Quadriceps: How to work them with squats?

Sergio Molina, coach at MASmusculo Fit, explains how we can use the squat to work and strengthen the quadriceps more effectively.

If you have been training for a while, you should already understand that if you want to develop a muscular, strong physique, you need to design your leg days as effectively as possible, and in this case, the quadriceps are highly relevant.

Fortunately, you can learn not only how to train your legs but also how to do so in a way that helps you gain size, strength, and muscle.

Why the Squat Is Essential

The squat is the ultimate lower-body exercise; it is the undisputed king of leg exercises, and for powerful quadriceps, it is a must in your leg routine.

It is a challenging, full-body exercise for the athlete that not only gives you that adrenaline rush but also causes significant DOMS (delayed-onset muscle soreness), but the results will show that it is worth it.

The squat is best performed inside a squat rack for safety reasons, and here we will not discuss how to develop it, but how to make it more effective.

Everyone knows that front squats are more «quadriceps-dominant» than back squats and therefore work those huge muscles at the front of the legs more, giving you an impressive physique.

Physics Matters When Training

Now, we could analyze the biomechanics of different squat techniques, observing how torque is generated and manipulated at the hip, knee, and lower back using a static mathematical model.

Imagine you are holding a 5 kg dumbbell in front of you at shoulder height… can you feel the weight trying to pull your arm down?

What you feel is the force of gravity, which always pulls downward; as gravity pulls on the dumbbell, it creates a rotational force in the shoulder joint.

This force is called torque, and we discuss it because the shoulder muscles must activate to overcome this force and prevent the weight from moving.

The distance between the force of gravity and the point of rotation (the shoulder joint in this case) is called the lever arm.

Like a wrench turning a bolt, the longer the moment arm, the more rotational force (torque) can be applied at the joint.

The “moment arm” is used to describe the distance from the point of force (the dumbbell) to the point of rotation (the joint axis in this case) at a 90-degree angle.

When the arm is at 90 degrees, the moment arm is the same length as the lever arm.

• Now imagine that someone tied a rope around the same 5 kg dumbbell and tied it to your elbow; the result: “it would now be much easier to hold your arm out in front of you.”
• This is because the length of the moment arm decreased, meaning that the shoulder required less force (torque) to keep the arm extended.

Does that make sense?…

The Squat and Physics: How Are They Related?

If we take a snapshot of a squat in the parallel position, we can calculate the amount of torque generated at each joint complex (hips, knees, and lower back).

As mentioned earlier, gravity always pulls downward, and during the squat it is often represented as a vertical line drawn through the center of the bar; this vertical line then passes through the body and bisects the thigh.

The distance from this vertical line to the center of a joint becomes a moment arm (like a wrench turning a bolt).

Sports scientists will often analyze the squat in a parallel squat position (the hip crease aligned with the knee).

The longer the moment arm in this position, the more torque will be generated at that joint during the squat.

Front Squat vs. Back Squat

When we analyze different squat techniques, we find some interesting things.

• The back squat has a longer moment arm than the front squat, making it more efficient for lifting heavy weights (this is known as leverage). Mechanically, our bodies can squat more weight when the moment arm at the hips is longer.
• The front squat—with a more upright torso position—creates a longer moment arm at the knee and therefore applies more torque to the knee joint.

Many will take these findings and claim that the back squat prioritizes the hips compared with the front squat, which prioritizes the quadriceps.

They will also think that because there is more torque at the hips or knees in a particular squat technique, the musculature surrounding that specific joint must work harder to overcome that force.

Unfortunately, that is not how the body works during multijoint movements such as the squat.

Anatomy: fiction or reality?

Much of the misunderstanding about this subject stems from the way we first learned about the body … our anatomy textbooks….

Think about how muscles and their function are described in the literature;

• We have muscles that cross only one joint (called monoarticular) and muscles that cross two joints (called biarticular).
• At the front of your thigh, for example, you have the vastus medialis and vastus lateralis.
• Both muscles cross only the knee joint and are therefore considered monoarticular muscles that extend the knee when they contract.
• The rectus femoris is another quadriceps muscle that helps with knee extension; however, because it also crosses the hip joint (making it a biarticular muscle), it is also capable of flexing the hip joint when it contracts.

On the opposite side of the thigh, we find the hamstrings and the gluteus maximus; the gluteus maximus is one of the most powerful muscles in the entire body; it is a monoarticular muscle because it only crosses the hip joint.

The semitendinosus (one of the hamstrings) is a biarticular muscle that crosses the hip and knee joints.

Therefore, this muscle can be used to extend the hip or flex the knee, making it a direct antagonist of the quadriceps.

According to “your anatomy textbook,” if the quadriceps contract forcefully to try to extend the knee, the hamstrings must relax to allow the movement to occur. Sound familiar?

Quadriceps: which squat?

