The shoulder is the only joint in the body that doesn't have ligaments to stabilise it.
On the plus side, this means that you can move your arm in almost any direction (known technically as circumduction); on the downside, it means that the tendons which form the end of muscles must do the job of keeping the joint in place.
I've talked before about the rotator cuff, a group of 4 muscles whose tendons surround the joint capsule at the shoulder (aka the glenohumeral joint). These tendons are fused to become a protective shell around the joint. The tendon of the bicep, as well as other muscles of the shoulder, neck and back attach very nearby.
It all means that if one muscle becomes fatigued, other muscles are close by to be recruited to help out. That in turn means that they will themselves become fatigued quite quickly - because they're not designed to do the job. In this way, it appears that sore and aching muscles can spread from the shoulder joint in one of several directions:
In the less common case of inflammation (usually of the bicep tendon, where it's been overused and rubs against the sheath that it runs in), the inflammation can seem to spread, bringing genuine pain down the arm and into the shoulder.
The good news is that if you have these sort of problems there are a set of exercises that you can do which might bring some relief, and keep the soreness at bay.
They're based on exercises devised for the Niel Asher Technique of treating Frozen Shoulder (aka adhesive capsulitis).
There are 2 versions of the same exercise, depending on how bad things are:
The aim of this exercise is to get the shoulder capsule moving. Try this one first: if you get pain stop immediately and go to the 2nd variation below (Passive shoulder swing)
Do these every day.
If the active shoulder swing above is painful, stop immediately - pain is a signal that something's wrong.
Instead you can do a very similar exercise that isn't actually using the tendon muscles (i.e. causing them to contract) but will still give them all a gentle stretch and help lubricate the joint capsule.
The stance is just the same - position yourself as above. This time, though, instead of creating circles with your arm, rock your body in a circular motion to get the arm swinging without actually using the shoulder muscles.
This can be tricky to do if your arm isn't completely relaxed & dropped down towards the floor - so concentrate on really relaxing the shoulder the arm.
Once you're sure you're relaxed get your body moving gently but not too slowly. The momentum of your body will cause your arm to swing. It might take several days of trying until you figure out how to get a circle in that arm - don't worry, just do it for a minute roughly clockwise, then roughly anti-clockwise, and within a few days it'll "click".
Of course, you may also need to seek treatment: if you think I can help, give me a call.