The Saturday Deep-Dive: Torque and Stuff

Yesterday, I outlined direction of resistance and how to identify it. I did this using the example of a cable curl (below). Today, we’ll expand on what you learned and illustrate how this impacts exercise.

Direction of Resistance & Bony Position

Direction of resistance in an exercise should always be looked at in relation to the body.

For every direction of resistance, there is a relationship between the forces imposed by that resistance and our bones/joints. This relationship is ultimately what determines muscle recruitment.

In the context of the above curl, the resistance pulls my hand toward the floor.

Because the resistance pulls my hand downward, it attempts to “open” up my elbow via my hand and forearm.

In response, the elbow flexors (the biceps, the brachialis, and the brachioradialis) react to the external resistance by contracting.

If the resistance were pulling my hand in the opposite direction (imagine a cable behind my head that pulls my hand backward), then we’d call this a “triceps exercise” instead of a “biceps exercise”.

Resisting a Single Direction

Each position within an exercise will have a single direction of resistance, but these directions may change from position to position.

If you were to freeze-frame an exercise (like we did with the above curl), you’d identify a similar direction of resistance that changes subtly between the two positions.

In other words: any exercise contains multiple directions of resistance because your body position changes in relationship to force as you move.

However, suppose we attempt to impose multiple directions of resistance simultaneously by using a cable to pull the hand downward (as in a curl) with another cable that pulls the hand sideways (as in a rotator cuff exercise).

In that case, our bodies respond by downregulating contraction in certain tissues (likely the biceps) to manage whichever force is most difficult to resist (likely the rotator cuff forces). This example may seem ridiculous to some of you, but I promise I see examples of it constantly.

The simple takeaway: your body will respond to the direction of resistance that is most difficult to respond to. Think about this like you’d think about the “lowest common denominator” in mathematics. The tissue with the highest challenge will be the one to limit the exercise you’re doing, regardless of how many cues you use to try to prevent it from fatiguing first.

If you impose multiple resistance directions simultaneously, you’re likely not fatiguing any single group of tissues significantly. Rather, you’re distributing effort through so many different directions that each muscle does a relatively low amount of work (common examples are any movement that people generally define as “functional” movements).

Why Does it Matter?

Because resistance is what determines the outcome of an exercise.

To reiterate: a single direction of resistance does not imply a single direction of influence - this is because our bodies move through space and our bones orient differently (relative to the resistance) throughout any exercise.

Remember that I’m now referring to a single resistance changing its influence as you move.

I’m NOT referring to using multiple different implements to load yourself. Recall the (single) direction of resistance can change during an exercise and that your body responds differently to the portions of a range of motion.

Using the example above, let’s look at how the change in direction influences the curl.

In the image above, I’ve indicated how the direction of resistance changes, and how that change in direction alters influence on the elbow in the bottom position compared to the top.

The red arrows indicate the direction of resistance. But the green lines represent how far away the resistance is from my elbow.

As a rule of thumb, the longer the distance of the green line, the more difficult that portion of the exercise will be.

In this example, the bottom position is far more difficult than the top position.

This is because the resistance acts much farther away from the elbow joint (a longer green line) at the bottom.

This is not “good” or “bad”. Rather, these are objective qualities that tell us how exercise influences our joints and muscles.

To understand how this works, we need to understand torque.

Torque

Think of torque as a property of force.

Torque describes a force’s effectiveness against our bodies - it is not a force in and of itself.

Some define torque as the “strength of rotation” of a force.

In this example, torque tells us why the bottom position of the curl is heavier than the top. It’s not because the weight of the cable stack got heavier (of course it’s the same) - it’s because the distance is longer.

The equation for torque = force x shortest distance.

This distance is called a moment arm, and I’ve indicated the moment arm in the above photos by drawing green lines.

A moment arm is an intangible line representing the shortest distance between a direction of force and an axis. In this case, the axis in question is the elbow joint.

So, we can draw the moment arm from the elbow joint to the direction of resistance.

An important feature of moment arms is that they always intersect a direction of resistance at 90º. This makes them the shortest distance (“perpendicular distance” is another synonymous term).

Moment arms can only be drawn accurately from a 90º frame of reference.

Imagine if you were looking at me performing this curl from straight-on - you wouldn’t be able to identify how long the moment arm distance is because you couldn’t accurately assess how far the direction of resistance is from my elbow.

This gets more complicated when we look at joints like the shoulder and hip, where there are many more movement options compared to the elbow and knee.

When looking at triceps and biceps exercises, looking at them from the above perspective is appropriate.

So What’s The Takeaway?

Torque alternation within an exercise creates a discrepancy in the magnitude of force we need to produce at various points in a range of motion.

Torque alteration also indicates which muscles need to generate higher or lower amounts of force, given that certain muscles have more or less leverage depending on the joint position and how it relates to the torque requirement of the weight we’re using.

Understanding torque and how changing the direction of resistance alters muscle recruitment IS understanding exercise.

Without understanding torque, we cannot ascertain which muscles are doing what, and to what degree each contributing muscle must contract.

Below are TWO videos from my online biomechanics course which covers torque in much more depth (30+ minutes of premium lecture). To view the videos, subscribe to the Daily Meathead for $5.

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