Biomechanics and Medicine in Swimming XI

More documents

Recommendations

Info

dIscussIon The kinetics of the stroking parameters (SL and SR) along the 200m is in agreement with the literature (Alberty et al., 2005). Moreover, the decrease of v along the test can be explained by different SR and SL combinations, as previously reported (Huot-Marchand, et al., 2005). The decrease of the SL values could be linked to the development of local muscular fatigue, reflecting a declining capacity to deliver power output. In addition, the swimmer tried to increase SR in order to compensate the SL decrease. The observed stability of IVVx and the larger magnitudes of IVV found for y and z than in x axis, are in agreement with the literature (Psycharakis et al., 2010). This IVVx stability suggests a coordinative adaptation of the upper limbs, as Figueiredo et al., (2009) reported no relationship between IVV and IdC in x, y and x axes during the 200 m front crawl effort. The coordinative adaptation pattern might be explained by the swimmer’s inability to minimise the resistive force as the arm coordination change (increasing the values of IdC) manly in the last 50m of the 200m front crawl (Alberty et al., 2005; Figueiredo et al, in press), however IdC maintained in catch-up mode (
BiomechanicsandmedicineinswimmingXi Measuring Active Drag within the Different Phases of Front Crawl Swimming Formosa, d. P. 1, 2 Mason, B.r. 1 & Burkett, B. J. 2 1 Australian Institute of Sport, Australia 2 University of the Sunshine Coast, Australia The aim of this study was to quantify the passive and active drag forces in front crawl swimming at the swimmer’s maximum swimming velocity and to present this data as a force-time profile. This method enabled the minimum and maximum force with respect to the phase within the stroke to be identified. Elite freestylers (n=18) completed three maximum swim velocity time trials to determine their maximum velocity. This was followed by three passive drag trials and three active drag trials using a towing device mounted upon a force platform. The computed active drag and the propulsive force profiles were represented as a forcetime graph, allowing identification of intra-cyclic force fluctuations. The force-time profiles were synchronised to video footage which provided unique quantitative stroke mechanic feedback to the elite coaches and athletes. KeYWords: biomechanics, swimming, front crawl, active drag, technique IntroductIon An elite swimmer’s success during the free swimming phase is primarily dependent upon their ability to minimise active drag, whilst optimising propulsive force. Active drag is defined as the water resistance associated with the swimming motion (Kolmogorov et al, 1997). Before 1974 passive drag, defined as the amount of water resistance that a human body experiences in an unchanging body position, was considered the best method of predicting active drag (Chatard et al, 1990). In the late 1980’s, a research team in the Netherlands developed the first system to measure active drag, known as the MAD system. The MAD system required the participant to swim at a constant velocity, whilst pressing upon fixed pads with the hands. The swimmer’s legs were elevated and restricted with pull buoy. This system was limited to front crawl only. Kolmogorov & Duplischeva (1992) developed the Velocity Perturbation Method (VPM) which measured active drag irrespective of swimming stroke. Using the VPM method participants were instructed to swim maximally during two conditions; without and with a hydrodynamic body. The hydrodynamic body was of a known resistance, therefore allowing active drag to be determined by the velocity differences between the two conditions. The common assumption made in calculating active drag was that at a constant velocity the propulsive force was equal to the opposing active drag (Kolmogorov & Duplishcheva, 1992; Toussaint et al, 2004). Regardless of the method adopted, active drag was calculated as a mean value, therefore ignoring the fluctuations in the propulsive force during the stroke