How is resistance band "weight" calculated?

[PhilD]

OK, I'm new to this and because I travel full-time with my job I can't do weights/pull-up bars/gym subscriptions etc.

So I've got myself some resistance bands and am simulating a lot of weights/pull-ups/rowing etc with them.

But I have a question that I can't seem to find the answer easily via Google and figured someone on here must know how this works.

I have a 5 band set which tells me these are the following resistance amounts.

1 yellow band 6-8lbs resistance

1 green band 9-11lbs resistance

1 red band 12-14lbs resistance

1 blue band 15-18lbs resistance

1 black band 22lbs resistance

To my knowledge they work something like this individually - Say I'm pulling the black band as weights, if I do this with a handle in each hand that's 22lb of resistance each side right? If I were to pull both handles with one hand would that be 44lb of resistance?

But then my main question is say I paired the black and blue band. I know it increases the resistance but doesn't just add them does it? i.e. 22lb+15-18lb = 37-40lb. It doesn't feel like that much of an increase, and it also doesn't seem to make sense that it would work like that. But I'm wondering if there is a way to quantify the weights (if only roughly)

Any ideas? Also please correct me if any of the above is wrong, I have no idea what I'm talking about in this area apart from what I've found online

[mksiemens]

the way you're calculating it is correct.

it just is a very rough estimate.

also those resistance levels are listed from maximum safe extension, which is usually 3x original length.

i can't remember the ratio for resistance based on stretched length, but it's dramatically less when only stretched to 2x original length.

so say you've got the band under your foot and 2 ft of band length on either side, the resistance value for those would be reached when they hit 6ft stretched and it would be dramatically lower at 4 ft.

but even with that those numbers are very much an estimate, more of a guide to compare resistance values of one companies bands, doesn't really cross over from company to company or anything, and even less so to real dumbbells and stuff.

[PhilD]

Thanks Mark,

That makes a lot of sense and is very helpful.

[aj_rock]

Time to (math) NERD OUT!

Forces imparted by an elastic band oppose the direction of stretch by a factor of k, which is usually assumed constant for most bands. The elastic resists from both directions, so if mksiemens is correct, assuming a 1 meter original length, if you fix the band at one end and stretch it to 3x original length, you experience 6-8 pounds of resistance, which actually doesn't make sense because the units are wrong, unless they mean pound-force (highly unlikely). What they actually mean is a resistive force EQUAL to 6-8 pounds of actual weight being pulled down by gravity.

Either way, so you only pull to half the maximum distance, you get half the resistance. Bands held in parallel should have additive resistance, just don't tie them end to end, because then the resistance formula gets more complicated.

Either way, the problem with bands is that through the majority of your range of motion, you aren't getting the full resistance... I mean if you start at 50% stretch and go to 100%, the average resistance is around 75%. That's good for people still getting used to working full ROMs, but less so if you want equal strength increases. Just keep in mind, and if you switch to free weights, use 75% of whatever band you used last unless you want a rather rude awakening.

[PhilD]

Thanks AJ.

That's the kinda math I was banking on with a question about anything involving numbers and physics

I might look at getting some free weights for home but unfortunately my schedule has me travelling around 16-24 days a month and those airline baggage allowances wouldn't hold up well if I took weights with me

[Tom Kenobi]

Phil, are you going to start a workout log so we can cheer you on? You can start one at this link if you aren't keen on getting into the challenges yet due to your schedule.