Functional Roles of Muscles (Prime Mover, Synergist, Antagonist, Neutralizer, Stabilizer & Fixator)

Functional Roles of Muscles (Prime Mover, Synergist, Antagonist, Neutralizer, Stabilizer & Fixator)

Muscles are not always the prime mover.
Sometimes, they got some other stuff they do. So what is the prime mover? What is
the definition of prime mover? I’m glad that you can read the first sentence up
there. What did you guys know as the prime
mover? The idea … I can write definitions all day, the idea is that you guys
understand it for yourselves. What would you call the prime mover; you can use
your own words, you don’t need to use technical terms…the main thing… by “main,” what do you mean? The muscle that does what? Okay so the muscle that can
produce the most force for that particular joint action. For the most
part that’s, that’s right. That’s important to think
about because it’s like how do you decide which is the prime mover? Well,
generally speaking, it’s probably going to be the, if it’s the muscle that
produces the most force, it’s also going to be the muscle that’s the largest, for the
most part. it is. It is the muscle that is largest. Sometimes it’s the muscle that
has the best angle. You guys get what I’m saying? That’s most well aligned to
produce that joint action. Sometimes the term agonist is used, have you guys ever heard that? The reason I don’t like agonist is because some
people use that term as prime mover and then some people use, “well technically an
agonist is anything that will do the thing you want, right. So it could be all
of the muscles that cause flexion like the graphs that we’re doing. Rather than
the one that is able to produce the most force for flexion. (So we should not worry
about agonist as a terminology?) No, you should know it. in the back
of your head. I’m just telling you I’m going to use prime
mover so that we are clear. (So prime mover, single muscle, agonist of course could be
lots of muscles) Agonists, if you look, if you technically think about what agonist
means, it could mean all. What I’m telling you guys is a lot of people will use the
term agonist to mean prime mover. A lot of people use those two synonymously. I
don’t think the word agonist is very clear. I’m not going to use it. I’m going to
use prime mover. Prime mover – muscle most responsible or the muscle that
produces the most force for the joint action we’re looking at, under load.
Synergists. What is synergy? (Working together.) Working together. So a synergist, you ready for this, is all the muscles that help the prime mover, or you could
think about it this way, they’re all the muscles that produce the joint action
we’re looking at, that aren’t what? The prime mover. That’s it. That’s it. This isn’t a memorization thing, remember
this whole course is built around you guys not doing what? Rote memorization. I want you guys
to understand. Antagonists. If I antagonize you what am I doing? Yeah, trying to resist you in some way,
right? Antagonists are all the muscles that oppose the prime mover and
synergists. Considering this in a, “How are we going to figure this out?” sort of way,
antagonists are going to be all the muscles to do what? The opposing joint
action. Antagonists. You with me? So we got the prime mover- the muscle that can
produce the most force, we got the synergists- all of the other muscles that
produce that joint action, the antagonists- all of the muscles that
produce the opposite joint action. Now we get tricky. Neutralizers. A neutralizer- a muscle that
opposes the unwanted joint motions is created by the prime mover and/or
synergists and/or muscles that prevent the ancillary motion, unwanted ancillary
motion in a movement. That doesn’t make a whole lot of sense yet right? Okay, so let me give you an example. If i do
hip extension, right, who’s my primary muscle for hip extension? The glute max.
The glute max does extension though and external rotation. But I don’t want
external rotation. I don’t want to run like this right,
like with my feet flipping out. So how do I prevent the external
rotation? I have to have my internal rotators tone up a little bit so that
they keep my legs straight. That’s a neutralizer. It’s when a certain
joint motion is paired with some ancillary motion we don’t want, we need
those other muscles to come in and keep us in a straight line. For today’s class,
the only part of that definition we’re going to worry about is the ancillary
motion of the prime mover. We’re going to neutralize that. So going back to the…hip extension example, forget everything else
that’s going at the hip, today we’re going to say neutralizers are the
muscles that will oppose the extra motion of the prime mover. You guys with
me on this? The extra motion yeah, not the main motion. Yeah. So, yeah exactly. So if I’m doing
hip extension and I want my glute max to fire, it’s going to produce extension and external rotation. We’re not opposing extension. That’s fine, you’re right that would be
the antagonists, but that external rotation, we don’t want. And remember, all
your glute max knows how to do is fire. It doesn’t know how to separate between
extension and external rotation. What’s going to control that is some
neutralizers coming in to keep me in a straight line. Stabilizers. I should warn
you with this definition. My definitions are not going to be the same as the
