This 12-week Half Marathon training plan requires the use of a heart rate monitor. It was designed by Eric Orton using his proven training principles developed from 11 years of coaching experience and detailed in the book Born To Run. The 12 week plan works well for runners who have be running consistently for the last 4-6 weeks or more. Following this plan will prepare you for your Trail Half Marathon by including all of the elements used by Eric in coaching his trail runners. The workouts included in most weeks allow you to customize the plan to your capacity for weekly volume. Workout descriptions are very specific, with a focus on "quality" runs. R&R weeks every fourth week when training is greatly reduced for 4-5 days. These R&R weeks will allow for adaptation and improved performance.