I am guessing you overcooked it.

If it was a boiling fowl then it would have needed slow cooking. By hen do you mean an old bird?

Yes, i mean an old bird. @linda, IME, my overcooked chicken has the texture of jerky. My recent experience was more like chewing on a rubber band--actually, i was taking it out of my mouth as i couldnt accept rhat texture as what chicken normally tastes/feels like. It was not every piece either.

Well when I re read and found that you had left the chicken in the marinade for 5 days....I am re-thinking my answer> What was in that marinade? Salt will originally add moisture to the meat.....but after FIVE days?? And acid softens the meat....and if you over cook it it may get rubbery.
Marinating meat doesn't normally toughen meat.....but one doesn't normally marinate meat for more than 12 hours....on occasion as much as 24> But 5 days....I wouldn't even eat chicken that had been in my refrigerator un-cooked for 5 days.
Likely the marinade disguised any spoiled flavor. All resources that I have found recommend keeping raw chicken for no longer than 1 or 2 days before cooking or freezing.

Ugh, i gave discarded it

oh boy! Went to food safety site and it said uncooked refrigerated chicken: 1-2 days. Miraculously we didnt kill ourselves. Linda, it was fajita seasoning but dont know specifics. Ive learned my lesson....

You mean you bought it already seasoned? Ugh...who knows what was on that....but likely...we will hope....lots of preservatives.
I never buy "pre-seasoned" anything. I suspect the seasoning hides a multitude of less than top quality stuff. It's easy enough to sprinkle on a little chili powder and some oregano leaves.....or some lemon pepper, or some garlic and rosemary.

Ive learned my lesson....

Islay, in the US, outside of Kosher butchers and perhaps another specialty meat market, all the chickens sold are "broilers"....between 3 1/2 and 4 1/2 pound birds. Raised in cages and specially bred to have huge breasts and be ready for market in 5 weeks. If she bought preseasoned chicken breast from a supermarket, there are zero chances that it was an old stewing hen.

Thanks for the info. Don't you eat old birds your side? Are all your "broilers" cage birds? Horrible for the birds. Won't touch one or cage eggs.

There is little market for "old hens". And yes most are cage birds, mass produced, marketed in less than 6 weeks hatch to slaughter. There are a lot of "cage free" bird sellers and also producers of organic free range birds. But we, in the US eat a LOT of chicken! Kids first solid food is chicken nuggets....not really but almost! Any kid when you go out to eat orders chicken nuggets or some variation. The fast food side of chicken is huge...we have KFC Chick-Fil-A McNuggets...General Tso's chicken, Hot Wings...other wing shops etc etc....all rushed to market!....and probably that's wehre those laying hens end up....because they certainly are not on the supermarket meat case.And most of those fast food things don't taste much like chicken at all!

Even the free range hertitage hens we get are more or less as Linda described, except not quite as top heavy.

we eat a lot of chicken too but most people are very ware of where their meat comes from and the welfare of the animals. I can't afford organic except organic eggs but never eat cage birds which, here, are rather scrawny and small. Free range is affordable and good and very well regulated.I think we're very lucky in that respect. The supermarkets are packed with industrial, processed chicken products but I don't know anyone who eats it. People must, though.

This winter I bought some BSCB and made chicken francaise. About half turned out so rubbery I could barely get a knife through it, let alone chew it. I've overcooked chicken before, this was nothing like that. I googled at the time (almost posted, but didn't) and found a lot of "it's the chicken, this just happens sometimes." Never happened before, never happened since.

Not helpful, but you're not alone.

Franken birds....

Foodonastump, that is how my experience was but what is BSCB

boneless skinless chicken breasts

That's so interesting! Blame the chicken! Which reminds me that I've also had a whole chicken (free range, known and trusted ethical grower whom I usually buy from, yada yada) that just wasn't normal in texture but which I'd cooked cooked in a standard way, where the only thing I could think was that it was a mutant chicken.

BTW, I had a minute figuring it out too: BSCB = boneless skinless chicken breasts

Certain things are just automatic to foodies....among them is BSCB....and EVOO...as well as AP flour.

I guess I'm not a foodie, then (which I suppose is a badge of honor considering what "foodie" means where I live). :D FOAS, he of the four letter abbreviation, is the first I've noticed with BSCB (might have been one in obvious context before that I didn't notice). 'Course, EVOO and AP are more normal to me than spelled out.

My sister raises chickens - free range. Those chick to roaster in 6 weeks birds are weird - oddly proportioned unhealthy. Now she tries to get a different variety that takes I think 12 weeks. Definitely more chicken-like. And happier if short lives.

My big complaint is big breasted, big birds. The heritage hens (which are still white, so how heritage-y are they?) have normal pelvises, at least, rather than the tiny ones that even the normal free range birds we get do. I won't buy big chickens, however, and the heritage ones run huge, and I don't want a five pound chicken! When I was young, they were mostly in the 3.5 pound range, and were labelled 8 weeks. Now, finding a decent (i.e., local free range, organic feed (i.e., allowed to eat bugs but the food they're given is organic) chicken under 4.5 pounds is hard! When I find one that's under 4 lbs., I celebrate. There's one grower, whose birds I'd have to go well out of my way to get, who sells them without giblets or wingtips to get them under three pounds. If they came complete, they'd still be even smaller than my ideal, but I might go out of my way to get them. And even if I wanted to raise my own, I don't have enough land (city code).

Agmss, Kudos to your sister for raising happier chickens.

An average free range bird here is about 1.3kg so about 3lbs. That's classed as a big bird Lol

Lucky you!