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Diagnostic and Prognostic Applications of the Strength-Duration Curve in Peripheral Nerve Lesions Isha Akulwar Tajane, Sikander Chimbaiwala and Amesh Bramhanand More
Diagnostic and Prognostic Applications of the Strength-Duration Curve in Peripheral Nerve Lesions
Diagnostic and Prognostic Applications of the Strength- Duration Curve in Peripheral Nerve LesionsBy Isha Akulwar-Tajane, Sikander Chimbaiwala and Amesh Bramhanand More
Diagnostic and Prognostic Applications of the Strength-Duration Curve in Peripheral Nerve LesionsBy Isha Akulwar-Tajane, Sikander Chimbaiwala and Amesh Bramhanand MoreThis book first published 2026Cambridge Scholars PublishingLady Stephenson Library, Newcastle upon Tyne, NE6 2PA, UKBritish Library Cataloguing in Publication Data A catalogue record for this book is available from the British LibraryCopyright © 2026 by Isha Akulwar-Tajane, Sikander Chimbaiwala and Amesh Bramhanand MoreAll rights for this book reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the copyright owner.ISBN: 978-1-0364-8245-9 ISBN (Ebook): 978-1-0364-8246-6
FOREWORDDear readers, “It is with great pleasure that I introduce this book, which revisits the timeless technique of the strength-duration curve (SDC) in the realm of electrodiagnosis for peripheral nerve lesions. This book serves as a testament to the enduring clinical utility of the SDC, which has been a cornerstone of electrodiagnosis for decades. Peripheral nerve lesions pose significant diagnostic and therapeutic challenges, necessitating accurate and quantitative approaches to electrodiagnosis. The SDC technique offers a unique window into nerve excitability and underlying pathophysiology and holds tremendous promise for improving diagnostic accuracy, monitoring disease progression, and tailoring treatment strategies. While technological advancements have led to the development of newer diagnostic modalities, the SDC technique remains a valuable tool in the clinician’s armamentarium. This book fills a critical gap in the existing literature by providing a comprehensive exploration of the SDC and illuminating its potential applications in electrodiagnostic medicine.The authors have carefully curated the content from the existing literature to provide a thorough understanding of the electrophysiological basis, technical aspects, and clinical correlations of the SDC and have also highlighted the practical applications, limitations, and nuances of the SDC in evaluating peripheral nerve lesions. The text is replete with diagrams, illustrative case studies, and practical examples, making it an indispensable resource for best practices in electrodiagnosis. While delving deep into the fundamentals of electrophysiology and neuromuscular science, it provides exceptionally thorough detailing and conceptual clarity.The authors have made meticulous efforts to revive interest in this established technique and vividly demonstrate its continued relevance in modern clinical practice. Having substantial experience in clinical neurology and physical medicine, they have crafted this book to cater to the needs of clinicians, researchers, and students. I commend the authors for their outstanding contribution to the medical literature, shedding light on a vital yet overlooked area of study. This book will surely transform readers’ understanding of the topic of SDC, and I wholeheartedly recommend it to anyone seeking to expand their knowledge and expertise in electrodiagnosis and peripheral nerve lesions.”Professor Dr. Subhash Khatri (PT) Principal, Maharashtra Institute of Physiotherapy, Latur, Maharashtra, India
TABLE OFCONTENTSPreface...........................................................................................................x Abbreviations.............................................................................................. xii Declarations............................................................................................... xiii Acknowledgement..................................................................................... xiv List of Figures............................................................................................. xv List of Tables........................................................................................... xviii Chapter 1.......................................................................................................1 A Scoping Review: Rationale, Methodology and Results Chapter 2.......................................................................................................7 History and Importance of Electrical Methods in Peripheral Nerve Injuries Chapter 3.....................................................................................................13 Electrodiagnostic Methods in Peripheral Nerve Injuries Chapter 4.....................................................................................................19 Electrophysiological Basis of the Strength-Duration Curve Chapter 5.....................................................................................................36 Procedure for Plotting and Documenting the Strength-Duration Curve Chapter 6.....................................................................................................50 Factors Affecting the Strength-Duration Curve Chapter 7.....................................................................................................57 Interpretation of the Strength-Duration Curve Chapter 8.....................................................................................................72 Neurophysiological Basis of the Strength-Duration Curve
