You can wear almost any style of shorts for most runs of 5 miles or less, but if you are running longer distances and training for a marathon, chafing becomes an important factor. Choose the wrong shorts and you may be uncomfortable at best, and distracted by painful chafing at worst. Your running shorts should add to your comfort, not add to your discomfort. I find most shorts bunch up on me when I run, so I wear fitted, cycling-style shorts. Depending on how much leg you want to show, you can find fitted shorts (or baggy shorts) with inseams ranging from 2 or 3 inches to 9 inches. Many men's shorts styles have breathable liners for extra comfort.