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The "GOOD FOR YOUR BACK" pack!

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SCS™ - Super Compression Suspension:

According to a study done by Dr. Allan Tencer, Director of the Biomechanics Laboratory at the University of Washington, the SCS™ (Super Compression Suspension) design is the only pack that actively reduces the risk of back pain or injury.

To learn more about Dr. Tencer’s study, please take a few moments and read a summary of his study below: A mechanical analysis was performed on three types of day packs, a conventional pack with shoulder straps attached to the inner (side against the wearer’s back) top edge, a fanny pack with waist belt and anti rotation strap attached between the top outside edge and the waist belt, and a suspender SCS™ (Super Compression Suspension) pack with a waist belt with anti rotation strap like the fanny pack but with accessory shoulder straps attached on the top outside edge of the pack. Key differences between the designs are summarized below:

  1. The conventional pack requires all the pack load to be transmitted through the shoulder straps and into the spine. It has no method for pulling the pack against the body to create frictional forces which dampen pack movement during dynamic loading. Because the straps are attached to the inner edge, only the horizontal component of the strap force controls rotation of the pack away from the torso. To control rotation, the wearer must either wear the pack higher which makes the shoulder strap angle more horizontal but increases the height of the pack center of gravity, or bend forward to move the center of gravity of the pack over the base of the spine. Bending forward significantly adds to load on the spine because of the additional force in the erector spine muscles to counteract the weight of the torso when bent forward.

  2. The fanny pack transmits pack load by tightening the waist belt sufficiently so that the belt is supported by the pelvic iliac bones. In addition pulling the pack against the torso creates friction which resists vertical slipping of the pack and controls motion during dynamic loading. With this design pack load bypasses the spine. Rotation of the top of the pack is controlled by an anti-rotation strap which pulls the top of the pack into the wearer’s back and prevents rotation. However, because of its location of attachment on the top outside surface, the vertical component of the anti-rotation strap tension actually counteracts the horizontal component, reducing control of rotation and necessitating greater waist band tension than would otherwise be necessary or requiring the wearer to bend forwards as with the conventional pack.

  3. The SCS™ (Super Compression Suspension) pack provides a variable combination of both conventional and fanny pack support systems with the additional feature that the shoulder straps are mounted to the top outside edge of the pack in contrast to the top inside edge mounting of the conventional pack. More of the load of the pack is transmitted down the spine than the fanny pack but less than the conventional pack, depending on the distribution of load between the waist band and shoulder straps. Rotation of the pack is controlled partly by the waist band with its anti-rotation strap, as with the fanny pack, but also by the shoulder straps. In contrast with the fanny pack, the shoulder strap force acts upwards so that both horizontal and vertical components resist rotation of the pack. The shoulder straps can be worn loosely but are still effective in controlling rotation because the moment arm distance of the vertical component of the strap force is twice that of the pack load and rotation is also resisted by the horizontal component of the strap force. The net result is that for relatively little force the shoulder straps are effective in controlling rotation and pulling the pack into the torso, while the waistband still transfers most of the weight of the pack into the pelvis, bypassing the load on the spine. Because rotation is effectively controlled the wearer would most likely walk in a more upright position, which would lessen the compressive loading acting on the spine compared with the other designs analyzed.

* Taken from: Allen F. Tencer Ph.D., Day Pack Comparisions, "Analysis of the forces required to support different day packs with particular reference to loads on the spine”. July 16, 1996, University of Washington.

For more information or to read the complete paper written by Dr. Tencer, please contact us at info@truenorthgear.com or 800-873-5725.

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