Studies on human perception have identified pelvis and torso motion as key discriminators between male and female gaits. However, while most observers would advocate that men and women walk differently, consistent findings and explanations of sex differences in gait kinematics across modern empirical studies are rare. In the present study we evaluated sex differences in whole body gait kinematics from a large sample of subjects (55 men, 36 women) walking at self selected speeds. We analyzed the data through comparisons of discrete metrics and whole curve analyses. Results showed that in the frontal plane, women walked with greater pelvic obliquity than men, but exhibited a more stable torso and head. Women had greater transverse plane pelvis and torso rotation as well as greater arm swing. Additional sex differences were noted at the hip and ankle. These kinematic results are in line with anectdotal observations and qualitative studies. In order to understand these observations and substantiate some of the explanations previously set forth in the biomechanics literature, we also explored possible reasons for dynamic sex effects, and suggested applications that may benefit from their consideration.

Sex differences in human locomotion are of interest in a broad variety of interdisciplinary applications. Although kinematic sex differences have been studied for many years, the underlying reasons behind several noted differences, such as pelvis and torso range of motion, are still not well understood. Walking speed and body size in particular represent confounding influences that hinder our ability to determine causal factors. The purpose of this study was to investigate sex differences in whole body gait kinematics across a range of controlled, non-dimensional walking and running speeds. We hypothesized that as task demand (i.e. gait speed) increased, the influences of modifiable factors would decrease, leading to a kinematic motion pattern convergence between sexes. Motion capture data from forty-eight healthy young adults (24 M, 24 F) wearing controlled footwear was captured at three walking and three running Froude speeds. Spatiotemporal metrics, center of mass displacement, and joint/segment ranges of motion were compared between sexes using 2x6 mixed-model ANOVAs. Three dimensional time-series waveforms were also used to describe the time-varying behavior of select joint angles. When controlling for size, sex differences in spatiotemporal metrics and center of mass displacement disappeared. However, contrary to our hypothesis, sagittal plane ankle, frontal plane pelvis, and transverse plane pelvis and torso range of motion all displayed sex differences that persisted or increased with gait speed. Overall, most spatiotemporal sex differences appear to be related to size and self-selection of gait speeds, while in contrast, sex differences in joint motion may be more inherent and ubiquitous than previously thought. Discussion on potential causal factors is presented.