-: Hey everyone.
So in this section we're gonna talk
about the stimulus progression on the physiological level
and why it's necessary and just the underpinnings
of why progressive overload needs to occur.
So some topics that we're gonna discuss,
on a physiological level,
what are the primary objectives we're trying
to accomplish when we train?
So essentially, what are the mechanisms of muscle growth?
Why do the muscles grow in response to training?
And then within that, what are some of the important
physiological objectives that govern our ability
to meet the the above objectives, the above mechanisms?
How do those work in concert with one another
to provide those outcomes?
And then what training tools at our disposal do we have
to accomplish these objectives and what role do they play
in the big picture?
And so just to back up for a second.
So with that things, tools being our programming variables:
sets, reps, load, proximity to failure,
and things like that.
So rest intervals, we're gonna talk about that a bit.
And I can't remember if I touched on that in the day two
lecture or not, but on the physiological level
why does ongoing adaptation require an increase
in stimulus over time?
And then how can this training stimulus impact
or how can training status impact how we manage
the training stimulus?
Should our progressions be different as a novice
versus an advanced athlete?
And why is that conceptually?
And then why is the rate
of stimulus progression so important?
And this kind of ties into the above bullet point
with training experience but hopefully give you
a good understanding of both conceptually
and on the physiological level
how things change over time.
All right, so, with regards to the first point,
what causes the muscle to grow?
There's three primary proposed mechanisms
for muscle hypertrophy, there's mechanical tension,
which is well accepted to be the primary mechanism
for hypertrophy and then there's metabolic stress
and muscle damage.
And these were both proposed in a paper by Brad Schoenfeld,
I think back in 2009.
And since then, most of the weight of the evidence
shows the mechanical tension is the driving factor.
Whether metabolic stress causes an additional role
on top of that, or more augments our ability
to create mechanical tension is still a little bit,
needs to be teased out.
It's a tough question to answer
because it's hard to create metabolic stress
without some form of mechanical tension,
and then the role of muscle damage I think
is more to do with scale.
And it's more related to your capacity for muscle growth.
And we're not gonna talk too much about that,
but
muscle damage can be, in excess quantities can be
pretty detrimental for managing the training stimulus,
placing mechanical tension where we want it,
but small doses or small amounts of muscle damage
can be beneficial in terms of sort of increasing
our capacity for muscle growth
through additional satellite cells and things like that.
So what is mechanical tension?
So mechanical tension is the primary mechanism
by which hypertrophy occurs.
So we have these sensors, mechanosensors at the fiber level.
They detect the loading on the muscle fiber,
both through the stretch, like the tendon to tendon tension
and like the act of tension within the fiber itself.
So the cross bridging that occurs between the myosin
and the actin within the muscle fiber that creates
that pulling force across the sarcomere.
And so it's two sort of types of tension
this absolute like tendon to tendon,
you kind of think of that as being influenced
largely by load and then the active tension
which isn't is directly influenced by load.
And we'll talk a little bit more about that
but these sensors can detect both types.
And then the other important aspect is it's sensitive
to both the magnitude and the duration of exposure.
So if it was only related to the magnitude of tension
something like a 1RM would be
the most hypertrophic stimulus possible,
that would be all you would have to do but we know
volume is the large player in muscle hypertrophy
and that sort of addresses the duration of tension.
It's sort of the dosing of the mechanical tension.
And so these sensors are influenced by both of those.
And these sensors, ultimately they sense this tension
it leads to a process called mechanotransduction.
It's the process that this mechanical stress leads
to a cascade of intracellular signaling processes
and this ultimately increases muscle protein synthesis.
So we're not gonna get deep into the pathways
or anything like that nor am I an expert
in those specifically.
But think of it as you place tension on a muscle fiber,
there's a response in terms of both muscle breakdown
but muscle protein synthesis as well.
And ultimately, if we're gonna grow,
synthesis has to exceed breakdown
across whatever period of time we're examining.
So it is the mechanical tension that ultimately
signals this increase in muscle protein.
All right, so how does mechanical tension occur?
I touched on the fact that active tension,
this force generated through cross bridging
but it requires a motor unit to be recruited.
So motor unit recruitment, ultimately it increases
on an as needed basis to meet or maintain force output.
So this can be based on the magnitude of load.
Obviously heavy loads require a large magnitude
of force out of the gate,
increased fatigue in a decreased proximity to failure
is motor units become fatigued and start to contribute less,
other motor units have to take over in a sense,
and a larger proportion of the absolute magnitude
of tension is going to be sort of shouldered
by those motor units.
And so, because fatigue exists across the set,
you can still place a high degree of mechanical tension
on these high threshold motor units.
And then the other one is contraction velocity.
Like plyometrics lead to high degrees
of motor unit recruitment but the duration of exposure
is very low.
So in order to accelerate rapidly even with a light load,
you're going to recruit these higher threshold motor units
but it's not a good hypertrophy stimulus
because it's such a short exposure there.
Then higher force demands result in slower contraction
velocities and greater degrees of cross bridging.
So if you think about a one rep max, it's a good example.
No one ever blows through a 1RM.
It's a grindy rep, especially as you get more well trained,
your ability to grind through reps increases.
And with that slow contraction velocity there's going to be
greater degrees of cross bridging
that are occurring simultaneously.
So that results in higher degrees of mechanical tension.
So what this ultimately means is that adequate load
and effort ensures that not only are these higher
threshold motor units recruited but also accommodate
these slower contraction velocities and these high degrees
of cross bridging at a given time.
