The Moment Model: First Principles

by Michael Jones, SSC | July 01, 2025

I hear it from the bros all the time. I also hear it from aspiring
coaches. “The front squat is quad-dominant.” There is also its
cousin coming from barbell enthusiasts, “We use the low-bar squat
technique because it uses more muscle mass” or, as more of the
barbell community is becoming aware of our mechanical analysis of the
lifts, “Because of moment arms.” These all come from a similar
line of thinking that isn’t quite fully thought-out.

Starting Strength uses
mechanical and physiological analyses to justify how we coach and
train barbell lifts. And it is important how we talk about what it is
we do because it is not only what separates us from the chaff, but it
is the bedrock of first principles in which we have our roots
planted. What then is Starting Strength?

Starting Strength is
two-fold: it is the moment-arm model of barbell training (informed by
mechanics as well as anatomy and physiology), and a cohesive model of
programming with an objective, systematic, prescriptive approach to
get the barbell lifts stronger. We choose which barbell lifts we
train with the four criteria.

 The dual treatment of mechanics and physiology is well exemplified by
SSC Mia Inman in her article, An Examination of Control of the Supine Hand in a Heavy Deadlift.

We don’t write or speak this way to be obtuse or pedantic, but
instead because when we say something about training, we want to do
so in a correct way that is intentional in logic, word choice, and
rooted in first principles. In this way, when we talk about why we
squat the way we do, the sequence of causation and “if this, then
that” is important. In the following, I trace such a line of
reasoning:

P1: If I put the bar in
the lowest stable place on my back, and

P2: if I want to
maintain mid-foot balance,

IC1: then I will have
to bend over more.

P3: If I have to bend
over more (IC1), and

P2: if I want to
maintain mid-foot balance,

IC2: then I will have
created a longer moment arm between the barbell and my hips, and

IC3: I will also have
brought my hamstrings into their strongest position.

P4: If I create a
longer moment arm between the barbell and my hips (IC2), and

P5: if a longer moment
arm allows for larger percentage of the load seen at the hip as
opposed to the knee,

IC4: then I will be
able to put more load on the barbell because the hips operate more
muscle mass.

P6: if I am able to put
more load on the barbell (IC3),

IC5: then more force
needs to be produced, and

IC6: then more motor
units will be recruited to complete the lift.

C: We low-bar squat to
more effectively train the muscle mass we have access to.

Said more succinctly,
we put the bar in the low position to facilitate a more horizontal
back angle. This means the hips must reach back further than in other
variations of the squat if we are to stay balanced. When we do this,
the longer the moment arm created between the hips and the load, and
the more moment seen at the hips (and less at the knees relative to
the hips and to other kinds of squats) means that we have longer
muscle belly lengths that can do more contractile work on the load.

For the hamstrings,
this work is largely isometric since the muscle bellies do not change
length to a significant extent. The hamstrings are supporting the
load that is being moved by the hips and the knees. The front squat
and the low-bar squat may use the same muscles, but the low-bar
position is more effective at doing work with that muscle mass, and
as a result you can squat heavier weights in that position.

As for the front squat
being “quad-dominant,” perhaps it is knee-dominant in that it
puts more range of motion about the knee relative to the hips. But,
at the risk of shocking no one, if you get your low-bar squat
stronger, the front squat and the quads will get bigger and stronger
even if you don’t train the front squat,
because the low-bar squat involves loaded knee extension with
increasingly heavy weight. And this is really hard for folks
to understand. I am not sure if they are averse to the simplicity of
doing the harder thing, or averse to thinking the logic through, or
even of thinking about it at all.

If we rely on
irreducible truths that cannot be refuted, and if we are honest with
ourselves about what we do and don’t understand about how these
truths work together, then we will undoubtedly come to the same
conclusions. Starting Strength has always been sincere in stating
that if there is something wrong in our analysis, then we will have
to change our thinking about it. Rip is of the same mind. But dammit
if he isn’t right most of the time. And of the few times I’ve
witnessed where he hasn’t been, he has been awfully gracious about
it.

Thanks to Brent Carter for his assistance in the aforementioned
analysis.