viiiTable of ContentsChapter 9.....................................................................................................93 Diagnostic Significance of the Strength-Duration Curve Chapter 10...................................................................................................97 Cascade of Pathological Events and Recovery after Nerve Injury Chapter 11................................................................................................. 106 Classification of Nerve Injuries Chapter 12................................................................................................. 112 Prognostic Significance of the Strength-Duration Curve Chapter 13................................................................................................. 117 Electrical Events Corresponding to Clinical Recovery Chapter 14................................................................................................. 121 Electro-Physiological versus Sensory-Motor and Clinical Recovery Chapter 15................................................................................................. 126 Optimal Timing of the Strength-Duration Curve Investigation Chapter 16................................................................................................. 131 Strength-Duration Curve in the Surgical Approach to Nerve Injuries Chapter 17................................................................................................. 136 Relative Merits of EMG/NCS and Strength-Duration Curve Chapter 18................................................................................................. 141 Strength-Duration Curve in Paediatric Nerve Injuries Chapter 19................................................................................................. 145 Strength-Duration Curve in Facial Nerve Palsy Chapter 20................................................................................................. 164 Strength-Duration Curve in Neuropathy Chapter 21................................................................................................. 168 Strength-Duration Curve in Radiculopathy Chapter 22................................................................................................. 172 Sensory Strength-Duration Curve
Diagnostic and Prognostic Applications of the Strength-Duration CurveixSummaryAnnexure 1Chapter 23................................................................................................. 179 Strength-Duration Curve Parameters Studied and Their Clinical Significance Chapter 24................................................................................................. 193 Psychometric Properties of the Strength-Duration Curve Chapter 25................................................................................................. 196 Advantages of the Strength-Duration Curve Chapter 26................................................................................................. 198 Limitations of the Strength-Duration Curve Chapter 27................................................................................................. 200 Clinical Implications of the Strength-Duration Curve Chapter 28................................................................................................. 203 Utility of the Strength-Duration Curve in Electrotherapy Treatment of Peripheral Nerve Injuries Chapter 29................................................................................................. 216 Perspectives of Physical Therapists and other Health Care Professionals regarding the Strength-Duration Curve Chapter 30................................................................................................. 218 Current Status of the Strength-Duration Curve Chapter 31................................................................................................. 221 Limitations of the Strength-Duration Curve Research and Future Directions
PREFACEThe strength-duration curve represents the relationship between the intensity of an electrical stimulus (strength) and the duration required to produce a muscle contraction (duration). It is used to assess nerve excitability and function. Originally developed in the 19th century by physiologists like Charles Scott Sherrington, the S-D curve has become a fundamental tool in neurology and neurophysiology. This curve extends beyond being just a laboratory demonstration; it acts as an essential diagnostic instrument, revealing details about nerve integrity and containing extensive information regarding the complex functions of the neuromuscular unit.The strength-duration (S-D) curve is an electrophysiological procedure employed in the diagnosis and evaluation of peripheral nerve injuries. The S-D curve is used to demonstrate or confirm normal muscle innervation, as well as the presence or progress of lower motor neuron disorders. It can be used to determine the predominant underlying pathology; estimate the extent and severity of axonal degeneration and follow recovery; and, to some extent, help to localise the lesion. In recent years, the use of the S-D curve has been largely superseded by EMG and NCS because of their higher accuracy in detecting nerve and muscle lesions. The S-D curve remains useful even though electrophysiological evaluation techniques have become more sophisticated in the past six to seven decades. From a clinical standpoint, therefore, it is valuable to recognise the relative merits of the S- D curve compared with other electrodiagnostic and clinical evaluation procedures. The present review was conducted to investigate the diagnostic and prognostic utility of the S-D curve in peripheral nerve injuries and to analyse its psychometric properties. Through this scoping review, we aim to establish the literature base of the S-D curve in a clinical context, identify gaps in the literature, and provide directions for future research.This book provides a comprehensive and detailed overview of the electrophysiological and neurophysiological basis of the S-D curve. Examples of typical applications in clinical neuromuscular conditions with their physiological basis have been provided. Methodological considerations in its plotting and interpretation have been explained. Further, while identifying limitations of extant literature, this book provides scope and directions for future research work.