definitions in every textbook, partly because the definitions in every
textbook vary wildly when you get to these more complicated terms. Also partly
because I like to teach in a conceptual way. I want you guys to be able to figure
this stuff out for yourselves. I’ve had to either scale down or modify
definitions to make sure that they stay clear and conceptual and separate from
each other. Stabilizers, in my book, are muscles that
basically, more or less, control that arthrokinematic motion. They’re muscles
that are closer to the joint whose main purpose is that stabilization function.
But the proximal stabilization function of a joint. So who are my stabilizers
always going to be for any shoulder motion? Rotator cuff. You guys get me
there? Fixators. Fixators are muscles that help
lock down the proximal joint, not the one we’re working, but the other one. You guys
get what I’m saying? Lock that one down so that I only get
motion and force production where I intended. Easy example for you guys, if
I’m doing hip extension, what joints need to be locked down? Sure, you could be right, too, if I was
doing something like a deadlift, sure, I might need to stabilize my knee. You’re not wrong, but you guys get what
I’m saying there? So if I need to work my hip, I need to fixate this. Who would my
stabilizers for my hip be? Deep rotators. Remember that? Remember those
deep, deep, deep muscles. In a wider definition of, this is where… so that’s a great it’s a great example guys, that’s a great
example of where definitions have a tendency to do this. I said this is a
fixator, the deep rotators of the hip are stabilizers for the hip and then I said
“What stabilizes?” and he said “Glute medius.” And yesterday I said that the glute
medius was the primary frontal plane stabilization mechanism of the pelvis. Yes, they’re both correct. The gluteus
medius has a very important stabilization function as many muscles
do. When you’re breaking down stuff for this, for specific joint actions,
stabilizers are the muscles that do what? Just work on those very small motions
that keep the joint moving the way it’s supposed to. You guys with me? Not that the gluteus medius doesn’t help stabilize the pelvis in a larger, more global picture of what we’re
looking at. So easy to confuse fixator and stabilizer that I guarantee those
two terms will never be defined the same way in two text books. (Are fixators usually like small, refined muscle) No, no. If I was working my shoulder, what would I need to fixate to be able
to move my arm well? My scapula. So all of the muscles of my scapula become
fixators. The stabilizer would be at the shoulder which would be my? My rotator
cuff. You guys kind of seeing how this is going. All you’re doing is is starting
to understand how everything works together. I’m not saying you won’t find other
definitions in other textbooks but for the assignment we’re about to do, I think
you’ll find these definitions useful. All right so let’s do shoulder horizontal
adduction. Let’s see if we can figure this out. You
want to do the first one together. Yes. No I will not think for you. Well
look, if you want to pay me my salary to follow you around and help you with your
clients, we can work something out. Or I could just take your test for you? I
think that’s cheating. I think there’s a problem with that
academically, but I could be wrong. If you find out that I’m wrong, you let me know.
Okay. Get back to me. So let’s do shoulder horizontal adduction, what movement are we talking about? So what, what exercise am I talking about? Benchpress, flyes pushups, you guys can think whatever you
want we’re doing shoulder. We’re just looking here though, not here,
just here, in a bench press. Cool, all right. Prime mover – almost wrote
agonist. Spent so much time talking about agonist, almost wrote it down. Actually that’s not gonna work, let’s do this. Prime mover, who’s the
prime mover? Pectoralis major. Synergists. (Anterior delt)
Antagonists. There could be if there
was more than one, it’s not for this case. Right. You’re going to see in some of our
other graphs, there’s a lot of muscles per category. Posterior delt.
There’s a reason I picked this graph to start with. Some of these graphs get very
complicated. Who’s next? Neutralizers. Neutralizers so
we got to go back up to pec major and think, “all right, my pectoralis major does more than just
horizontal adduction, what else does it want to do? Probably internally rotate. It
actually does a few things, but we’ll stick with internal rotation because
that’s a big one. The last thing I want to do is take up a heavy bench press and
internally rotate. I’m guessing that’s dangerous, guessing that’s a dangerous
thing to do. So who would I used to neutralize
internal rotation? Which ones? Specific. The external rotators. So it externally
rotates very nice, it is infraspinatus, teres minor One more. Muscles can be in two different
categories. Posterior delt. Stabilizers. What stabilizers for the shoulder? Would be
rotator cuff. Yes so would be … I’m just
going to write down infraspinatus and teres minor since we already went there. Who
are the other two? Subscapularis and supraspinatus. Fixators. Who my fixators? Muscles that’s
that stabilize the scapula. I have five muscles that cross my axial-scapular
