Stimulus To Fatigue Ratio: How To Individualize Exercise Selection For Better Results

The single biggest piece 95% of you intermediate and beyond trainees struggling to achieve the results you'd expect (or any at all) are missing?  

An understanding of how to apply the concept of stimulus to fatigue ratio (SFR) to you training.

Understanding SFR allows you to get the most aesthetic/hypertrophy gains out of every set, rep, and unit time invested in the gym. 

Even better, applying SFR allows you to tailor your training to the movements that are most effective for you as an individual… no more force-feeding movements that leave you feeling beat up and little else for months. 

So if you’re ready to unlock quicker gains, better fatigue management, less pain, and put an end to your training frustration... let’s dive in.

The last thing I need to say here - all credit for these concepts is due Mike Israetel and the team over at Renaissance Periodization

Their recent book THE SCIENTIFIC PRINCIPLES OF HYPERTROPHY TRAINING does these concepts much better justice than I can. If you’re truly invested in getting the best possible results, I can’t recommend enough you check out their book here.

Understanding stimulus to fatigue ratio

Some movements just inherently “feel better” to you than others, and you probably can’t explain why. 

Let’s say you love Romanian Deadlifts (RDLs) - you feel like your glutes & hamstrings are smoked after performing 2-3 sets, you have a good amount of soreness in said muscles the next few days (a.k.a soreness is present, but far from crippling), and have seen good glute/hamstring gains since substituting the movement in for conventional deadlifts. 

You also notice that while 2-3 sets of conventional deadlifts left you feel absolutely exhausted, your RDLs don’t seem to be nearly as fatiguing, and you can get more out of your subsequent training because of this.  

This is an example of a movement that currently has a good stimulus to fatigue ratio for you. 

Not only do your RDLs seem to be stimulating more muscle growth than your conventional deadlifts did, but you’re also generating less fatigue - so you’re able to be more effective with your training across the rest of the training day, week, and mesocycle. 

Now, let’s say that your friend/training partner hates RDLs.  

While you feel a massive amount of tension and stretch in your hamstrings with each rep, they just feel their lower back. On top of that, they’re absolutely exhausted after 3 sets of RDLs (despite likely not feeling any “disruption” in their glutes and hamstrings), which carries over negatively to the rest of their training day, week, and mesocycle. 

This is an example of someone who the RDL has a poor SFR for. 

After determining that this is not simply an execution error (which is common, and exactly why form videos are such a key component of our online coaching service to help clients master execution), your friend would see better gains from plugging in a different hip hinge variation with a better SFR.

Measuring stimulus to fatigue ratio

Upon reading the above, you’re probably already realizing a few movements that you’ve been plugging away at for months that don’t really seem to do much for you by way of “feeling” like you’ve actually fatigued the target muscle to create new growth… but also leave you feeling absolutely exhausted.  

So the question is, how do we determine which movements have a good SFR, and which movements I should swap out?

The graphic above illustrates the components of both stimulus and fatigue that we're taking into consideration. At the end of the day, we're looking for the movements that have the best ratio of stimulus to fatigue.

components of stimulus

→ Mind-Muscle Connection: Can you “feel” the target muscles working throughout the movement?  

In my experience, this is one area people tend to overthink. It’s all too easy to fall into the trap of…

“I don’t feel a good mind-muscle connection… I need to go slower/light/think harder about the movement!” 

...and while control, focus, and intention are important, you also need to realize that developing a good mind-muscle connection is rarely a product of “thinking harder”.

Most often, the lack of a mind-muscle connection during a movement is a result of poor execution of said movement. Either... 

- You’re not taking the movement through a full range of motion (ROM)

- ROM is getting shorter as the set goes on 

- You’re not controlling the negative component of the movement for 2-4 seconds 

- You’re not pushing yourself to be more explosive through the actual “lifting” portion of the movement 

- You’re not pushing the movement to your Reps In Reserve (RIR) target

- You’re in your first set of said movement (where mind-muscle connection is usually lower) 

- You’re focusing too hard on breathing/bracing, and your cardio system is becoming the limiting factor before the actual muscle 

- Your technique is inadequate to apply tension to the target muscles

...or any combination of the above. 

In a nutshell, the mind-muscle connection is a byproduct of proper execution of a movement (and this is where the lack of a mind-muscle connection usually stems from), and not necessarily the result of “thinking harder”

Also, be aware that the more joints and muscle groups involved (the more compound the movement, we could say), the less you should just feel a single muscle working in isolation (e.g. it’s OK if you’re feeling ALL of your lower body during squats, as long as the target muscle - probably quads - is the rate limiter.)

