Animal sinew (from the tendon of an animal) is one of the strongest natural fibers known to the world. And with only a few duly-noted drawbacks, knowing how to access and process sinew is an absolute must for the modern Primitive.
Tendons (sinew) are found throughout the body of mammals. They attach muscles to bones (or other body ‘structures’, like the eye). They’re what allow the impulses of the muscles to move the skeletal framework of the body. (Whereas ligaments attach bone to bone — and hold the whole thing together.)
What’s the difference between sinew and tendon? That’s easy.
‘Tendon’ is what we call it when it’s in the body; living tissue – like the ‘Achilles’ Tendon.
‘Sinew’ is when we take that tendon, dry it, and process it into tiny fibers for use as cordage/string, etc.
In this article, I’ll use the terms this way. (Tendon = living, in the body, whole. Sinew = out of the body, dried, processed.)
Think of tendons/sinew as a very fibrous material. They come in a variety of shapes, sizes, and matrices, but they are a ridiculously-strong, natural, fibrous material.
Sinew has endless applications in a natural or primitive setting, most relating to cordage/twine/rope/string applications. But it also makes for one of the world’s greatest bow ‘backings’ – and the only one that will actually increase the draw weight (poundage) of a bow.
Being that this is the time of the year you’ll likely have the best access to fresh sinew (it’s big game hunting season here in the U.S.), here’s how to locate, harvest, and process animal sinew for the variety of tasks it can be used.
View our video tutorial on processing sinew here:
Pros & Cons of Animal Sinew
Talking about sinew begs a larger discussion comparing animal fibers to plant fibers. The general pros/cons of each are:
Animal Fibers (sinew/tendon, hide, intestine/’gut’):
Pros: Incredibly strong
Cons: Stretch/loosen when wet, difficult/invasive to harvest, attractive to rodents, processing takes time/energy
Plant Fibers (outer bark, inner (cambium) bark, grasses, stalky fibers, husks, leaves, etc.)
Pros: Easily harvested (plants don’t run away), strength varies based on species/part/time of year, do not stretch when wet
Cons: Strength varies, time of year/growing season matters, some plants/parts take time/energy to process, species vary greatly by location
Not mentioned here are fibrous animal products like hair/fur. While these products don’t have the same issues with dampness that tendon or hide do, they do stretch and are likewise more problematic to harvest. They’re strong, but should be treated more like fine plant fibers when using.
Check out our related article “How to Make Rawhide Lashing”:
Although tendons are found throughout the mammalian body, if you value your sanity you’ll want to only look for and harvest tendon from two parts of the animal. (And, generally, only focus on big game like deer, elk (red deer for you Europeans), moose, pronghorn, lion, bear, etc.)
**See below for a story regarding sinew-harvesting and sanity.
The two main places you’ll look for sinew are:
The tibia/fibula (tib-fib) area of the lower leg is your best bet. There is a long, soft ‘sheath’ of material running along the edge. (Think Achilles Tendon. Go ahead, reach down and feel your Achilles, at the back of your ankle. See how it’s soft and not bony?) It’s the longest tendon in the human body and contains the most sinew fibers for its size. It’s what you’ll want to use for string/cordage and bow backings.Leg sinew is rather cylindrical when it’s in the body (tendon), contained within a ‘sheath’. It’s typically more of a “Y” shape, but overall cross-section is round. More on this later.
The meat along both sides of the spine is known as the ‘backstrap’. (It’s sometimes mis-called the ‘tenderloin’, but that’s not accurate.) Reach back and feel your spine. Then roll your hands to either side of the spine. Feel where it gets ‘meaty’? That’s the backstrap. Backstrap sinew is located on top of the backstrap meat. (Wow, didn’t see that coming, did you?) Backstrap sinew comes as a wide, VERY flat, splayed-out structure. It probably goes without saying, but there are only two on any mammal. The narrow end is toward the tail and it grows wider toward the neck. But always flat. Sinew from the backstrap makes for decent bow-backings, but the quantity of sinew harvested is far less than leg sinew, so it’s not harvested as frequently (or easily) as leg sinew.
If you’re a hunter (or know someone who is), you’ll have ready access to any animal harvested. Interestingly, most contemporary hunters leave the lower legs in the field, despite the minimal weight added when carrying-out. If you’re not the hunter, request that they bring the legs along, too. If you’re not a hunter, it’s easy to criticize not ‘using the whole animal’. But the reality is, when you kill an animal, it’s typically packed-out on your back. How much weight can you carry, on top of the gear you’re already carrying to hunt? Elk can weight 1,000 pounds or more and are typically quartered (hind legs carried out separately, from the body, head/rack, etc.). It means multiple trips, hiking meat out, then going in again, and again. Every pound shed onsite is a pound less carried over miles hiking back out of the wilderness. If you stop and consider that, it’s a bit easier to see why many hunters leave the guts, head, hide — and even de-bone an entire animal in the field. Only carry the meat out.
