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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