All that said, at the end of the set you should feel like the target muscle “did the work”, and definitely experienced a lot of tension from the load you lifted.

Probably the most common pitfall for lifters struggling with the mind-muscle connection, is selecting movements where the target muscle isn’t the rate limiter (the thing that forces you to stop the movement). For example: 

- With a Zercher squat, you quads probably won't be the rate limiter. Your core & arms will be.

- With a Farmer’s Carry (done without straps) your core won’t be the rate limiter, your grip will be.

- For most rowing movements, it’s a good idea to use some type of straps or Versa Grips to keep your back muscle the rate limiter when the goal is hypertrophy/aesthetics.

The most common “rate limiters” to look out for:

- Grip 

- Core strength

- Unstable exercises

- Cardiovascular fatigue 

→ Pump: Blood & fluid traveling to your muscles as a result of repeated, intense contractions, resulting in a muscle that’s engorged with blood and feels “pumped”.  

You’ve probably experienced the pump after a few sets of bicep curls of hip thrusts where a strong mind-muscle connection/lots of tension & burn was present, and afterwards, the muscle felt much more “full” than normal.  

Now, similar to the mind-muscle connection, it would be wise not to focus solely on the pump as a proxy for a good/bad exercise. 

The pump does seemingly have some benefits to muscle growth - but if you were training strictly for great pumps, you’d likely spend your training time exclusively doing high rep isolation work.  

We know that focusing on progressing mechanical tension (lifting heavier loads over time) with variations of squat/hinge/lunge/push/pull is going to be the quickest way to build muscle. 

So similar to the mind-muscle connection, your training shouldn’t be focused on/designed for solely achieving a great pump. But rather, a good pump in the target muscle(s) usually comes as a byproduct of proper execution, and the target muscles experiencing lots of tension. 

A good (or great) pump by the end of a few work sets of a movement is a good sign that you’re ticking the boxes needed to stimulate growth.

→ Disruption: Likely the most foreign term to you here. 

Basically, “disruption” refers to how disrupted a specific muscle tissue feels post-training… both immediately and over the next few days. 

Disruption could be experienced as: 

- Tightness in the target muscle(s) 

- Stiffness in the target muscle(s) 

- Soreness (both close after the session and/or over the next few days)

Similar to the other proxies (pump and mind-muscle connection), while you’re not directly “training to get sore”... you should generally be able to tell that you trained a muscle after your session - it should feel “disrupted”.

KEY:

- If you’re never sore (especially in lagging muscle groups), never feel fatigued, and don’t seem to be building said muscles - it’s a good sign that something is off in your execution or effort with the corresponding movements. 

- If you’re never sore (especially in lagging muscle groups), feel extremely fatigued, and don’t seem to be building said muscles - it’s a good sign you need to find movements with a better SFR.

On the other hand, we all have “strong” muscle groups that we have no trouble developing a mind-muscle connection or pump with. These muscles still seem to grow, and can definitely “feel” the tension/disruption during a training session, but will rarely be noticeably sore over the next few days unless you hit them with a lot of training volume (hard sets) or novel exercises. 

For “strong point” muscles like these, the lack of noticeable disruption in the days after a session is much less to worry about than for weak point muscles.  

So in simplest terms, you should usually be able to tell by the way a muscle feels… 

 “Oh yep, trained that today.” 

It doesn’t need to be excessive soreness, but the “disrupted” sensation should be present.

components of fatigue

The Yang to Stimuli’s Yen.  

If we didn’t have to worry about managing fatigue, and only needed to focus on the stimulus, we could basically just do whatever movements “felt best” for endless sets until we all had the physiques we wanted.

Unfortunately, this isn't the case... fatigue/fatigue management is a critical part of exercise selection you must understand in order to get the results you want. 

This is because we know that once you’ve hit a threshold level of effort and execution, volume (a.k.a number of hard sets - usually thought of in a weekly context, per muscle group) is going to be the main driver of muscle growth.  

Fatigue management is crazy important for achieving the physique you want from both ends of the spectrum:

- STIMULUS: It doesn’t matter how much deadlifts stimulate your back, hamstrings, and glutes… if your posterior training is basically a no go for the rest of the week because you’re so fatigued post-deadlift… you probably won’t be able to rack up enough volume to actually grow your posterior. 

