Human gait, stumble and… fall? Mechanical limitations of the recovery from a stumble Arturo FORNER CORDERO De promotiecomissie is gevormd door: Voorzitter en secretaries: Prof. dr. ir. Kals Universiteit Twente Promotor Prof. dr. F. C.T. van der Helm Universiteit Twente Technische Universiteit Delft Assistan -Promotor Dr. ir. H.F.J.M. Koopman Universiteit Twente Leden Prof. dr. ir. H.J. Grootenboer Universiteit Twente Prof. dr. ir. P.J. Veltink Universiteit Twente Prof. dr. J.H . van Dieën Vrije Universiteit Amsterdam Dr. ir. A.D. Kuo University of Michigan Dr. A. Nene Het Roessingh RRD Forner Cordero, A. Human gait, stumble and...fall?. Mechanical limitations in the recovery from a stumble Thesis, University of Twent e, Enschede, The Netherlands ISBN 90 -365 -1912 -8 A. Forner Cordero, Enschede, The Netherlands, 2003 Cover image: Human gait, stumble and… fall?, A. Forner Cordero, 2003 HUMAN GAIT, STUMBLE AND…FALL? MECHANICAL LIMITATIONS OF THE RECOVERY FROM A STUMBLE PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Universiteit Twente, op gezag van de rector magnificus, prof. dr. F.A. van Vught, volgens besluit van het College voor Promoties in het openbaar te verdedigen op vrijdag 13 juni 2003 te 16.45 uur door Arturo Forner Cordero geboren op 26 augustus 1969 te Valencia, España. Dit proefschrift is goedgekeurd door: De promotor: Prof. dr. F.C.T. van der Helm De assistant -promotor: Dr. ir. H.F.J.M. Koopman CONTENTS Preface v Abstract vii 1 INTRODUCTION 1 1. 1 I NTRODUCTION 3 1.2 T HE PROBLEM OF FALLS IN FRAIL POPULATIONS 3 1.2.1 F ALLING DURING GAIT 4 1.3 T HE STABILITY OF GAIT 5 1.3.1 T HE LIMITS OF GAIT STABILITY 6 1.3.2 T HE MECHANICAL LIMITS OF GAIT STABILITY 7 1.3.3 T HE IMPORTANCE OF THE GAIT STABILITY LIMI TS 8 1.4 G OAL 8 1.4 .1 R EVIEW OF PREVIOUS EX PERIMENTS ON GAIT PE RTURBATIONS 9 1.5 O UTLINE OF THE THESIS 15 2 MULTIPLE -STEP STRA TEGIES TO RECOVER FR OM ST UMBLING PERTURBATION S 17 2.1 I NTRODUCTION 19 2.2 M ATERIALS AND METHODS 21 2.2.1 M EASUREMENTS AND APPA RATUS 21 2.2.2 D ATA ANALYSIS 23 2.3 R ESULTS 25 2.3.1 E FFECT OF THE EXPERIM ENTAL SETUP ON THE T READMILL GAIT PATTER N 25 2.3.2 C LASSIFICATION OF THE PERTURBATIONS 26 2.3.3 P ERTURBATION ANALYSIS 27 2.3.2 R ECOVERY OF THE NORMA L GAIT PATTERN UNDER DIFFERENT PERTURBAT ION CONDITIONS 29 2.4 D ISCUSSION 37 2.5 C ONCLUSIONS 40 3 USE OF PRESSURE IN SOLES TO ESTIMATE JO INT POWERS DURING WA LKING 43 3.1 I NTRODUCTION 45 3.2 M ETHODS 46 3.2.1 M EASUREMENTS 46 3.2.2 D ATA PROCESSING 