joint, you guys remember what they were? Rhomboids, trapezius, levator scapulae …no, just muscles that move
the scapulae, you remember? You guys have totally forgotten your protractors.
Pec minor…and…thank you. Serratus anterior. Serratus anterior
may be the most important stabilizer of the scapula. Kind of interesting to think
that all that’s working during shoulder horizontal adduction. How’d you guys do? Horrible. (laughs) All right that’s what we just did. All right,
scapular protraction. Hit it! I got to go back into superstar status, we got to get this next one up right you, guys ready? All right I can go on rants for forever
about stuff but we have to get this done. This was a little tougher, right? Scapular
protraction leads to a lot of really confusing little relationships, but if
you put a little thought into it, you’ll figure it out. Scapular protraction.
Who is my primary scapular protractor? Serratus anterior. Yeah, that one’s a little
stronger. Serratus, I think. Honestly guys I’m not really worried about your… the
way you say it. I’ll correct you if I think something will get you embarrassed in
your clinic. I would never correct you. Neutral… if you said neutralizers I’d
have to go ahead and, and say something that sounds a little bit like neutral
lizard and I don’t know what a neutral lizard is. Synergists. Pec minor. Remember we’re talking about protraction, so these muscles have to
cross from axial, the ribcage, to the scapula, or the spine of the scapula.
Antagonists are going to be all the muscles that do what? Retraction. So what are retractors? Rhomboids, mid-traps. Neutralizers. Well, what are we trying to
neutralize the radius anterior does… protraction and upward rotation. That’s a
good one too, it does, you’re not you’re not wrong, it
does posterior tipping, so we could say we need to neutralize posterior tipping.
But we’re going to say neutralize the upward rotation force which means I need
to find all the…all the muscles that do downward rotation. What is
downward rotators? Levator scapulae, rhomboids. Man, evidently I didn’t teach this muscle
very well yesterday, pectoralis minor. Stabilizers. This is a tough one
with this one. This is a really tough one. Yeah, I mean there’s a lot of ways
to think about this one. Serratus anterior is actually probably considered
the primary stabilizer for your… for your scapula but it’s also our prime mover. If
you didn’t put anything down. that’s okay. If you want to say lower traps
you want to say serratus anterior, I wouldn’t be mad at you either, because
those two muscles are almost always under active individuals and usually
need a little bit of work. So we can, we can say that serratus anterior. Oh you’re
not being given charity don’t worry about it. (student speaking) Depends on what we’re talking about, right? What if we were talking about external
rotation of the shoulder? Would your stabilizers become your prime movers?
Fixators, what am I trying to fixate? (Wouldn’t levator be a stabilizer?)
It could be it could be, it honestly, this term doesn’t
work real well for this graph and that happens. It’s okay. This is a mental
exercise, the fact that it’s getting you thinking is good. Fixators. What is going to
need to be stable and functioning well for your scapula to move well. Your spine
and trunk. Usually we move proximally, okay, yeah. In order for your scapulae to move well, all
this has to be nice, right, it has to be a nice cylinder. So now all of our fixators
are what? All our core muscles. Should we try to list them all? Well yeah I
mean we could say that too, you’re right, depending on what motion we’re talking
about, it could go all the way down to my toes, but let’s start with core. Let’s
just start with the trunk muscles, right. So we said transverse abdominis and with
your transverse abdominis we could talk about something called your intrinsic
stabilization subsystem. Stay with me here, guys. You’re ISS, all right so your
intrinsic stabilization subsystem. Your intrinsic stabilization subsystem
is made up of your TVA, multifidus, diaphragm and pelvic floor. We then can
add the more superficial movers on top of that right. Which are going to be my
rectus abdominis, let’s say obliques, since we know both are included. What else? Starts with an E… erector spinae
Starts with a Q… quadratus lumborum It is deep, but it’s still part of our
core so it’s, and it’s one of the bigger movers. How did we do? Am I missing anything? I think we’re okay. I just wrote obliques -internal and external. Good. Oh I guess we could throw the lats up
there, but that’s going to get a little tricky because the lats also connect into the shoulder and how does it affect the scapula? Guys these are the…
this is what I’m setting you up for, is the never-ending mental game that you can
play with yourself. All right so let’s go ahead into hip
extension. All right, guys let’s do hip extension.
Gluteus maximus, done. All right, hip extension prime mover – glute max.
Everybody’s favorite muscle, now let’s go for the synergists though. Biceps femoris,
the long head, good. Getting a little bit more specific, right. The short head only
goes up to about halfway up on the femur. Doesn’t actually cross the hip. What else? So biceps femoris long head
semi’s and posterior adductor magnus.
There is no such thing as abductors for muscles. There are muscles that abduct, there are adductors. Just realize if you do you’re just
