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If you look at the typical product description of a resistance band (Amazon is a good place to see a lot of these), you'll see that nearly all of them give a range of resistance. For example, one band might say 25-80 lbs of resistance while another says 50-125 lbs.

What do these ranges mean and how do I achieve the resistance levels in between? Does the amount of resistance depend on where you're stabilizing the band? If it's 50-125 lbs of resistance, how do I know when it's 50, 75, or 125? What do I have to do to get 50 lbs if I want to do curls? How would I use the same band differently if I wanted 125 lbs for leg exercises?

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  • Good question. I'm interested in how the pound resistance relates to the first inch of stretch and the last inch of stretch before it snaps. – Eric Feb 17 '15 at 21:31
  • So, what about the tubes that don't have a range. For instance I just bought a pack of 3 resistance tubes. The yellow one is 5#, the green one is 15# and the blue one is 25#. Do you feel like they are referring to the amount of weight being when you start pulling to stretch them or at their maximum stretch? Hmmmm.... – Lauren S Aug 21 '19 at 18:47
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Basically, they are all giant versions of rubber bands. As such, when they are near their normal shape, they offer much less resistance. This increases in a (mostly) linear fashion until the stretch limit, so you can calculate resistance just by how much the stretch is.

So, if you have a band that is rated 50-100 lbs, with a maximum stretch of 3 feet, it will take 50 lbs of force to start it stretching, from that point it will take 75 lbs of force to stretch it 1.5 feet (18"), and so on.

You can also "stack" them to increase initial resistance, and modify the "weight" that you are using.

One thing to look for in the flat bands is layered versus molded, as the layered will be tougher and less prone to ripping, which you can avoid by making sure that it isn't wrapped around sharp edges, don't store in sunlight, etc.

Did run across this study examining the mechanical resistance of various colored bands, as well as the instruction manual for Thera Bands, which are one of the most popular brands used in injury rehabilitation.

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  • It made so much sense when you compared it to a rubber band. I can't believe I didn't think of that. Now to find the rated stretch limit on the one I want and I should be good! – oscilatingcretin Feb 18 '15 at 0:17
  • What do you mean by "it will take 50 lbs of force to start it stretching"? My resistance band that is rated "50lb" only takes me my index finger (probably 2lb of force) to stretch it an inch. Do you think the rating is inaccurate? It says the maximum stretch length is 3x its length. – CreativiTimothy Nov 29 '20 at 6:18
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A resistance band rated for 50lb means that it requires 50 lbs of force to extend it to its maximum stretch. Think of this rubber band as a spring. The spring follows the equation F=kx where F is the force, x is the displacement of the spring in inches from its natural length, and k is the spring constant in lb/in. This is a linear relationship. So as you stretch the exercise band from zero to its maximum stretch, it requires 50 lbs of force at its maximum stretch point. It requires 25 lbs at the middle of its stretch. If the total stretch length is 30 inches, then the spring constant k is 50 lb/ 30 in or 1.6 lb/in. So it takes 1.6 lb of force for each inch you stretch the band. I hold two engineering degrees and have 40 years of industrial experience in the chemical industry.

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  • Awesome answer. Welcome to the site! – JohnP Jan 8 at 15:02
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Most of the pull up bands sites use a confusing chart, but in reallity the band resistant doesn´t have nothing to do with your weight and you must select a band only based in the "unassisted" pull ups you cand do.

This amazon seller is using a very easy to understand graphic in the product image section: http://www.amazon.com/dp/B00Z7IRAQ2/

Also see "product description" to understand a little bit more of other exercises that you can perform with the band.

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