47 3.2.3 I NVERSE DYNAMICS CALCULATIONS 51 3.2.4 E RROR ANALYSIS 53 3.3 R ESULTS 54 3.3.1 V ERTICAL FORCE AND AP PLICATION POINT MEAS UREMENT 54 3.3.2. E STIMATION OF THE GRF 55 3.3.3. E STIMATION OF THE JOI NT KINETICS 56 3.4 D ISCUSSION 62 3.4.1 M EASURING ER RORS 62 3.4.2 E RROR ANALYSIS IN THE ESTIMATION OF GRF AND COP 63 3.4.3 C RITICAL REVISION OF THE ESTIMATED JOINT POWERS 64 3.4.4 G ENERAL CONSIDERATION S 64 3.5 C ONCLUSIONS 66 4 DESCRIBING GAIT AS A SEQUEN CE OF STATES 67 4.1 I NTRODUCTION 69 4.2 M ETHODS 70 4.2.1 C ONCEPT 70 4.2.2 C ALCULATION PROCEDURE 71 4.2.3 V ALIDATION 72 4.2.4 A PPLICATIONS 75 4.3 R ESULTS 76 i Contents 4.3.1 V ALIDATION OF THE SEQ UENCE OF STATES METH OD 76 4.3.2 C OMPARISON WITH THE P ERCENTAGE CONVERSION 80 4.3.3 A PPLICATION TO ANALYS E SMALL PERTURBATION S DURING GAIT 81 4.4 D ISCUSSION 85 4.4.1 A RE THE CHANGES IN TH E STRIDE DUE TO NOISE OR THEY CONTAIN INFORMATION ABOUT THE CONTROL MECHANISMS OF GAIT? 85 4.4.2 V ALIDATI ON : O CCURRENCE OF EQUIVAL ENT STATES 86 4.4.3 C OMPARISON WITH THE S TRIDE PERCENTAGE NOR MALISATION 87 4.4.4 A PPLICATION TO ANALYS E PER TURBATIONS DURING GA IT 87 4.4.5 G ENERAL REMARKS ON TH E SEQUENCE OF STATES METHOD 87 4.5 C ONCLUSIONS 88 4.6 A PPENDIX 89 5 ENERGY ANALYSIS OF HUMAN STUMBLING: THE LIMITATIONS OF REC OVERY 91 5.1 I NTRODUCTI ON 93 5.2 M ETHODS 95 5.2.1 E XPERIMENTS 95 5.2.2 D ATA ANALYSIS 96 5.3 R ESULTS 100 5.3.1 E LEVATING STRATEGY 102 5.3.2 L OWERING STRATEGY 105 5.3.3 D ELAYED LOWERING STRA TEGY 110 5.3.4 C OMPARISON OF STRATEG IES 112 5.4 D ISCUSSION 114 5.4.1 O VERVIEW OF THE RECOV ERY REACTIONS 114 5.4.2 E LEVATING STRATEGY 115 5.4.3 L OWERING STRATEGY 116 5.4.4 D ELAYED LOWERING STRA TEGY 117 5.4.5 E NERGY VS . STABILITY ? P OSSIBLE LIMITATIONS TO RECOVER 117 5.5 C ONCLUSIONS 120 6 MECHANICAL MODEL O F THE RECOVERY FROM STUMBLING 121 6.1 I NTRODUCTION 123 6.2 M ATERIALS AND METHODS 126 6.2.1 E XPERIMENTS 126 6.2.2 M ODEL 127 6.2.3 M AXIMAL HIP TORQUES 129 6.2.4 N ORMAL DOUBLE STANCE : H IP BETWEEN BOTH COP 130 6.2.5 S IMULATING THE FORWAR D FALL : H IP AHEAD OF LEADING COP 131 6.2.6 D ATA ANALYSIS 132 6.3 R ESULTS 133 6.3.1 C LASSIFICATION OF STR ATEGIES 133 6.3.2. A NALYSIS OF THE MEASURED PERTURBED STRIDE 135 6.3.3 A NALYSIS OF THE MEASURED TRUNK ANGLES AT LEFT FOOT CONTACT (HS L) AFTER THE PERTURBATI ON 137 6.3.4. M EASURED HIP POSITION AT THE SECOND DOUBL E STANCE AFTER THE P ERTURBATION 138 6.3.5 S IMULATION OF THE REC OVERY DOUBLE STANCE 139 6.4 D ISCUSSION 142 6.4.1 