The Fatigue/Tension Principle

Factors to Optimize

  • Number of exercises
  • Exercise selection
  • Exercise sequence
  • Rest length between exercises

  • Number of sets
  • Rest length between sets
  • Number of reps
  • Rep speed

Operative Principles

  • Athlete's experience
  • Functional strength/Isolation Exercises
  • Interdependency Principles
  • Fatigue/Tension Principle
  • Athlete's experience
  • Fatigue/Tension Principle

  • Fatigue/Tension Principle
  • Fatigue/Tension Principle



" Researchers have spent a lot of time trying To figure out what makes muscles grow. They've understood pieces of the puzzle for some time-the idea of overloading, for example. We all know forcing ourselves to more than we think we can lift is essential growth.

We also know timing is important. All three the following limit growth: doing individual rep's too slowly within a set; resting too long between sets; not resting long enough between workouts

These two principles-overload and timing-have produced the well-known formula for muscle growth/strength increase:

  • Do three to five sets
  • Use a weight with which you can only do six to eight reps
  • Work at a moderate pace
  • Work a body part no more than three times per week.

Now we introduce a new wrinkle. Recent research has shown that timing and overload are not independent of one another. It's not a question of just finding the best timing or just determining the optimal overload. These two are inextricably intertwined. For a particular overload, there is a maximum allowable amount of rest. For a particular amount of rest, there is a minimum overload necessary for maximum growth.

If, for example, you lift 80% of your max weight, you must rest no more than 30 seconds between sets to sustain maximum growth. If, on the other hand, you use 95% of your max, you can rest about one minute and still sustain maximum growth.**

Timing and Overload act together. One determines the other.

**Numbers listed are for the intermediate bodybuilder - 1 to 2 years' training. These numbers change depending on the lifter's experience.

Overload creates a particular tension level in a muscle. The greater the weight you lift, the greater the tension level:

Greater overload (more weight) » Higher tension level

The speed with which you perform your reps and the time between sets creates a particular muscular fatigue level. The faster you work, and the less time between sets, the higher the level of fatigue:

Greater rep speed,
Shorter rests
between sets

» Higher fatigue level

In combination, these two factors determine your fatigue/Tension Level. This is a way of expressing that it is the combined effect that reflects how "hard" you have worked. We can say ...

fatigue plus tension » Amount of work done

Increase the fatigue level (faster reps, less time between sets), and it takes less tension (less weight) to achieve the same Fatigue/ Tension level. Decrease fatigue (slower reps, more time between sets), and it takes more tension (more weight) to achieve the same Fatigue/Tension level.

Now for the interesting part. It turns out muscle growth depends not only on overloading, not only on timing, but on surpassing a particular fatigue/Tension level called the fatigue/Tension Threshold. Unless your exercise scheme (overload plus timing) bumps you over this threshold ... no growth!

This has some interesting implications for structuring an optimal workout. It means overall workout speed is important, as well as length of rest between sets and speed of reps within sets!


You see, the fatigue level of any muscle is constantly changing. Before you start a set, the muscle's fatigue level is low; during the set, it rises; as soon as you finish, it begins to drop as the muscle recovers from the effort. In fact, if you rest long enough, the muscle's fatigue level will drop back to the level from which it began

Fig_3-1.gif - 1503 Bytes
Fig. 3-1 Fatigue level during 1 set

A series of sets, with long rests in between, has a fatigue curve that looks like this:

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Fig. 3-2 Fatigue level during 3 sets: Long rests

Notice that as a result of letting the muscle's fatigue level drop so low in between sets, it doesn't get more tired during the second set than during the first, or more tired during the third than during the first.


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