The human foot contains 26 bones, 33 joints and a number of muscles,
ligaments, tendons, blood vessels and nerves. When standing, the feet
hold up the body, and thus bear a tremendous amount of weight. Walking
puts even more force on the feet. According to the American Podiatric
Medical Association, a one-mile walk for the average 150 pound person
puts a force of 63.5 tons of pressure on each foot. Over the course of a
day, that can add up to several hundred tons of force.
Taking it in Stride
Stride is defined as the distance between two successive ground
contact points on the same foot. For an average adult, stride length is
about 2 to 3 feet. Stride patterns vary, depending upon the type of shoe
we are wearing (sneakers versus high heels), surface on which we walk
(asphalt versus gravel or sand) and type of terrain (smooth vs. uneven,
like a trail).
Jinger Gottschall, Ph.D., Kinesiologist from Penn State University
in University Park, PA, says stride length changes during pregnancy,
because the woman must adapt her walking to maintain center of balance
to keep from falling. Stride may also change after a lower limb injury
because a patient needs to keep the full weight off one leg.
The body learns to compensate fairly quickly to changes in stride.
However, when alterations in stride are significant, one foot takes on
more pressure than the other. This causes walking to become less
efficient. In addition, the limb that bears more weight endures greater
stress and may be at risk for injury.
The Dual Treadmill
Penn State University investigators have developed a special type of
treadmill to study stride alterations. Instead of a single walking
belt, the dual treadmill contains two belts - one for each foot.
Although dual treadmills have been around for several years, the new one
incorporates some unique features. It can tilt up or down, mimicking
the ability to walk both uphill and downhill, as well as side to side,
allowing researchers to measure ground forces separately for each foot
in vertical, horizontal and lateral directions. Belt speed can be
altered to mimic a limp or correct "asymmetric" walking. In addition,
reflective markers can be placed on patients. Video cameras capture the
movement of the reflective markers, enabling the measurement of stride
length, stride frequency and joint angles.
In a new study, investigators will have volunteers wear GPS units
while walking around campus, measuring speed while going uphill,
downhill and over flat and non-flat surfaces. The information from the
GPS units will be inputted into the treadmill computer. The treadmill
can then be used to mimic a person's walking on the charted surfaces.
During the simulated walking, the investigators use the cameras and
reflective markers to record stride, muscle activity and oxygen
The new dual treadmill allows researchers to see exactly how a
person responds to different types of real-life terrain, rather than a
just a flat treadmill surface. This information may be used to detect
alterations in stride and help therapists plan an appropriate
Research compiled and edited by Barbara J. Fister
AUDIENCE INQUIRYFor general information on walking or foot problems:
American Academy of Orthopaedic Surgeons, http://orthoinfo.aaos.org
American Podiatric Medical Association, http://www.apma.org
BIBLIOGRAPHYIf you need a list of the research titles supporting this story, please contact Barbara Fister at (610) 395-1300 ext. 238.
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