Model and measurement studies on stages of prosthetic gait.


Aim of the thesis

In the current thesis ’Model and measurement studies on stages of prosthetic gait - Predictions on how not to walk symmetrically with a mechanical prosthetic limb’, we use several two dimensional (2D) inverse and forward dynamics mathematical models to investigate principles of TF amputee prosthetic gait. For every aforementioned stage of gait a mathematical model is designed which allows us to conceptually analyze phenomena observed in the real world (figure 1), based on the ideas of Dym 51.

’In an elementary picture of the scientific method (see figure 1), we identify a ”real world” and a ”conceptual world”. The external world is the one we call real; here we observe various phenomena and behaviors, whether natural in origin or produced by artifacts. The conceptual world is the world of the mind - where we live when we try to understand what is going on in that real, external world. The conceptual world can be viewed as having three stages: observation, modeling, and prediction.
In the observation part of the scientific method we measure what is happening in the real world. Here we gather empirical evidence and ”facts on the ground”. Observations may be direct, as when we use our senses, or indirect, in which case some measurements are taken to indicate through some other reading that an event has taken place. For example, we often know a chemical reaction has taken place only by measuring the product of that reaction.
In this elementary view of how science is done, the modeling part is concerned with analyzing the above observations for one of (at least) three reasons. These rationales are about developing: models that describe the behavior or results observed; models that explain why that behavior and results occurred as they did; or models that allow us to predict future behaviors or results that are as yet unseen or unmeasured.
In the prediction part of the scientific method we exercise our models to tell us what will happen in a yet-to-be-conducted experiment or in an anticipated set of events in the real world. These predictions are then followed by observations that serve either to validate the model or to suggest reasons that the model is inadequate.
The last point clearly points to the looping, iterative structure apparent in figure 1. It also suggests that modeling is central to all of the conceptual phases in the elementary model of the scientific method. We build models and use them to predict events that can confirm or deny the models. In addition, we can also improve our gathering of empirical data when we use a model to obtain guidance about where to look.’

The outcome of the mathematical models are used to make predictions about certain choices in strategies that can be made when walking with a prosthesis. In the current thesis, data of TF amputees and AB subjects using a kneewalker prosthetic device 52 are used to validate the models, which are all checked for (internal) consistency, conservation of energy and unrealistic values 51. The four stages that were studied are described in separate chapters in this thesis.
The outcomes and insights gained from these studies are used to predict how TF amputees can compensate for the limitations in the active control of the CoP position during gait initiation and termination, and the absence of active knee extension control during weight bearing on the prosthetic limb. Also, these findings are used to predict which strategies contribute to successful weight bearing and prosthetic limb forward swing during obstacle avoidance. They provide insights into what should be taken into account during obstacle avoidance. These models can be of interest when forming new ideas about how to improve prosthetic limbs and how to improve rehabilitation programs.


Figure 1: An elementary depiction of the scientific method that shows how our conceptual models of the world are related to observations made within that real world 53 (original figure from Dym, 2004).
A: Phenomena and observations, described in the thesis of dr. A.H. Vrieling (2009).
B: Observations, models and predictions, described in the current thesis.
C: Predictions verified in the real world.


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