Introduction to Sports Biomechanics: Analysing Human Movement ...

More documents

Recommendations

Info

The load rate (Figure 5.25(h)) can be calculated as the rate of change with time t (d/dt) of the contact force F (dF/dt). The load rate has often been linked to injury. Other calculations that can be performed include whole body power (P = F.v) (Figure 5.25(i)), which does not have x, y and z components, as power is a scalar (see also Appendix 4.2). All the above variables can be presented graphically as functions of time, as in Figure 5.25, providing the qualitative analyst with a rich new set of movement patterns and the quantitative analyst with further useful data. In addition, the forces acting on the performer can be represented as instantaneous force vectors, arising from the instantaneous centres of pressure (a side view is shown in Figure 5.26(a)). Front, top and three-dimensional views of the force vectors are also possible. The centre of pressure path can also be shown superimposed on the plate surface (Figure 5.26(b)). MEASUREMENT OF PRESSURE CAUSES OF MOVEMENT – FORCES AND TORQUES As we noted in the previous section, force plates provide the position of the point of application of the force, also called the centre of pressure, on the plate. This is the point at which the force can be considered to act, although the pressure is distributed over the plate and foot. Indeed, there may be no pressure acting at the centre of pressure when, for example, it is below the arch of the foot or between the feet during double stance. Information about the distribution of pressure over the contacting surface would be required, for example, to examine the areas of the foot on which forces are concentrated during the stance phase in running to improve running shoe design. In such cases, a pressure platform or pressure pad must be used. These devices consist of a set of force transducers with a small contact area over which the mean pressure for that area of contact (pressure = force ÷ area) is calculated. For just a few selected regions of the contact surface, pressures can be measured using individual sensors; problems with this approach include choosing the appropriate locations, and movement of the sensors during the activity being studied. Various types of pressure plate are commercially available, and have been mostly used for the measurement of pressure distributions between the foot or shoe and the ground. They have been used only to a limited extent in sport, partly because their usually small size causes targeting problems for the performer. Also, the distribution of pressure is altered if the platform is covered with a sports surface. Pressure pads have been developed for the measurement of contact pressures between parts of the body and the surroundings. Specialist applications have included pads for the study of the dorsal pressures on the foot within a shoe. Plantar pressure insoles are commercially available (for example, Figure 5.27) and can be used to measure the plantar pressure distribution between the foot and the shoe. This is generally more important, for the sports performer, than the pressure between the shoe and the ground measured by pressure plates. These insoles allow data collection for several foot strikes and do not cause problems of targeting. 213
INTRODUCTION TO SPORTS BIOMECHANICS Figure 5.27 A plantar pressure insole system – Pedar (Novel GmbH, Munich, Germany; www.novel.de). 214 Data processing All pressure insoles have certain drawbacks for use in sport. First, they require cabling and a battery pack to be worn by the performer. Secondly, the insole may alter the pressure distribution because of its thickness. Thirdly, all commercially available devices currently only record the normal component of stress (pressure), not the tangential (shear) components. Furthermore they are susceptible to mechanical damage and crosstalk between the individual sensors. The durability of the sensors is a function of thickness – the thicker they are, the more durable – but mechanical crosstalk also increases with sensor thickness. Although very thin sensors may be suitable for static and slowly changing pressure measurements, durability is important in sports applications involving rapid pressure changes, such as foot strike. Pressure plates, pads and insoles suitable for use in sports biomechanics are based on capacitive, conductive or piezoelectric transducers (for further details, see Lees and Lake, 2007; Further Reading, page 222). Many data processing and data presentation options are available to help analyse the results from pressure measuring devices. In principle, all of the data processing options available for force plates also apply to pressure plates. In addition, displays of whole foot pressure distributions are available, similar to those below for pressure insoles. The centre of pressure path – the gait line – measured from pressure insoles and plates is far less
Page 2:
Introduction to Sports Biomechanics
Page 5 and 6:
First edition published 1997 This e
Page 8 and 9:
Contents List of figures x List of
Page 10 and 11:
Study tasks 216 Glossary of importa
Page 12 and 13:
FIGURES 1.26 Underarm throw - femal
Page 14 and 15:
FIGURES 5.9 Typical path of a swimm
Page 16 and 17:
Tables 2.1 Examples of slowest sati
Page 18 and 19:
Preface Why have I changed the cove
Page 20 and 21:
Introduction MISSING TEXT The first
Page 22:
INTRODUCTION principal movements in
Page 25 and 26:
INTRODUCTION TO SPORTS BIOMECHANICS
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Page 51 and 52:
Page 53 and 54:
Page 55 and 56:
Page 57 and 58:
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Figure 2.2 ‘Principles’ approac
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
Page 83 and 84:
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Page 91 and 92:
Figure 2.13 Identifying critical fe
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Page 139 and 140:
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Page 149 and 150:
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
Page 157 and 158:
Page 159 and 160:
Page 161 and 162:
Page 163 and 164:
Page 165 and 166:
Page 167 and 168:
Page 169 and 170:
Page 171 and 172:
Page 173 and 174:
Page 175 and 176:
Page 177 and 178:
Page 179 and 180:
Page 181 and 182:
Page 183 and 184:
Page 185 and 186: INTRODUCTION TO SPORTS BIOMECHANICS
Page 235: INTRODUCTION TO SPORTS BIOMECHANICS
Page 265 and 266: Figure 6.8 Main skeletal muscles: (
Page 287 and 288:
Page 289 and 290:
Page 291 and 292:
Page 293 and 294:
Page 295 and 296:
Page 297 and 298:
Page 299 and 300:
Page 301 and 302:
Page 303 and 304:
Page 305 and 306:
INDEX 282 balls air flow past 173 b
Page 307 and 308:
INDEX 284 energy 219 kinetic 219 mi
Page 309 and 310:
INDEX 286 isokinetic contraction 24
Page 311 and 312:
INDEX 288 muscle length-tension rel
Page 313 and 314:
INDEX 290 three-dimensional 146-7,
Page 315:
INDEX 292 validity 220 vantage poin
show all

Introduction to Sports Biomechanics: Analysing Human Movement ...

Create successful ePaper yourself

Delete template?

Save as template?