Myalgia and myositis

Myalgia
This means simply "muscle pain". Not everyone accepts that muscles can become injured through repetitive use, and those who do not, assert that pain in muscle is either fatigue from unaccustomed work (and will go away in time with rest), or is imagined. They cannot believe that muscles can be damaged from low level activity.

Those who do believe that low-level activity can cause myalgia argue that with low-level activity carried out for prolonged periods, only certain muscle fibres are used - the load is not shared or rotated throughout the whole muscle. Another factor may be that when the muscle is contracted, intramuscular pressure rises to such an extent that normal blood flow and oxygen exchange is restricted. This can lead to pain, inflammation and scar tissue. It's important to note that this muscle activity can be for the purpose of holding a static posture as well as for movement, so holding a fixed position for long periods of time can also be a factor in muscle pain.

Myositis
Myositis is an umbrella term for a number of muscle diseases in which inflammation and degenerative changes occur. Some doctors consider mysotis to be an automimmune condition. It is not clear what causes myositis, but it a number of factors may be involved including genetic pre-disposition plus exposure to chemicals, viruses or other infectious agents.

Sometimes people with mysositis go on to develop Raynaud's Disease. Like Raynaud's, mysositis is not an RSI-type condiditon but it does have some features in common and may be one of the conditions a rheumatologist or neurologist will be looking out for during the diagnostic process.