Periodization is one of the most effective ways to prevent overtraining syndrome- the point where physiological maladaptions can occur for months to years.  A periodized program will typically organize workouts into macrocycles, mesocycles and microcycles; 12 week, 4 week and 7 days blocks, respectively.  Within each cycle, overload is progressively increased, then decreased to allow for recovery.
- 50% Preparation
 - 25% Precompetition
 - 15% Competition
 - 10% Active rest
 
Applying this schedule to a program, this is how RPE (Ratings of Perceived Exertion) varies week-to-week.
Macrocycle (12 weeks): 5, 6, 8, 4, 6, 7, 9, 4, 7, 8, 10, 4
- Three moderate intensity weeks (preparation)
 - Three moderate to high intensity weeks (precompetition)
 - Three high duration or volume OR race speed weeks (competition)
 - Three recovery weeks (active rest)
 
Mesocycle (4 weeks): 5, 6, 8, 4
- One moderate intensity week (preparation)
 - One moderate to high intensity week (precompetition)
 - One high volume/ duration week (competition)
 - One recovery week (active rest)
 
Microcycle (7 days): 6, 7, 8, 5, 8, 9, 4
- Two easy days (active rest)
 - Two hard/ high intensity days (competition)
 - Three moderate intensity days (preparation/ precompetition)
 
Resources:
- Plowman, Sharon A., and Denise L. Smith. Exercise physiology for health, fitness, and performance. 3rd ed. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2011. Print.