Iowa State University


Inside Iowa State
August 11, 2000

Smooth rolling

by Laura Boskelly
Tim Derrick never thought his love for running would turn into a career in biomechanics. But his jog from computer science to biomechanics, while at the University of Oregon, set him in the right direction for a promising career.

At the University of Oregon, Derrick's research focused on the stress impact running causes throughout the body. Derrick, now an assistant professor in health and human performance at Iowa State for four years, has taken that research a step further to see how the body deals with stress.

The results could affect people nationwide. His focus has been on two projects, wheelchair casters and farm injuries in children.

"In the human body it's important to put some stress on the bones, or the bones will start to shrink," Derrick said. "But too much shock can lead to injury."

For example, repetitive motion by wheelchair users can cause many problems associated with pain and discomfort. The pain can be widespread, from the legs to the back and head.

"Wheelchair users receive a lot of jarring to their chairs from different surfaces such as grass and cracks in concrete and bumps," he said. The jarring "sets a tremor in their legs and actually can cause shaking in their legs."

Derrick was approached by a representative from Frog Legs Inc., a Vinton company that manufactures wheel casters. Frog Legs wanted Derrick to analyze the effectiveness of their wheelchair casters.

Frog Legs' newest caster reduces vibrations through shock absorbers and enables wheelchair users to travel more easily over a variety of surfaces. Derrick's research tested the wheelchairs for vibrations and to see how well the chairs go over bumps and different surfaces.

"Certain amounts of cushioning can relieve stress on the body," he said. "It's a safety and comfort issue."

The data Derrick collected confirmed Frog Legs' claim that its wheel casters reduced vibrations in the wheelchair, which reduces injury and makes life more comfortable for wheelchair users.


Farm research
Derrick's other research project looks at stress- induced farm injuries in children, a problem that hits close to home for many Iowa families.

Derrick joined forces with Steve Freeman, associate professor in industrial education and technology, to research causes of stress-related injuries on the farm. Freeman specializes in injuries within the farm industry for ISU Extension. They plan to begin their research Sept. 1.

The work will focus on shoulder and elbow injuries in farm children recruited through 4-H clubs. They will measure the stress levels at these joints experienced by children to see if they are high enough to cause an injury. The research will focus on how the children carry five gallon buckets. These buckets are significant because many farm chores are done using a five gallon bucket.

"We're going to look at the size of the bucket children carry and how that affects them," he said. "An adult can carry a five gallon bucket with a fairly straight arm. Children are much smaller and they have to force their arm outward and that puts a lot more stress on the shoulder.

"We're also going to look at using smaller buckets or splitting the task into two buckets," he said. "Perhaps that will reduce the stress on the shoulder."

Derrick said he hopes to come up with recommendations about using two buckets or smaller buckets, or possibly defining an age or height and weight requirement for children who can safely use the buckets.

Any information or recommendations gathered by Derrick will be distributed throughout Iowa by Freeman.




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