Shoulder Strap Education

[CW]

There seem to be a lot of MYOG packs being made recently, and they all (ok, maybe not every single one, but most) share a common problem. We don't have square shoulders. Yet everyone is sewing their shoulder straps on at 90 degrees. This kind of configuration, and the resultant weight distribution, can cause unnecessary soreness, numbness, and even permanent nerve damage. The average slope of the male shoulder is 67.5 degrees **, and shoulder straps should be sewn on at a similar angle so they lay properly on the shoulder. Women have a slightly different slope and should be adjusted for accordingly.

** This was medically studied and published.

[Jerry Adams]

You mean:

[CW]

Not really. That still results in the shoulder strap being effectively mounted at 90 degrees due to the seam, so it won't lay on the shoulder correctly.

This Laufbursche pack is the closest I've seen to getting it right. Photo courtesy of http://www.beuteltiere.org/

[Ken Thompson]

Check out the Cloud 9 strap system at Jandd. They have a nifty solution for this that also makes it easy to trade out different size and styles of straps.

http://www.jandd.com/Technotes/technotes_Fitting_C9.asp

[CW]

Ken, Ryan J. mentioned a similar solution. That would work fine if the pack is riding low as it is in their photos. But if the top of the strap will be at the top of the shoulder, you'd wind up with the webbing resting on your shoulders instead of the padding. Doesn't sound too comfortable to me. You also increase the points of failure considerably. With that said, if you did it right and somehow had padding under the mounting point for the webbing, you might be able to get around the comfort issue.

There are probably several good solutions, and my intent wasn't to say one is necessarily right over another. I just want people to be aware of the potential problems that can be caused by something that isn't anatomically correct.

[Ken Thompson]

I have a Tozi Kletter from Jandd. Very comfortable. No weird contact with the straps either. Only 1 attachment point to fail. Similar to sewn on straps too. Seen them rip out. You can adjust the distance from the pack to strap too.

[CW]

You have webbing attached to the pack, webbing attached to the top of the strap, and at least one piece of plastic hardware to allow the two pieces of webbing to attach to one another. That's at least 3 points of failure vs. one if the strap is sewn directly to the pack. Either scenario can obviously fail, but I'd rather have one point of failure than several.

[Jerry Adams]

you mean:

[Ken Thompson]

Life is full of compromises. All I can say is that system works for me.

[Daryl and Daryl]

Most older frame packs attached the top of the shoulder strap to the top bar of the pack with a single clevis pin running through a grommet. The top of the strap was free to rotate and thereby adjust to the shape of the user.

Does that system address the problem you raise?

[CW]

Jerry – yes, that looks correct on paper.

Daryl – both yours and Ken's posted solutions effectively solve the problem, albeit in way that's more complicated than necessary.

An unpadded fabric panel between the pack and padded straps like Osprey uses on their Mutant also effectively solves the problem. At least it would appear to. Photo courtesy of http://www.livefortheoutdoors.com

[Jerry Adams]

Actually, my first solution solves the problem if you think about it

My pack:

If you fold the strap over at the same angle, then yes, it's still at the undesireable 90 degree angle:

But if you fold the strap over like when you actually use it, straight down, it forms the desired angle on the shoulders:

One thing good about this is the seam on the pack is horizontal so maybe it distributes the load a little better. And it's about as simple as you can get, which is good if it works.

[Daryl and Daryl]

Jerry,

Thanks for the second drawing. That clarifies the issue for me.

Daryl

[CW]

Jerry, that's ok if the pack is riding a fair bit below your shoulders. Not exactly ideal (unless you're on a bike) and the straps will pinch your neck and upper traps if you have it riding too high or don't have a very thin neck.

This also doesn't work very well if you have any kind of functional frame, which should (ideally) extend above the shoulders.

[Daryl and Daryl]

The pack design I have been using for the last 10+ years addresses the problem by replacing the traditional shoulder strap with this:

[CW]

Interesting design. Does the thin webbing not cut in to your shoulders, upper traps, upper chest, etc?

[Daryl and Daryl]

Jerry,

The ribbing on your backpack (where it would touch your back) looks interesting. How did you make that?

Daryl

[Daryl and Daryl]

Chris,

"Does the thin webbing not cut in to your shoulders, upper traps, upper chest, etc?"

No, I usually don't feel the 1/2" webbing at all. The pressure from the front system is distributed along the upper portion of the front bag.

Here's a more detailed explanation:

Everything is adjustable and I adjust things so the 1/2" webbing just kisses the front part of my shoulders. It doesn't touch the top of my shoulders at all because it is mounted at a point on the pack that is above my shoulders (see side photo). The mounting points on the pack's top bar are 12" apart so the 1/2" straps don't touch my neck or upper traps.

I load the front bag with enough weight to pull the pack forward and keep everything in balance. For normal trail walking I don't bother to cinch things up at all. The pack rides much like the double bagged (front and back)canvas bags that paper delivery kids used to use.

If I'm bushwacking or want the load to be more secure I tighten the two straps leading from the front bag to the pack frame bottoms (barely visible in side photo). This squeezes the pack together, horizontally, (from front to back) much like a large wood clamp might squeeze something (in this case my upper torso). The carbon fiber stays in the back bag are flexible and give elasticity to the "body clamp" so when I move the pack moves with me. The pressure from this tightened system runs across the upper chest but it is well distributed by the front bag and not uncomfortable for me. I made a similar pack for a friend and he reports no discomfort after a year of using it.

Daryl

[Jennifer McFarlane]

Chris
WHen you say it's been medically studied, can you cite the source?
I was wondering about this recently as I'm having Chris Z make a pack for me, so I'd like to read the full article so I can understand better what might work best for me.
Thanks
Jenny

[Jerry Adams]

Chris – the geometry is the same if the pack is higher, for example if the shoulder strap attachment seam is above my shoulders, the straps still have the desired angle on the shoulders.

And there's a gap between the pack and my shoulders so the straps are spread apart by the time they get to my neck and don't cut into my neck. Obviously, you can move the strap attachment to the pack out sideways to make the gap between straps where your neck is the desired width – if you have a thicker neck move the straps out sideways a little.

I don't know about frames : )

Daryl – the ribbing is 1/2 inch closed cell foam. 3/8 inch wide. I sewed another layer of nylon on the back with slots that are 3/4 inch wide. My idea was to get more airflow. I don't think this works very well. Maybe the next iteration of my pack will have a foam strip on each side. Maybe each one 3 inches wide with a 3 inch gap between them. Or maybe I'll just go back to just nylon.

[CW]

Jennifer

Here's one article referencing a study of it.

http://www.faa.gov/library/reports/medical/oamtechreports/1960s/media/AM65-14.pdf

That was done in 1965, but I had my PT wife check mine with one of her fancy tools, and it's almost identical to what they came up with. I measured the slope of her shoulders as well, and it's slightly different. I'd have to check again to verify the exact angle.

[Diana Vann]

Daryl,

Can you give a make and model for the pack you are wearing in the photos?

Thanks

[Jennifer McFarlane]

What is the name of the fancy tool your wife used so I can get one of the PTs at work to measure me? :)

This whole topic is interesting to me because I end up with numb arms.hands/fingers from most packs, but not the Osprey Hornet, which attaches the same way the Mutant does. My only problem is the Hornet's hip belt does not work for me.

[CW]

Orthopedic Goniometer

It looks pretty close to this one.

Depending on how they measure they should either get something in the 60-70ish range or something in the 110-115ish range. If it's the latter, just subtract from 180.

[Jennifer McFarlane]

Thanks Chris!

[Author]

Posts