- FATIGUE: Actually building new muscle from all of the volume you just hit requires first recovering from the stimulus you created with your training. It doesn’t matter if stimulus is super high… if the amount of fatigue created alongside it is too much to recover from, you’ll fail to grow.

Makes sense, right? 

Cool, let’s dive into the components of fatigue. 

→ Stress On Joints & Connective Tissue: Let’s say that as of late, doing a neutral grip pull-up is causing you a lot of elbow pain. 

Whereas you used to feel a great pump, mind-muscle connection, and disruption from the movement… now you really just notice that your elbow is hurting.

Joint pain is the “rate limiter” here. Again, once you’ve cleared up any concern of a potential error in execution, it’s probably a good idea to sub a different movement in.  

The thing to realize here is - all movements will stress your joints and connective tissue to an extent, but:

1. If during or after the movement you’re experiencing a large amount of pain in said joints/connective tissues, pain is (or will soon be) the rate limiter for the movement. 

You’re better off finding a pain-free sub (again, assuming your execution of said movement is on point). 

2. If you feel a bit of joint discomfort, it might be worth playing around with grip position/width, foot position/width, etc., as oftentimes you’ll be able to find a position that feels great for you as an individual, with good stimulus and no joint pain.

With things like positioning of hands/feet, try to avoid any dogma about where things “should” be (this is of course different than saying to ignore biomechanics), and feel free to play with things and find the position that feels best for you. 

→ Perceived Effort: Basically, how hard a set feels. 

This can be actual physical exhaustion, the amount you have to “ramp yourself up” mentally to do a set (which also has a physical toll), or a combination of both.  

I like to use the personal example of Bulgarian Split Squats (BSS) here. 

There was a nearly year long period of time where I was progressing my Bulgarian Split Squats. 

They were a movement that I enjoyed (as much as one can enjoy the BSS), and provided a great stimulus for my quads and glutes without a huge amount of fatigue. 

Over time though, I noticed the movement was getting MUCH harder as I got to the point of being able to use 90lb+ DBs in each hand for 10+ reps (partially due to the fact that the split squat has a shorter range of motion - in retrospect, doing a deficit variation with a lighter load would’ve made more sense)

By the last few months, the BSS turned into a weekly mental battle for me... 

I would hype myself up all day on Thursdays to go do my split squats, and felt like it was something I had to do to prove to myself that I wasn’t “soft” mentally.  

If I quit, those damn split squats (a.k.a. the darkside a.k.a all that is evil) had won. 

Eventually it got to the point where BSS were giving me a massive exertion headache, and I was absolutely exhausted after just a few sets. From both a mental and physical perspective, the toll was large.  

Now, I believe to my core that proving to yourself you can do hard things consistently is important. 

In the case of the BSS, I was still getting a good stimulus... but I was also unable to train nearly as effectively the rest of my session, and was racking up a huge amount of fatigue.

I (not surprisingly) started to see much quicker progress when I swapped out the BSS for a different movement. 

So again, it’s important to understand that effective training will feel hard, and the ability to push yourself is important. If you’re looking to build your best physique and avoid any challenging training, good luck. 

But, it’s also important to ask… 

“Could I be getting as good of/a better stimulus with less fatigue using a different movement here?” 

Conventional deadlifts are another movement that have come up a lot in this blog as one that doesn’t have a great SFR for most people with aesthetic goals. This is because if we look at our criteria we use with online clients for exercise selection:

The conventional deadlift doesn’t meet many of the criteria we’re looking for here for good movements for building muscle. But it also happens to be one of the single most fatiguing movements you can do in the gym. 

As always, context is important here. There are many other variations of the deadlift (we’re very fond of Romanian Deadlifts, Trap Bar Deadlifts, and Stiff Leg Deadlifts), and many of our clients with strength or powerbuilding focused goals still training the conventional deadlift. 

But everything in this blog is through the lens of what 90% of our clients are chasing - primarily aesthetic-based goals.

→ Non-Target Muscle/Joint Stress - Are other muscles heavily (or even moderately) taxed when training a movement? Some non-target muscles will inevitably be fatigued a bit no matter what movement you’re training. 

This is not necessarily a bad thing. 

One of the main benefits of focusing on big compound lifts is exactly that - they allow you to effectively train a large amount of muscle(s) at once, and make your training much more efficient.   

But, if doing Barbell Bent Over Rows fatigues your low back so much that low back fatigue is the limiting factor when you train lower body two days later, you’re likely better off subbing in a chest-supported row variation (or at least one that involves less spinal loading). 

This is the crux of looking at non-target muscle stress. 

