Shoe-Embedded Pressure Sensors

Introduction

Runners at the London 2012 Olympics will be under a great deal of pressure to be the first to the finishing line. There is increasing pressure on monitoring an athlete’s performance at the most prestigious sporting event in the world. At London’s 2012 Olympic event, advanced electronic starting blocks will be introduced to track the force of the runner’s heel to give a better representation of how quickly the runner has left the starting block.

There are a number of sensors currently being used to create ’smart’ technology in shoes to help monitor the performance of an athlete. Pressure sensors and accelerometers are commonly used to advance sports-performance technology.

Pressure Sensors

Ground reaction force is measured using a pressure sensor to provide data on the speed of a person’s gait. The ground reaction force is the force applied as a result of contact of the body with a surface. In this instance, the pressure sensor works to measure changes in the loading to predict speed. The pressure impacting the point where two surfaces interact (i.e., between the shoe and the foot) is known as the plantar pressure. In a study by Lee, A.J.Y., et al, used insole pressure sensors to investigate the relationship between peak treadmill acceleration, peak plantar pressure, and peak ground reaction force during a running exercise. The method involved using a dual axis accelerometer with a data acquisition system attached to a treadmill running board which gathered information on the peak treadmill acceleration during a running exercise. Figure 1 illustrates a standard accelerometer used to measure peak treadmill acceleration.

Figure 1. The use of an accelerometer on a treadmill to measure peak treadmill acceleration. Source: Estivalet, M., Brisson, P. (2008). The Engineering of Sport 7. Volume 1. France, Paris: Springer Science and Business Media. 

During a running exercise, the accelerometer was activated by an electronic pulse. In this study, the accelerometer only measured speed in a vertical direction. The study revealed linear correlation between peak treadmill acceleration and the speed of running.

Three-axis accelerometers in connection with a wireless interface are commonly used in research to measure shoe-integrated sensing. For example, Oshima, K, et al, implemented such a system to the heel portion of a shoe together with two sensors (one sensor embedded at the toe end of a shoe and the other sensor positioned at the heel of the shoe). Field experiments that involved monitoring participants gait patterns revealed fluctuation patterns in y-axis acceleration relating to up-down movement of the foot indicating that shoe-embedded sensors are useful for monitoring gait pattern.

Measurement of gait pattern is particularly useful in rehabilitation programs. It is particularly challenging to measure gait patterns for patients when considering the space required to carry out such measurements. Sugimura, Y, et al, have developed a shoe-embedded sensor device specifically for measuring gait pattern for rehabilitation (figure 2).

Figure 2. Basic outline of a shoe-embedded sensor network for rehabilitation. Source: Dossel, O., Schlegel, W.C. (2009). Ifmbe Proceedings. Volume 25/9. World Congress on Medical Physics and Biomedical Engineering. 7–12 September 2009. Munich, Germany. Germany, Berlin: Springer Science and Business Media. 

This study involved use of a shoe-embedded sensor network (consisting of pressure sensors and an accelerometer to detect information on the length and width of a step and the plantar pressure) with a wireless module to transfer the data from the sensor network to a display. The accelerometers used to measure the three axes were positioned inside the shoe with two transmitters placed on the surface of the heal inside a shoe. Pressure sensors were also used to measure the change in plantar pressure during a gait pattern. The display screen, as mentioned, was used to present a gait pattern for interpretation by the physician.

Use of a pressure sensor to monitor gait patterns is a highly useful tool for applications such as rehabilitation as discussed. Development in this field of research has seen shoe manufacturing companies design shoes with the shoe-embedded sensor insole. The shoe-embedded sensor technology is also attractive to the sports industry as it helps athletes keep track of their speed and performance.

References

· Lee, A J Y., Chou J., Liu Y., et al. Correlation between treadmill acceleration, plantar pressure, and ground reaction force during running. (P52). Published in:  Estivalet, M., Brisson, P. (2008). The Engineering of Sport 7. Volume 1. France, Paris: Springer Science and Business Media.

· OSHIMA, k., Ishida, Y., Konomi, S., Thepvilojanapong, N., Tobe, Y. A Shoes-Integrated Sensing System for Context-Aware Human Probes. Published in DASFAA’10 Proceedings of the 15th International Conference on CDatabase Systems for Advanced Applications. Volume Part 2. Germany, Berlin: Springer Science and Business Media.

· Sugimura, Y., Wada, F., Makino, K., et al. Development of a shoe-type device for collecting gait information. Published in: Dossel, O., Schlegel, W.C. (2009). Ifmbe Proceedings. Volume 25/9. World Congress on Medical Physics and Biomedical Engineering. 7–12 September 2009. Munich, Germany. Germany, Berlin: Springer Science and Business Media.

· Duffy, V.G. Digital Human Modeling: Third International Conference, ICDHM 2011. Germany, Berlin: Springer Science and Business Media.