Ergonomic shoulder straps that reduce shoulder pain

[Nenta WAKO, Dr.Eng.]

Companion forum thread to: Ergonomic shoulder straps that reduce shoulder pain

Two methods for reducing backpack shoulder load have been well known.
One is the load distribution to the lower back with hipbelt or lumbar pad. The other is the load distribution within the shoulder area…

[Rex Sanders]

Interesting! If I understand your video correctly:

– Keeping heavy weight close to the back is very important for reducing pain.
Good to know that measurements confirmed conventional backpacking wisdom.

– Changing shoulder pad thickness can also reduce pain.
The diagram looks like pad thickness and pressure was less over the clavicle, transferring more pressure across the top of the shoulder, and just below the clavicle.

As you noted, with only 8 male subjects, hard to know if this design works for a wider range of people. Are you planning any more tests?

— Rex

[Nenta WAKO, Dr.Eng.]

Rex,
Thank you for your comment.

In the experiment, the strap didn’t have an buffering effect by itself as it was made of solid PVC sheet. And the pad for padded level was the same material. The purpose was to investigate the effect of load separation.

Regarding the small number of subjects, I couldn’t perform the experiment fully owing to Covid pandemic.
Now this research has closed, but when the product whose spec is applied is developed, I will confirm this effect, again.

For the loading on the clavicle, some adverse effects are reported. So, its load needs to be reduced. What I have to investigate is the adverse effect due to loading on the portion under the clavicle.

[Russell Biser]

Have you compared this to Klattermusen’s butterfly bridge / carry on bone system which seems to do the same thing?

[YoPrawn]

Interesting stuff. As someone who suffers from spinal birth defects and can’t hold much weight on my shoulders regardless of strap design, I have found that once a pack is beyond the 20lb mark, using a front pack eliminates all of my shoulder and back pain. It does require a more robust hip belt to then take the load, but the system works great. My front pack only adds 1 ounce of weight because I modified my bear bag to clip to my shoulder straps and hip belt.

I personally think not anywhere close to enough people are using chest/front packs that hook into either the shoulder straps or go around under the armpits and connect directly to the main pack. Beside shoulder pain, there is also a lot of energy loss in trying to keep one’s body balanced with a huge imbalance in the load.

 

[Nenta WAKO, Dr.Eng.]

Russell,

Thank you for your comment.
I haven’t tried butterfly bridge.
It seems easy to establish the strap position onto the clavicle when users wear the backpack to place V-shaped frames over the clavicle.

And regarding the clavicle load, it would be designed for applying larger in lateral part than in medial part. It might be reasonable design for the clavicle to avoid moving downward that compress the brachial plexus and axillary artery, relatively.

But, on the whole, it is designed to support the load on the clavicle positively. So, I think it would be an opposite concept for my suggestion.

[Nenta WAKO, Dr.Eng.]

Johan,

Thank you for your comment!
Even if shoulder load is distributed within shoulder area, the compressive load of intervertebral discs can’t be reduced. So, in your case, I think that distributing to the lower back is necessary. Also, it is necessary for your lumbar spinal moment to be reduced by way of keeping load balance between front and back even.

Contrarily, the constraint due to hip belt generally brings compensation in walking motion.
It reduces the relative phase between thorax and pelvis in walking with backpack and hip belt, comparing to that in natural walking. And, to keep the same walking speed, it’s necessary for stride larger, regardless of less range of pelvic rotation.

Considering both aspects, users should choose a better way to reduce shoulder load depending on their situation.

[Russell Biser]

Nenta,

“But, on the whole, it is designed to support the load on the clavicle positively. So, I think it would be an opposite concept for my suggestion.” It doesn’t feel like it. Having used it myself it does seem to deload the clavicle itself if one side of the V is on each side of the clavicle, and the stiffening provided by each arm of the V accomplishes something like the thickened padding does in your straps.

“it would be designed for applying larger in lateral part than in medial part.” I have not noticed this in actual use.

Achieving this with differing padding thicknesses is more elegant, manufacturable, and ultralight though, so style points to you.

[Nenta WAKO, Dr.Eng.]

Russell,

Thank you for sharing user review!
Sorry, I haven’t actually try it.
Therefore, my comment was a design review only based on the description of official site. The actual performance seems to be different.

I want to try it, one day! Thanks.

[Eric Blumensaadt]

Since I have L4 and L5 spinal dic problems my backpack shoulder straps only touch the front of my shoulders and merely keep the pack from falling backwards. All the weigh is on my hip belt and thus my pelvic girdle and legs, not my spine.

My Osprey day pack is always under 15 pounds so the design of those shoulder straps work well.

 

[Ron Bell / MLD]

Six main factors of shoulder strap comfort in lightweight frameless packs.

1. Width – Total width of the padded strap over the shoulder area. Bound,  non-padded binding at edges of the straps do no count,  but are always listed in the specs and they are faster to make.  Inverted and stuffed uses the whole width as padded area- PITA to stuff and build. Stuff 15 sets and your hands are numb all day.

2. Thickness :  .5 ” EV50 foam  +  1/8″  spacer mesh is pretty good.  Maybe 25-40% nicer than only 3/8″  EV 75 (harder) foam. Harder the foam = faster to build.

3. Shape: Varies in comfort perception person to person. When we used to make J and S straps there was little correlation of preference, small to large, men to women. A slight curve seems to fit a very wide range of people.

4. Foam Type:  Varies, EV 50 is pretty good and lasts a good long time. Some pack makers use .75″ slightly softer foam on light-ish framed packs and that also works well.

5: Strap spacing at neck.  Varies person to person. 3″ seems about right for most. 2.75″ for Small. 2.5″ for smaller.  Big neck people need custom.

6: Entry angle over shoulder.  Varies. Everyones should slope is different. Somewhere between 8 and 12 degrees seems to fit a wide range of people well.  A nicely padded wide strap also add a wider measure of perceived variance compatibility here.

[Nenta WAKO, Dr.Eng.]

Eric,

Hipbelt is the one method that I described the former one. In this topic, I introduced the latter method.

[Nenta WAKO, Dr.Eng.]

Ron,

Thank you for your comment.
What I want to say in this topic is the way of load distribution is important if pain is set to the evaluation function for comfort.

It is generally known that strap width, shape, and entry angle contribute contact area (physical fitness) that reduces the mean load if it increases. Also, it was demonstrated that the overall foam thickness and material combination of the strap contribute to reduce pressure hotspot. Those are the factors that you showed.

I showed that there is a design possibility to reduce the overall pain sensation more, depending on the way of load distribution even if the load is partially increased under the same pack weight conditions.

In my research, I investigated the relationship between mechanical stimuli and overall shoulder pain intensity, and made reglession model. If you want to know in detail, please watch my YouTube video on the link.

[Author]

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