It’s less about looking at how said “unused” muscles are impacting the current movement you’re training, and more about how they’ll impact your ability to train effectively the rest of the week and mesocycle. 

In general, it’s important to understand that movements that put a lot of stress on the spine especially are going to create a higher fatigue cost, which is why the advice of… 

“Just do lots of heavy squats, deadlifts, and barbell pushes/pulls” 

…doesn’t pan out for most. 

Generally, it’s a good idea to limit the amount of movements that involve a significant amount of spinal loading (e.g. most... deadlift variations, barbell squat variations, standing press and row variations) to 1-2 per session. 

While these are often the most stimulative movements, they’re also the ones that’ll rack up fatigue the quickest.

how to achieve the best stimulus to fatigue ratio

To wrap this up, a few pieces of advice that we implement with our online clients to help them get the best SFR (and thus, results) from their training:

1. Use a full range of motion (relative to the joint the muscles you’re training are acting on).

This will often require you to use a lighter load, which - while a hit to your ego - will both reduce the fatigue cost (lighter weight = less stress on joints and nervous system) and increase the stimulus (a more full range of motion = more stimulus with each rep) simultaneously. 

The two muscle groups range of motion is most criminally cut short on: - Any squatting pattern. If your goal is to stimulate a building effect with your squats, you’re better served to drop the load and achieve a full degree of knee flexion.  

- Any pulling pattern (rows, pull-ups, etc.). Allow your shoulder blades to roll up or forward at the end of the “negative” portion of these patterns. Pull the bar/DB/yourself to a consistent point at the top/end of every rep, rather than stopping shorter & shorter as the set goes on.

2. Make movements more stable.

Because unstable movements are an easy way to wrack up a lot of fatigue/expend a lot of effort, with little direct stimulus to the target muscle. 

For example:

- If you struggle with balance on your Bulgarian Split Squats, add hand support (like this).  

- Probably don’t do handstand push-ups to try to build your delts (range of motion is cut short here as well)

- I don’t think I need to explain Bosu Ball Squats.

3. Use a decent amount of chest supported and seated movements.

These will reduce axial loading a.k.a. load/stress on your spine, and as a whole, keep fatigue lower. It’s about finding a balancing of the few movements with significant axial loading the provide a great stimulus for you, and the reducing axial loading the rest of the time.

4. Potentially quit bracing so hard. 

A tip I recently picked up from Steve Hall of Revive Stronger - many of us have learned to focus hard on bracing our core, to keep our backs safe while lifting. 

And while proper bracing is helpful (especially in the context of a heavy deadlift or squat), it’s often overdone, even in the context of a higher rep set of Back Squats of Romanian Deadlifts. 

A full stop + massive valsalva maneuver breath at the top of every rep is VERY fatiguing.  

Now, I’m not necessarily recommending you implement this (it’s up to you to weigh the risk vs. reward with your own training/injury history), but we’ve personally found that often times focusing on bracing/breathing so much actually creates a LOT more fatigue than is needed.

5. Use “lifting tools”.

These can be seen as ways to prevent other muscles from becoming the rate limiter, so that the fatigue you’re racking up is at least coming with a very good stimulus for the desired muscle(s). Things like... 

- A lifting belt. Very optional, but useful to reduce stress on the low back during movements that can create a lot of axial loading. I personally like/use this belt.

- Wrist straps/Versa Gripps. If anything here is a “must have”, these are it. If your grip is giving out on pulling movements, Romanian Deadlifts, etc. before the target muscle (hint: it probably is), you’re racking up a lot of fatigue for very little stimulus. These help make the target muscle the rate limiter. Highly recommend checking out Versa Gripps. 

- Olympic Lifting Shoes. Another very optional one. If you have trouble hitting a squat depth that allows for a lot of knee bend without also putting excess stress on your low back, these can help.Or you can simply elevate your heels. 

And that’s how to apply the concept of stimulus to fatigue ratio, and get the most out of every rep, set, and training day. 

Again, I can’t give enough credit to Renaissance Periodization for these concepts. I highly recommend you check out their related YouTube Series and Hypertrophy Book to gain a much better understanding of the application of SFR and smart training principles.

If you’re ready to be coached 1-1 through a training program built exclusively for your individual goals and needs, that applies the science-based principles detailed in this blog & constantly evolves to best fit you, click here now to apply for online coaching with our team.


About The Author

Jeremiah Bair is a certified nutrition coach, strength coach, and owner of the online coaching business Bairfit. Check out his Podcast and Instagram  for more educational content.

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