Does the rest of that go to waste? It can, sure. But there is no shortage of animals in the woods that would love to have an easy meal (and all the proteins, fats, vitamins, and nutrients) left from bone, hide, hair, fat, antler, sinew, stomach contents, and everything else left behind. What hunters leave feeds coyotes, crows & ravens, vultures, rodents, foxes, (wolves, if they’re in your area), bears, and a huge number of other animals plus bacteria and the forest.
All that being said, if you can convince a hunter to carry out the lower legs, too, it’s easy harvesting for 4 leg tendons from every mammal.
These are shops that take-in wild animals that have been hunted and process them for the hunters. They turn whole animals into something more palatable by Americans (steaks, burgers, sausage, jerky…). It’s a great skill and one that puts people closer to death and food than most of us typically are.
I’ve spent a fair amount of time at game processors, skinning animals (to take the hides myself), pulling legs and heads out of dumpsters (smashing skulls for brains), and so on. In my crude ‘study’, only 1 in 10 animals reaches the processor with the hide, etc. still intact. (Again, most hunters skin/field dress an animal in the wild.) It’s much more common for the animal to still have all 4 legs than the hide (conventional thinking is to skin the animal ASAP so that it can cool faster) — so if you’re after sinew, approaching a game processor may be your best bet.
But a game processor is still about ‘processing’, so legs are hastily removed and tossed in the ‘stink truck’ or dumpster. Again, if you want to go fishing (or develop a relationship with processors), you can obtain a ridiculous number of legs from processors.
One local, small town Colorado processor I deal with takes in about 100 pronghorn (antelope) per day during the 8-day season in early October. Assuming they’re all 4-legged pronghorn, you do the math.
Check your local grocery store or (if you have it) hometown butcher. While the species will tend to be domestic and not wild (unless farmed), you might gain even easier access to legs/tendons. If you explain what you’re doing and the butcher thinks it quaint, they might even do some of the work for you. But don’t bet on it. It’s also often best to always do your own processing yourself.The species you can access at a butcher shop will tend toward the cow, pig, goat, etc. Which begs the question of differences of sinew among various species. The point is noted, and probably begs some scientific study, but in my experience the most difference is in the size of the animal (bison yields longer, larger sinew than goat — duh). I think that the diet of an animal being wild (grasses/forbs/bark) rather than conventional agriculture (e.g. corn) has more to do with the quality/strength of the sinew than the species. But that’s only circumstantial, personal experience talking.
Harvesting (Leg & Backstrap)
Harvesting Leg Sinew
is fairly easy. The big question is whether you’re receiving the leg with the hide/hair still on AND do you intend to keep/use the hide?If the leg you receive has no hide (or you don’t care to preserve the hide), it’s super simple: With your offhand, feel for the cylindrical shaft of softer tissue running along the lower leg bone. Got it? Feel up and down. That’s the tendon. Pinch under it, and pry away from the bone. Take a sharp knife and carefully slide it through the hide, between the tendon and bone. Slice as far as you can in one direction. Then remove/reinsert the knife in the other direction and slice. You’re mostly cutting through hide and some connective fascia. The goals are to not cut the tendon and to retrieve as much length as possible. Look inside the hide and notice the whitish sheath you’ve been pinching. Continue to dissect the hide and connective tissues to remove the whole tendon. At the ends it will attach to bone (or enter a tube in the bone). Pry/cut it away there as necessary.If you want to carefully remove the hide from the lower leg for other uses (often done with sizeable moose legs — for making hock bags), here’s the process I use:
- Grab the leg from below, your palm up, as if someone handed it to you (they were holding the foot), with the tendon side of the leg facing up. Your thumb should be on one side of the leg, your fingers on the other.
- Pull back and down with both thumb and fingers, effectively tightening the hide on the top/tendon side of the leg (hide slices much easier when held taut).
- Insert the tip of a sharp knife (blade up), into the cutoff end of the leg, just below the hide.
- Give a quick slice-flick up. It should begin a short cut in the hide.
- Repeat this knife technique several times. Once the cut is started, it should be easier to slide the knife farther in, but you want to focus on neatly slicing the hide and NOT damaging the tendon.
- Continue to the foot bones, then peel bag the hide from the bone. (The fascia typically peels away easily enough, without the use of a knife.)
- Remove the tendon from the leg bone as above.
Harvesting Backstrap Sinew
involves a little more effort and finesse. After skinning, look for the whitish, fibrous layer over the backstrap. You’ll need to get under that with your knife (try a skinning knife, with a nice slicing motion) to begin to separate it from the meat. Once it begins to lift, try getting your fingers under the tendon to separate/pry it from the meat. Sounds simple. More difficult.
