One of the world's oldest and most famous chairs sits in Aachen, Germany, where the legendary Charlemagne lived, reigned, and died in the early ninth century. The colossal marble structure witnessed Napoleon and Czar Alexander bow before its grandeur. The chair is encased in Charlemagne's tomb today.

From schoolchildren to professional athletes to world leaders, everyone sits - although not on something as lavish as Charlemagne's throne.

The Philadelphia Museum of Art is currently offering a review of sitting's past, while designer Peter Opsvik rethinks it. In his new book, Rethinking Sitting, the Norwegian industrial designer explores the idea of comfort versus functionality, suggesting that the two qualities exist on a similar plane.

"Comfort is one of the main criteria of functionality and belongs in the same path. For a chair in which you sit for long periods of time, functionality takes precedence over appearance, whereas in other circumstances, the sculptured look of the object may be more important," Opsvik says.

Revisiting modern chairs, "A Taste for Modern: The Jeanne Rymer Collection of Twentieth-Century Chairs" and "Visual Delight: Ornament and Pattern in Modern and Contemporary Design" are now exhibited in the Collab Gallery of the Art Museum's Perelman Building.

Rymer, a former University of Delaware professor, donated 36 chairs to the museum in 2007. Associate curator Donna Corbin wanted to highlight her collection because it tells the 20th century's story. She grouped the chairs accordingly.

"I always say when looking at 20th-century items: You don't have to do too much thinking. They tell the story themselves," Corbin says.

That story is one of functional, affordable, but still elegant furniture. Her favorite piece is the lily chair, a Plexiglas structure shaped like a flower bud. It lies on a round base, with no legs.

"It drives me nuts every time I see it. I love it," Corbin says of the piece indicative of 1950's challenging design choices.

Displaying contemporary furniture, "Visual Delight" showcases ornamental pieces from everyday life.

"I think that people loved modern and contemporary design because they can relate to it. Many chairs were done within our lifetimes and everyone uses chairs, dishes, and lighting fixtures," Corbin says. "It tells a lot about who we are - sometimes more than paintings, sculptures can."

And who we are is changing.

The movements of modern people may be limited to "minimal and often repetitive" acts, such as nudging a computer mouse. Opsvik combats what he calls "passive sitting" by producing chairs that "are designed for dynamic sitting to allow the sitter mobility and a variety of comfortable positions without having to move from the chair."

His ideas on body comfort are in line with what some health experts say is a common complaint. Since 2007, people with lower-back and backside problems have contacted kinesiologist Taras Penkalskyj about sitting.

"They are convinced - as I am as well - that this is from incorrect or prolonged sitting," said Penkalskyj, of the American Massage and Kinesiology Center in Northeast Philadelphia.

He advises patients who have had recent accidents to avoid leaving "their bodies in the same position for more than 20 minutes." Although not a general rule for everyone, Penkalskyj says it wouldn't hurt to vary positions when in chairs.

Constant motion fits right into Opsvik's designs.

"The human being [should] become more aware of body signals and change posture accordingly," he says. "After a while, the best and most comfortable position is always the next one."

Although Opsvik's chairs sometimes resemble exercise equipment, many are designed to allow for different positions.

Over time, Opsvik has produced coiled, snakelike chairs, functional chair swings, and even leg-support chairs for hairdressers. He has won numerous Scandinavian and international design awards.

Rethinking Sitting shows off some of Opsvik's ordinary and unorthodox designs and provides a succinct seating and design history, while also suggesting dynamic solutions for the future.

Although it sometimes reads like a catalog of Opsvik's works, Rethinking Sitting offers an honest alternative to furniture's status quo. Like the chairs exhibited at the Perelman Building, Opsvik's pieces provide a reflection of the past with a nod to the future.

Chairs: Sitting, Reading, Seeing

"Visual Delight: Ornament and Pattern in Modern and Contemporary Design" and "A Taste for Modern: The Jeanne Rymer Collection of Twentieth-Century Chairs," through September at the Collab Gallery of the Perelman Building of the Philadelphia Museum of Art, Fairmount and Pennsylvania Avenues. Open 10 a.m.-5 p.m. Tuesdays through Sundays. Perelman Building admission: $7, $6 ages 65 and older, $5 students with valid ID, $5 for ages 13-18, free for children 12 and younger. Sundays: Pay what you wish. Admission is free with Art Museum ticket. A shuttle runs between the two buildings every 10 to 15 minutes.

Rethinking Sitting by Peter Opsvik, published by W.W. Norton & Co., $39.95.

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