When you tire, you'll revert to a bone-supported posture, and problems will ensue. The answer to this is to start with rather short distances and only gradually work up to longer ones. It is true that anybody in normal health can ride a bicycle for 10 miles, but someone who is not accustomed to riding with good posture will find such a ride uncomfortable. See my article on Frame Sizing for more on this. If you have pain in just one shoulder, it may be due to an asymmetry.
Some people have one arm that is longer than the other.
For these people, it may help to deliberately set the handlebars slightly askew with respect to the front wheel, turning them away from the longer arm. Thighs Cyclists who do longer rides in hot weather are at risk for painful chafing on the inner thighs. This is usually the result of an in-appropriate saddle. The best saddles for preventing chafing are traditional leather saddles . Wearing proper cycling shorts will help, but beware shorts with excessive padding, which can make it worse.