Patterns of Selection of Human Movements II: Movement Limits, Mechanical Energy, and Very Slow Walking Gaits

TL;DR

This paper models the mechanical and biomechanical limits of human movement, especially walking, to understand how these limits influence gait selection and decline due to aging or disease.

Contribution

It introduces principled models for movement limits based on energy restoration and force exertion, and extends these models to very slow gaits, distinguishing them from normal walking.

Findings

Lower walking speed limits derived from energy restoration models.

Upper step length limits based on force exertion during external work.

Very slow gaits below normal walking speeds are distinct and relevant to clinical observations.

Abstract

The biomechanics of the human body allow humans a range of possible ways of executing movements to attain specific goals. This range of movement is limited by a number of mechanical, biomechanical, or cognitive constraints. Shifts in these limits result in changes available possible movements from which a subject can select and can affect which movements a subject selects. Therefore by understanding the limits on the range of movement we can come to a better understanding of declines in movement performance due to disease or aging. In this project, we look at how models for the limits on the range of movement can be derived in a principled manner from a model of the movement. Using the example of normal walking gaits, we develop a lower limit on the avg. walking speed by examining the process by which the body restores mechanical energy lost during walking, and we develop an upper limit on the avg. step length by examining the forces the body can exert doing external mechanical work, in this case, pulling a cart. Making slight changes to the model for normal walking gaits, we develop a model of very slow walking gaits with avg. walking speeds below the lower limit on normal walking gaits but that also has a lower limit on the avg. walking speed. We note that the lowest avg. walking speeds observed clinically fall into the range of very slow walking gaits so defined, and argue that forms of bipedal locomotion with still lower speeds should be considered distinct from walking gaits.