Unfortunately, a muscle firing has nothing to do with cool laser beams shooting from your double bicep pose… much to my immense disappointment… but instead it’s a much more confusing term that has people scratching their heads or assuming some part of their body “doesn’t work”.
It’s a strange crossover phrase which refers to both your brain and your muscles. When a motor neuron sends a signal to your muscles, we say it’s “firing”, and when it fires it activates/contracts the motor units in your muscles that it’s in control of.
Like with anything, you can be good or bad at it. If you don’t use a muscle very much (or very well) you won’t have very strong motor neuron patterns, meaning it’s possible that only a few motor units in your muscles are activated, or that the signals are a bit slow or erratic.
You should always be wary of “your [x/y/z] muscles aren’t firing” advice and start to question what might be going on.
I want to give you THREE things to consider if you think you have a problem with muscle firing/activation:
3. Are you just lacking muscle awareness?
1. Were You Tested Out of Context?
There are many tests that can be used to determine weakness in a muscle and some tests put you immediately into a disadvantaged position, namely, lying down on a table or never having performed the test before. If you don’t know what you’re meant to be doing or even know what it’s meant to feels like… well, no you probably won’t use your muscles very well.

If pain is discovered, further medical investigations would take place, but, if you just seemingly had a big weakness in one direction… simply being shown better posture and bracing will vastly improve your performance. Which comes back to the earlier point of trying to pinpoint a specific weak muscle – your body works as a unit. Putting pressure specifically on your shoulder joint without the support of your upper back and core probably will cause a reduction of strength.
Another common test for Glutes is lay belly down on a table, lift a leg up and resist it being pushed down. Problem is, by lying down and lifting your leg your hips are already fully (or over) extended, so your glutes are already at the limit of what they can do. To try and achieve this goal of “resist being pushed down”, your body will probably extend your spine to get even more height. The result? Oh, your glutes don’t seem to be firing.
But if I take that same bum and let you stand, brace and flex from the hip first and then push back into extension by squeezing your glutes without extending your spine, it’ll work fine.

2. Do You Have Complete Strength or Have Gaps in Your Muscle Strength?
Muscles rarely work in isolation. Even when you’re doing bro curls in front of the mirror, the very fact that you’re standing up and able to do reps means that your legs, back and core must be keeping you upright.
But the fix is so simple it’s crazy: move your joints like joints are supposed to move! It’s not rest, it’s not getting your 3kg dumbbell and doing isolated external rotation exercises, it’s going through full ranges of motion.

If joints don’t feel mobile or that it doesn’t have wiggle room at any angle then of course it’s going to feel like they’re switching off or cutting out on you, they’re trying to protect you from putting your max effort into something and wrecking yourself.
When you adjust your mindset and think about full joint movement rather than hating on a particular muscle it’s a much easier life and takes up less time… as you can avoid that inevitable cycle of doing 10,000 clamshells to fire your glutes every day or 30,000 face pulls to retract your shoulders.
Another issue that can seemingly present itself as a muscle “switching off” is a weakness in the opposing muscle, i.e. not the one you think is the problem. One of my favourite muscle group pairings to illustrate this is the relationship between the Adductors and Abductors.
All the commonly prescribed exercises to fix hip dysfunctions and back pain, even knee valgus (when the knees collapse inwards) are all Glute focused and Abduction centred (abduction is moving your leg out, away from your body).
In all my years of working with people, I have seen those who could win the Glute Bridge Olympics, that could Clam a Shell until it crumbled… but give them a simple Adduction exercise (moving your leg in, towards your body) such as a Copenhagen plank and they would be shaking or even completely unable to perform it. And this isn’t just your average joe I’m talking about here, I’ve seen this multiple times with advanced, competitive athletes – these things can just be missed, and people can spend years chasing down the wrong rabbit holes!

Yes, your glutes feel like they’re firing, you’re getting an awesome burn! …but as soon as you take the band off, your weak adductors simply don’t have the strength to resist your awesome glutes, so they have nothing to work against. You’ve only worked one half of the pulley system so it can seem like you’re doing “everything right” but making no progress.
This can quite obviously present itself as a problem for squatting when people get extreme knee valgus and it can affect running through your ability to decelerate and absorb force through the hips, meaning the knees or back will take more impact than it should. You could get away with these weaknesses for years (your body is great at adapting), but eventually it will catch up with you.
You can find out more about the Glutes vs Adductors in this video.
This is not to start saying that you should totally get obsessed with your adductors and internal hip rotation, it’s just to always keep the big picture in mind and treat your body like a whole and when one area is presenting you with a problem.
3. Are You Just Lacking Muscle Awareness?

I want you to try a couple – right now if you can! Just do them as you normally would and see what you do (don’t worry, I’m not judging you….)
Try around 10 reps like that and feel the difference.
If you can’t get it at first keep practicing, this can take some people weeks to get the hang of.
So, even though you can’t always get maximum contraction, you can still create muscle activation through awareness. This is what so many people miss: their muscles are strong; they just don’t know how to use them.
The deadlift has two main muscle groups that we want to bring awareness to: hamstrings & glutes.
In the start position, your hamstrings will feel tension (which is a good thing) as you flex the hips and elongate them – imagine the string of a bow being pulled back ready to be let go. However, you can’t feel your glutes very much here because your hip is flexed the same as at the bottom of a glute bridge.
But even though we can’t feel them much, you want to imagine that same sensation in our glute bridge, as if you’re trying to activate your glutes through the full range of motion and drive your hips forwards using strength.
The magic happens when you get the bar past your knees and the roles reverse: your hamstrings start to go quiet and your glutes will suddenly feel more active – but this time there’s no delay, pause or struggle during this handover because you’ve continuously been bringing awareness to your glutes through the full lift.

Of course, this is only one piece of the puzzle, if your ability to hinge or brace aren’t great then your spine won’t feel safe, or you won’t be using your hamstrings properly etc. But it just goes to show you that simply by bringing awareness and conscious effort to your technique could literally be all you needed to improve your lifts. Without hours of accessory work or crazy warmups.
Poking or pressing the muscle/area you want to work can create extra stimulus for your body, pretty much making it go “Ohhh, you meant that one!”. Then filming yourself may reveal a funky position or movement pattern that you were never aware of before!
Assess Your Body Regularly
Keeping on top of muscles getting lazy/weak is always a good thing. I like to have quick assessment exercises that will immediately let me know if something’s off, and the best assessment exercises are those which you can’t just muscle through and compensate if something is wrong.
Who’s the best person to know this and make you do this? YOU, you are the best person to get more in tune with your body, no one else.