About the easiest part in this whole process is drying the sinew. Here’s the highly-technical process:
Lay the sinew in the sun.
That’s pretty much it. It’s helpful to place it on a surface that will get airflow, like chicken wire or an old window screen, but not necessary.
Also note that humidity and sun are the biggest factors. Here in Colorado, with 300+ days of sunshine per year and low humidity, stuff dries pretty quickly.
Backstrap sinew dries MUCH quicker than leg sinew.
The sinew should be rock-hard when dry. As the sun begins to dip on the first afternoon, if you’re not sure whether it’s dry or not (Leg sinew should not bend. Backstrap sinew should be ‘crinkly’.) bring it in for the night, before the dew begins to set. Place it outside again in the morning.
Beware domestic and wild animals: The biggest challenge to my drying sinew freely outdoors is my dogs. I’ve found entire leg tendons GONE, or at least hanging from Annie’s mouth…while the expression on her face is…”what?”. Can’t blame the dog. She’s a dog, afterall. Coyotes, foxes, etc. are particularly drawn during those dusk/dawn hours (they’re corpuscular). Best to bring in animal parts at night.
One of the cool parts about a lot of animal parts is that, if they’re appropriately cleaned and dried, they’ll keep for almost forever. After you sufficiently dry the tendons, feel free to store them away in a (preferably mouse-proof) container, for when you have time to process them.
One additional note: If you’re in a rush, just dry the leg tendons whole. (Most of us do. You just cut the tendon out and let it dry.) But if you have a few extra minutes, slice through the ‘sheath’ surrounding the fibers with a sharp knife — stick the tip of the knife in the end, blade up, and slice up. Repeat. You’ll ‘open the package’, allowing more airflow and the tendon will dry faster.
You may also be interested in: Primitive Skills, Bushcraft & Survival – Explained
Once the tendon/sinew is completely dry (whether yesterday or a yesteryear), you’re ready to proceed.
There’s very little processing to be done on backstrap sinew. You can glue it down as-is onto the back of a bow, or peel away a few fibers easily for use in smaller fibrous applications (like quickly hafting an arrow point onto a shaft). If you want to turn the whole piece into separate, small fibers, check out the “comb technique” below.Depending on how cleanly the sinew came away from the hide/backstrap/fascia, you may want to explore scraping away additional material. Use a sharp knife blade, scraper, or stone flake to carefully remove bits of fascia, etc. Use the blade in a scraping motion (not slicing) to avoid cutting the fibers.
Processing sinew from leg tendons requires a bit more labor. It’s not difficult, just takes time, a bit of sweat equity, and will build forearm strength.The basic 3-step process is this:
- Crack open the sheath with a hammer
- Split the main tendon into 4 parts
- Repeatedly pound each quarter, removing the sheath, and separating individual fibers
The easiest way to start is with a ball peen hammer and hard surface. (You could also use a palm-sized hammerstone and rock surface.) The ball peen is nice because it isolated the force into a small location, without being sharp. A cross peen hammer, or even the smooth face of a claw hammer, can function too. Avoid the ‘waffle’ face present on some framing hammers.
Lay the tendon across your ‘anvil’ and stabilize it at the end with your offhand. Start at the opposite end and give it a series of hard, sharp smacks with your ‘hammer’ to crack through the hardened sheath.
Note: The sheath is basically the same material as the rest of the tendon, but it’s oriented in a much nastier matrix of fibers, rather than a relatively parallel one. I’ve never heard of anyone actually taking the time to process the sheath into individual fibers for use in cordage, etc. However, I do keep the sheaths and occassionally simmer them for an animal glue similar to hide glue. Most people just throw them away.
Your goal at this point is just to move through the tendon quickly busting open the sheath. Usually a quick pass or two is enough to do it. If you’re process a lot of tendons, you may want to work all of them through this step first, before moving on.
When it seems like the sheath is cracked open reasonably well, move on.
Grab a split end of the tendon with both hands and rip it apart (hopefully in half, lengthwise). Don’t give yourself an aneurysm trying to do it; if it doesn’t come apart reasonably easily, go back to Step 1 for a bit longer.
Once you’ve pulled it in half, rip each half in half again. You should end up (roughly) with 4 quarters of the original tendon, each approximately the full length of the original. Again, if you’re having trouble, give it a few more cracks with the hammer.
If I’m processing a medium-amount of sinew at once (ie 6-8 tendons), I might actually complete Steps 1 & 2 with each tendon all at once, taking each tendon all the way to quarters before grabbing the next.
It’s about efficiency. Do what feels right to ya.
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Now comes the fun part. I should have put fun in quotes. Now comes the forearm building part. It’s more about endurance than power.