referring to several muscles. Antagonists. Who are my antagonists? All the muscles that do hip flexion so iliacus, psoas… psoas, rectus femoris. Keep going. TFL. Gluteus minimus, nice. (Sartorius) Nice. PBLMG anterior adductors, right?
Pectineus, brevis, longus, magnus gracilis. Anterior adductor magnus
on that one. Neutralizers. What are we trying to neutralize? So we’re trying to do, we’re trying to get some internal
rotation activity because my glute max wants to do extension and external
rotation. All right so who are my internal
rotators? TFL, definitely. The glute min, and…anterior fibers of glute medius, if
you want to write it down. Although we’ve also talked about how the
posterior fibers of gluteus medius externally rotate and are usually
ones that become under active and the ones that I was talking about
yesterday that we need to work, work, work, work, work. TFL, glute min. (Student question. Those are which type of rotators.)
All of my adductors. We’re missing some. We already have it up there too. It’s up there in a different category, it’s
going to be in this category too. Nice job. Semi’s.
Stabilizers. Already kind of mentioned this, these are the ones that are close to the joint who are going
to help us keep, yeah, the deep rotators of the hip. (Student question) They are, but they’re also, they’re stabilizers of the hip. Fixators. Who do we need to fixate? (Oppostite hip) That’s an interesting idea. So if I needed to kick a ball, would I have
to fixate the side? Potentially. Potentially. If I’m just walking though,
who needs to stay pretty stable or if I’m running. Core. Should we write down
all of them again. I’ll let you get away with core this time. Okay, let’s do it. Okay, you said it. All right so, let’s go. Intrinsic
stabilization subsystem what are those guys? TVA, multifidus, diaphragm, pelvic floor. Keep going. Now we’re onto
our global stabilizers – obliques. Okay, keep going. Rectus abdominis, keep
going. Erector spinae, keep going. One more. QL.
Nice job, guys. That was quick too. All right, I think we got one more joint
action. Hip abduction, let’s hit it, and then you guys will be back to me talking
for a little while until we get to lunch. Which movement am I looking at? Abduction. Okay, good. Prime mover? Gluteus medius, for sure. Synergists. Gluteus
minimus and TFL. Antagonists. Adductors, nice job. That
was kind of easy on this one. Adductors, right. What’s my acronym for adductors? And since this is the last, since this is the last one “Peanut Butter Leaves Me Greasy” this
is the last time we’re going to write the adductors up on the board, I think for this two-day workshop, let’s break them out. So what are all my
adductors, ready? Pectineus, that’s the “P.” Peanut butter… brevis. Leaves…longus. peanut butter leaves… longus. Peanut butter leaves me….magnus. Greasy, peanut butter
leaves me greasy… gracilis. And then we can put post adductor here, since for most
of the weekend we’ve been considering “Peanut Butter Leaves Me Greasy’ as the
anterior adductors and kind of the posterior head of the adductor magnus
separately. Neutralizers. (Student question) Yep, this is definitely one of those
graphs where one of our terms starts looking a little funny right. Yeah because we have posterior and
anterior fibers of the gluteus medius, I mentioned that a couple times, some
internally rotate, some externally rotate. We do have two internal rotators as
synergists, right. So the TfL and the gluteus minimus are both synergists and
both strong internal rotators for the hip. Usually what happens is we get
internally rotated bias, right. People tend to do this, that knees cave-in and
internally rotate. So if I’m just going to kind of think through logically,
maybe a little beyond this assignment, we look at neutralizers and we go, “Why, what way am I neutralizing?” and then I would think to myself, well with this much of a bias towards internal rotation,
I might go, “I need more external rotation force.” Right so we could do glute max, biceps femoris, TFL is an internal rotator. What about my piriformis and the
deep rotators right? Oh haha, nice job. Psoas and iliacus too. Both external rotators of the hip. Could even put down adductor magnus, if you really
wanted to. Yeah nice job. Nice job thinking through
that. Stabilizers. Yes, so this is going to be deep rotators of the hip again and then what my fixators going to be? Your core, just like the
last graph we did. Yeah, so all I did is the intrinsic stabilization subsystem is
those intrinsic muscles that have more of a role in stabilization than they do
in movement and then all of the other muscles that cross the lumbar spine.
Which are, we could look at as global movers or global stabilizers of the
trunk. Nice job guys. You did a good job with this, these
activities. These graphs aren’t easy. Now if you like doing these graphs, your 20
minutes a day, I wrote down one of these graphs for every joint action for every
major joint and it’s up on the website. I’m talking all of the joint actions for
the shoulder, the elbow, the scapula, the hip, the knee and ankle. It’s under
kinesiology. It says kinesiology of the hip, kinesiology of the ankle, kinesiology
the shoulder. B2C fitness is the old name of the company, you guys just happened to
get some old workbooks for this workshop.

