Like the names state single factor aka Supercompensation is based on a single factor and dual factory aka Fitness Fatigue is based on two factors.Single Factor is based on that training depletes certain biochemical substances, glycogen, etc.. Thus, an athlete's preparedness aka physical fitness, varies according to how much substances is available for use. According to the theory the body must be rested and must get nutrients that are loss through training. Then in theory your body will increase protein synthesis and store more nutrients than before.
The most important part of this theory is timing. Too short and preparedness decreases, too long it doesn't change. Usually with programs that advocate single factor, they also recommend going to failure. With the ever so popular, blast one body part a week into annihilation and rest until next week.Dual Factor is based on preparedness aka physical fitness and fatigue are separate factors. Fitness doesn't change fast; it changes very slowly over time. However, fatigue can increase/decrease very rapidly compared to fitness. A workout induces two processes first one is a gain in fitness and the second is fatigue. Fitness will increase because of training but will also decrease because of fatigue.
Fitness increase is medium in magnitude but long lasting, while fatigue is greater in magnitude but short lasting. There is a 1:3 relationship between fatigue and fitness. For instance, if fatigue lasts 24 hrs than the gain in fitness will last for 72 hrs.Single factor is most commonly used in traditional bodybuilding routines, while dual factor is favored for strength programs. Dual Factor perodization would be used for athletes in the intermediate to advanced athletic status.