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fitbod there's a bit of controversy in
the world of strength and conditioning
research around this question
what is core strength this seems like it
should be a straightforward question
just define the muscles of the core and
find a way to measure their strength but
it's more complex than that first off
there's no definitive list of core
muscles some scientists include all the
muscles that attach all the way up the
vertebrae up the cervical spine while
some only include the deep abdominal
muscles like the transverse abdominis
and second many of these muscle actions
don't lend themselves to straightforward
strength evaluation it's easy enough for
the rectus abdominis or for the lumbar
extensors but way harder for say the
multifidus and these are important
caveats because it allows research and
fitness products to claim that they
improve core strength when in reality
maybe only one core muscle was affected
by their effort so in this video we'll
go over the different ways of imagining
core anatomy and try to make sense of
the core strength paradox
if you're new to the channel welcome my
name is patrick and this channel is all
about anatomy and how we learn about it
now before we get into the different
schools of thought around core anatomy
we need to talk about what common ground
they all share in general the core is a
set of muscles that stabilize the spine
increase pressure within the abdomen and
support limb movement and the fact that
we're narrowing in on muscles only is an
important detail we do have ligaments
along our spine but without muscles our
spines would be incredibly fragile an
experiment from 2004 showed that the
spine would collapse under 20 newtons of
compression without muscular support for
reference we can produce around 140
newtons of compression during walking
over 3000 newtons during sit-ups 6 000
during rowing and have recorded over 36
000 newtons for athletes doing heavy
lifts our delicate little spines need
this core musculature to hold it
together and depending on which
definition you're using there are up to
29 pairs of muscles that stabilize the
spine hip and pelvis that might be
considered as core muscles but to
understand the problem we need to split
these muscles into groups based on the
movement of the spine global muscles are
generally long muscles and can produce a
lot of torque muscles like the rectus
abdominus erector spinae and so as major
on the other hand local muscles are
generally shorter attach directly to
vertebrae and create stability of
individual vertebral segments these
muscles include the transverse abdominis
the diaphragm the quadratus lumborum and
internal obliques now this is our first
spot of controversy in general global
muscles move the spine while local
muscles depending on how they contract
stabilize the spine but patrick you say
as you notice the ql and internal
obliques on the local muscles list those
muscles do move the spine hey good eye
and you know what i'm proud of you for
catching that that's our next point of
confusion because the local muscles need
more contact only the transverse
abdominis or what i'll call the ta for
the rest of the video and multifidus
earn the title of primary local muscles
or muscles that always need to contract
to stabilize the spine the ta is the one
that looks like a corset and it's the
deepest of the abdominal muscles
attaching to the iliac crest of the
pelvis inguinal ligament thoracic and
lumbar spine is processed via the
thoracolumbar fascia and the linea alba
interiorly good luck making the flash
guard for that one the multifidus is a
little different these tiny muscles
cross anywhere from one to three
vertebrae and originate on the vertebral
arch of one vertebrae and insert on the
spinous process of another more inferior
vertebrae we find these things all the
way from cervical to lumbar and since
they have such short moment arms they
don't contribute to gross spinal motion
no matter what movement the rest of the
body is doing the ta and multifidus fire
a split second before everything else
giving us a base of spinal stability and
making them universally agreed upon core
muscles these other local core muscles
are secondary stabilizers since yes they
do keep the core in a stable position
when they fire but they can also move
the spine and here's the deal with that
when they contract other muscles
contract at the same time and it results
in a spine that doesn't budge and of
course different definitions of core
musculature go past the ones i listed
here i'm basing my list on a paper
published in the strength and
conditioning journal in 2007. that's
linked in the doobly-doo if you'd like
to see it these global muscles then are
muscles that move the spine into flexion
and extension rotation or bending
kinesiologists have noticed that these
muscles have long levers and moment arms
making them capable of producing a bunch
of torque and power and they have the
physiology to match it too
global muscles have a greater proportion
of fast twitch type 2 muscle fibers
while local muscles have more slow
twitch type 1 muscle fibers for greater
endurance that brings us to the last
part of confusion the strength of these
muscles like let's say that we've
decided to define only local muscles as
our core muscles in order for an
exercise to truly be a core strength
exercise according to that review from
2007 it must challenge muscles to
stabilize the spine through contraction
and by increasing pressure within the
abdomen the misconception is that if an
exercise requires core stability like a
