Despite the summer weather outside, researchers at the Toronto Rehabilitation Institute are donning parkas and heading into a frigid lab to design a winter boot that helps prevent slips and falls on ice.

At the institute's climate-controlled laboratory, student researcher Jennifer Hsu is trying to determine how and why winter falls occur with the aim of designing a boot that helps people stay sure-footed on a variety of winter surfaces. Researcher Jennifer Hsu watches as a subject tests footwear on a patch of ice in the Controlled Climate Performance Lab in Toronto. (Patrick Dell/Canadian Press)

For now, Hsu, who studies the biomechanics of gait, is focusing specifically on the kind of falls that postal workers experience. Mail carriers are particularly at risk of slipping and falling since they work outdoors in all types of weather and on all kinds of surfaces.

"The reason why we're focusing on postal workers is because they're young and healthy and agile, but at the same time, they also experience all these problems of slips, trips and falls," said Hsu, a PhD candidate in biomedical and mechanical engineering at the University of Toronto.

"They have a lot of lost hours due to accidents because of this."

The climate-controlled lab resembles a walk-in freezer whose temperature can be set from –20 C to 35 C. In the lab, volunteers willing to slip for science don down jackets and stride across walkways that mimic various surfaces, such as steep ramps or ice-covered stairs.

Volunteers wear a safety harness to stop them from actually hitting the floor while motion sensors record their movements so Hsu can later determine how their body moved. For example, she looks at how much a heel slipped when it met the ice and at what velocity.

Hsu is also testing how people walk in different types of footwear, depending on the degree of friction and the type of surface.

Research suggests people are most susceptible to falling when it is around 0 C outside and a thin layer of water forms or after a thick layer of snow falls on top of ice.

Black ice tripped up postal worker

It was black ice, or ice under snow, that caused Canada Post letter carrier Sandy Laflamme's fall last winter. The cleats and tread on a pair of Canada Post's existing boots. (CBC)

As the Toronto woman went to put mail in a mail box on a porch, her foot twisted, jerking her knee and rendering her unable to walk down the stairs. She had ligament problems in her knee as a result and was off work for a month.

For Laflamme, the best boot that science could come up with would be a "snow tire boot" that is:

• Flexible enough to offer range of motion for the foot.
• Includes sharp cleats to dig into ice.
• Absorbs the shock of walking.

Canada Post issues cleats for letter carriers to wear over their boots, but the problem is they need to stay sharp, and they don't work well on black ice, Laflamme said.

Cleats work in some conditions but might need to retract on harder surfaces, Hsu said. Canada Post's cleats are one of the types of footwear she is studying.

Eventually, the researchers aim to expand their focus to seniors who use canes and crutches. One in three seniors fall every year, Hsu noted.

In 2004 to 2005 alone, more than 21,000 Ontarians of all ages visited an emergency room because of injuries related to a fall on ice or snow. Such fall-related injuries have been estimated to cost the Canadian health care system $2.8 billion a year, according to the institute.

Hsu is doing the work for Canada Post with the help of a grant from Ontario's Workplace Safety and Insurance Board.

With files from The Canadian Press