PrefacexiIn terms of clinical applications, the contents of this book reinforce the need for detailed, quantitative, and carefully directed evaluation of patients with peripheral nerve lesions, and for reinstating electrodiagnostic evaluation using the S-D curve in clinical practice.This book provides a comprehensive and detailed overview of the electrophysiological and neurophysiological basis of the S-D curve plotting and interpretation along with its applications as a diagnostic and prognostic tool in clinical neuromuscular conditions.It offers the details of the S-D curve, investigating its foundational principles, clinical uses, limitations, and significance in enhancing our grasp of neuromuscular physiology.
ABBREVIATIONSCMAP: Compound Muscle Action Potential EDX: Electro-diagnosis EMG: Electromyography NCV: Nerve Conduction Velocity S-D curve: Strength-Duration Curve SDTC: Strength-Duration Time Constant mA: milliamperes V: Volts mV: millivolts ms: millisecond/s R: Rheobase C: Chronaxie RT: Rise Time UT: Utilization Time AQ: Accomodation Quotient RD: Reaction of Degeneration PRD: Partial Reaction of Degeneration CRD: Complete Reaction of Degeneration MRC scale: Medical Research Council scale QST: Quantitative Sensory Testing
DECLARATIONSFunding This work received no specific funding from any public, commercial, or not-for-profit funding agency.Ethical Approval Not applicable, as this book material does not involve the collection or analysis of new data from human participants or animals.Conflict of Interest The authors declare no conflict of interest related to the content of this book.Data Sharing Statement Not applicable. No new data were generated or analysed for the preparation of this book material.
xivACKNOWLEDGEMENTFirst and foremost, I express my heartfelt gratitude to the Almighty for His divine blessings, guidance, and strength throughout this academic journey. His grace has been a constant source of inspiration, perseverance, and wisdom in the pursuit of knowledge and academic excellence.I sincerely thank my mentors, colleagues and workplace for their professional support, encouragement, and conducive academic environment.I am especially thankful to my students, whose curiosity, enthusiasm, questions, and eagerness to learn continually inspire me to explore new perspectives and translate knowledge into meaningful educational experiences. I am deeply grateful to my patients with peripheral nerve injuries, whose clinical experiences, recovery journeys, and responses to treatment have enriched my understanding and provided valuable insights that helped shape and write this book. Above all, I dedicate this book to my beloved parents, whose unconditional love, sacrifices, and blessings have been my constant source of strength and inspiration.This book is a humble tribute to their enduring influence, love, and the values they instilled in me. With profound gratitude, I acknowledge everyone who has contributed, directly or indirectly, to this academic endeavour. This book reflects not only an individual effort but also the collective wisdom, encouragement, and inspiration received from the people who have been part of my journey.
LFIST OFIGURES1. Figure1.1:PRISMA 2020 flow diagram for scoping reviews 2. Figure 3.1:Types of electric currents used for electrodiagnosis: a) Galvaniccurrent (DC), b) Pulsating current, c) DC intermittent, d) Alternating current (AC), e) Faradic current and f) Neo faradic current3. Figure 3.2:Classification of Electrodiagnostic methods 4. Figure 4.1A and B:Action potential of a nerve and muscle 5. Figure 4.2:Stimulation pulse characteristics 6. Figure 4.3A:“Schematic”Action Potential and B:“Real”ActionPotential 7. Figure 4.4: Schematic representation of the effect of increasing amplitude(A) and increasing duration (B) of a constant current stimulus on the transmembrane potential of a nerve cell8. Figure 4.5: An illustration of the Chronaxie-Rheobase relationship 9. Figure 4.6: The time-constant and exponential equation of strength-duration curve10. Figure 4.7: The slope and intercept of strength-duration curve expressed asa function of Charge and Energy11. Figure 4.8:Current level versus pulse duration, according to thehyperbolic rheobase model12. Figure 4.9: Unipolar and bipolar electrode configuration 13. Figure 4.10: Strength-duration curve measured with cathodal and anodalstimuli14. Figure 5.1:Diagnostic neuromuscular electrical stimulator for plottingStrength-Duration curve15. Figure 5.2 A and B:Constant Current (CC) mode and Constant Voltage(CV) mode16. Figure 5.3: Placement of electrodes as per Unipolar and Bipolar electrodeconfiguration17. Figure 5.4: Schematic plotting of the Strength-Duration curve 18. Figure 6.1: Chronaxie as a function of energy 19. Figure7.1: The fundamental parameters of strength-duration curve 20. Figure 7.2 : An example of Rheobase and Chronaxie 21. Figure 7.3 A and B : Rise time in the strength-duration curve
