Before discussing the Dual Factor Theory it is first necessary to describe its core component which is called the Theory of Super Compensation–also known as the Single Factor Theory. This states that after working a muscle group with intensity, your neuromuscular system passes through different stages mostly during rest periods in order to get stronger. First, you have a certain baseline fitness level. Second, you train by doing a particular resistance exercise with an above average level of intensity. Third, after the training is the recovery time. And finally, fourth, after recovering completely, your body has come back stronger than ever and you are ready to lift more weight than before.
The Analogy Used for Supercompensation (Single Factor Theory)
This process is sometimes compared with digging a hole in the ground and then filling the hole back up with more dirt than before so you have a short mound where it was once flat. Digging the hole was the training and recovery part of the process. Filling the hole back up was also part of the recovery process. The amount of dirt in that “hole” that exists at any given time during the process represents your baseline fitness. The increase of dirt to make a little mound represents your increased fitness level.
Where does that extra dirt come from? For the most part, it’s usually the result of neuromuscular adaptation. Through intense exercise, motor neurons from your spinal cord learn to synapse more efficiently with muscle fibers to render more superior contractions than before. What is a motor neuron relationship to your muscles? Motor neurons are special nerve cells that transmit movement information and attach to corresponding muscle fibers. The grouping of a motor neuron with muscle fibers is called a motor unit. The muscle fibers attached to a motor neuron can be of only one type, for instance, slow twitch or fast twitch. Motor units that make up a muscle are called a motor unit pool.
Each exercise you do involves a different combination of motor units in which their controlling motor neurons fire at different times in order to execute the exercise movement. If you train very intensively with a heavy weight, you may be placing too much of a demand on your central nervous system to recover quickly enough to repeat the performance any time soon. This is not a problem with the Theory of Super Compensation. You simply rest long enough for your body to adapt and then you perform the exercise before the applicable motor unit pools begin to atrophy. The advocates of the Theory of Super Compensation (or the Single Factor Theory) make it a practice to train hard and then rest adequately with a period of recovery between workouts before attempting personal records again and again with the same exercises.
You Eventually Hit a Wall with Single Factor Training
If only it was so simple to just train hard and then rest workout to workout. Eventually the gains stop with this type of repetitive ritual. And why do they stop? It is because the body adapts to the repetition itself and settles into its own equilibrium. You can huff and puff against the bar with all your will to get that extra rep on the same exercise you have been doing the same way for weeks if not months but to no avail; all progress has stopped. The body did what you wanted. It mastered the exercise you taught it. When the exercise was new to the nervous system, the needed motor units re-wired themselves to accept the new poundage and leverage angles but after awhile the movements became second nature, mechanical and habitual.
This problem of halted progress can be solved temporarily by rotating exercises from time to time. You can, for instance, switch the flat bench to the decline bench or the preacher curls to cable pulls and this works quite well for most. The key here is not to get too attached to any one exercise. If you stop making gains with it then switch it.
Even with exercise rotation, you may still eventually settle into the same old groove, so to speak, with different exercises for the same muscle group (motor unit pool).
What if you knew that it was okay not to rest so much between workouts? But you’ll reply, “If I don’t rest enough, I won’t get personal records. I will be overtraining and surely then all progress will stop.”
Enter Dual Factor Theory Training
According to the Dual Factor Theory of training, there are both positive and negative effects left on the body after a heavy workout. There is the negative effect of fatigue and the positive effect of fitness gain. It has been tested that the fatigue ratio of fatigue to fitness is 1:3. This means that your fitness benefit will last 3 times longer than how fatigued you are. Your fatigue level is a fast changing factor that can accumulate rather quickly. It can also dissipate relatively quickly. Your fitness level, however, takes longer to be affected and so takes longer to fade.
Another name for the Dual Factor Theory is the Fitness-Fatigue theory.
According to the fitness-fatigue ratio, it may take 3 days for your fatigue to go away but your new fitness level will last well to the ninth day. This does not mean that you have to wait until the fourth day to exercise again. You may, if you want, train again before the fatigue has gone away. This will further push your fitness level higher and higher. Instead of training a muscle group or exercise only once a week, you can now push yourself harder and train a movement twice a week. Your fatigue level will also increase but it is important to remember that fatigue dissipates relatively quickly in relation to fitness gain.
There is, of course, a catch to all this. If you are thinking there may be a possibility your strength may regress after a month or so of this training then you would be right. You may become apparently weaker if you train more often but the operative word is “apparently.” That is why along with rotating exercises when you can, you back off after a few weeks of pushing yourself. If, however your strength decreases by 10% or more then it would be wise to decrease the frequency and or volume of your training.
Basically you slam hard for a month or two during the “loading phase” and then back off for a week or two. Each lifter has to find out what works for them. Maybe you work out for a couple months and then take recovery time for a couple weeks. Older lifters may find it better to work out for 3 weeks and then take 7 to 10 days of recovery. Recovery can be either active or passive. If you are recovering for longer than a week, you may want to try some light lifting or experiment with movements you have never done before. If you are recovering for a week or less, you may not want to lift any weights. This is a good time for border line injuries to heal.
You will be Stronger after the Rest
After your recovery or “de-loading” phase, you will find that you have become a bit stronger after you resume your workouts. You’ll also see that if you appeared to regressed strength-wise during the previous training phase it was only part of the process and was temporary. In the Dual Factor Theory of training, the fatigue component of training is not treated as the hobgoblin of progress as it is in the Single Factor Theory. Fatigue as the negative component co-exists with the fitness gain or positive component for the time being in a macro cycle. You should think of the loading phase as one block of time just as you used to think of training an exercise once a week as one block of time. There are 2 additional things to know about fatigue: It is okay to train fatigued as long as you keep injury free and also keep in mind that emotional stress can add to fatigue.
One final note: Lifters new to weight training should think and train in terms of super compensation or the single factor theory. As their nervous systems and motor units become more sophisticated, they should push themselves a little more with fitness-fatigue to continue to progress with their programs. Elite athletes and long time lifters around the world are not unfamiliar with dual factor theory.