55 Replies to “Functional Roles of Muscles (Prime Mover, Synergist, Antagonist, Neutralizer, Stabilizer & Fixator)”

  1. Great tutorial video. I don't really like you but, I love the way you simplify difficult and complicated things.Good job!

  2. Amazing as usual Sir,ur videos helps me alot in understanding human movements, thanks for sharing this and keep posting ur awesome videos,u r such an excellent teacher.

  3. Hey Brent, At 6:13 you mention that "all your glute max knows what to do is fire. It doesn't know how to separate between extension and external rotation."

    Does this mean that all muscles perform ALL their functions all the time when they are activated but are kept in check by the neutralizers so that the unwanted functions/movements are not performed?

  4. This is almost like cheating. Such an informative video to be access by everyone. amazing and totally loving it. Visit us down under soon.

  5. Thank you so much for this video! It really helped me to understand the functional roles of the muscles! Very informative!

  6. I am currently studying Nasm CPT and your videos are helping me tremendously! Just wanted to say thank you!! You break it down a lot more than my book, you're awesome!!

  7. Studying Anatomy and Physiology Level 3 Personal Trainer. Have exam in 2 weeks.  Brents simple explanations are helping so much, as how an earth could I train someone without understanding. Trainers going to fast with teaching and cramming in course too much.  Have had to break down, to understand what is being used in Giant Sets, Tri Sets.  Thank you for throwing agonist out the window, and there's me thinking fixators and stabilisers are the same thing.   Text books are too confusing, and conflicting.

  8. Peanut butter leaves me greasy!! This guy teaches how I learn. Have to learn nutrient, but this is way more interesting.  May have to use this learning for nutrient to make it easier for tomorrow.  So so helpful can you please come to UK London to teach.  My teachers spend 15 to 20 minutes teaching, then say right now go to the gym and practice.  Practice what!!! I don't understand.

