Rebuttal from Weyand and Bundle

Abstract

POINT:COUNTERPOINTArtificial limbs do/do not make artificially fast running speeds possibleRebuttal from Weyand and BundlePublished Online:01 Apr 2010https://doi.org/10.1152/japplphysiol.01238.2009bMoreSectionsPDF (38 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat We agree that minimum leg repositioning, or swing times, and mass-specific ground reaction forces are critical determinants of sprint running performance.Swing times: biologically normal or artificially brief?Our conclusion that the bilateral artificial limb swing time (0.284 s) measured at top speed (10) is artificially brief is based on the well-established practice of evaluating single observations vs. a comparison sample population's mean and variance with a threshold of >3.0 standard deviations (SD) for identifying outliers (7). In comparison to an intact-limb reference population (9) of 33 active, treadmill-tested subjects [mean (SD) = 0.373 (0.026) s]; four performance-matched track athletes (10) during treadmill running [0.359 (0.019) s]; and 22 male, world-class, 100-m sprinters (6, 8) in competition [0.330 (0.014) s]; the double-artificial-limb value is −3.4, −4.0, and −3.3 SD units below these three respective means. It is also 15.7% shorter than the mean of the five former 100-m world-record holders (0.337 s) in the competition sample.Even in comparison to individuals with the most extreme gait adaptations for speed in recorded human history, the double-artificial-limb value is not simply an outlier; it is quite literally off the biological charts.Our colleagues recently published (4) conclusion that the double-artificial-limb value is not artificially brief is not supported by the data we have published with them (10) or the valid data from field (6, 8) and laboratory (9, 10) settings analyzed above. Instead, television footage of Olympic races acquired for entertainment purposes is cited (4). Low shutter speeds, frame rates (30 Hz), wide fields of view, and force-video offsets (9) make television-estimated swing times highly uncertain. For example, the swing time of the one Olympian purportedly more brief (0.274 ± 0.004 s; Ref. 4) than the double-amputee value, is actually 16.2% greater (0.318, 0.318, and 0.320 s) when measured using research-quality, high-speed, motion-capture techniques (6).Reduced force requirements for speed.Given that the stride-averaged vertical force must equal the body's weight, lesser ground support forces at the same speeds should not be interpreted as a limb strength deficiency, but here (Fig. 1) represent the inevitable physical consequence (3) of ground contact times lengthened, and aerial times shortened by artificially compliant and lightweight (2) lower limbs. Our double amputee subject “bounces” on his compliant lower limbs while holding his upper biological limbs relatively straight (2; Fig. 1, inset). More erect limb posture (1) and reduced ground force requirements co-reduce the muscular forces required to attain the same sprint running speeds to less than one-half of intact limb levels.REFERENCES1. Biewener AA , Farley CF , Temanar T , Roberts J. Mechanical advantage during walking and running: implications for energetic cost. J Appl Physiol 95: 1955–1962, 1998.Google Scholar2. Bruggeman GP , Arampatzis A , Emrich F , Potthast W. Biomechanics of double tanstibial amputee sprinting using dedicated sprint prostheses. Sports Technol 4–5: 220–227, 2009.Crossref | Google Scholar3. Cutnell JD , Johnson JW. Physics, 6th edition. New Jersey: John Wiley and Sons, 2004.Google Scholar4. Grabowski AM , McGowan CP , McDermott WJ , Beale MT , Kram R , Herr HM. Running-specific prosthesis limit ground-force during sprinting. Biol Lett; doi:10.1098/rsbl.2009.0729.Google Scholar5. Kram R , Grabowski A , McGowan C , Brown MB , Herr H. Counterpoint: Artificial limbs do not make artificially fast running speeds possible. J Appl Physiol; doi:10.1152/japplphysiol.01238.2009.ISI | Google Scholar6. Mann R. The Mechanics of Sprinting and Hurdling. Las Vegas: Compusport, 2004, p. 2006–2008.Google Scholar7. Mendenhall RJ , Beaver RJ , Beaver BM. Introduction to Probability and Statistics, 13th edition. Belmont, CA: Thomson Brooks/Cole, 2006.Google Scholar8. Moravec P , Ruzicka J , Susanka P , Dostal E , Kodejs M , Nosek M. The 1987 International Athletic Foundation/IAAF Scientific Project Report: Time analysis of the 100 metres events at the II. World Championships in Athletics. New Studies Athletics 3: 61–96, 1988.Google Scholar9. Weyand PG , Sternlight DB , Bellizzi MJ , Wright S. Faster top running speeds are achieved with greater ground forces not more rapid leg movements. J Appl Physiol 81: 1991–1999, 2000.Link | ISI | Google Scholar10. Weyand PG , Bundle MW , McGowan CP , Grabowski A , Brown MB , Kram R , Herr H. The fastest runner on artificial limbs: different limbs similar function? J Appl Physiol 107: 903–911, 2009.Link | ISI | Google Scholar Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation More from this issue > Volume 108Issue 4April 2010Pages 1014-1014 Copyright & PermissionsCopyright © 2010 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.01238.2009bHistory Published online 1 April 2010 Published in print 1 April 2010 Metrics