The Pendulum of Specificity Part II: Fatigue

By Jordan Feigenbaum MS Anatomy and Physiology, Starting Strength Staff,  HFS, CSCS, USAW Club Coach

In part two of this series, we’re going to discus the concept of fatigue and review what we’ve learned so far (you can read the first part here). As always, we’ll start out by defining our terms so we can be sure of the actual discussion taking place. First, let’s define fatigue.

According to Webster’s, Fatigue means :

weariness or exhaustion from labor, exertion, or stress;   the temporary loss of power to respond that is induced in a sensory receptor or motor end organ by continued stimulation

While I can appreciate the second part of the definition as it pertains to training, we’re going to be using fatigue in a slightly different manner in order to fully describe the quantities we want to. Usually when discussing training, people will often start discussing volume, tonnage, and/or intensity, with varying definitions being used in different contexts. To keep things straight and narrow let’s list our terms and their definitions for the purposes of this article:

1. Volume- Classically, volume refers to sets multiplied by reps (sets x reps). So if you did 10 sets of 10 reps, your volume would be 100 reps.
2. Tonnage- Tonnage typically refers to weight x reps. So if you did 10 sets x 10 reps with 135lbs, that’s 13,500 lbs of tonnage.
3. Intensity- Intensity describes the load on the bar, i.e. how heavy (or light) it is with respect to the lifter’s ability. Percentages are often used in exercise science literature, with rate of perceived exertion (RPE) being used less common. RPE, as applied to strength training, is getting more popular- with the following breakdown being pretty well accepted:
   1. RPE 10= maximal effort, 1RM, possibly a miss
   2. RPE 9= heavy, 1 rep left “in the tank)
   3. RPE 8= moderately heavy, 2 reps left in the tank
   4. RPE 7= fast “warm up set”, 3 reps left in the tank
4. Frequency- How often either a movement pattern (e.g. squat) is trained or how often a person trains, period. For instance, a person who trains 5x/wk has a higher frequency of training than someone who trains 4x/wk. Conversely, a person training 4x/wk but who squats each session has a higher squat frequency than someone who trains 5x/wk but only squats 2x/wk.
5. Fatigue- This is a term that gets used in various permutations depending on the author. For instance, some use it to prescribe prospective volume for a given workout, i.e. the prescription might be do “5 reps @ RPE 9, then do back off sets of 5 reps with 4-6% fatigue”. What this means is that the lifter would be trying to do- at a minimum– the most back off sets of 4 reps they could until taking 4% off the bar from the top set of 5 @ RPE 9 is ALSO an RPE 9. Alternatively, this fatigue range also defines the maximum volume for a lifter, as they would not take off more than 6% of the top set’s weight. When using this definition of “fatigue”, there tends to be a limit to the minimum and maximum amounts of stress a lifter would impart upon themselves. Others will use the term fatigue to describe feeling “tired” or “run down”, which as a subjective description might be useful- it doesn’t necessarily do us much good when it comes to comparing programs to programs.

With all these terms in mind, I present to you a working definition of “fatigue”. Fatigue is the integration of volume, tonnage, intensity, frequency and overall stress on an individual for  a given amount of training. Fatigue, therefore, can be calculated for a single workout or a series of workouts (e.g. over a week or even a month). One might ask, why is this necessary? Good question.

If we do a little thought experiment, we can see that any of the initial three terms, i.e. volume, tonnage, or intensity, are wholly inadequate in isolation for adequately describing a particular training protocol. For instance, if we’re strictly looking at volume- we can imagine a scenario comparing the following:

1. Person 1
   1. Volume= 10 sets x 10 reps = 100 total reps over 3 sessions in 1 week
2. Person 2
   1. Volume= 20 sets x 5 reps = 100 total reps over 4 sessions in 1 week

In the above scenario, we can easily see that even though the volume is the same over the week, the way in which it is accumulated has the potential to be markedly different. Moreover, the implications of the altered frequency, loading, etc. all equate to a large potential for different levels of fatigue on the individual. We haven’t even discussed tonnage yet! Let’s consider the following:

1. Person 1
   1. 400lb squat x 5 sets x 5 reps = 10,000 lbs over 3 sessions per week in 25 reps
2. Person 2
   1. 500lb squat x 10 sets x 2reps= 10,000lbs over 3 sessions per week in 20 reps

In the above scenario, the frequency is the same, i.e. 3x/wk, the tonnage is the same (10,000lbs/wk), and the volume isn’t markedly different. In a 600lb squatter however, there’s likely a very real difference in the total amount of fatigue or accumulated stress that the lifter sees using either protocol. It’s reasonable to assume that the heavier of the two protocols likely induces more fatigue, but that assumption means taking into account the volume (reps x sets), tonnage (reps x weight), frequency (times/wk) intensity (% of 1RM or RPE), and frequency. In other words, because one is heavier, but with similar volume/tonnage/frequency- then we intuit that the fatigue is different. Isn’t it obvious that we need a term that includes all available variables from an exercise protocol if we’re going to compare them?

In the next part of this series, we’re going to discuss hypertrophy and in the final part, we’ll talk about strength and practical application of these concepts. For  now, let’s just chew on these two articles so everyone is on the same page 🙂

-Jordan