Stimulus To Fatigue Ratio

Decoding "Stimulate, Not Annihilate"

Hello, it’s me again, the Grinch Who Stole Your Favorite Exercise. Today, we’re going to further break down a key concept laid out in the post “What Makes a "Good" Exercise?”—Stimulus To Fatigue Ratio.

If you’re new to lifting, go to the gym right now, and read this post once you’ve built a decent base. If you’ve been doing this for a while, let’s expand your knowledge base so we can continue to make intelligent choices in the gym that will increase your lifting longevity and thus progress.

I wanted to skip this and write in detail about exercise selection, but this and another post will lead us to that article in the next few posts, these need to be understood before we can begin to truly evaluate exercise selection.

Not all exercises are created equally and we have to account for the total stress the body goes under, per session, per week, per training block, to ensure we are at a happy medium for stress and fatigue on the body.

Why does this matter?

Fatigue Management = Recovery Management

If we are consistently doing highly fatiguing exercises without factoring in how this is affecting our recovery, we can very easily accumulate fatigue to the point we need to take deloads more often to allow our body to reset back to baseline—this will slow down our growth.

Instead, we can intelligently and methodically design our workouts in a way we can get the most out of our stimulus in the gym and our recovery outside the gym without overwhelming our bodies.

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Stimulus:Fatigue

The stimulus-to-fatigue ratio is less a quantitative equation and more common sense with a hint of exercise science.

Essentially, it is evaluating how much stimulus an exercise provides along with how much fatigue it causes.

In most cases, we want to see as much stimulus with as little fatigue as possible, this will provide sufficient stimulus for muscle growth while allowing for maximum recovery due to the fact we don’t have much to recover from.

All lifts will cause fatigue and fatigue is relative even with “easier” exercises to a degree, but take compound lifts that work multiple muscles vs something that isolates the target muscle better.

The more load & other muscles involved will cause more fatigue across the entire body, whereas something more isolated is going to limit systemic fatigue and provide greater stimulus per isolation to the target muscle.

Where we especially have to consider this is when factoring volume and how much we are actually working a muscle on a specific lift. If we do some heavy compound lift but only isolate the muscle, say 50% vs. an exercise we can lift lighter loads but target the muscle at say 90% then the latter exercise has a much better stimulus-to-fatigue ratio.

For example, we could compare back squats to something very mild like Bulgarian split squats. The back squats require much more different muscles & much greater overall load to sufficiently work the muscle (I need 405lbs to get 10 hard reps near failure on back squat vs only 50lbs or so for 10 hard reps near failure on Bulgarian split squats).

That load from back squats is on our back and the nature of the movement is going to recruit muscles around the entire body, hence fatigue to the entire system, and while yes, the Bulgarian split squats cause systemic fatigue to a degree, it is nowhere near the systemic fatigue from a back squat.

Now, this might sound like a benefit, not a flaw, but the fact back squats use more muscles, some would think this means more overall body growth, however, they would be mislead as that is not exactly how hypertrophy works, we need more specific demands and stimulus to grow a muscle.

Hence, in this example, the Bulgarian split squats have a much better stimulus-to-fatigue ratio.

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Let’s Back Up For a Second

You get the general gist from the above, but let’s further break down some of these concepts as to leave no stone left unturned: