Chair's gas spring eases back pain

Six-time world speed-skiing champion Franz Weber knows the importance of a comfortable chair. The gold medals he accumulated during the 1970s cost him four shoulder surgeries, three knee surgeries, and a back surgery or two, so he's had to spend some time sitting during each of his recoveries.

Now that Weber is well into his 40s, sitting at a desk for long periods of time while running his own business aggravates his back. "One day my wife saw this new chair at the chiropractor's office, and it helped alleviate the back pain I've had for years," says Weber.

The chair to which he refers is the Swopper from Aeris GmbH. "Unlike other chairs that place the seated person in a static position, the Swopper's unique engineering puts the user in active motion," says Dr. Michael Nelson, a Reno chiropractor and owner of a Swopper. "Your body needs motion for circulating blood and spinal fluid." He adds that the lubricating sinovial fluid that surrounds our spinal disks relies entirely on motion for its supply of nutrients, rather than on blood flow like the rest of the body.

Swopper's industrial de-signer, Hennar Jahns, says he didn't want it to look like a regular stool. "I realized it was a new way of sitting and that's a strong concept," says Jahns. "It needed to look different in order to reflect that."

The engineer behind the Swopper Chair is Josef Glockl, who explains that his objectives included producing smooth movement in all three dimensions. "For the lateral movements, the resistance should increase with the size of the movement to avoid tipping over," says Glockl. "For the vertical movement, there should be no damping, as this increases pressure on the spine's disks."

Vertical movements rely on a gas spring from Suspa (Altdorf, Germany). "It is responsible for the adjustment of height, not vertical bouncing," says Glockl.

Oil and air fill the gas spring. But as Glockl points out, the more air used the softer the gas compresses when someone sits in a seat. "Most manufacturers do this to reduce the shock when you sit down."

As occupants sit and compress the gas, a sleeve bearing moves. "If the movement is not smooth, you feel the resistance," says Glockl. He notes that the resistance is undesirable. "To avoid this, we reduced the amount of air in the gas lift." The result-the occupant sinks in very little when seated. Vertical movement in the sleeve bearing is also minimized.

Skier Franz Weber appreciates minimal vertical movement now more than ever. In September, when Design News interviewed him, Weber experienced a "mean spill" on his bike. He ruptured one disk and herniated four others.

For more information about gas springs from Suspa: Enter 535