Team Members: Brant Kochsiek BSAC Steve Pauls Team Leader Tim Rand Communicator Brian Schwartz BWIG

Client: David Beebe, Ph. D Biomedical Engineering Advisor: Naomi Chesler, Ph. D Biomedical Engineering

Abstract Many running injuries are caused by continued use of improper or worn running shoes. The increase in incidence of injury can be directly correlated to the degradation of the materials used in shoe sole construction. The degree to which a shoe sole degrades is directly related to the changing elasticity of the material. Two different methods are proposed to measure elasticity in a shoe sole. Strain gauges and Flexi-Force piezoelectric force sensor devices have been added to an integrated circuit that will indirectly measure shoe sole elasticity. Once calibrated, each circuit will have a diode that lights when a shoe sole is worn past its useful life.

Problem Motivation Running shoes last miles Worn shoes do not always appear worn Incidence of injury increases with worn shoes

Client Requirements Design a device that: –Measures shoe sole elasticity –Fits ergonomically into the shoe sole –Is lightweight and small so as to not hinder performance –Operable for the life of a running shoe ( miles) –Has a clear indicator so the runner will know when the shoe is sufficiently worn

Shoe Materials Ethylene Vinyl Acetate (EVA) Polyurethane (PU) Outsole Midsole Upper Footbridge

Nominal Running Style Heel strike Inward pronation (rolling action of the foot) Ball of foot strike Forefoot push off

Pressure Distribution while Running Maximum pressures in the midsole occur beneath the heel, the middle to inner portion of the forefoot, and the big toe.

Comparator/LED Differential Amplifier Drive Circuit Voltage regulator Force Sensor Circuit

FlexiForce® Sensors Comparison of forces from top to bottom

Strain Gauge Circuit Comparator/LED Differential Amplifier Strain Gauge

Constant Poissons Ratio (v), Stress-Strain (δ-ε) for Elasticity (E) HowPage002.html

Variable Force Sensors Strain Gauge Cost34 Measurement accuracy 53 Durability33 Circuit integration 23 Size33 Performance?? Total = Worst 5 = Best

AdvantageDisadvantage FlexiForce® Force comparison -Paper thin -Allows for fine adjustments -More precise -Complicated construction -Complex comparative circuit -More expensive Strain Gauge Measurement -Cost -Simple circuit -Simple construction -More of an indirect measurement -More bulky

Preliminary Testing

Current Standing Preliminary tests showed flaws in our circuit and sensor set up Circuit is being reworked and future testing will soon follow Research into exact placement of sensors in shoe sole is ongoing

Testing Procedure Apply static loads to sensors imbedded in silicone polymer Apply static loads to sensors imbedded in silicone polymer Loads applied in sets of 4000 which correlates to about a 6 mile run Following each set: –Elasticity of material will be measured –Output of circuit will be read from multimeter –Output vs. elasticity will be plotted

MTS Servohydraulic Machine We plan to use an older version of this machine found in the Materials Testing Lab in Engineering Hall

Future Work Mold strain gauge into silicon mold Test both prototypes to simulate 500 miles of running wear Determine the correlation between the output of each device and elasticity Determine shoe sole wear threshold value Integrate chosen device and corresponding circuit into a shoe sole for testing Research and go through necessary human subject testing procedures Undergo human testing of the prototype shoe Possible patent application

References 1000 Hz High-Cycle Fatigue Testing Systems. MTS Inc. Accessed 4/28/04 URL: Anatomy of a Running Shoe. American Running Association. Accessed: 04/26/04 URL: Accessed: 04/26/04 URL: Biomechanics Laboratory. Accessed: 04/24/04 URL: BTopenworld. Accessed: 04/24/04 URL: FlexiForce Force Sensors. Tekscan. Accessed: 04/25/04 URL: Forrest Gump Pictures. Cox Members High Speed Internet. Accessed 02/26/04 URL: Hennig, E. M., & Milani, T. L In-shoe Pressure Distribution for Running in Various Types of Footwear. Human Kinetics Publishers Inc., New York. Mills, N., & Verdejo, R Performance of EVA Foam in Running Shoes. Blackwell Inc., UK, Birmingham. Runners World. Runners World. Accessed:04/27/04 URL: Running Shoes. ePodiatry. Accessed: 04/26/04 URL:

Special Thanks Professor David Beebe Professor Naomi Chesler Amelia Cosgrove John W. Dreger Ivar Meyvantsson Professor Tim Osswald Professor Tim Osswald Professor Mitch Tyler Paul Victorey Professor John Webster