Researchers are using a new model to learn more about how toe strength can
determine how far people can lean while keeping their balance.
The results could help in building robotic body parts that will closely
imitate human movement, and might lead to a new generation of advanced
prosthetics.
Hooshang Hemami, professor of electrical and computer engineering at Ohio
State Univ. built a complex computational model of the human foot to look at
the role of the feet and toes in determining the body’s movement and balance.
Many studies concerning human balance have emphasized the legs and upper
body while ignoring the feet, he said.
Hemami is one of a handful of researchers who are analyzing how manipulating
toe strength can affect human balance.
“In order to reduce the complexity of the problem, the feet are often either
neglected or modeled using simple shapes that don’t really give full credit to
the importance of feet,” Hemami continued.
Hemami and a colleague, Laura Humphrey, designed a computer model of a body
and foot which assigned four different sections to represent different parts of
the foot, while assigning the body one section. This allowed Hemami and
Humphrey to focus primarily on the pressure of the feet and toes as they
manipulated the forward motion of the body.
Hemami and Humphrey’s work was published in the Journal of Biomechanics. The researchers
performed simulations of static balance and forward leaning in the
computer-modeled body, and compared the results to those observed in the
scientific literature.
Static balance is when a subject stands either straight or at a certain
angle, and is able to remain stabilized in that position with the entire
surface area of the bottom of the foot on the ground. The computer model can
perform forward leaning indefinitely, but human subjects will experience muscle
fatigue eventually, explained Hemami.
The model that Hemami and Humphrey built allowed them to produce results
that supported the findings of balance shown in real subjects. They conducted
tests for three different cases: static balance in healthy subjects, static
balance in subjects with diminished toe strength, and forward leaning in
healthy subjects.
In order to have the model mimic a subject with diminished toe strength,
Hemami and Humphrey weakened one of the sections in the computer-modeled foot,
which represented a muscle located just above the big toe. This muscle helps
control the foot’s arch, which provides support to the body while standing.
Results indicated that in a healthy person, toes became increasingly important
as the person leans forward.
As the computer-modeled body leaned forward, the pressure underneath the
toes increased, and the pressure underneath the heel decreased in a similar
fashion.
When the same tests of static balance were performed on the computer-modeled
body with diminished toe strength, the pressure underneath the toes remained at
zero. Initially, the pressure underneath the heel was higher than in the
healthy subject, and as the body leaned forward, the pressure underneath the
heel only decreased by half the amount that it did in the healthy subject.
The maximum angle that a healthy computer-modeled body could lean forward
from the waist without its heels lifting off the ground was nearly 12 degrees
from vertical. The model with diminished toe strength could only lean forward
nearly 10 degrees.
The computer model supports past studies on real people, Hemami explained.
One discrepancy: his computer model was able to lean forward 12 degrees without
lifting its heels, while real people were only able to lean two-thirds as much—8
degrees.
“This discrepancy could be psychological – that people do not feel
comfortable using their maximum theoretical range of motion,” said Hemami.
“Now that we have a reasonable computer model, we hope to explore, in the
future, the sensory apparatus and other functions of the toes in diverse human
activities,” Hemami said.
In the future, Hemami wants to model the human spinal cord and develop a
mathematical system that can determine the level of reaching and pushing
required for certain tasks. Hemami uses the example of how much pressure one
should administer to hold an egg in your hands without dropping or crushing it.