phases. The swimming stroke is typically segmented into distinct phases consisting of the entry and catch, pull, push and recovery (Chollet et al., 2000). The primary aim of this study was to quantify the passive and active drag values as a force-time profile by using a motorised towing device. The secondary aim of this study was to examine the force-time profile to determine in which segment of the stroke phase a swimmer produced minimum and maximum force, and therefore providing unique biomechanical feedback to elite coaches and athletes. Methods Following human ethics approval by the University of the Sunshine Coast and the Australian Institute of Sport, eighteen Australian na- 82 tional front crawl swimmers (10 male aged 21 ± 2.2 years, 8 female aged 20 ± 3.0 years) were tested to determine the participant’s passive and active drag profile. Firstly, the swimmers completed a typical 20 min individual race preparation warm up, followed by three individual maximum swimming velocity trials. The maximum velocity trials were measured over a 10 m interval using two 50 Hz cameras (Samsung model: SCC-C4301P). The cameras were time coded. Using a custom computer program, the mean velocity was calculated for each trial. The trial with the highest mean velocity was selected for the passive and active drag trials. The passive and active drag testing was conducted using a motorised towing device, which enabled a constant towing velocity to be accurately set. The towing device was positioned directly upon a calibrated Kistler force platform (Kistler Instruments in Winterthur Switzerland Dimensions: 900 x 600 m Type Z12697). The towing device and the force plate enabled the force required to tow the swimmer through the water to be measured. The validity and reliability of the system was determined prior to data collection. During the three passive drag trials the swimmers were towed at their maximum swimming velocity. The swimmers were instructed to hold the end of the tow line around the middle finger of their dominant hand, with the nondominant hand interlocking to minimise any additional movement. The criteria for a successful passive trial was that the swimmer maintained a streamline position just below the water surface, with no arm strokes nor kicking nor breathing, and there was visible water flow passing over the head, back and feet. Three active drag trials were completed at a velocity five percent greater than the swimmer’s maximum swimming velocity. The active drag trials consisted of the participants actively swimming whilst using their typical stroke characteristics with an Eyeline ® tow belt attached to the lumbar region and the dynamometer. Through pilot testing the five percent increase in towing velocity was considered to not have any major effect on the swimmer’s stroke pattern while still allowing continuous force measurement. Data capture was collected for a total of seven seconds, one second prior to and six seconds after the synchronisation trigger was depressed. The sensitivity of the amplifier was set at 5000 pC for both conditions. Data was processed using a 12 bit A to D card, sampled at 500 Hz, and a 5 Hz Butterworth low pass digital filter was applied to the force data collected (Formosa et al, 2009). Each trial was video-recorded at 50 Hz using three genlocked cameras; a side-on underwater, side-on above and head-on camera. The side-on underwater and side-on above water cameras were synchronised with an Edirol video mixer (EDI-V8). The following formulas were used to determine active drag: 1 2 1 F = 0. 5C ⋅ r ⋅ A⋅V (1) 2 0. 