Would be very surprised if it is brachialis/brachioradialis tendinitis. What are your symptoms? presumably diffuse lateral arm pain, possibly often associated with squeezing and manteling? Doesn't seem to go away despite resting, warming up well and ice/non-steroidals in abundance..?
I don't know a great deal about John O, but don't think that he's the best person for this type of thing. Hallamshire Physio (Alison McFarlane or Steve Hodgson) are both very good.My opinion on this type of pain (obviously I haven't seen it, and therefore my 'diagnosis' really means nothing), is that it is caused by mild instability at the shoulder, which causes a combination of forward or upward displacement of the humeral head with squeezing/mantling. This displacement causes impingement of various structures (depending on the position of the arm), which is why pain can be in different places.There are various reasons why this happens, and often it only happens under high loads, which is why it won't get picked up by most physios. It doesn't fit the classic impingement picture either, so again, it often gets missed.I wrote a long 'article' on this somewhere on UKB - i think if you search shoulder instability you'll find it.I find a combination of pec stretches and rotator cuff exercises with a theraband help a lot.I have to disagree with fatdoc, this is likely to be a movement dysfunction; massage type stuff may clear your symptoms, but without movement re-education, the problem will return.
I had chronic brachioradialis tendinitis, especially bad with any pinching movement, to the point where I could not lift a cup of water without intense discomfort. A long time off did nothing for me but the supplement celadrin (see www.celadrinforjoints.co.uk) and massage have sorted it out nicely. Just the golfer's to work on now!
