Basic Concepts of Training Theory Part 2.2 : Generalized Theories Of Training - My notes of the book Science and Practice of Strength Training by Vladimir M. Zatsiorsky & William J. Kraemer.

Generalized Theories Of Training : Part 2

Today we're looking at the second model that's widely accepted as a great tool for planning training cycles. 

Two-factor theory (fitness-fatigue theory)

In contrast with the one-factor theory, the two-factor theory/fitness-fatigue theory is based upon the assumption that preparedness is not something stable, but rather varies with time.  

There are two parts of an athlete's level preparedness : parts that are slow changing, like physical fitness and parts that are fast changing, like fatigue, sudden illness, etc. 

Physical fitness isn't something that is there one moment and gone the next. It doesn't vary over several minutes, hours or days. You're either fit or you're not. 

But symptoms like fatigue, illness or stress can change your disposition towards a competition quickly. 

The two-factor theory will look at the immediate training effect after a workout as a combination of two processes :

• Gain in fitness level due to the workout itself
• Fatigue

So by looking at it in this light, an athlete's preparedness after workout should look like this :

• Preparedness increases due to fitness gain, but
• Decreases because of fatigue.

So a coach using the two-factor theory will decide if the accumulated fitness gain outweighs the fatigue when deciding if you're ready for your next training session. 

Fitness gains from 1 training session are relatively moderate in magnitude but longer lasting, while fatigue is greater in magnitude but shorter in duration. For example, fatigue may last 24 hours while positive traces of workouts last up to 72 hours.

This means that time intervals between two consecutive workouts are selected so that all negative "fatigue like symptoms" are gone but the positive fitness gains persist. 

Supercompensation model VS. Fitness-fatigue model

You may have been wondering what model is the most effective for optimal results. Well to be honest, I don't really know either. All I can point out is that the One-Factor Theory (supercompensation model) is more based upon guessing/estimating when the supercompensation period takes place, while the Two-Factor Theory (fitness-fatigue model) is more centered around looking for the optimal rest period so that fatigue doesn't bother you and physical fitness levels persist.

PS : My personal choice is the fitness-fatigue model because I like to go by feel, and to be honest I rarely have a workout session where I feel like I needed more rest. Again, do what's in your best interest. It may take some time to get to know your body as we all react different to certain training styles, sleep schedules, alcohol consumption, etc.

Thank you for reading,

- Thomas

Sources : 

Zatsiorsky, Vladimir M. & Kraemer, William J. Science and Practice of Strength Training 2nd Edition (2006)