Upper arm and shoulder aches

Not pushing myself too hard, just riding 5-10 miles every couple of days. Why are my shoulders and upper arms so achy? Is it because as I ride my arms are constantly pulling on the handlebars? Or is it just the vibrations from the road?

 

Typically such pain from bike rides is either the result of riding with your arms straight (without a slight bend at the elbow) and not relaxed or having too much weight on your arms. It'd help to see you on your bike.

 

Now that you mention it I do tend to lean back and keep my arms rigid. I will make an effort to lean forward a little and bend my elbows a bit.