You probably need a bit more cushioning around your waist or arse depending in your harness. There won't be so much pressure on your arms when a gust hits.
Select to expand quoteboardsurfr said..
I got tendonitis a few years back on a winter vacation, when we got tons of wind on the first day after not sailing for a couple of months. It slowly got better over time, but stuck with me for 14 months. It finally disappeared completely when I discovered eccentric exercises - 3 days later, it was gone (details at boardsurfr.blogspot.com/search/label/tendonitis). I still use the same exercises a few times a year, when I feel that the tendon acts up a bit. It never gets to the point where it really hurts, though. I could probably keep it away completely by doing the exercises every week, but I'm too lazy. I sail only carbon booms, on average 3 sessions per week, often 80-100+ km per session.
Definitely try to find a good physiotherapist. If he does not use eccentric exercises as a key element, keep looking. I don't trust doctors at all with tendonitis. My wife had upper hamstring tendonitis, and her doctor did not diagnose it correctly at all. The usual steroid pills helped a bit, but did not make it go away. Once she figured out what it was and she found the right eccentric exercises on Youtube, it was gone within a few weeks, without any pills or surgery. In a clinical study where they compared the eccentric exercises to standard physical therapy for tennis elbow, they cut the study short because it would have been unethical to withhold the better treatment from the control group.
thanks for this tip/blog/info/product...worth giving it a crack..will order one, glad it has the correct link on the blog though..cause I googled 12" flexible rubber personal muscle relaxation tools and got.....!!! 
on a slightly more serious note, rather than carbon v Ali boom being an issue , was wondering if the slimline C booms have a higher issue of RSI complaints that more standard shape booms...?
my new Unifibre has a big fat wide end, skinny front (opposite of my Streamlined) feels weird at first, but it also means you have different grip diameters on each hand all the time,, may help RSI issues don't know.
From my understanding of this article https://www.researchgate.net/publication/9018686_Optimum_Tool_Handle_Diameter_for_a_Cylinder_Grip
A non optimal diameter for a certain hand length would require more muscle force and strain therefore make injury more likely. Ideally you want maximum grip with minimal force.
I don't think the people designing narrow diameter booms do much evidence based research, I think they just think "yeah that feels comfortable to hold onto, lets make this"
ABSTRACT from article "The ideal diameter for a tool handle for males and females has been determined using an existing biomechanical model of the hand validated in previous works. The model estimates a 33-mm optimum diameter tool handle for the general population (males and females). When the optimum diameter for a tool handle is selected, the muscles exert the minimum force needed to hold the tool and perform gripping activities. Optimal handle design reduces the force required for gripping a tool, protects the underlying joint structures, and reduces the risk of developing cumulative trauma associated with repetitive task requiring high grip forces and awkward postures. This article provides a design parameter for optimal tool diameter to aid the therapist in the selection of assistive devices, built-up handles, or for the fabrication of a tool handle."
Select to expand quoteTwisted said..
A non optimal diameter for a certain hand length would require more muscle force and strain therefore make injury more likely. Ideally you want maximum grip with minimal force.
That makes sense. I'd be careful in interpreting the results of the study, though. A lot of tool studies focus on things like exerting torque with a screw driver. In such tasks, a bigger diameter handle will give you more leverage, so the optimum diameter is larger than when just holding on. Plenty of studies give different optimum diameters depending on the task. For example, a 40 mm diameter may be optimal for "power grips", and 16 mm for "precision grips".
For windsurfing, the more relevant studies may focus on "breakaway strength", which measures just holding on. Breakaway strength can be significantly higher than grip force, mostly due to friction. I did not find any decent studies that looked at diameters similar to windsurf booms, though. So we're stuck with using what feels best (or what we have).
Select to expand quoteMainbreak said..
So did the injuries arise beforeikw777 said..
I have a chronic shoulder with rotator cuff issues. Been on carbon booms for two years and about 6000km sailed and have had zero problems.
I dont understand that you dont have problems yet you have shoulder issues, which came first boom or shoulder issues?
I have had ongoing shoulder problems for about 6 years. Rotator cuff disease and adhesive capsulitis. The condition was not related to windsurfing, but likely from too much weight training. It did improve with rest and therapy, and sometime after that I changed to carbon booms (after breaking an alloy about 2k out to sea). My observation is that the switch to carbon booms did not cause my condition to relapse or deteriorate. My conclusion is, for me, carbon booms have caused no issues.
Select to expand quotefiriebob said..
I'm not a physio a/hole but me thinks 
I've been down the golfers elbow road, not a lot of fun, bloody doc said give windsurfing away for awhile, yeh sure. Started thinking about it and realised my troubles started after a mate talked me into short harness lines, like 22" instead of the 26" I used to use. I went back to 26ers and my elbow slowly came good, I now use 30"s and haven't had trouble for years. If you already have long lines just have a giggle and say silly old bastard 
Just saying, uncle Bob
Long lines rule! 
Also, Old Guys Rule. It says so on my tee shirt!
Ok I guess it must just be a rare coincidence. Ill try some longer harness lines if no luck then I might glue some extra grip on the boom and thicken it up.
I increased the length of my harness lines by 2 inches (28 to 30) and the improvement in my tendinitis has been immediate
