Understanding Torque in Strength Training
When we train, most of us focus on sets, reps, and load. Those are essential parts of lifting, for sure. But on a more fundamental level, physics—specifically, torque—influences every exercise we do.
Torque is a twisting force that causes an object to rotate. Unlike simple linear movements, most human motion involves rotation around a joint. How much effort your muscles must produce depends on the lever arm, the force applied, and the location of the fulcrum or pivot point.
We'll break down those terms later, but for now, just know that understanding torque allows you to tweak your training for maximum benefit. In this article, I'll go over torque, levers, and force and explain how they apply to a few common exercises.
Section 1: The Basics of Torque and Levers
In simple terms, torque determines how much rotational force is needed to move a limb or weight around a joint. We can calculate torque using the following formula:
Torque = Force x Distance
Force is the weight you are lifting. Distance is the perpendicular distance from the fulcrum (the joint) to the point where force is applied (the weight you are holding). This perpendicular distance from the joint to the weight is called the lever arm (or moment arm). When we lengthen the lever arm, the torque required to overcome the force increases, making an exercise harder.
Understanding Levers in the Human Body
The human body is essentially just a system of levers. A lever is a simple machine consisting of a rigid beam that rotates around a fixed point called a fulcrum. The three main components of a lever are:
Fulcrum: The pivot point, also called the axis of rotation (typically a joint)
Effort: The force exerted by muscles
Load: The external resistance (e.g., a dumbbell, barbell, kettlebell, cable, body weight, etc.)
In our bodies, bones acts as rigid beams and joints are the fulcrums. Muscles generate force to move bones around these joints, creating rotational movement. This system allows us to produce motion efficiently by modifying torque and force distribution across different muscle groups.
Three Classes of Levers in the Body
Not all levers are the same. Here’s a rundown of the three types:
First-class levers: The fulcrum is between the effort and the load (e.g., the neck moving the head)
Second-class levers: The load is between the fulcrum and effort (e.g., a calf raise)
Third-class levers: The effort is between the load and the fulcrum (e.g., bicep curl, most limb movements)
Section 2: Practical Applications in Strength Training
Let's examine real-world examples to see how torque and force distribution affect your lifts. We'll break down a few movements to see how torque affects each exercise's difficulty, efficiency, and muscle activation.
Example 1: The Bicep Curl
The bicep curl is a third-class lever and an excellent example of how lever arms affect difficulty.
Fulcrum: Your elbow joint
Effort: Your biceps muscle contracting
Load: The dumbbell (or any external weight in your hand)
When your forearm is horizontal (i.e., at a 90-degree elbow angle), the lever arm is the longest, creating maximum torque and therefore making the middle of a bicep curl feel the hardest. As you raise or lower the weight, the lever arm shortens, reducing torque and making the movement easier.
At the very top of the curl (when your hand is directly above your elbow) and the bottom (when your hand is directly below your elbow), the torque on your bicep is minimal, exerting little to no force. However, that doesn't mean the stretched position isn't important—starting from a fully extended position increases the range of motion and places the biceps under a loaded stretch, which can benefit muscle growth.
Example 2: The Squat
The squat is more complex because it involves two primary levers: the hip and the knee.
Fulcrums: Your hip and knee joints
Effort: Your quadriceps, glutes, and hamstrings contracting
Load: The barbell on your back
A hip-dominant squat (e.g., a low-bar squat or any squat in which you sit back aggressively) directs more torque to the hips and less to the knees, requiring more glute and hamstring activation. This happens because your center of mass shifts backward, increasing the moment arm at your hips while shortening it at your knees.
With hip-dominant squats:
Your shins are more vertical
Your torso is more angled
A knee-dominant squat (e.g., a high-bar squat, front squat, or any squat in which you push your knees forward aggressively) directs more torque to the knees and less to the hips, requiring greater quadriceps activation. This happens because as your knees track forward and your torso stays more upright, the moment arm at your knees increases while it shortens at your hips. This shift in force distribution keeps your center of mass over your midfoot for balance and stability.
With knee-dominant squats:
Your knees travel forward
Your torso is more upright
As a side note, using weightlifting shoes with a heel or placing your heels on wedges or small plates is one way many lifters can more comfortably achieve a deeper, more knee-dominant squat. The heel lift provides artificial ankle mobility, allowing the knees to track forward more, thus resulting in greater quad activation.
