If you have a few 5Ks and 10Ks under your belt, you’re probably thinking about running your first half marathon. Doubling your racing distance means building endurance by increasing your weekly mileage. Don’t be daunted by this! Try this 16-week training schedule that adds miles safely. There are cross-training, strength-training and stretching, and rest days built into the program to help prevent injury. Plus, the long runs are on Saturdays when you have time to go the distance, giving you Sundays to recover.