The Ideal Exercise Resistance Curve: What it is & Why it Matters

Barbell Curl Exercise
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Every exercise has a resistance curve. Knowing what it is and choosing exercises with the best resistance curve to build muscle will help you get the most out of every exercise you perform. Let’s investigate.

What is the Resistance Curve?

The resistance curve is the changes in difficulty that you experience at different parts of an exercise. When you are ready to begin an exercise, the resistance curve is at 0 percent. At this point, the operating lever is parallel with the resistance, so it takes no effort to hold the weight. Then when you move the weight to a position where it is 25 percent between parallel and perpendicular, you are using 25 percent of the force required to lift the weight. When the weight comes perpendicular to the resistance, you will be using 100 percent of the force required. Then as you move beyond perpendicular, the force reduces back to zero at the end position.

We can illustrate this resistance curve with the barbell curl exercise. When the bar is at full arm’s length, there is zero resistance. Then when you begin to curl, the resistance increases. When you get to a point where your arms are bent at a right angle, you will be at 100 percent of the resistance curve – this is the hardest part of the curl. As you continue curling, the resistance decreases until, at the very top, there is no resistance again.

Not every resistance curve is the same. They differ based on the direction of the resistance and the body’s position in relation to the resistance. Before we identify the ideal resistance curve, let’s take a look at the types of resistance commonly found in the gym.

Free Weights
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Free Weights

Free weights (including your own body weight) always produce a gravity resistance which is straight down. A lever will be 100 percent when it is perpendicular to gravity (such as when curling at the midway point).

Cable Machines

Cable machines produce a resistance that is in line with the angle of the cable. In this way, the cable can redirect the direction of gravity. A lever will be at 100 percent when it is perpendicular to the cable.

Resistance Bands
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Resistance Bands

The direction of the resistance comes from the anchor point of the resistance band. However, resistance bands do not provide a consistent resistance. As the band stretches, the resistance increases.

The resistance curve that you get from bands is opposite to what you ideally want. When you use a band, the resistance is easier initially and hardest as the band is maximally stretched. However, muscles have a natural resistance curve that allows them to be strongest at the elongated (beginning part) of an exercise and weakest at the exercise’s contracted (end part). A good exercise will give you more resistance at the start of the exercise and less resistance at the end of the movement. That is the opposite of what you get with resistance bands.

Circular Cam Machines

Exercise machines will either have a circular cam or an oblong cam. A circular cam machine will provide you with an even level of resistance through the entire range of motion. That is because the cable is always the same distance away from the center of the cam.

Oblong Cam Machines

Arthur Jones of Nautilus fame invented the oblong cam machine. When the cable goes around the wider portion of the cam, the resistance increases, this is meant to simulate the natural strength curve that muscles go through. A major problem with machines is that they force you into a position that is probably not ideal for your body proportions.

Curve Treadmill
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The Best Resistance Curve

As we can see, each type of exercise device provides a different resistance curve. So, which is best? Well, the ideal resistance curve will match the body’s natural strength curve. This is that the muscle is stronger at the start and weaker at the end of the movement. So, when you do an exercise, it is ideal to follow that natural resistance curve.

Of all the types of resistance that we considered above, cable machines do the best job of simulating the natural strength curve of a muscle. When you do an exercise with cables, you get what we call early phase loading. This means that the exercise is hardest during the first half of the movement, and then it gets progressively easier as you move toward the point of full contraction.

We can illustrate the cable’s benefit by comparing the side lateral raise on a cable versus with dumbbells. When you do the exercise with dumbbells, there is no resistance at the start of the exercise. Yet this is where the deltoids are at their strongest. As the dumbbells come up, the resistance increases until it is hardest at the top position of the movement, This is, though, the weakest point of the resistance curve.

We can see that the strength curve of the standing side lateral raise with dumbbells is the opposite of the muscle’s natural strength curve.

When you do the side lateral raise one arm at a time on a cable pulley machine, the resistance curve perfectly matches your natural strength curve. When you position the pulley’s height at the same height as your wrist when your arm is at your side in the start position, the cable will be perpendicular to your forearm during the first part of the movement. This provides the early phase loading, which is ideal. Then, as the cable goes up, the resistance decreases, which also follows the muscle’s strength curve.

The Bottom Line

All muscles follow a natural resistance curve where they are stronger at the start of an exercise and weaker at the exercise’s finish. Look for exercises that follow this natural strength curve by providing early phase loading. Cable machines will do this better than any other choice of resistance.