5C ⋅ r ⋅ A⋅V 2 Fb (2) F = − 2 Where C a constant, ρ is a water density, A is the frontal surface area of the swimmer & Fb is the force needed to pull the swimmer at the 103 increased Biomechanics velocity, and Medicine which XI was Chapter measured 2 Biomechanics by the force platform. F 1 = force applied by the swimmer during free swimming (unaided) and is assumed Where Cto a constant, be equal ρ is a to water the density, total A drag is the force frontal surface during area free of the swimming. swimmer & F 2 = Fb is the force needed to pull the swimmer at the increased velocity, which was the force applied by the swimmer during free swimming in the assisted measured by the force platform. F 1 = force applied by the swimmer during free condition. swimming (unaided) and is assumed to be equal to the total drag force during free Here swimming. it was F 2assumed = the force applied an equal by the power swimmer output during free in swimming both the in free the assisted swimming condition. and the active drag swimming conditions existed: Here it was assumed an equal power output in both the free swimming and the active drag swimming conditions existed: 1 2 P P = (3) If 1 2 P P = and therefore F1 ⋅V1 = F2 ⋅V2 (4) substitution of 1 F and F 2 gives: 3 3 0. 5C A V 0. 5C A V Fb V ⋅ − ⋅ ⋅ ⋅ = ⋅ ⋅ ⋅ ρ ρ (5) 1 2 2 Rearranging the formula to find C: Fb ⋅V2 C = 3 3 0. 5ρ ⋅ A⋅ ( V2 −V1 ) (6) substitution of C gives the following formula for active drag: 2 Fb ⋅V2 ⋅V1 F1 = 3 3 V2 −V1 (7) V 1= the swimmer’s free swim maximum velocity and V 2 = 5% greater than the swimmer’s free swim maximum velocity (Kolmogorov & Duplishcheva, 1992) (Note: equation was modified for assisted, rather than resisted). To identify the force distribution within the stroke cycle, phases were considered as entry and catch, pull, push and recovery (Chollet et al, 2000). RESULTS The coefficient of variation between the towing device velocity and the side-on cameras was 0.6 % (90% Confidence Intervals (CI) 0.5 to 0.7). The Pearson product moment
Page 1 and 2:
Biomechanics and Medicine in Swimmi
Page 3 and 4:
Bibliographic information: Biomecha
Page 5 and 6:
Biomechanicsandmedicinein
Page 7 and 8:
Page 9 and 10:
Page 11 and 12:
Page 13 and 14:
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
Page 25 and 26:
Page 27 and 28:
Page 29 and 30:
Page 31 and 32: Biomechanicsandmedicinein
Page 81: Figure 1. General biomechanical par
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:
Page 187 and 188:
Page 189 and 190:
Page 191 and 192:
Page 193 and 194:
Page 195 and 196:
Page 197 and 198:
Page 199 and 200:
Page 201 and 202:
Page 203 and 204:
Page 205 and 206:
Page 207 and 208:
Page 209 and 210:
Page 211 and 212:
Page 213 and 214:
Page 215 and 216:
Page 217 and 218:
average VO2 measured during resting
Page 219 and 220:
Page 221 and 222:
Fourteen highly trained male swimme
Page 223 and 224:
Page 225 and 226:
Page 227 and 228:
Page 229 and 230:
Page 231 and 232:
Page 233 and 234:
Page 235 and 236:
Page 237 and 238:
Page 239 and 240:
Page 241 and 242:
Page 243 and 244:
Page 245 and 246:
Page 247 and 248:
Page 249 and 250:
Page 251 and 252:
Page 253 and 254:
Page 255 and 256:
Page 257 and 258:
Page 259 and 260:
Page 261 and 262:
Page 263 and 264:
Page 265 and 266:
Page 267 and 268:
Figure 2. Repeatability of the LTin
Page 269 and 270:
Page 271 and 272:
Page 273 and 274:
Page 275 and 276:
Page 277 and 278:
Page 279 and 280:
Page 281 and 282:
Page 283 and 284:
Page 285 and 286:
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:
-ARM * 5 Biomechanicsandmedic
Page 301 and 302:
Page 303 and 304:
Page 305 and 306:
Page 307 and 308:
Page 309 and 310:
Page 311 and 312:
Page 313 and 314:
Page 315 and 316:
Page 317 and 318:
Page 319 and 320:
• Without restriction; • Blinde
Page 321 and 322:
Page 323 and 324:
Page 325 and 326:
Page 327 and 328:
Page 329 and 330:
Page 331 and 332:
Page 333 and 334:
Page 335 and 336:
Page 337 and 338:
Page 339 and 340:
Page 341 and 342:
Page 343 and 344:
Page 345 and 346:
Page 347 and 348:
Page 349 and 350:
Page 351 and 352:
Page 353 and 354:
Page 355 and 356:
Page 357 and 358:
Page 359 and 360:
etween experimental groups and cont
Page 361 and 362:
Page 363 and 364:
Page 365 and 366:
Page 367 and 368:
Page 369 and 370:
Page 371 and 372:
Page 373 and 374:
Page 375 and 376:
Page 377 and 378:
Page 379 and 380:
Page 381 and 382:
Page 383 and 384:
Page 385 and 386:
Page 387 and 388:
Page 389 and 390:
Page 391:
Pahlen Norge AS Pahlen Norge AS Cha
show all

Biomechanics and Medicine in Swimming XI

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?