Changes of Direction: Forces and Moments on the Human Talus

Lautzenheiser, Steven. Changes of Direction: Forces and Moments on the Human Talus. Diss. U of Washington. 2019.

Abstract: This dissertation explores the evolution of the human foot by understand the forces that impact foot morphology. The talus is a prime first suspect to focus this endeavor because it is the only bony connection between the foot and the rest of the body. Three separate studies were designed to examine the ability to utilize palpable landmarks to locate the internal location of the talus, to determine if ground reaction forces (GRFs) are different when an individual changes direction while moving, and to examine how the position the foot is placed influences the GRFs applied to the foot. The presented results indicate that the in vivo location of the can be predicted reliably from the location of external markers of the navicular tubercle and both malleoli. Due to their close proximity to the talus, it is unsurprisingly that these three bony landmarks were predictive of the location of the joints. Nonetheless, the degree to which variation in internal position of the joints was predicted by external landmarks is encouraging for future FEA of the talus. Changing direction while walking produces higher side forces that are applied to the human foot. I was able to illustrate the GRF components required to make a turn differ from those required to move in a straight path in both braking and propulsive phases of stance. Finally, the presented results illustrate that foot placement does influence the forces applied to the foot. In both early and late stance, maximum mediolateral forces are greater in the established foot coordinate system (FCS) than the world coordinate system (WCS). The increase in side forces in the FCS averages between 150-200 N, with some individuals exhibiting increases of greater than 350 N. The direction of the force also changes. In WCS the maximum force is directed toward the centerline, while in FCS it is lateral. Since the GRF magnitude does not change, this increase in side forces is due to decreases in the other two components. In the end, this dissertation illustrated that our understanding of how the foot interacts with the ground is more complex than we typically thought as a result of the common phenomenon of changing direction.

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