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.