General Adaptation Syndrome explains basic stages of response to stress:
Alarm Phase-Iinitial soreness or shock from stimulus on they system, such as performing a new exercise or coming back after a long break.
Resistance Phase - Adaptation occurs and systems are returned to normal - bye bye soreness and achyness in places that you have never felt before.
Supercompensation Phase - GAinz! you have hit new heights of fitness and are not getting sore from the work that you are performing. Great work, now its time to Over reach!
Over reaching - side bar here. this isn't actually a part of the GAS system. This is when we are shredding our 400m time or 40yard dash. Hitting PRs, and getting a sub 4 min Fran.
Overtraining Phase - Damn... you have no gainz, and your soreness isn't going away, and your gainz may actually be going backwards - you pushed it to hard, or maybe overreached for too long. ie 2 hours work outs seven days a week and everyday is PR day---
The foundation of periodic training is keeping one's body in the resistance phase without ever going into the exhaustion phase. By adhering to cyclic training the body is given adequate time to recover from significant stress before more training is added. The goal in sports periodization is to reduce the stress at the point where the resistance phase ends so the body has time to recover. This way, the Overtraining phase doesn't kill your gainz. and your body can recover and remain above the original equilibrium point. The next cycle of increased stimulus then improves the response further and your equilibrium point continues to rise after each cycle.