WHAT IS ACTIVE
INSUFFICIENCY?
Any muscle that crosses over more than one joint is capable of producing
force at more than one joint. Makes sense right? I mean, that’s what muscles
do. They generate force, either to move us around or lift things, or provide
stability. What most people don’t realize is that a muscle can only shorten by
a certain amount, typically up to 50% of its resting length. What this means is
that if a muscle is already shortened about one joint, then it cannot
forcefully contract to produce movement over the other joint that it crosses.
This is referred to as ACTIVE INSUFFICIENCY, and explains a lot about why
certain muscles are more or less active at certain joint angles.
WHAT DO THE LONG
HEAD OF THE TRICEPS, THE SHORT HEAD OF THE BICEPS, THE MEDIAL HAMSTRINGS, THE
RECTUS FEMORIS, AND THE GASTROCNEMIUS ALL HAVE IN COMMON?
They are the major superficial muscles worth noting that cross both the
shoulder and elbow joints (long head of the tricep, short head of the bicep),
hip and knee joints (semimembranosus, semitendinosus – medial hamstrings,
rectus femoris – quad), and knee and ankle joints (gastroc – calf). These
muscles are the most popular ones that are affected by exercises selection and
execution, and active insufficiency in the weight room.
For instance, many people have heard that standing calf raises work more
the gastroc (beefy part of the calf), and seated calf raises work more the
soleus, but no one can really explain why that is.
The same goes for the long head of the triceps. Everyone knows, or has
heard at some point, that overhead exercises recruit the long head of the
triceps more so than any other variation of arm extension movements. But does
no one ever wonder why? Or do they, but the person, or people, that they ask
have no idea why that is, and they attempt to mask it by just giving an answer
like, “that’s the way it is”, or “I read that once”?
HOW CAN ACTIVE
INSUFFICIENCY INFLUENCE EXERCISE SELECTION, AND THEREFORE DEVELOPMENT?
If a muscle that crosses over more than one joint, is only really capable
of producing force at one joint at a time, then you may think that an exercise
that is ‘supposed’ to work that muscle, is actually doing that, but in reality
it isn’t. Below is a breakdown of the muscles highlighted above, and how active
insufficiency affects them.
LONG HEAD OF THE
TRICEP
The long head of the tricep is responsible for two movements – elbow
extension, and shoulder extension (the same type of movement that the lat isprimarily responsible for). This means that when the shoulder is extended, and
the arm is beside (or close to) the body, that the long head of the tricep is
already in a shortened state at the shoulder joint, and therefore is not
capable of producing high levels of force at the elbow joint.
That is why overhead movements preferentially recruit the long head of the
triceps! It’s not that lying triceps extensions, pressdowns, or even kickbacks
work the lateral and medial heads more than the long head, it’s that the long
head is not capable of producing force due to being in a shortened position at
the shoulder joint, and by default the only two primary muscles left that are
responsible for extending the elbow are the lateral and medial heads of the
triceps.
SHORT HEAD OF THE
BICEP
The short head of the bicep is responsible for two movements – elbow
flexion, and shoulder flexion (think of performing a front raise). This means
that when the shoulder is flexed, and the upper arm is in front of the body, or
raised out to the side, that the short head is already in a shortened state at
the shoulder joint, and therefore is not capable of producing high levels of
force at the elbow joint.
This is why movements like two-arm high-cable curls, concentration curls,
or even preacher curls preferentially recruit the other primary elbow flexors
(long head of the bicep, brachialis) at the expense of the short head. It’s not
that movements where the elbow is placed in front of, or at the side of the
body, put the long head and brachialis at a mechanical advantage, it’s that the
short head is at a mechanical disadvantage, so by default the only two primary
muscles left to flex the elbow are the long head and brachialis.
MEDIAL HAMSTRINGS
The medial hamstrings are responsible for two primary movements – hip
extension, and knee flexion. This means when the hip is extended (as in a lying
leg curl or standing single-leg curl), the medial hamstrings are already in a
shortened state at the hip joint, and therefore are not capable of producing
high levels of force at the knee joint.
This is why lying leg curls, or standing single-leg curls preferentially
recruit the lateral hamstrings at the expense of the medial hamstrings (given
that the feet are placed in a neutral position. Tension can be redirected by
altering foot position).
On the other hand, when the hip is flexed (as in a seated leg curl), the
medial hamstrings are in a lengthened state at the hip joint, and therefore are
capable of producing higher levels of force at the knee joint.
This is why seated leg curls preferentially recruit the medial hamstrings
to a greater percentage than when the hip is extended (think lying leg curl, or
standing single-leg curl again) given that the feet are placed in a neutral
position (tension can be redirected by altering foot position).
As far as hip extension is concerned, when the knees are bent the hamstrings
are in a shortened state at the knee joint, and therefore are not capable of
producing high levels of force at the hip joint.
This means that hip dominant movements like deadlifts, RDL’s (Romanian
deadlifts), good mornings, etc. preferentially recruit muscles like the glutes,
and erectors to a greater percentage when the knees are bent.