L IMITATION OF THE MAX IMAL TRUNK TORQUES D UE TO THE STRATEGY 142 6.4.2 F ALLING DURING THE EX PERIMENTS 143 6.4.3 S ENSITIVITY OF THE HI P TORQUES TO THE HOR IZONTAL FORCES 143 6.4.4 B ODY CONFIGURATION AT THE END OF THE SWIN G PHASE 144 6.4.5 A NALYSIS OF THE RECOV ERY STRATEGIES BASED ON THE HIP-COP DISTANCE 145 6.4.6 C ONTROL OF THE FALLIN G TRUNK 146 6.4.7 I S THE MAXIMAL STEP SPE ED THE LIMITATION TO RECOVER ? 147 6.4.8 L IMITATIONS OF THE MO DEL : CRITICAL REVIEW . 147 6.5 C ONCLUSIONS 148 7 RECOVERY FROM STUM BLING IN ELDERLY PEO PLE: A QUICK STEP CAN AVOID FALLING 149 7.1. I NTRODUCTION 151 ii Contents 7.2 M ATERIALS AND METHODS 154 7.2.1 E XPERIMENTS 154 7.2.2 D ATA ANALYSIS 156 7.3 R ESULTS 157 7.3.1 C LASSIFICATION OF STR ATEGIES 158 7.3.2 A NALYSIS OF THE PERTU RBED STRIDE 159 7.3.3 A NALYSIS OF THE BODY TILT AT HS L 162 7.3.4 H ORIZONTAL GROUND REA CTION FORCES 164 7.4 D ISCUSSION 165 7.4.1 C OMPARISON BETWEEN HE ALTHY YOUNG AND ELDE RLY 165 7.4.2 F ALLING DURING THE EX PERIMENTS 166 7.4.3 R ECOVERY WITH NEGATIVE STEP LENGTHS : C ONFIGURATION OF THE BODY AT THE END OF T HE SWING PHASE 167 7.4.4 T IME OF RESPONSE 168 7.4.5 L EARNING EFFECT 169 7.4.6 I S THE MAXIMAL STEP S PEED THE LIMITATION TO RECOVER ? 169 7.4.7 L IMITATIONS OF THE RE SULTS 170 7.5 C ONCLUSIONS 171 7.6. A PPENDIX 172 7.6.1. M ODEL 172 8 CONCLUSIONS 175 8.1 W HICH QUESTIONS HAVE BEEN ANSWERED ? 177 8.1.1 M ECHANICAL LIMITATION S TO RECOVER FROM A PERTURBATION 177 8.1.2 G AIT ANALYSIS: M EASURE MORE THAN AN INCOMPLETE STRIDE 180 8.2 P RACTICAL IMPLICATION S 182 8.2.1 T HE WALKING STABILITY PERFORMANCE INDEX A ND THE LIMITATIONS O F THE RECOVERY 182 8.2.2 E VALUATION OF THE CON DITION TO AVOID FALL ING 182 8.2.3 P ROPOSED PREVENTIVE T HERAPIES 183 8.3 N EW QUESTIONS AND FUT URE LINES OF RESEARCH . 183 8.3.1 H UMAN GAIT CAN BE DES CRIBED AS A SEQUENCE OF STATES 183 8.3.2 F UTURE DEVELOPMENTS O N A TREADMILL 184 8.3.3 A FINAL REMARK ON GAIT ANALYSIS 184 REFERENCES 185 SUMMARY 191 RESUMEN 193 SAMENVATTING 195 CURRICULUM VITAE 197 iii PREFACE This research project started in the extremely cold winter of 1998 and ends in the warm summer of 2003. It was made possible by the Institute for Biomedical Technology and the Biomechanical Engineering department of the University of Twente. In first place, I have to acknowledge the contribution of two persons that co - authored the papers resulting from this research, my promotor , Frans van der Helm and my assistent -promotor , Bart Koopman.