Cara M. Wall-Scheffler

Gender differences in walking and running on level and inclined surfaces

BACKGROUNDnGender differences in kinematics during running have been speculated to be a contributing factor to the lower extremity injury rate disparity between men and women. Specifically, increased non-sagittal motion of the pelvis and hip has been implicated; however it is not known if this difference exists under a variety of locomotion conditions. The purpose of this study was to characterize gender differences in gait kinematics and muscle activities as a function of speed and surface incline and to determine if lower extremity anthropometrics contribute to these differences.nnnMETHODSnWhole body kinematics of 34 healthy volunteers were recorded along with electromyography of muscles on the right lower limb while each subject walked at 1.2, 1.5, and 1.8m/s and ran at 1.8, 2.7, and 3.6m/s with surface inclinations of 0%, 10%, and 15% grade. Joint angles and muscle activities were compared between genders across each speed-incline condition. Pelvis and lower extremity segment lengths were also measured and compared.nnnFINDINGSnFemales displayed greater peak hip internal rotation and adduction, as well as gluteus maximus activity for all conditions. Significant interactions (speed-gender, incline-gender) were present for the gluteus medius and vastus lateralis. Hip adduction during walking was moderately correlated to the ratio of bi-trochanteric width to leg length.nnnINTERPRETATIONnOur findings indicate females display greater non-sagittal motion. Future studies are needed to better define the relationship of these differences to injury risk.

Optimal running speed and the evolution of hominin hunting strategies.

Recent discussion of the selective pressures leading to the evolution of modern human postcranial morphology, seen as early as Homo erectus, has focused on the relative importance of walking versus running. Specifically, these conversations have centered on which gait may have been used by early Homo to acquire prey. An element of the debate is the widespread belief that quadrupeds are constrained to run at optimally efficient speeds within each gait, whereas humans are equally efficient at all running speeds. The belief in the lack of optimal running speeds in humans is based, however, on a number of early studies with experimental designs inadequate for the purpose of evaluating optimality. Here we measured the energetic cost of human running (n=9) at six different speeds for five minutes at each speed, with careful replicates and controls. We then compared the fit of linear versus curvilinear models to the data within each subject. We found that individual humans do, in fact, have speeds at which running is significantly less costly than at other speeds (i.e., an optimal running speed). In addition, we demonstrate that the use of persistence hunting methods to gain access to prey at any running speed, even the optimum, would be extremely costly energetically, more so than a persistence hunt at optimal walking speed. We argue that neither extinct nor extant hominin populations are as flexible in the chosen speeds of persistence hunting pursuits as other researchers have suggested. Variations in the efficiency of human locomotion appear to be similar to those of terrestrial quadrupeds.

Electromyography activity across gait and incline: The impact of muscular activity on human morphology

The study of human evolution depends upon a fair assessment of the ability of hominin individuals to gain access to necessary resources. We expect that the morphology of extant and extinct populations represents a successful locomotory system that allowed individuals to move across the environment gaining access to food, water, and mates while still maintaining excess energy to allocate to reproduction. Our assessment of locomotor morphology must then incorporate tests of fitness within realistic environments--environments that themselves vary in terrain and whose negotiation requires a variety of gait and speeds. This study assesses muscular activity (measured as the integrated signal from surface electromyography) of seven thigh and hip muscle groups during walking and running across a wide range of speeds and inclines to systematically assess the role that morphology can play in minimizing muscular activity and thus energy expenditure. Our data suggest that humans are better adapted to walking than running at any slope, as evidenced by small confidence intervals and even trends across speed and incline. We find that while increasing task intensity unsurprisingly increases muscular activity in the lower limb, individuals with longer limbs show significantly reduced activity during both walking and running, especially in the hip adductors, gluteus maximus, and hamstring muscles. People with a broader pelvis show significantly reduced activity in the hip adductor and hamstring muscles while walking.

Reconsidering the Effects of Respiratory Constraints on the Optimal Running Speed

INTRODUCTIONnAlthough both humans and quadrupeds frequently coordinate breathing and limb movement during running, early studies in humans focused on how increased breathing flexibility in humans allowed for relaxed or even transient coordination during locomotion. This difference was used to explain why quadrupeds had an optimal running speed whereas humans did not. Recent research, however, has clearly demonstrated that humans, like quadrupeds, have an optimal running speed. Because these findings are new, it remains unclear why this is true: whether because entrainment in humans was more important than initially predicted or because another restraint is acting. Here, we try to explain the observed minimum cost of transport (CoT) by analyzing metabolic cost with respect to entrainment and a standard set of anthropometrics.nnnMETHODSnWe measured the energetic cost of human running at five different speeds and calculated individual CoT curves for each participant (N = 9). Simultaneously, entrainment was determined by the degree to which a poststimulus histogram (breaths per 0.05-s bin after a footfall) differed from a uniform plot.nnnRESULTSnWe compared the degree of entrainment to each participants optimal running speed and found that although all of our subjects clearly entrained at some speeds, entrainment was not a function of CoT (P = 0.897). Because entrainment was also not correlated with speed (P = 0.304), it seems that bipedalism removed the respiratory constraints associated with quadrupedalism as originally suggested.nnnCONCLUSIONSnUnlike quadrupeds, for whom respiratory constraints remain implicated in the speed dependence of CoT, constraints that lead to a minimum CoT for people must involve other mechanisms of efficiency such as the storage and release of energy in the lower limbs.

Running With A Stroller: Kinematic And Energetic Changes Across Different Stroller Pushing Techniques: 770 Board #86 June 1, 2: 00 PM - 3: 30 PM.

Following the transition to parenthood, people often initiate stroller running. While the benefits of physical activity are well established, limited literature exists surrounding the potential disruption in gait and energetic cost caused by stroller running. Three commonly used stroller-pushing methods were investigated to detect potential changes in metabolic cost, speed, and stride length. Significant changes in kinematic and physiological variables were observed between stroller running and running independently. Additionally, significant differences were found between the pushing methods tested in this study.