Muscle Fatigue vs. Muscle Failure: How to Actually Build Strength as a Woman
Written by Dr. Lizzie Kieffer, DPT.
If your muscles are burning during a workout, that means you’re building muscle…right? Well, not necessarily!
That burning sensation can certainly tell us that our muscles are working and becoming fatigued, but muscle fatigue and the stimulus needed for muscle growth are not exactly the same thing. You can hold a squat until your legs are shaking or do 30+ reps of an exercise and feel an intense burn, but that doesn’t automatically mean you’re creating the best stimulus for building strength or actual muscle.
And I think this distinction is especially important for women because so much of the fitness advice marketed toward us has historically centered around doing more reps, lighter weights, longer holds, and chasing the burn rather than teaching women how to progressively build strength.
Muscular endurance absolutely has a place in a well-rounded fitness routine. But if your goal is to actually get stronger and build muscle, we need to understand what creates that adaptation, and how to appropriately challenge the body over time! But even that is only one part of the equation.
After years of working with women through pregnancy, postpartum, pelvic floor recovery, strength training, and the many different seasons that come after, I’ve found that strength is best built when we look beyond the workout itself. How you breathe and manage pressure matters. Your connection to your core and pelvic floor matters. How you progress your exercises matters. And what happens outside of your workouts…like your recovery, stress, sleep, hydration, and nutrition…all that matters too!
Those are the pieces that eventually became the framework behind how I program inside Mind Body Core → B.U.I.L.D.
So before we break down each part of that framework, let’s start with the fitness misconception that inspired this entire conversation: What’s the difference between muscle fatigue and muscle failure…and which one actually helps you build muscle?
muscle fatigue vs. muscle failure…what’s the difference?
First, let’s clear up what we actually mean when we talk about muscle fatigue versus muscle failure, because although they can happen within the same workout, they aren’t interchangeable.
Muscle fatigue is the temporary decline in your muscle’s ability to continue performing at the same level. It’s often what you’re experiencing when your muscles start to burn during a long hold or a high-repetition set. Think 30+ squats, pulses, or holding a wall sit until your legs are on fire. This type of training can be great for muscular endurance, which is your muscles’ ability to keep working for longer periods of time, but the intensity of the burn itself isn't a reliable measure of how much muscle growth you're stimulating.
Muscle failure, on the other hand, is the point where your muscles can no longer complete another repetition with good form at the given resistance. You don't necessarily need to reach absolute failure with every set, either. Training close to failure, often within a few reps of it, can provide the stimulus needed for muscle growth when it's paired with appropriate resistance and progression over time.
And a little bonus tip that’s important to remember → failure looks different depending on the exercise and the person doing it. A weight that challenges one person within 8–12 reps may be far too light or heavy for someone else. That's why an arbitrary rep count isn't the main focal point. The focal point should instead be on choosing an appropriate resistance that makes those final repetitions genuinely challenging while still maintaining good form, breathing, and pressure management.
So, should you avoid workouts that create that muscle-burning feeling? Absolutely not! Muscular endurance matters, and there are plenty of reasons to train it. We just don't want to confuse “this burns” with “this is automatically building more muscle” (which is what I personally have been seeing on my algorithm as of late…and maybe you are too!).
So, to bring this full circle, if building strength and muscle IS the goal, then we need another piece of the puzzle → progressive overload.
what is progressive overload and why does it matter?
If your muscles are going to get stronger (aka - build actual muscle), at some point they have to be given a reason to adapt. That’s where progressive overload comes in!
Progressive overload simply means gradually increasing the challenge placed on your muscles over time. As your body adapts to what you’re currently doing, that same workout, weight, or resistance eventually becomes easier. Continuing to create change means appropriately increasing the demand rather than repeating the exact same stimulus indefinitely.
And adding heavier weights is only one way to do that. Other ways to incorporate progressive overload can also look like…
Increasing resistance with weights or bands
Progressing to a more challenging variation of an exercise
Changing your position or angle to increase the demand
Increasing reps or sets when appropriate
Improving your range of motion or control
Gradually increasing the overall amount of work you're able to tolerate
This is also why progressive is such an important part of the term. We aren’t trying to jump from a 10-pound dumbbell to a 30-pound dumbbell overnight or push yourself to failure during every workout. Instead, we want to give the muscles enough challenge to create adaptation while allowing the rest of the body to keep up with that demand.
And for women, that progression may not always be perfectly linear. Pregnancy, postpartum recovery, sleep, stress, hormones, illness, and simply different seasons of life can all affect what an appropriate challenge looks like at any given time. Sometimes you're progressing the load, other times maintaining your current strength or temporarily scaling back is the appropriate training decision!
Progressive overload gives us the strategy for continuing to build strength, but it's still only one piece of how I approach women's health and exercise. Because before we can keep adding load, reps, or difficulty, I want to know that the body has the tools to manage that challenge well…and that's where my B.U.I.L.D framework comes in!
the BUILD framework: my approach to strength & women’s health
As I alluded to above, progressive overload is an important piece of building strength, but it’s not the only piece! Over the years, both as a pelvic floor physical therapist and through programming for Mind Body Core, I’ve found there are five components that continually come up when helping women build strength in a way that supports their whole body.
I call it the B.U.I.L.D Framework:
B = breath
U = understand your core
I = increase strength gradually
L = lifestyle support
D = daily nourishment
Each piece serves a different purpose, but together they create the approach I use throughout MBC! Let me go into each a little bit more…
Breath: Learn pressure management + diaphragmatic breathing
Breath is always where we start because how you breathe directly affects how you manage pressure during movement. Diaphragmatic breathing teaches you to use the full 360° expansion of your rib cage while coordinating what’s happening through your core and pelvic floor.
