Abstract

Results

The In Shoe Pressure System project is a research effort to reduce running injuries and prevent FootStrike. Despite the money that has been dispensed into reducing running injuries by designing better shoes, the ideal way to reduce running injuries may be to simply work on foot posture finding a way to see the impact of the force and pressure in different parts of the foot while running. In Shoe Pressure System seems to be the very reasonable solution to prevent FootStrike.

Saba NaghipourDepartment of Electrical and Systems Engineering

Overview

Procedure Highlights Experiment Setup

Biomechanics of Running

Heelstrike runners experience more running injuries such as hip injuries, IT band syndrome and hip bursitis. The Heelstrike runners land on their heel first so that the impact force of the heel on the ground causes significant transient force to their body via the skeletal system. Even though the heel is the hardest bone of the body, it does not absorb the impact force but it combines the gravitational forces and compresses them toward the skeleton. Daniel Lieberman, a researcher at Harvard University said: “Heelstrike can cause a direct force of up to three times more than a runner’s body weight on the feet, ankles, knees and hips between 1000-1500 times per time.” Since MidFoot Strike is considered a preferred type of FootStrike and we consider the HeellStrike as the worst case, Mid and Heel are the most important parts of foot that we consider in this research.

Effects of running barefoot or with shoes in relation to foot strikes

Barefoot runners are mostly front foot strikers when running. The heel cushions and arch supports within athletic shoes have made our feet weaker and adapted many people to favor HeelStrike. That is the reason that changing back to barefoot may cause injury to weakened feet.

Three basic types of FootStrikes:

I. Heelstrike(75%)

II. Midfoot strike (24%)

III. Toestrike(1%)

In Shoe Pressure Measurement and Analysis in relation to Foot Strike

References

http://barefootrunning.fas.harvard.edu/4BiomechanicsofFootStrike.html

http://www.livestrong.com/article/553745-the-impact-of-running-sneakers-on-the-foot/#ixzz1rPBjHyRI

http://www.tekscan.com/medical/system-fscan1.html

http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=05378500

Future Work

1.Develop a portable technology suitable for outdoor activities.

2.Add additional sensors to reduce the error and be more accurate

Sensor selection criteria• Pressure range for running(2.5-76psi)• Sufficient accuracy(5%)• Corrosion and dust resistance• High sensitivity • Extremely thin & easy to adjust in shoes

Sensor position selection There are 15 areas on the sole foot that support body weight but we select the heel and metatarsal areas to see if a person, favors HeelStrike or Forefoot Strike.Circuit Design • Design & develop an electronic interface circuit for the resistive

sensors • Extract voltage signals from the sensors • Filter out the noise using a low pass filter at 15Hz.As the frequency increases above 15Hz the gain decreases. 15Hz is the frequency of the steps, and anything above that is noise that need to be filtered. The attach shows that my experimental result matches my theoretical result.

The final design of the circuits ended up as an inverting low-pass amplifier with variable input resistance. Each of the FlexiForce pressure sensors in the insole are connected to a 2.2nf capacitor, a 5M resistor , LM324N

and grounded though the connector. The -0.5 voltage is input to 𝑂𝑝 𝐴𝑚𝑝each of the sensors.

Data processing • Convert embedded analog to digital (A/D) using the Elvis board• Convert voltage to pressure using calibration using multiple known masses to came up with voltage for given pressure then the system convert it to linear equation for easier analysis.• Convert the data to an array of numbers, record and sample data.Data analysisWhen the pressure increase the resistance of the sensors decrease and the voltage increase. The Voltage and pressure are proportional by a constant of k=0.040885.

Acknowledge

I would like to thank Professor Morley for all of his help. I am so grateful to Professor Richter, who made this project possible . Many thanks to the Electrical Engineering

Department at Washington University for their support .

Challenges Using Different Methods

Using accelerometer Advantage: most smart phones have the application and no need to do

any additional programing on the phone. Disadvantage: the output is the peak force and there is no way of seeing the comparison pressure range in different parts of the foot.

Using versatile Tekscan sensor Advantage: It gives us a perfect picture of foot pressure Disadvantage: High resolution requiring advance equipment and skill

Background

Goal: To display the maximum pressure in different parts of foot while running and to inform the person if they run on their heels. Approach:1. Design a circuits to collect data output from sensors 2. Convert the data to pressure3. Use the data to calculate peak pressure, mean pressure, center of

pressure in both recorded and real time.

Application:• Footwear research for design• Compare, screen, and isolate food function • Identify pressure range for medical purposes and personal running

regulation.

Vout= -Vin()= -Vin(=-Vin

HeelForefoot