The biggest concern at this point is NOT smashing the fibers between two hard surfaces. If you’ve been using two steel surfaces (hammer and anvil, stone and stone, etc.) you’ll want to switch up your tools. I tend to favor a hard, rounded ‘hammerstone’ (object), against a piece of wood, like a tree stump. Even though wood is still ‘hard’, it will forgive more of the force and not pinch the fibers the same way that two steel or stone surfaces will.
You’ll want to continue pounding (this time lightly) the sections you have, from one end to the other. Think ‘light taps’. Tap. Tap. Tap. Tap. Tap. Tap. Rotate the tendon section and continue.
As smaller fibers appear to separate, peel them away. Don’t pull too hard. The smaller you separate the fibers, the easier it will be to actually break them when pulling. Pull them off as they become easier to separate. Go back to tapping. And repeat. And repeat. Ad nauseum.
Depending on the size, species, and quality of the sinew you’re working with, the sheaths will begin to separate at different times. The sheath remains more papery/cohesive than the softer fibers separating. You’ll want to pull off the sheath as it becomes possible and either throw it out or save for simmering into glue later.
Aim for final fibers about the thickness of wispy dental floss (the cheap, flat kind).
If you want to get your sinew fibers extra fine or soft (or need to work-over especially difficult sections of tendon), consider this technique.
Make yourself a ‘comb’, typically from a slew of finish nails and piece of scrap wood. Hammer the nails through in two or three rows (random is best) – you want to create a ‘field of teeth’. The teeth should be pointing up, so you may want to clamp the wood down or fashion the nails into a stable surface.
Grab a length of the sinew from both ends and rub it back and forth vigorously through the comb. It will further shred-separate the fibers from one another.
If you’re beginning with a piece of backstrap sinew, this can help separate the fibers from the start.
As mentioned earlier, appropriately-dried sinew will keep nigh forever. If you’re storing it in a location that rodents are even remotely likely to enter, you’ll want to store it in a container that can’t enter. If the container is airtight, you’ll want to make absolutely sure it’s dry before sealing it. You could consider adding one of those desiccant packets (but I never have).
Depending on your planned application for the sinew, you may want to sort your sinew collection before just shoving it all in one big container. For most applications (cordage, bow-backing) it’s more important to sort by ‘diameter/size’ than length. Later, when working with the sinew, conformity of diameter is better than length.
Working with Sinew (soaking/applying)
Even though we process and store sinew dry, for most purposes, you’ll want to work with sinew while it’s wet. So you’ll need to rehydrate it.
- Work in small batches. Only soak/hydrate what you’ll use in the next few hours.
- Add some lukewarm water to a small bowl.
- Pinch off a small amount of fibers and add to the water. (If you’re going to go through a decent amount, pinch off bundles of ~¼” diameter at once to soak.) Be sure to completely submerge them. They need to be hydrated throughout.
- Sinew can hydrate in as little as a few minutes. Soaking for 20-30 minutes will typically fully-soak the fibers — returning them to a near-life consistency. (Indigenous peoples are known to have hydrated/processed sinew by ‘soaking’ it in the mouth and chewing it to a supple consistency.)
- If you’re going to need more than your ¼” bundle, be sure to add more dry sinew to your soaking pot ahead of time so that you can keep working.
Sinew, like other animal fibers, sticks well to itself, rendering additional glue not necessary (but preferred). You can attach an arrow point (haft) to a shaft with as little at neatly wrapping a single strip of sinew around the point/shaft and ‘smoothing’ it back onto itself. Allow to dry without touching and it will hold like a clamp and glue in one.
If you want to do more with ‘using the whole animal’, here’s how to make Nature’s superfood: pemmican.
**A Final Story
In my younger years (and early days of Practicing Primitive), I once picked up a road-killed squirrel, headed to a friend’s backyard, and set about to harvest every last bit of useful-anything (until a Cop arrived).
I took my time skinning that sucker (the squirrel, not the Cop). I took pride in the task. Took the face and paws off pretty clean. Whiskers stayed with. Claws too. Peeled away the skin and fur from the bony tail. Carefully separated each tendon from each ‘finger’ of each ‘hand’ on that little animal.
I learned more from that one squirrel than I have, perhaps, from any other singular teacher in my life.
After taking off the hide (‘unzipping’ it, you’ll hear me call it, today, like a fur coat), the similarities between the mammalian structure of a squirrel and a human are unmistakable. Stunning, actually. The biceps, the musculature. So familiar. (Except for an elongated skull, the tail, and those claws…it looked like a little human.)
I stripped every last bit of tendon, ligament, bone, hide, organ, and anything else I could identify. Took hours. It’s an exercise in self-punishment, I think, to separate the soft tissues that connect the musculature of the hand to the skeletal structure. I did that (and wouldn’t wish it on anyone). On a squirrel. I think I learned more about that squirrel than it knew about itself.
And then I took what was left, put it in a stew pot. Boiled the hell out of it. And ate it.
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