Gentlemen! Your faith in my advice is both flattering and humbling. Please do remember that I am not a licensed practitioner of any sort, and if I were, I wouldn't be so bold as to diagnose something without first getting my hands on it.
In general then: this type of injury is often caused by a series of minor traumas to the soft tissue, perhaps as a result of overuse, strain, improper movement patterns or previous acute injury. In response to these insults, the area becomes inflamed and swollen with fluids (edema). If proper motion and fluid flow are not restored to the area, it becomes hypoxic (short on oxygen) and the body begins to send scar tissue forming fybroblasts in order to support the healing process.
The adjoining muscles, which optimally glide over each other begin to get "stuck" together. Now as you attempt to use muscle, its neighbor get drags along. You will need to use a greater percentage of maximum force in order to produce the same motion. You will also be creating more trauma, and hence more edema, less oxygen and more scarring.
Nerve bundles and blood vessels pass through muscles, optimally gliding through the tissue as the muscle is contracted or released. Some of the scarring that takes place as the muscle becomes more and more fibrotic, will be in those places a nerve or vessel passes through. Once that structure gets "stuck", smaller portions will be forced to stretch longer distances possibly twanging that nerve like a guitar string and/or reducing flow through the blood vessel.
Now you've got a classic case of Cumulative Trauma Disorder.
I recommend you make an appointment with an Active Release Therapist, if you are able. He or she has special training in "unsticking" soft tissue.
In the meanwhile, some questions for you Nethernik:
1. Have you had pain or injury in your neck or shoulder on the left side?
2. Have you had these splints or similar pain before?
3. Does anything make them feel better? worse?
4. Do they feel better in the morning or better at night?
5. Do you feel them during or immediately after any particular lifts?
6. Is there anything you do at work that irritates this area?
Self massage may help, as will the judicious use of anti-inflammatories. Rest is a good idea for now... you definitely don't want to do what hurts.
Give me a little more background and I'll see if I have any more specific advice for you.
Happy healing!
Kate