What Is Variable Resistance Training?

A dumbbell weighs the same at the bottom of a press as at the top. A band does not. I hung one from a crane scale and measured the force every 20 cm, so you can see the curve instead of guessing it.

The short version

With a dumbbell, a barbell, or a cable stack, the number on the weight is what you lift the whole way. That is constant resistance.

A band works the other way. Resistance comes from stretch, so the further you pull, the harder it pulls back. A band press is light at your chest and heaviest at lockout. A band squat is lightest in the hole and heaviest when you stand up. That is variable resistance.

A 2022 systematic review and meta-analysis of 17 studies and 491 adults (Andersen et al., Journal of Science and Medicine in Sport) found variable resistance training and traditional resistance training equally effective for improving maximal strength and muscle power. The difference is where the work lands in the rep. Bands are lightest where your joints are most stretched and heaviest where you are strongest. That is why a lot of people find them easier on the joints.

It also explains the label. A band prints a range instead of one weight because stretch is the load. Same band, different height or grip, different force.

How I measured it

I anchored one end of a Serious Steel purple loop band and clipped the other to a digital crane scale. A laser distance meter set the length. A spirit level kept the pull straight, so the scale was reading tension, not a sideways tug.

I started at 1.33 m, added 20 cm at a time, and wrote down the force at each stop. Ten readings. Finished at 3.13 m.

The numbers below are what the scale showed, converted to pounds and feet in code. Nothing is smoothed or fitted. The chart stops at the last reading because that is as far as I measured.

Reading the curve

Every bar is taller than the one before it. More stretch, more force. That is the whole idea of a band.

The shape is the interesting part. A band fights hardest in the first few inches, while the slack comes out. Then it settles. Each extra centimetre costs about the same, and the curve turns into a long, nearly straight line. Near the end of what the latex can take, it stiffens hard again, right before it would tear. You do not want to train in that last section.

This test caught the first two parts. The first 20 cm added 2.10 kg, then each step settled to about 0.92 kg. In its working range the band is close to a plain spring: roughly 4.6 kg per metre of extra stretch, or 3.1 lb per foot.

Where the rest of the S would be

Ten readings only cover the middle of the curve. To sketch the rest, I fitted a standard rubber model from 1940 (Mooney). It sits within 0.06 kg of every reading, and it puts the band's resting length at 1.15 m.

That checks out. A new 41 inch band hangs about 1.04 m slack, and latex grows a little with use. So the first reading was only about 16% stretch. I cannot say where this band would break, so the chart marks the practical limits instead.

Three takeaways

• Force goes up. The jump does not. Total force still climbs every step, so the rep gets heavier toward lockout. After the first stretch, each extra 20 cm adds about the same amount.
• Stay inside the printed range. The label's 35 lb top lands at 3.9 m, about 3.4x rest length. Bands in use fail from a nick or fatigue long before the latex itself gives out. Treat anything past the label as failure territory.
• Stretch is the load. 2.4x the length gave 5.2x the force. A taller lifter, a wider grip, or a higher anchor all add stretch. Two people with the same band are rarely lifting the same weight.

What it means for training

On most presses and squats you are weakest at the bottom and strongest at lockout. A band matches that. You can push hard at the top without the bottom being limited by the heaviest weight you can get out of the hole.

Rows and curls flip it in a useful way. The hardest point is the squeeze, which is where you want the fight.

The number on the band is a range for a reason. The low end is a light stretch. The high end is a hard one. Where you land depends on your anchor, your limb length, and your grip. That is why the band resistance calculator works in ranges, and why Rubber Bands builds progression around the bands you actually own instead of treating a band like a single weight. If you are choosing between band types, the loop vs. tube comparison covers why loops publish a range and tubes publish one number.

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