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Normal human locomotion has been the focus of intense clinical observational analysis for several decades. Through these efforts, the basic components of the gait cycle, its phases, and subphases have been identified, defined observationally, and linked to their kinematic, kinetic, and muscle behaviors. More in-depth analysis has revealed combinations of subphases that define the operational features of gait—organized components of the gait cycle reflecting functional features that achieve important operating objectives of the locomotion system. These objectives include advancement of the body’s center of mass by means of swing phase and stance phase propulsion mechanisms, foot–floor clearance mechanisms of the swinging limb, and antigravity stability mechanisms that operate during loading of body weight and the subsequent period of single limb support. Common gait deviations have also been analyzed in terms of how they relate to the larger context of the operational features of gait, providing insight into rehabilitative strategies that can best address operational features gone awry.
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KEY CONTRIBUTORS TO HUMAN LOCOMOTION
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This chapter describes human locomotion as a sequence of repetitive bodily motions organized functionally as a gait cycle. The chapter provides working descriptions of the gait cycle, its phases and sub phases, its kinematics, kinetics, and muscle kinesiology. Major objectives of the gait cycle are delineated including advancing the body’s center of mass, controlling upright stability against gravity and clearing the foot from the floor in order to avoid stumbling and falling. The chapter goes on to develop the concept of operational features of gait, namely, clinically observable components of the gait cycle that work together to achieve major gait objectives such as translation of the center of body mass and maintaining upright stability. Based on concepts developed in the paper, the chapter ends with case scenarios of patients with gait dysfunction that will hopefully alert the reader to useful ways of analyzing and treating problems of human locomotion. In analyzing human gait, the examiner must be knowledgeable about three contributors that have key roles in locomotion: ground reaction force, joint moments, and center of mass.
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Ground Reaction Force
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A force is a push or pull on an object that results from its interaction with another object. Forces result from interactions. Some forces result from contact interactions; normal, friction, and tension forces are examples of contact forces. Other forces are the result of interactions of the action-at-a-distance type (eg, gravitation and magnetic forces). According to Newton, whenever objects A and B interact with each other, they exert forces upon each other.
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When a person stands on the floor, the body exerts a downward force on the floor (at minimum, the force of body weight). In a reciprocal manner, the floor exerts an upward force on the person’s body. Two forces result from this interaction: a force on the floor, and a force on the person’s body. These two forces are ...