Ergonomics deals with the whole person: the physical, perceptual, cognitive, and mental state. Each one affects the other. If you are physically less than optimum, it affects your cognitive and mental states. As well, it can affect perception, from perception of pain, through touch, through hearing, through vision.
Ergonomics also looks at the person through all the activities of daily life. What is done in one sphere affects the body just much as what is done in another. For this reason, an ergonomist doing an evaluation may ask what seem to be irrelevant questions such as: "what hobbies do you have and how often do you do them?" or "do you do the cooking at home?"
Each of these activities can compound work related stress. Our bodies are our bodies wherever we are and whatever we do. It does not differentiate wear and tear by where we are or whether its caused by work or play.
By the same token, a true version of what you do at work can probably not be gained by looking at only one aspect of the job. I have often found that when I am puzzled by a symptom or weakness it is because I don't have the full picture.
Someone presenting with lower arm, wrist, and hand pain may ask for a desk evaluation. In reviewing the desk setting, there may be some minor problems with the keyboard and mouse that can be easily corrected. Although the mousing and spacebar issues may contribute, the real problem may be a filing task involving heavy volumes, tight fitting spaces, and slippery file covers. I may not hear about the filing until I start asking questions.
By taking the time to get as full a picture as possible of the person and the job, the best solutions can generally be determined. It may involve asking the client to take a few weeks break from crocheting that blanket, or it may be suggesting a trial with different filing tools such as a file puller or file gloves (they do exist) - or all of the above.
Before injury is apparent, prevention can often be achieved by addressing only the high risk activities. Because the ergonomist doing an evaluation is often dealing with situations where symptoms already exist, many approaches may be needed. If injury exists, the stress level needs to be less than would normally be acceptable. Reducing stress to the lowest possible level allows healing to occur.
This is the purpose of suggesting decreased crocheting at home and also the idea behind use of splints. Splints support the joint and prevent movement into ranges that place stress the tendon/muscle combination. Using splints at work however, can create other problems.
All tools are designed to be used by limbs that have many pivot points. The arm for example, has the shoulder, elbow, wrist, palm, and fingers. Restricting the movement of one of these areas changes the way the others need to position themselves in order to effectively use the tool.
Suddenly the joints are not only receiving their normal stress levels, they are being stressed with new, awkward, and biomechanically disadventageous postures. Over time, this can lead to an expansion of the problem. Not only is the injured part still injured but new aches and pains begin.
If the ergonomist knows that you are using a splint and can see how you work using the splint, the added stress can be minimized. Note that it cannot be eliminated, but some techniques or adaptations may assist in control.
Ideally, the ergonomist will have the opportunity to consult with your occupational therapist and describe the particular problems you are having at work.