So the force velocity relationship at the fiber level,
this probably oversimplified graph just illustrates
that on the left side of this graph
is contraction velocity
or fiber force is going to be going up
as contractual velocity goes down.
So if we're on the far right of that
you know that you're going to see fiber force
on an individual fiber level be a little bit slower.
And so, or fiber force be lower.
So ultimately I think this concept,
the force velocity relationship is often misunderstood
because there's a difference between the movement velocity,
so like your ability to squat and perform a rep
like with an empty bar, your contraction velocity,
movement velocity are going to be very high
but the fiber force is going to be on an individual
fiber level is going to be low.
So, but once things start to slow down,
mechanical tension, when there's high forces,
high absolute loads, there's going to be higher degrees
of mechanical tension on the fiber level
with that decrease in contraction velocity.
So we think of movement velocity.
It's when we're talking about accelerating a bar,
if there's a low mass, but high acceleration,
you're still gonna get a decent amount of force output
but at the fiber level, that's still gonna be pretty low.
So hopefully you can understand there's a difference
when you're looking at the whole movement
versus the fiber level.
So mechanical tension toolbox.
So what are our tools available programming wise?
So we kind of wanna break this up
into this per fiber force tension
and then kind of the duration of exposure.
So we're talking about per fiber force
just to reinforce what we've talked about,
intensity of load, intensity of efforts,
so proximity of failure, and then contraction velocity.
Duration of exposure, we have the number of reps
within a set.
We have evidence to suggest that there's a rough number
of reps that should be achieved in order to accrue
enough mechanical tension across a set for it
to really contribute an appreciable amount
on a set to set basis.
So it doesn't mean that sets below six reps
are going to
they're not going to contribute to hypertrophy,
but when we look at research that's equating sets
and shows non-significant changes in hypertrophy.
It's usually somewhere between like six and 30 reps.
So sets below that can still contribute
but usually it requires an additional amount of sets.
And I mentioned this mostly because just to illustrate
on a per set basis, reps do matter, but hypertrophy,
just to reiterate, we don't know,
over a training career over a macro cycle,
how the influence and if hypertrophy
would necessarily be equal.
It's likely if I had to hypothesize on this,
it's likely that there is going to be some differences
between training at six reps versus 30 reps
over an extended period of time.
It's a different type of stimulus,
but in the research that we have available
in the shorter time frames that we have,
it doesn't seem to make as big of a difference.
So yeah, the number of sets, this is sort of like
the dosing of the tension.
So all else equal, the more sets, the greater
the overall volume of stimulus.
And the all else being the key component to that
'cause the volume of stimulus is going to be related
to the per fiber force as well as the duration of exposure.
So more sets that are not at a high enough intensity
of effort, isn't necessarily going to mean
an overall larger volume of stimulus.
So it needs to be adequate enough effort.
And then the dosing of that is going to the number
of sets is going to really influence the total volume
of stimulus, which can kind of be thought
of as the impulse, so to speak,
so it's the force times duration of exposure.
And then we also have tempo.
And I'm sure everyone's heard the term time under tension.
Obviously that's going to influence
the duration of exposure on a per rep basis.
You can emphasize different areas of the range
of motion to, or bias specific ends of the range
of motion where it's most demanding.
So that the tempo aspect is like long reps
aren't necessarily always better.
And generally, in most cases, lifting with high intent
on the concentric is going to be advisable.
There are some caveats to that which Cass can discuss,
but tempo does play a role in dosing
of that mechanical tension.
So per fiber times duration of exposure
the volume of the tension stimulus.
Okay so-
-: Brian, maybe this would be a great place to just
do a quick recap on mechanical tension
before we move on of just like the take aways
from that whole last section, right?
So I'll summarize and then in as simple as terms,
and then you let me know.
So just so that everybody gets this like one more time
in kind of rapid fire, what we're gonna be looking at
in terms of this model for progressive overload
is it's gonna be based off of mainly mechanical tension,
and mechanical tension magnitude is basically gonna be
based off of well how much active tension are we producing,
which is how many motor units and to what degree
are we recruiting them?
What the force velocity curve brings into a place
is that it's not just our recruitment of those fibers
but they have to be acting on a resistance
because tension comes from force from the fibers
against the resistance.
And that's why that force velocity curve
of the unvoluntarily slowing of reps.
That's where it's like, okay, you're getting a high degree
of recruitment against a high degree of resistance,
and that's what makes the reps slower.
So it's not that the reps speeds being slower
is the mechanism, it's that the rep speed being slower
is happening because of the high resistance being placed
on top of that high threshold of motor recruitment.
So that's our magnitude.
And then the volume is gonna come from the rep, sets, tempo,
and how you can coordinate and arrange that or whatever.
And we'll get more into that as we look
into the practical side of that thing.
But I think when we're looking at mechanical tension,
we'll talk more about this is whatever it just,
that reps and sets and tempo.
Those are all things that are gonna affect the volume
but they don't necessarily affect the volume the same way
because you can only get so much stimulus
within a given set.
So there will be a certain,
like sets will kind of be a variable
that has to be looked at a little bit separate,
whereas reps and tempo are gonna kind of overlap
in the way that they're gonna affect like volume of tension.
Does that seem like a pretty
fair? -: Yeah, no,
that was excellent.
-: Okay. -: Yeah.
-: Okay, cool. -: Yeah, thank you.