The training period wherein the athlete focuses on building work capacity in the fundamental components that make up the event being trained for. Usually an early phase of a training program focused on building endurance and aerobic capacity through lower-intensity, longer-duration workouts. In the Uphill Athlete methodology, the Base Period follows the Transition Period and precedes the Sport-specific Period. Base Periods of training typically last 16-20 weeks but can be as short as 8 weeks and as long as 28 weeks or more.