Being able to identify and correct weaknesses in powerlifting is a critical aspect of long term progress. But one of the issues that some athletes run into is selecting the exercise best suited to fix their deficiency. In this article we’ll explore some fundamental concepts of biomechanics to elucidate what exercise(s) should be used to address this weak point and build more muscle and strength in your quads.

First we need to introduce the term Torque which is defined as a twisting force that tends to cause rotation (1). To express torque we use the equation T = F * r * sin(theta)

T = torque

F = linear force

r = distance measured from the axis of rotation to where the linear force is applied

theta = the angle between F and r

Another way to express torque is T = F*r. In this equation we multiply the linear force by the distance from the axis of rotation. For simplicity sake we’re going to use this equation. Lets take three types of squats for our example: the low bar squat, the high bar squat and the front squat.

The red dot in the image represents the barbell and its relative location. You can see that in each squat variation the line of force (the dotted line) changes in relation to the hip and knee joints. In this case the knees and the hips are the primary axis of rotation and since we know that the calculation for torque is F * r we can determine which variation has the most impact on the quadriceps. To keep things simple we can assign arbitrary numerical values to each variation to demonstrate how each squat variation loads your musculature. The load of the bar will remain constant at 100N (newtons) in each variation.

In the image above the numbers located between the dotted line and the joints represent the distance between the axis of rotation and the linear force. These are just units of measurement for the sake of this example and are not actual values from any data set.

Using these values we can calculate torque to see which joint generates the most torque for each variation. The chart below uses the distances outlined in the above diagram with a standardized force of 100N.

As you can see, the low bar squat generates the most torque in the hips, the front squat generates the most torque in the knee and the high bar squat has a relatively even distribution of torque between the hips and knees.

Since the quadriceps primary role is knee extension they are responsible for overcoming the external torque applied to the knee by the load (2). So we can see that front squats develop the quads the most. However I want to highlight a point; just because an exercise should theoretically produce a specific outcome does not mean the outcome is guaranteed.

There are many factors that could change the outcome, one such factor is technique (3). If you’re doing a high bar squat but on the ascent your hips shoot up and your knees travel backward then you change the leverages. So what was initially intended to develop your hips and quads relatively equally has now become a more hip and back dominant movement.

When one of my athletes is struggling with a particular part of a lift the first thing I do before prescribing a “corrective exercise” (and I use this term loosely) is to watch the lift. I want to first rule out technical errors that may be the cause of the breakdown in the lift. More often than not it’s a technical issue, so a specific exercise isn’t necessary and would likely do little or nothing to improve the main lift since it may not address the technical issue limiting the performance of the primary lift.

But lets assume that your technique is not an issue, and you still want to develop your quad musculature and strength. In many cases the front squat variation may be a good break to reduce training staleness or prevent overuse injuries. But since it’s less specific there is the potential drawback of spending less time practicing the competitive movement. So depending on where you are in your competitive cycle its implementation may or may not be appropriate.

As you get closer to your powerlifting meet your volume will decrease relatively and your exercises will become more specific as the intensity increases (4). So depending on the individual, the last month of a competition cycle may not be the best time to introduce front squats into the mix. However, you can still build significant strength and size in your quadriceps by implementing belt squats. This is one of my favourite exercises for a few important reasons.

The movement pattern is virtually identical to a low bar squat and since there is no axial load and the overall load has decreased it’s substantially less fatiguing than barbell squats (5). Because of this, the stimulus to fatigue ratio ends up in your favour. This is an effective alternative to front squats if you are getting closer to your meet and still want to spend a bit more attention on building or maintaining your quad strength.

Now that we’ve covered the basic biomechanics of torque, lets look at muscle physiology and how different phases of the squat relate to building muscle and strength. This is important because by understanding the force velocity curve and basic muscle physiology we can implement strategies to maximize the training benefit at each phase of the lift. The basic contractile unit of a muscle is called a sarcomere (6). These are arranged in a sequential stripped pattern along each muscle fiber as show below.

Within each sarcomere are actin and myosin filaments. When they receive instructions from the motor neurone to contract these actin and myosin filaments attach to each other and pull the Z lines closer together. This process is called sliding filament theory and describes the process of muscular contraction (6). What researchers have observed is that there is an optimal length by which the sarcomere can generate the most force. This is known as the length tension relationship (7).