On the other hand, when the knees are extended, the hamstrings are in a
lengthened state at the knee joint, and therefore are capable of producing
higher levels of force at the hip joint.
This means that hip dominant movements like stiff-leg deadlifts, good
mornings, etc. preferentially recruit the hamstrings to a greater percentage
when the knee is exteded.
RECTUS FEMORIS –
QUAD
The rectus femoris is responsible for two movements – knee extension, and
hip flexion. This means that when the hip is flexed the rectus femoris is
already in a shortened state at the hip joint, and therefore is not capable of
producing high levels of force at the knee joint.
To put this to the test for yourself, try lifting your knee up as high as
you can (flexing at the hip), and then straighten your leg. You may notice that
it is extremely difficult to fully straighten your knee forcefully, depending
on your level of flexibility, then if your hip is extended and you try to
straighten your leg (flexing your quad in a standing position). There’s no
question that you can flex your quad harder when your hip is extended and you
are standing up straight, then when your leg is raised in front of you (even if
it is resting on a stable surface).
This means that the rectus femoris is preferentially recruited during leg
extensions when the hip is in a more extended position (laying back as far as
possible), and the other knee extensors are preferentially recruited when the
hip is in a more flexed position (sitting up, or leaning forward as much as
possible).
Tom Platz, who is said to have the greatest leg development of all-time in
the bodybuilding community, took advantage of this biomechanical law by often
performing his leg extensions while laying down (unfortunately most leg
extensions made these days do not allow for this at the seat is often
irremovable) and therefore recruiting more of the rectus femoris, and thus
leading to some of the deepest separation between the heads of the quad that
the world had ever seen.
GASTROC – CALF
The gastroc is responsible for two movements – ankle extension, and knee flexion.
This means when the ankle is extended, the gastroc is already in a shortened
state at the ankle joint, and therefore is not capable of producing high levels
of force at the knee joint.
This means the hamstrings are preferentially recruited during leg curls
(lying, seated, etc.) when the ankle is in an extended position. When the ankle
is flexed (toes pointing up toward the knee), the gastroc is lengthened at the
ankle joint, and therefore can contribute forcefully to produce knee flexion
(therefore improving your ability to lift more weight as the gastroc is
primarily fast twitch dominant).
As far as ankle extension is concerned, when the knees are bent the
gastroc is in a shortened state at the knee joint, and therefore is not capable
of producing high levels of force at the ankle joint.
This is why seated calf raises preferentially recruit the soleus at the
expense of the gastroc. Because the gastroc is already shortened at the knee
joint, due to the leg being bent, the soleus is the primary muscle left that is
responsible for ankle extension.
When the knee is extended, the gastroc is in a shortened state at the knee
joint, and therefore is capable of producing high levels of force at the ankle
joint.
This is why the gastroc is preferentially recruited during standing calf
raises. The soleus contributes to ankle extension as well, but to a much lower
percentage than when the gastroc is inhibited by a seated (bent-knee) position.
HOW TO PRACTICALLY
APPLY ALL THIS INFORMATION ABOUT BIOMECHANICS
-
Triceps
If you want to prioritize the long head of the triceps, then movements
where the elbow is above the head are most effective.
If you want to prioritize the lateral and medial heads of the triceps,
then movements where the elbow is closer to the body are most effective.
-
Biceps
If you want to deemphasize the short head of the biceps, then movements
where the elbow is either raised in front of the body, or elevated to the side
of the body, are most appropriate.
-
Hamstrings
If you want to prioritize the medial hamstrings while doing leg curls,
then movements where the hips are flexed are most effective.
If you want to prioritize the lateral hamstrings while doing leg curls,
then movements where the hips are extended are most effective.
If you want to prioritize the hamstrings as hip extensors, then keep your
legs as straight as possible during hip dominant movements.
If you want to prioritize the glutes during hip dominant movements, then
keep your legs flexed as much as necessary.
-
Quads
If you want to place as much emphasis on the rectus femoris as possible
while doing leg extensions, adjust the machine so that your upper body can lay
back as far as possible while maintaining stability.
If you want to place as much emphasis on the other heads of the quadriceps
as possible while doing leg extensions, adjust the machine so that your back is
tight against the pad, or even lean as far forward as possible while
maintaining stability.
-
Calves
If you want to prioritize the gastroc while doing calf raises, then
perform them with the knee as extended as possible (standing).
If you want to prioritize the soleus while doing calf raises, then perform
them with the knee bent (seated).
If you want to place as much emphasis on the hamstrings as possible while
doing leg curls, point your toes away from your body (flex your calf).
If you want to rely on your calf to assist with your leg curl, and
therefore help you lift more weight, point your toes toward your knee.
If you have any questions
about biomechanics or active insufficiency, feel free to contact me at ben@paramounttraining.ca. I'm
available for online consulting and personalized program design, as well as one
on one training if you are located in the Greater Toronto Area (GTA).
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