The development of kinematic and kinetic multisegment foot models for gait analysis

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The measurement of human musculoskeletal motion and forces using motion capture systems and mechanical models has been routinely used in research for many years. To date, most gait research has modeled the foot as a single rigid segment consisting of two rotational degrees of freedom, or as a vector with one degree of freedom. These simplistic models limit our understanding of the very complex multi-joint structure of the foot. To increase our knowledge of the mechanics of the typical and atypical foot, multisegment mechanical models of the foot have recently been developed. These models divide the foot into multiple compartments or segments allowing the relative motion between segments to be measured. To date, most multisegment foot models have been kinematic in nature. The number of segments used and the locations of reflective markers vary greatly across these models. Further differences can be found in the location and orientation of anatomical reference frames and the methods used to compute angles. This lack of standardization makes it difficult to compare across studies. A comparative study of multiple foot models would provide insight on optimal methods of defining and analyzing the mechanics of the foot. To date, few comparative studies of multiple foot models exist and a greater consistency in the methodological design of foot models is required. Only 5 studies have examined kinetic multisegment foot models. Multisegment kinetic models may provide greater insight into typical and atypical foot mechanics. These studies have been limited by small sample sizes, varying foot models, and technological limitations. For example, great controversy exists over the best way to simultaneously measure shear forces, vertical forces, and pressure during gait (i.e. force plates do not provide information on the location of the foot or the distribution of load under the foot). In contrast, pressure mats provide data on foot location, load distribution, and vertical reaction forces but do not quantify shear force in the anteroposterior or mediolateral directions). Studies that compare various means of obtaining kinetic data using force plates versus force plates and pressure mats could provide important information on the effects of the underlying assumptions of current kinetic models. As multisegment foot research is a relatively new field in biomechanics, the factors that affect foot motion are also not well understood. Very little research exists on the effects of age, walking speed, gender, and arch type on multisegment foot mechanics during gait. In addition, modeling and technological issues must be addressed in order for these models to be used extensively in research. As the foot aids in shock absorption and provides a base of support and propulsive power during walking, it is essential that researchers gain a greater understanding of the role of this complex segment. The long-term goals of this research program are to: 1) establish optimal foot mechanical models and force measurement techniques, and 2) increase our understanding of foot mechanics in typical populations. This work has four short-term objectives: 1) to examine the effects of 3 multisegment foot models on kinematic and kinetic gait measures, 2) to compare joint kinetics computed using force plates versus force/pressure mats for the 3 multisegment foot models, 3) to examine the effects of age, gender, and arch type on multisegment foot mechanics during gait, and 4) to examine the effects of walking speed on multisegment foot mechanics during gait.