Potential risks of sitting upright on the saddle during a daily commute I ride my bike to work Monday through Friday, about forty minutes both ways.  The elevation changes a bit but not too much.  I'm not a huge fan of holding the handlebars, and I often ride with no hands for as much of the distance as I can.  I know this throws off my balance a bit (and a large bump is more likely to throw me off my bike) but beyond that should I be worried about how this affects my muscles?  E.g. could I be straining them/stretching them in the wrong way?  In general is it bad to consistently ride using that posture?
Of course, you will have less control over your bike if you don't hold the handle bars, especially if something unexpected happens (like a truck coming out of nowhere at full speed for example).

Regarding sitting upright, you are very lucky to be able to keep your back straight like that, most people have a bad posture, and are not comfortable sitting upright on bar stools for example (or any chair without something to hold your back). Being upright like that uses your lower back muscles and your core more generally, which is a very good thing. Also you will relieve potential stress in your forearms, because they are not resting on the bar (with your weight).