At the beginning of the 1900s, there was a biomechanist named W.P. Lombard who investigated how the body really works, beyond our textbook understanding (1).

The “paradox” described occurs when muscles that technically should oppose each other are active during certain movements. For example, when we perform a squat, the hamstrings and quadriceps are activated.

If the hamstrings (which flex the knee) are activated at the same time as the quadriceps (which extend the knee), shouldn’t the body simply freeze and not move?

So, any conclusions about what happens during the squat?

• The glutes can indirectly extend the knee joint.
• The quadriceps can indirectly extend the hip joint.

Basically, the glutes and vastus muscles of the quadriceps function as force and work generators, while the hamstrings and rectus muscles distribute torque and power between the two joints.

Now we can use this knowledge to help answer the question, “Are the quadriceps activated more during a front squat than during a back squat?”

• Although more torque is placed on the knee joint during a front squat, the body does NOT activate the quadriceps more to overcome this force.
• The quadriceps are already “switched on” during the squat to lift the weight; instead, the body redistributes power from the hips to the knees to help the body complete the lift.

Therefore, the quadriceps are not activated more in a front squat; it all depends on how you activate them.

Remember, whenever you train hard, you require a nutritional stimulus.

Quadriceps: what is the paradigm?

During the ascent of a squat, ideally the chest and hips rise at the same time; this keeps the bar centered over the midfoot, which means the body is balanced and able to produce efficient power.

However, as athletes become fatigued while squatting (near the end of a high-repetition training session or when attempting an almost-maximal weight), they often lose their ability to stay balanced and maintain perfect coordination, allowing their chest to fall forward.

Excessive forward torso lean causes the hips to rise faster than the chest during the squat ascent, which lengthens the hamstrings.

Because the biarticular hamstrings are now lengthened, the body loses the ability to transfer force from the quadriceps to help the glutes extend the hip.

Dr. Gregory Myer and Dr. Brad Schoenfeld have explained this failure as a problem with suboptimal motor recruitment patterns (that is, the body's ability to activate the right muscles at the right time to maintain technique) (2).

What this means is that this is not caused solely by a lack of strength in the quadriceps, but rather by problems with coordination and motor control that lead to a breakdown, resulting in the Lombard paradox (1900).

The conclusion here would be that, rather than considering quadriceps weakness, the most likely cause of this technical failure is the ability to “activate” the glutes at the right moment due to fatigue.

Quadriceps: how do you train them?

Although a squat may appear more “hip-dominant” or “quadriceps-dominant,” the squat does not train the quadriceps, hamstrings, or glutes exclusively.

All the muscles in the lower body activate together to extend the hips and knees, regardless of what the squat looks like or how much torque is applied to the joints.

The solution proposed by Sergio Molina is to use a safety bar with a handle (security bar ), increasing quadriceps engagement because there is less hip flexion, while even improving wrist comfort.

In the case of a front squat, the forces change and therefore the demand placed on the muscle changes, with a much more upright torso, making quadriceps involvement greater.

The point is that in bilateral movements supported by the hands, athletes can express the intent and development of force that cannot be achieved with standard heavy unilateral work.

This leads to improved adaptations and, ultimately, peak performance, by using manual support from the handles on the bar.

Quadriceps: More efficient training?

Using a safety squat bar with a handle is the remedy for several of the problems addressed above.

Historically, Fred Hatfield originally popularized it, and the eponymous “Hatfield Squat” has appeared in some circles, including bodybuilding.

Dr. Fred Hatfield, also known as Dr. Squat, was the first man, at age 45, to set a world squat record by lifting 1,014 pounds in the 100 kg weight class, the first person to squat more than 1,000 pounds.

According to the logic, when the “sticking point” is reached, you can use your hands to help you get past it (3).

This unique feature allows you to work with heavier weights in the ranges of motion where you are strongest and gives you assistance when you are weaker, working closer to your maximum effort throughout the entire range of motion.

For everyone, the goal is to work as close as possible to maximum effort; in Hatfield's case, he liked using the movement to add volume at higher intensities than could be achieved with conventional squats.

Hatfield also preferred the weight distribution offered by the safety squat bar.

• The conventional squat places the weight behind you, about 10 cm behind your body's midline; this may cause you to lean forward to maintain balance.
• With the safety squat bar with a handle, the weight is distributed directly in line with your body's midline, reducing the need to lean forward and placing much more of the effort on the quadriceps.

References

• (1) Cavanagh PR & LaFortune M. Knee flexor moments during propulsion in cycling – a creative solution to lombard’s paradox. J. Biomechanis. 1985; 18(5): 307-316.
• (2) Sinclair J, Atkins S, Vincent H, et al. Modelling muscle force distributions during the front and back squat in trained lifters. Central European Journal of Sport Sciences and Medicine. 2016; 14(2):13-20.
• (3) Power: A scientific approach, Frederick C. Hatfield – 1989