Training & Nutrition - shoulder pain

I have been getting this pain in my right shoulder, by the A.C. joint, when I ride my rode bike. I had my bike "fitted" to me a couple of summers ago, so I am hoping that fit is not an issue.

When I got back from my ride tonight, just under two hours, I felt this nagging pain in the shoulder, again, and found myself favoring it.

Once I got home I jumped on my mountain bike to see how that would feel. The upright ride of the mountian bike gave me no problems, but is not the way I would prefer to ride on city streets and bike trials.

Any suggestions?

Jon

Has this been the first time with this problem since getting your bike fitted?
Was it fitted by a "professional"?
Is this a previous injury problem?
Are you relaxing your shoulders and arms while riding?
blah, blah, blah...

I had my bike fitted last summer and felt great.
I wasn't able to ride most of this summer due to a new baby at home. Now I have been out almost everday for the last two weeks.
I ride 1 1/2 to 21/2 hours a day, plus get some time in the pool- Ymca has free daycare while you workout!
The pain only starts after the first hour is done.
The fitting was done by a professional with 15 years of fitting experience. He has written aritcles on it and used to work for "Seven Cycles" manufacturing. I am highly confident that he did a good job.
I think that I am relaxed when I ride, but am not sure if I might be spending too much time on the drops vs. the hoods- if that's possible?
I had hurt that shoulder a couple years ago while swimming. I joined a masters swim club and improved my stroke- no more problems. I can have my shoulder hurt on the ride at night, but it will feel fine in the pool the next morning, maybe even better after I get a few laps in.

A buddy of mine said that I was startign to get old an to just get used to it.;)

Jon