As exercises become more challenging, this becomes even more important. Whether you're doing a bodyweight squat, picking up your child, or progressing into heavier strength training, knowing when to inhale, exhale, brace, and manage pressure gives you a skill you can carry into virtually every type of movement!
understand your core: Build your deep core + pelvic floor connection
Your core is so much more than your visible or “6-pack” abs, and learning how it actually functions is an important part of progressing beyond basic exercises. Your diaphragm, deep core, pelvic floor, back, and surrounding muscles all contribute to the stability and support you need as you move!
This is why MBC spends time helping you understand that connection, rather than simply telling you to “engage your core”. When you know what you’re trying to feel and how to coordinate it with movement, you can take that awareness into squats, lunges, lifting, running, jumping, and everyday life, and not just traditional core exercises.
increase strength gradually: Progressively overload your body over time
This is where we put what we talked about earlier into practice. Once you have the foundations, the goal isn't to stay there forever. Your body needs opportunities to be challenged if you want it to continue adapting and getting stronger.
Inside MBC, that means gradually progressing exercises, resistance, complexity, and different types of movement as appropriate. Some days that may mean heavier weights. Other times it may mean a harder variation, a different angle, more stability demands, or eventually incorporating things like running and higher-impact movements.
The goal is never to make an exercise harder simply for the sake of making it harder. We progress when your body is ready for a greater challenge.
lifestyle support: Consider sleep, stress, walking, recovery + hormones
We can write the perfect workout program and be as consistent as we possibly can be with that, but your body doesn't experience that workout in a vacuum! Maybe you slept terribly because your baby was up all night. Maybe you're going through a particularly stressful season. Maybe your hormones are shifting, you're recovering from pregnancy and birth, or your body simply needs more recovery than it did at another point in your life. These are NOT excuses, and these things matter and affect the way that you function!
This is why I don't believe a successful program should require every week to look exactly the same. Walking, rest, mobility, stress management, sleep, and recovery all have a place alongside strength training. Sometimes supporting your long-term progress means knowing when to push, and sometimes it means knowing when your body needs something different!
daily nourishment: Prioritize protein, hydration + adequate fueling
Finally, we have to give our bodies the resources they need to actually do everything we're asking of them.
→ Protein supports muscle repair and growth.
→ Hydration affects everything from exercise performance to recovery.
→ And adequate overall nutrition provides the energy your body needs to train, recover, and adapt…especially during demanding seasons like pregnancy, postpartum, breastfeeding, or periods of increased training.
This is also why nutrition is incorporated into MBC (rather than treating movement as the entire picture). You can follow a great strength program, but consistently under-fueling your body can make it much harder to recover and get the results you're working toward!
BUILD isn’t about doing everything perfectly…
Now, before you look at those five pieces and think you need to have perfect breath + perfect core connection + constantly progressing workouts + eight hours of sleep + zero stress + flawless nutrition all happening at the same time…welcome to being human! And let me remind you that doing all 5 of these things perfectly at the same time is very unlikely and also, not the goal!
I like to think of each component of B.U.I.L.D as a brick. Not every brick is going to be perfect all the time, and depending on the season you're in, some may need more attention than others.
Pregnancy may change what progressing your strength looks like. Early postpartum may mean breathing, core connection, nourishment, and recovery take priority. There may be seasons when you're ready to push your strength and others when maintaining what you've already built is a win. And sometimes sleep and stress are simply not things you have complete control over!
We are not trying for perfection within every category. It's continuing to layer these pieces together over time so that you're creating something sturdy and resilient…hello momsistency!
Because when an unexpected season does come (and trust me, in one way or another, it will) you aren't starting from scratch. You have a foundation you've already built that you can continue to lean on, adjust, and come back to.
And that is really the entire philosophy behind B.U.I.L.D inside Mind Body Core.
this is why mind body core is more than a workout app
If there’s one thing I want you to take away from the B.U.I.L.D framework, it’s that getting stronger isn’t just about finding a workout and checking it off your list. Mind Body Core doesn’t just tell you what workout to do. It teaches you how to build a body that can continue adapting WITH you.
That’s why MBC was designed as an entire ecosystem for women’s health rather than a collection of random workouts. You can learn the foundations of breath, pressure management, and core + pelvic floor connection, then actually progress those skills into strength training, more challenging workouts, cardio, higher-impact movement, and whatever comes next for you.
And because your needs will change throughout your life, your membership gives you access to support through ALL phases and stages of womanhood:
Prenatal → Labor Prep → Postpartum Rehab → Core → Mobility → Progressive Strength → Weekly Workouts → Cardio + Higher-Impact Movement → Nutrition → Education + Resources
You don't have to leave one program behind and go searching for something completely different when your body is ready for the next step. The next step is already there!
And the other pieces of B.U.I.L.D aren't forgotten either. You’ll find nutrition guidance and recipes to help you fuel your body, mobility and recovery options for days when you need something different, education to help you actually understand your body, and programming that gives you opportunities to continue progressing rather than staying at the same level indefinitely.
You can join Mind Body Core with a monthly or annual membership and get access to the entire MBC library and ongoing programming. Individual Prenatal and Postpartum programs are also available for lifetime access if you’re looking for support during one specific season!
But if you want the fullest expression of BUILD, the ability to move between programs, revisit foundations, progress your strength, adapt when life changes, and continue finding new ways to challenge and support your body, the MBC Membership gives you all of it in one place!