Example 3: The Deadlift
The deadlift is primarily a hip extension movement, with some contribution from knee extension, making it another multi-lever system. Torque distribution depends on your positioning and biomechanics, as well as the proximity of the barbell to your body.
Fulcrum: Your hip joints—mostly
Effort: Your hip extensors (glutes, hamstrings, spinal erectors)—mostly
Load: The barbell in hands
If you bend forward instead of hinging at your hips, or if the bar drifts too far in front of you, the moment arm between the bar and your hips increases. This forces your lower back to handle excessive torque rather than allowing your posterior chain (glutes and hamstrings) to move the load efficiently.
The farther the bar is from your body, the more strain it places on your lower back, increasing the risk of injury. Keeping the barbell close reduces the moment arm, putting you in a stronger position and making the lift safer.
A good deadlift setup involves positioning your armpits directly over the bar. This helps ensure that your hips function as a lever, allowing the torque needed to overcome the force of the barbell to come from your glutes and hamstrings, not your lower back.
Section 3: How Segment Lengths Affect Torque
Limb proportions—such as femur length relative to tibia/fibula length or humerus length relative to forearm length—significantly affect torque in different exercises. These variations influence the moment arm's length, altering movement mechanics.
Squat: Long vs. Short Femurs
Long femurs, shorter tibia/fibula: This creates a longer moment arm at the hips, making hip-dominant squatting (low bar, sitting back) more natural and mechanically efficient.
Short femurs, longer tibia/fibula: This allows for a shorter moment arm at the hips and a longer one at the knees, making knee-dominant squatting (high-bar, front squat) more efficient.
This is why some lifters struggle to maintain an upright torso in a deep squat—long femurs require more hip flexion to keep the center of mass over the midfoot. These lifters may compensate by using heel lifts or adjusting their squat technique to achieve a more balanced position (though heel elevation can potentially help a wide variety of body types squat deeper).
Deadlift: Torso vs. Femur Length
Long torso, shorter femurs: This generally allows for a more upright pulling position, reducing lower back torque.
Short torso, longer femurs: This often results in a more bent-over pulling position, increasing the moment arm between the bar and hips and requiring greater back engagement.
Anthropometric differences like this partially explain why some lifters naturally excel at conventional deadlifts, while others may find sumo deadlifts, which shorten the moment arm, more comfortable.
Bicep Curl: Humerus vs. Forearm Length
Shorter humerus, longer radius/ulna: This increases the lever arm, making curls feel harder since the weight is further from the elbow joint.
Longer humerus, shorter radius/ulna: This decreases the lever arm, reducing torque at the elbow.
These differences help explain why some lifters naturally experience greater tension in their biceps with the same weight, as they fundamentally change the distance from the force application point (the hand) to the axis of rotation (the elbow).
Section 4: Lever Arm Manipulation
Ever notice how holding a dumbbell with straight arms feels much harder than keeping it close to your chest, like in a goblet hold? That's because the farther the weight is from the joint, the more torque your muscles must generate.
Bringing a weight closer to the joint reduces torque and makes the lift easier. For example, doing a lateral raise with bent elbows brings the weights (force) closer to the axis of rotation (shoulder joints), shortening the lever arm and making the lift easier.
Extending a weight farther from the joint increases torque and makes the lift harder. For example, doing a lateral raise with straight elbows moves the weights (force) farther from the axis of rotation (shoulder joints), lengthening the lever arm and making the lift harder.
Implications for Strength Training
A longer lever arm creates a higher force demand (e.g., an exercise feels harder).
Adjusting joint angles can bias different muscle groups and alter force output (e.g., allow a stronger muscle group to take over or force a weaker muscle group to pick up the slack).
Technique modifications (e.g., hand width in a bench press or bending your knees on a leg raise) can manipulate torque for greater efficiency (advantageous for strength goals) or challenge (advantageous for hypertrophy goals).
Conclusion
To wrap things up, do you need to understand torque to grow muscle, gain strength, and stay injury-free? Probably not. But it certainly won't hurt, especially if you've experienced a lower back or joint injury.
In the most basic terms, remember that we want to keep torque within the primary muscles that create joint movement for our exercise—we don't want it traveling around all willy-nilly.
Next time you train, for each exercise in your workout, see if you can identify the axis of rotation and at what point the lever arm lengthens or shortens. What manipulations can you make to lengthen or shorten the lever arm, and how does that affect the effort you have to exert to move the load?
