Routledge Handbook of Biomechanics and Human Movement Science

Youlian Hong, Roger Bartlett, Youlian Hong, Roger Bartlett

• Editore: Routledge
• Anno: 2008
• ISBN:
  9781134132331
• Edizione: 1
• Argomento: Ciencias biológicas
• Categoria: Biofísica

The Routledge Handbook of Biomechanics and Human Movement Science is a landmark work of reference. Now available in a concise paperback edition, it offers a comprehensive and in-depth survey of current theory, research and practice in sports, exercise and clinical biomechanics, in both established and emerging contexts.

Including contributions from many of the world's leading biomechanists, the book is arranged into five thematic sections:

• biomechanics in sports
• injury, orthopedics and rehabilitation
• health and rehabilitation
• training, learning and coaching
• methodologies and systems of measurement.

Drawing explicit connections between the theoretical, investigative and applied components of sports science research, this book is both a definitive subject guide and an important contribution to the contemporary research agenda in biomechanics and human movement science. It is essential reading for all students, scholars and researchers working in sports biomechanics, kinesiology, ergonomics, sports engineering, orthopaedics and physical therapy.

Section III Methodologies and systems of measurement

DOI: 10.4324/9780203889688-13

11 Measurement of pressure distribution

Ewald M. Hennig

University of Duisburg-Essen, Essen

DOI: 10.4324/9780203889688-14

Introduction

Movements originate from forces acting on the human body. For events of short duration, cinematographic techniques can not be used to estimate the forces and accelerations experienced by the body’s centre of mass (COM) or any one of its parts. Therefore, transducers are necessary to register forces, accelerations and pressure distributions that occur during human locomotion. Ground reaction force and centre of pressure information can be determined with force platforms. These data are important to estimate internal and external loads on the body during locomotion and sport activities. Ground reaction forces represent the accelerations experienced by the COM of a moving body. These forces provide little information about the actual load under defined anatomical structures of the foot. To understand the etiology of stress fractures, for example, a more detailed analysis of foot loading is necessary. This is only possible by many separate force measuring sensors that cover the area of contact between the foot and the ground. Researchers in anatomy and human movement science have been interested in the load distribution under the human foot during various activities for more than 100 years. Early methods estimated plantar pressures from impressions of the foot in plaster-of-Paris and clay. Later techniques included optical methods with cinematographic recording. Only in recent years, the availability of inexpensive force transducers and modern data acquisition systems has made the construction of various pressure distribution measuring systems possible. Force transducers rely on the registration of the strain induced in the measuring element by the force to be measured. Pressures are calculated from recorded forces across a known area. Because all force measurements are based on the registration of the same phenomenon — strain — similar technical characteristics apply to all types of transducers. Desirable transducer characteristics for biomechanical applications may differ from the characteristics which are advantageous for engineering usage. Measurement of pressure during sitting or lying on a bed requires a soft and pliable transducer mat that will adapt to the shape of the human body. However, such a transducer will normally not have good technical specifications concerning linearity, hysteresis and frequency response. Based on different technologies, several pressure distribution systems are sold today. Most of them are used for the analysis of the foot to ground interaction as pressure platforms or as insoles for in-shoe measurements.

Sensor technologies

Pressure is calculated as force divided by the contact area on which this force acts. It is measured in units of kPa (100 kPa = 10 N/cm²). Force measuring elements are needed to determine pressures and pressure distributions. There are only a few measuring principles that are commonly used to measure force. In the following section these principles will be described and their advantages and disadvantages will be discussed. Electro-mechanical transducers produce a change in electrical properties when subjected to mechanical loads. Depending on the type of transducer, forces can create electrical charges, cause a change in capacitance, modify the electrical resistance or influence inductance. Because inductive transducers are based on relatively large displacements, they are rarely used in measuring instruments for biomechanical applications.

Resistive transducer

A variety of different sensor types belongs to the category of resistive transducers. The electrical resistance of the sensor material changes under tension or compression. Volume conduction has been used as a method for measuring forces. Silicone rubber sensors, filled with silver or other electrical conducting particles, were produced in the past. With increasing pressure the conducting particles are pressed closer together, increasing the surface contact between the conducting particles and thus lowering the electrical resistance. These transducers show large hystereses, especially for higher frequency impact events. Resistive contact sensors work on a similar principle to the volume conduction transducers (Tekscan Inc., Boston, MA). Typically, two thin and flexible polyester sheets with electrically conductive electrodes are separated by a semi-conductive ink layer between the electrical contacts (rows and columns). Exerting pressure on two intersecting strips causes an increased and more intense contact between the conductive surfaces, thus causing a reduction in electrical resistance.

Piezoelectric transducers

Most high precision force transducers use quartz as the sensor material. The electrical charge that is generated on the quartz surfaces is very low (2.30 pC/N for the longitudinal piezoelectric effect) and charge amplifiers have to be used for electronic processing. Piezoceramic materials show very small and highly elastic deformations. As compared to quartz, piezoceramic materials generate approximately 100 times higher charges on their surfaces when identical forc...