Week 6 Readings Flashcards
Why was the arm force field (AFF) developed?
Purpose: produce an approach that can be incorporated into existing DHM software with the ability to predict female hand force capabilities for any combination of force direction, hand location and torso orientation
To predict manual arm strength for a wide range of body orientations, hand locations, and any force direction.
What is the independent joint axis static strength method?
What limitations of the Independent joint axis static strength (IJASS) method does this paper point out?
estimate the reaction moments required about three axes at the shoulder, one axis at the elbow and up to three axes at the forearm/wrist, to balance the moments caused by both the weights of arm segments and the external force applied at the hand
The required moments are then compared to population strength values, which are estimated for each joint axis with equations based on empirical strength data Typically, comparisons are made with estimated 25th percentile values, for each joint axis, to determine if 75% of the female working population is capable of producing the required joint moments
Limitations:
Strength equations are based on empirical data that are typically from outdated studies of the shoulder
Errors, from multiple strength prediction equations (up to 7 axes), can be compounded when predicting a single manual arm strength (MAS) value
Strength, produced about any axis at a particular joint, is assumed to be independent of the strength requirements about any of the other two orthogonal axes of that joint
For the shoulder and wrist joint, it assumes that the changes in strength resulting from a rotation about one axis are not affected by rotations from the other two axes
How did the AFF authors test their hypothesis?
Bayesian regularization training algorithm is a method used to train neural networks by minimizing a combination of the error on the training data and a penalty on the network’s weights
What are the advantages of the AFF method over other methods such as 3DSSPP and The shoulder tool?
Simple inputs and good generalizability
Can be used for a variety of work
Simple inputs reduce the accumulation of errors. IJASS can accumulate errors across 7 joint strength predictions
Can be readily integrated into existing software
Better validity and reliability when estimating strength capabilities of the arm during ergonomic assessments
Takes into account the rotation about one axis interacting with rotations about other 2 axes and how it affects changes in strength
What are the limitations of arm force field?
Only used female participants in empirical studies
Developed to predict capabilities of arm only, in isolation of other factors that may limit hand forces such as strength of other joints, balance, or foot friction
MAS measurements are based on with the hand oriented parallel to trunk
How were limit values determined for The Shoulder Tool?
S-N curve derived from in vitro (petri dish) tendon fatigue failure tests
How were the results validated for The Shoulder Tool?
Approximately 300 workers were evaluated for 5 separate shoulder outcomes. After adjusting for personal factors such as sex, age, BIM, and plant size, the tool demosntrated strong relationships to multiple shoulder outcomes
Which tool was used to determine postural estimates? Do you see any limitation with this approach?
The most awkward shoulder posture for a task was used for postural analysis. Used video footage to estimate angles.
Dependent on filmer taking photos completely in a sagittal or coronal view to most accurately estimate angles.
Determination of most awkward posture was based on epidemiological evidence
How did they determine the number of cycles to failure?
Data from study that did in vitro tendon fatigue failure tests
Study used 90 specimens of human EDL
What are the advantages and limitations of shoulder tool?
Advantages
- Demonstrated strong relationship to several shoulder outcomes (pain today, pain last year, records for injury data for neck and shoulder, subject outcome attribution of the current job’s relationship to injury or pain)
- Records: first time office visit
Limitations
- Does not account for all loading conditions such as arm held straight in line with shoulder (ex: push forward action when stress in the shoulder will be generated even though no moment is present OR arm held straight above shoulder where low moment is created by intense muscle contraction is taking place which can contribute to physiological and material fatigue)
- Other risk factors such as personal characteristics, speed of work, and duty/rest cycles were not considered
For the Shoulder tool study - what were the study limitations?
Study limitations
Only most difficult postures were included in analysis
Other risk factors such as personal characteristics, speed of work, and duty/rest cycles were not considered
Assumption that the higher value of cumulative damage between shoulder is responsible for higher probability of shoulder outcome