front squat then it's a core exercise
same with functional exercises like when
a football lineman does chest flies and
a split squat their core muscles are
certainly active but not all functional
exercises are core exercises and the
same could be said about any exercise or
really any daily activity you had to
engage your core during the exercise but
that wasn't necessarily a core exercise
that's kind of like saying that just
because your pizza had a tomato slice on
it then it's a salad unfortunately when
we leave the fitness world and enter the
realm of kinesiology research our
definitions are still all different like
our methods for measuring a strength or
rehab program's effectiveness are all
over the place the methodology isn't
consistent and the vast majority of
research is done on patients with low
back pain not healthy adults or athletes
so for instance we could do a
prospective study where we measure
transverse abdominis cross-sectional
area on mri before and after a training
program but that would tell us muscle
size not necessarily strength or you
could do some kind of endurance test
like max number of sit-ups or prone
planks for a minute but then you're
involving global core muscles and you're
conflating endurance and strength which
aren't the same thing okay well we could
use clinical biofeedback as an endpoint
then a common physical therapy exercise
involves doing poor exercises with a
blood pressure cuff under the small of
your back the less the needle moves
supposedly the less your lumbar spine
moves and the more core muscles are
working right my point is oftentimes
when we say that we're evaluating core
strength clinically we're evaluating
neither the local core anatomy nor
strength the logical follow-up question
is so what if we mix up words from time
to time what should i do about
unfortunately it's not that simple
either there is no best exercise but
there are different exercises in my mind
the biggest benefit of core exercise is
preventing back pain i couldn't care
less about showy ab muscles honestly
forget a six-pack exercise because you
love your body and you want your back to
feel healthy forever we have years of
research at this point showing that a
technique called abdominal hollowing
strengthens the transverse abdominis and
that training this muscle leads to a
greater lumbar and sacroiliac joint
stability but as a reminder the vast
majority of that research was conducted
on participants with low back pain but
there are progressions of that exercise
like we could move our limbs during
hollowing or if we wanted a challenge we
could do abdominal bracing activating
all the abdominal muscles at the same
time all right so to circle back to the
opening we've landed in a weird kind of
paradoxical spot still if you define the
core based on stability provided by
local muscles you're almost certainly
not measuring strength and if you
measure core strength via the motion
from global muscles you're ignoring
spinal stability which is the point of
the core so knowing that this paradox
was a thing i did a little bit of extra
investigation based on this question
what about training on unstable surfaces
like this has always been advocated to
me as a great way to improve core
strength so what does the research say
so far the research around training on
unstable surfaces has mixed results and
just like before there's nuance
regarding what information we can pull
from each study for example a study
published in the journal of sport
rehabilitation in 2019 brought in
healthy adults and had them do a bunch
of isometric core exercises some of
which were done on an unstable surface
then they use real-time ultrasound
imaging to measure changes in muscle
thickness during those exercises and as
you probably guessed this is a similar
technology to seeing fetuses in utero
but this time it's narrowed in on
muscles they saw some muscles including
the transverse abdominis get thicker
during certain exercises meaning they
contracted harder during exercise on
unstable surface and that's a fun fact
but there are still multiple steps
between this observation and evidence
that training on unstable surfaces will
lead to greater stabilization of the
spine over stable surfaces and look i
know that's a mouthful to say but we
need this level of nuance to decipher
what studies are actually saying pay
close attention to this experiment from
the scandinavian journal of medicine and
science and sports from 2015. they took
39 teenage soccer players and gave them
a 9 week long core strengthening program
to do during their normal season
half of the group did exercises on an
unstable surface while some did them
normally
they measured core strength with
isometric trunk flexion and extension
which looks like something you'd find in
the pit of despair and there was a
significant difference in trunk
extension strength but not trunk flexion
strength after the 9-week program they
concluded that trunk muscle strength
could be improved by training on an
unstable surface which is a fair
conclusion given their data global core
muscles the spine extensors got stronger
but again that only works if your
definition of the core is based on
spinal motion not spinal stability
uncertainty aside unstable surfaces can
still be a great tool for training
balance especially for older folks who
are at risk of falling but just
anecdotally i've seen this concept go
way too far like power lifters try to do
split jerks onto balance pad which is
dumb and dangerous please don't do that
you know what's not a dumb decision
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