xvii22. Figure7.4 A and B: Utilization time in strength-duration curve 23. Figure 7.5 A and B : Comparison of the utilization time and chronaxie ofnerve and muscle24. Figure7.6: Response upto in strength-duration curve 25. Figure 7.7 : Kink in the strength-duration curve 26. Figure7.8: Shape of the strength-duration curve 27. Figure7.9: Normal strength-duration curve 28. Figure 7.10 : Strength-duration curve of total denervation 29. Figure7.11: Strength-duration curve of partial denervation 30. Figure8.1 A and B: Action potential of a nerve and muscle 31. Figure8.2: Accommodation and factors determining electrical excitability 32. Figure8.3: Differences between the excitability of a nerve and muscle 33. Figure8.4 A and B: Different chronaxie based on diameter of the nerve 34. Figure8.5:Strength-duration curve for a set of slow versus quick fibers 35. Figure8.6: Clinical data from a patient showing change in paresthesiacoverage when only the pulse width is varying36. Figure8.7:Effectofelectrode-nervedistanceonstimulation 37. Figure8.8:Effectofelectrode-to-nervedistanceoncurrentthresholdandstrength-duration curve: (a) Relationship between current threshold and distance, (b) Effect of distance on the strength-duration curve, and (c) Anatomical basis38. Figure8.9: Strength–duration curves for Soma and Node of RanvierStimulation39. Figure8.10: Strength-duration curve of an innervated muscle 40. Figure8.11: Strength-duration curve of a completely denervated muscle 41. Figure8.12: Strength-duration curve of a partially innervated muscle 42. Figure8.13: Differential electrical properties of sensory and motor nerves 43. Figure 8.14 : Triangular impulse of electric current 44. Figure 8.15 : Strength-duration curve obtained by stimulation withrectangular impulses and by stimulation with triangular impulses45. Figure 10.1 : Wallerian degeneration 46. Figure10.2: Peripheral nerve regeneration 47. Figure11.1: Seddon’s classification of peripheral nerve injury 48. Figure13.1:Evolution of Strength-Duration curve parameters following anerve injury
xviii49. Figure 15.1: Optimal timing of the strength-duration curve investigation 50. Figure 19.1 : The anatomy of the facial nerve (from Blocker, 1968) 51. Figure19.2: Electro diagnosis by Strength-Duration curve of facial nervelesions showing normal, partial denervation and complete denervation (from Blocker, 1968)52. Figure19.3 A and B:Schematic and elaborate illustration of Facial motorpoints to stimulate major divisions of the facial nerve (May, 1970)53. Figure19.4. Orientation of axons in the facial nerve A-original from thesource May, 1970 and B-recreated for elaborate description54. Figure19.5: Indications of electrodiagnostic tests according to the degreeof evolution of peripheral facial palsy55. Figure 19.6 : Electrodiagnostic decision algorithm in facial nerve palsy 56. Figure 20.1: Strength-Duration Time Constant (SDTC) 57. Figure 22.1 A and B: Principle and construction of the sensory strength-duration curve (Friedli and Meyer, 1984)58. Figure 22.2: Basis of the Sensory strength-duration curve 59. Comparison of Motor and Sensory strength-duration curves 60. Figure 23.1 Overview of strength-duration curve parameters 61. Figure 23.2: Measurement of Rheobase 62. Figure 23.3: Measurement of Chronaxie 63. Figure 23.4: Changes in Chronaxie following peripheral nerve injury 64. Figure 23.5: Comparison of strength-duration curve morphology 65. Figure 23.6: Relationship between curve slope and excitability 66. Figure 23.7: Mechanism of kink formation 67. Figure 23.8 : Evolution of the strength-duration curve during recovery 68. Figure 23.9: Clinical interpretation algorithm 69. Figure 23.10 : Why the complete strength–duration curve is preferred 70. Figure 28.1 A and B: The principle of selective stimulation of denervatedmuscle71. Figure 28.2 : Comparison of Utilization Time and Chronaxie of nerve andmuscle on the strength–duration curve72. Figure 28.3: Selection of electrical current based on muscle innervationstatus73. Figure 28.4: Clinical decision-making using the strength–duration curve
