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Muscular disorders: tendonitis
A tendon is a tissue that connects a bone to a muscle to transform a muscular contraction into a bone movement. In this sense, I consider it together with the muscles.
A tendonitis is simply an inflammation of the tendon. It is commonly caused by overuse, excessive friction with surrounding tissues or ageing. The picture below shows how typing with the wrist excessively bent sideways (ulnar deviation) may cause excessive friction between the tendon of the 5th finger flexor muscle and the outer bones of the wrist, causing tendonitis and subsequent pain.
A tendonitis is not a bursitis, which is described in the next page, together with the joint disorders.
Other muscular disorders
Generally speaking, muscles become painful when they are
- overused or misused, in terms of intensity or repetitiveness
- kept for prolonged periods in a shortened position, or contracted
- insufficiently inervated or vascularized.
Note that whilst muscles kept in shortened position tend to remain tight (adaptative shortening), muscles that remain in an elongated position may exhibit a stretch weakness. Both are pathological.
Therefore, uninterrupted repetitive tasks (e.g. typing without taking breaks) and prolonged static postures (which de facto keep certain muscles in a shortened position) have to be avoided. Simple measures include alternating sitting and standing postures (standing 10-15 minutes per hour), using a network printer rather than a local printer, etc.
It is common to find so-called trigger points in painful muscles, which tend to develop pain according to predictable patterns.
Nerves and vessels compressions
Internal compressions (e.g., resulting from intramuscular pressure, awkward postures or local inflammations) as well as external compressions (e.g., from resting against hard surfaces) are the most common risk factors for nerves and blood vessels in an office environment.
In order to avoid such compressions, impingements or entrapments, one should adopt postures that are close to the neutral ones (i.e. postures that minimize muscular shortening) and use padded rests (elbow, wrist).
Practical examples
- Muscle pain due to prolonged contraction: Keeping the hand on the mouse while reading an internet page keeps the shoulder in an abducted (away from the body, to the side) position, typically inducing contraction of the supraspinatus. Another example is dragging and dropping with the mouse, which overuses the wrist extensors as the first finger stays flexed so as to keep the click during mouse travel
- Compression of a nerve or a blood vessel due to muscular tension: In the neck, the scalenus anterior and medius muscles form a "gate" through which emerge the plexus brachialis (nerve branches innervating the arm) and the subclavian artery. Tension in these muscles closes the gate (and pulls the first rib upwards), leading to vessels closure (or partial closure), the effect of which can be felt along their whole length, until the hand. A main risk factor for tension in the scalene muscles is to keep the head forward (e.g., when working on screen with insufficient visual correction, or when slouching with a round low back)
- Compression of a nerve or a blood vessel due to pressure on a hard surface: Resting the elbow on the driver's door while driving with one hand creates pressure on the ulnar nerve in the elbow, which can result in tingling in the 4th and 5th digits. Similar symptoms can occur in waiters carrying trays at shoulder level on the palm of the hand: such posture stretches the ulnar nerve while elbow flexion increases the pressure on the latter
