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Walking Biomechanics Using a Force Plate

We recently visited Dr. Deborah Schenberger’s biomechanics research lab at the University of Portland in Portland, OR. She has designed some experiments to look at issues related to barefoot running, a running trend popularized by Christopher McDougall’s book Born to Run. Without the padding provided by traditional running shoes, barefoot runners minimize their heel strike, thus changing their gait.

Using a wooden ramp fitted with a Vernier Force Plate, Dr. Schenberger’s students collected force data using LabQuest Mini and Logger Pro software. Through analysis in Logger Pro, her students investigated the effects of various types of shoes on walking force profiles.

Dr. Deborah Schenberger in her biomechanics lab
Dr. Deborah Schenberger in her biomechanics lab

As shown in the picture above, the testing ramp consists of two inclined platforms that are 22 inches wide and 37 inches long. In the center, there is a level section that is 13 inches long and 22 inches wide. The center piece is secured to the two inclined ramps with a set of 2 x 4s underneath. The supporting 2 x 4s are notched to allow the inclines to come up flush with the center section. The center platform also has a cut-out on one side that is 11 x 11 inches. The force plate was placed into this cut out section.

During our visit, we collected walking data in traditional running shoes, low-profile running shoes, and barefoot. We set up data collection in Logger Pro to be Timed Based, with a sampling rate of 100 samples/second for 30 seconds. We started data collection in Logger Pro, and walked across the testing ramp several times (e.g., five) in the first type of shoe (e.g., running shoes). In order to emulate natural walking, our walker tried to maintain a steady stride. A second person observed the walker’s impact on the Force Plate to ensure that the entire impact force was measured by the Force Plate and not shared with the ramp. The strikethrough feature in Logger Pro was used to remove force data shared between the plate and ramp from further analysis. We then repeated this procedure with low-profile running shoes, and barefoot.

We analyzed the data in Logger Pro by examining force profile graphs of Force vs. Time. We looked for features in the profile associated with the heel strike and toe-off of the walker. Typically the heel impacts the Force Plate first, followed by the toe, allowing us to use the temporal aspect of the data in combination with the peak in force to identify these events. We found that all profiles exhibit peaks associated with the heel strike and toe-off of the walker. We were interested to see that when barefoot, the toe strike is relatively lower in magnitude than the heel strike.

Force Exerted Upon Impact Graph

We were also interested in calculating step impulses from the data. Impulse is defined as an integral of force with respect to time. Using Logger Pro, we selected the non-zero region of a force profile, and selected Integral from the Analyze menu. A helper box is then displayed, indicating the calculated impulse in Newton-Seconds.

Calculated Impulse Graph

After integrating a force profile for each of the shoes, we manually typed the calculated impulse values into a new Logger Pro file to generate a bar graph to illustrate the comparison. To do this, we entered shoe types into the first column and the corresponding calculated step impulse values in the second column, then selected “Bar Graph” within the Graph Options. The comparison of these step impulses suggests that reducing the padding in the shoes also reduces the step impulse.

Step Impulse Comparison Graph

Dr. Schenberger is currently working with Vernier Biology Staff Scientist, John Melville, PhD, to implement a similar experiment for analyzing running.

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