xixLIST OF TABLES1. Table 3.1 Changes in the excitability occurring in the reaction ofdegeneration2. Table 3.2 Comparison of Qualitative and Quantitative Electrodiagnosticmethods3. Table 6.1 Comparison of Constant-Current and Constant-Voltagestimulators4. Table 7.1 Standardized terms for interpretation of strength–duration curveparameters5. Table 7.2 A quick interpretation guide to strength-duration curve 6. Table 11.1Classification of nerve lesions 7. Table 11.2 Correlation of Seddon and Sunderland classifications 8. Table 11.3 Strength–Duration curve findings 9. Table 12.1 Signs of Progressive Denervation versus Reinnervation 10. Table 12.2 Prognostic interpretation of Strength–Duration curve changes 11. Table 12.3 Clinical value of serial Strength–Duration curve assessment 12. Table 14.1 Comparison of Electrophysiological and Clinical Recovery 13. Table14.2 Electrophysiological parameters during recovery 14. Table 14.3 Evidence supporting the prognostic value of the Strength–Duration curve15. Table 18.1 Developmental changes affecting strength–duration curveparameters16. Table 18.2 Clinical applications of the strength-duration curve in paediatricpatients17. Table 21.1 Guide for localization of lumbar disc lesion 18. Table 22.1 Parameters of the Sensory strength-duration curve 19. Table 22.2 Comparison of Motor and Sensory strength-duration curves 20. Table23.1 Clinical significance of strength-duration curve parameters 21. Table 23.2 Changes in strength-duration curve following peripheral nerveinjury22. Table 23.3 Why a complete strength–duration curve is preferred 23. Table 28.1 Electrophysiological basis of selective stimulation
xx24. Table 28.2 Clinical guidelines for electrical stimulation of a denervatedmuscle25. Table 28.3 Advantages and Limitations of different current forms 26. Table 28.4 Role of strength–duration curve in electrical stimulation 27. Table 28.5 Comparison of electrical stimulation of innervated anddenervated muscle
In this comprehensive guide readers are introduced to the clinical significance of the strength-duration curve as a diagnostic and prognostic tool in evaluating peripheral nerve injuries. The book delves into the pathophysiology of nerve lesions, exploring how changes in excitability patterns can reflect underlying nerve damage and recovery potential. Through detailed case studies, evidence based discussions, and practical insights, healthcare practioners and researchers alike will gain a nuanced understanding of strength-duration testing and its predictive value in rehabilitation. This textbook is essential for clinicians, neurologists, and researchs seeking to improve patient outcomes by integerating electrophysiological assesments into the evaluation and management of peripheral nerve disorders. Isha Akulwar Tajane holds a MPTh degree in Neurosciences and is a PhD scholar. She is an Associate Professor at K J Somaiya College of Physiotherapy, India and has more than 16 years of teaching and clinical experience. She is a renowned academician and researcher, her expertise being neurorehabilitation, advanced technology, and electro diagnosis Sikander Chimbaiwala is a Physiotherapist with a BPTh degree from K J Somaiya College of Physiotherapy, India and an MSc in Sport and Exercise Medicine. He is a graduate Research Assistant at the University of Exeter and Imperial College London (UK). His research focuses on Parkinson’s disease, dementia, neurorehabilitation, gait analysis, zeroburden technologies, motion capture, and functional nearinfrared spectroscopy.Amesh Bramhanand More holds a Bachelor’s degree in Physiotherapy from K J Somaiya College of Physiotherapy, India and a Master’s degree in Sports and Exercise Medicine from the University of Exeter, UK. His research interests include evidence- based rehabilitation, literature based reviews, and technology- assisted physiotherapy interventions.Cover by CSP 9781036482459 www.cambridgescholars.com