  9. failed my practical personal trainer assessment yesterday. failed the fact i did a bicep curl with a barbell and and a tricep extension with one arm..also due to nerves called a squat an isolation and a leg extension a compound. resit 100 pounds

  10. tri sets i got issues with this comment got my client to shoulder press front raise lateral raise. technique failure hips shooting fwd arms swinging facial expression said too heavy ..assessor said weight was not heavy enough.

  11. i work for the probation prison service..7am to 7pm studying inbtween. was up unti 12.00am till 5.30am to study. takes 2 hrs to travel to sth east london fr work. so had only 4 hrs sleep day of exam.

  12. Hey brent, good news I've passed my practical assessment.  Was waking up 6:15am studying before work, and was studying from 5:15pm till 12:00am for 11 days straight. Broke down the whole body, and each exercise approach. So eccentric/Negatives.  To remember.  I adapted a saying 'My client thinks negative, I think positive, positive ='s the lifting phase, negative = lowering phase. My assessor picked supersets, Prime vs Opposing muscle. I did biceps curl and triceps pulldown.  Tri Sets, = Shoulder press, front raise, lateral raise. pre exhaust, quads – leg extension – isolation and leg press for compound. Forced reps, lat pulldown, last 4 offered the help. Although with the triceps, my client tried to pull rope overhead after me showing her to pull the rope down in front, we went back to this so she had more range of movement.  My mother is now hooked on your video's, and now wants to learn more to try out new exercises in the gym.   Thank you so much for your unique teaching skills. I'm becoming obsessed with the body and it's mechanics.

  13. thank you, sir, for amazing videos.I have one question as I'm slightly confused, wouldn't the lower traps also behave as neutralizers to prevent the ancillary motion of upward rotation of the scapula when the serratus anterior contracts?

  14. is this whole serious of lectures you had with these students available on your site? I really enjoy these lectures and find them helpful – or are they all on youtube? thanks!

  15. Prime mover- the muscle that has the best angle to make the movement. Produces the most force.
    Synergistic the muscles – Working together – all of the muscles that assist the Prime Mover.
    Antagonist – resist – all of the muscle that oppose.
    Neutralizers- the muscles that will oppose the eg- Hip extension – glute max – main muscles Stabilizers are muscles that are closer to the joint – rotator cuff stabilising muscles
    fixator muscles – lock down

  16. I have a little query regarding rectus abdominus, Though it is one muscle, does reverse abdominal crunch work more on lower part of rectus abdominus?

  17. Thank you very much for these videos.  I discovered your website and have been learning so much from your videos and articles.  Then I discovered several of your videos here on YouTube.  Your way of teaching to understand vs. memorizing is so helpful and has me actually interested in learning vs. just drudging through to get it done.

  18. oh my gosh. I'm study for my NASM CPT right now, have a few weeks til I take my test. I wish I would have found your videos sooner. thank you so much for making it so much easier to understand. Amazing

  19. I am in the same boat, Megan Williams! The visuals, interaction, and helpful memorization techniques for the terminology make this ideal! Thank you, Dr. Brent!! I will certainly be following through with my CEUs through your website and workshops! Please come to Austin as often as possible! 😀

  20. Very interesting…. And learning biomechanics by Brent is awesome…. Thank you very much sir

  21. Dr. Brookbush, could you explain the "fixator" portion again? I understood that it is proximal to the joint you are working with. Locking it down, to only allow the distal joint to work. But could you explain what the fixator would be for hip extension again?

    Thank you. Awesome approach and excellent teacher.


  22. there were no need to humiliate the guy who read the first sentence on the slide. If it was me i would had felt bad and stopped speaking or answering any of your questions, scarred from your reaction to the "wrong" answer. Prof Brent Brookbush ……

  23. Great! I admire your way of teaching. Wish you would be my teacher. Thanks for this amazing online class 🙂

  24. my test is tomorrow and I'm glad I saw this video looking for some examples of prime movers and synergist , it was really helpfull, now everything is so much easier to connect. Thank you!!!

  25. Thank you so much, your style of teaching is so great, I like how you engage with so many questions, it keeps me from falling asleep. ☺

  26. i think you should visit Northewest university potchefstroom campus , things we hear out here are complicated…and you just make them simple

  27. What's the role of triceps in shouler horizontal adduction or a bench press for that matter? Is it acting as a synergist??

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