If you notice your toenail turned black or dark purple after a long run, it may be due to a subungual hematoma, or bleeding under the nail. This happens often after trauma or an injury, but it also happens after micro trauma or repetitive pressure/injury to the nail, such as your big toe rubbing up against the top of your running shoe several tens of thousands of times on a typical long run.  To learn more about running and toenail injuries, read here.  To make sure it is nothing more serious and to take care of that toenail before it becomes worse and leaves you in pain, make an appointment with one of our doctors.  We are all runners, and we have all been there, and we will get you back on your training plan in no time.