thermoregulation.

A Regressional Analysis of Sex Differences in the Cost of Human Walking

Mike Tilkens and Karen Steudel-Numbers

Here we reassess the question of sex differences in the energetic cost of walking using a more careful experimental design than those characteristic of previous approaches and using regression analysis for the data analysis rather than ratios. We detect no gender differences in the cost of locomotion.

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

Marcie Myers, Cara Wall-Scheffler, Paul Wardrop, and Karen Steudel-Numbers

Bipedalism effects on the energetics of pregnancy and lactation

Cara Wall-Scheffler and Kristina Geiger

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 want to test whether the energetic cost of carrying an infant in one’s arms is greater than having a tool to carry the infant.  We suspect 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 working to test this hypothesis in modern humans.

Leg length effect on lateral excursion of the pelvis

Cara Wall-Scheffler, Bryan Heiderscheit and Liz Chumanov

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 of shorter legs by testing the role of limb length on the medio-lateral motion of the pelvis. 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.

The role of methods in VO2 collection

Mike Tilkens and Anna Kelton

VO2 collection techniques vary dramatically in the primary literature, often times resulting in recorded VO2 values that may not represent steady-state aerobic respiration. In order to remedy these situations, several current projects in our lab, focusing on issues such as the duration of each collection period, number of repeat trials per subject and the time of day effect on energetic values, are designed to investigate the necessary protocol variables needed to insure the collection of aerobic VO2 values.

Effects of arm swing on the cost of human walking

Lisa Powers

My research focuses on the role of upper limbs pendular mechanics in human walking.  Previous research in the field of biomechanics has indicated that pendular mechanisms of limbs conserve energy through maximal exchange between kinetic and potential energy.  I am interested in determining if the pendular action of the free-swinging upper limbs effects locomotor efficiency.  I am currently engaged in experimental research that simulates the pendular period of various limb morphologies by adding mass at different locations along the upper limbs of human subjects. The energetic cost of the simulated morphology is measured (as volume of oxygen consumption) to determine if variation in pendular properties resulting from different morphology impacts the overall cost of walking.