Arms are surprisingly important for running. The opposing effect they have on the stability of the trunk allows for efficient running. The leverage effect they have due to their maximal distance from the shoulder joint allows the potential for lots of force to be generated, even though the muscles are small in comparison to the leg muscles.
Having massive arms wont particularly help but making sure you train your upper body correctly makes a difference to the overall balance of your gait cycle.
Using arm weights and performing quick bicep curls, and tricep pull downs (not too heavy!) making sure that the arms move forwards and backwards, but not across your torso.
