Automotive

With the ageing population, ingress/egress becomes an increasingly important topic. This egress model demonstrates how the position of an assistive handle on the window frame influences the knee joint forces as well as the muscular effort of egress. For an elderly individual with arthritic knees, this can be of tremendous importance to the usability of the vehicle.

The idea behind the study is that placement of a handle on the window frame might allow car drivers to divide the load of egress between the legs and the arms, thus reducing the maximum load on any of the elements. In such a situation, the AnyBody Modeling System™ automatically recruits muscles such that the effort is distributed between the body parts and indeed between the individual muscles to share the load between the elements according to their individual strengths.

The parameter study investigates four different positions of the handle as indicated on the figure. The distance between the positions is 0.1 m. The graphs show the muscular effort, and the right knee joint forces over the movement for all the handle positions. Notice that in particular the low handle position causes a sharp increase of the knee joint force roughly in the middle of the movement and also causes the highest muscular effort. In terms of effort as well as knee joint force, a high position of the handle is preferable.

Design problem

What is a good pedal? In some sense it should provide effortless and yet precise operation. This model example demonstrates how the pedal stiffness and the distance between the seat and the pedal influences the muscle effort of operating the pedal.

Consider a pedal hinged at one end and equipped with a torsional spring that stretches when the pedal is depressed. The dilemma is the following: If the spring is too weak, then the pedal will not provide much support for the leg, and the operator consequently has to extend the leg and hold it up against gravity. This will become very tiring. On the other hand, if the spring is too rigid, then the muscular effort of depressing it will become too large and repetitive operation of the pedal or statically maintaining a particular pedal position will cause fatigue. Similarly, different seat positions influence the muscular effort.

Even a simple model problem like this is much too complicated to be thoroughly investigated by experimental methods. With musculoskeletal modeling it is possible to perform a systematic variation of the model's parameters and obtain a complete overview of the problem.

Solution

It is possible to execute the AnyBody Modeling System™ in batch mode and thereby create a systematic loop of analyses for each parameter combination. For each analysis, the system stores the maximum effort of any muscle at any point of the movement of the pedal. In this example, Matlab was used to control the process and plot the graph, but any other pertinent software such as Excel or a simple home-made C or Basic program could also be used.

Notice that the surface reveals that a spring stiffness around 20 Nm/rad will result in a comfortable pedal operation with little influence from the seat position.