Development and Validation of Portable and Wearable Dynamometry Systems for Quantitative Assessment of Knee Muscle Strength = 무릎 근력의 정량적 평가를 위한 휴대형 웨어러블 다이나모미터의 개발과 검증

국문 초록 (Abstract)

무릎 근력은 재활의학, 스포츠 과학, 노인 보건의료 분야에서 필수적인 임상 지표이며, 일상생활동작, 균형 유지, 낙상 예방에서 핵심적인 역할을 한다. 그러나 기존의 평가 방법은 중대한 한계를 가진다. 널리 사용되는 도수 근력 검사는 정성적 등급만을 제공하며 검사자 의존적이다. 핸드헬드 다이나모미터(HHD)는 정량적인 측정이 가능하지만 검사자 근력의 한계로 인해 강한 근육군의 측정 시 재현성이 낮다. 등속성 다이나모미터(IKD)는 높은 정확도와 신뢰도로 표준 장비로 인정받지만, 고가이고 부피가 크며 전용 공간을 필요로 하여 일상적인 임상 모니터링과 현장 기반 평가에 대한 접근성이 제한된다.
본 논문은 두 가지의 새로운 다이나모미터 시스템인 휴대형 관절 다이나모미터(PADS)와 웨어러블 다이나모미터(WDS)를 개발하고, IKD 기준 대비 측정 성능을 평가하는 것을 목표로 하였다. 연구는 두 단계로 구성되었다. 연구 1에서는 접이식 알루미늄 프레임에 장착된 로드셀을 사용하는 PADS를 개발하고, 등속성 모드에서 작동하는 IKD 대비 성능을 평가하여 임상 적용 가능성을 확인하였다. 연구 2에서는 일관된 착용을 통해 재현성을 높이기 위해 개선된 웨어러블 디자인의 WDS를 개발하고, 등척성 모드에서 무릎 신전 및 굴곡에 대해 IKD와 성능을 비교하여 검증하였다.
연구 1에는 72명의 건강한 성인(평균 연령: 29.3 ± 4.6세; 남성 36명, 여성 36명)이 참여하였으며, 이 중 40명이 검사-재검사 평가를 완료하였다. PADS는 IKD와 강한 일치도를 보였다(급내 상관계수[ICC]: 0.935; 표준 측정 오차[SEM]: 13.96 Nm [9.75%]; 최소 감지 변화[MDC]: 38.70 Nm [26.66%]). 평가자 간 신뢰도(ICC: 0.979; SEM: 7.94 Nm [5.51%]; MDC: 22.01 Nm [15.25%])와 검사-재검사 신뢰도(ICC: 0.954; SEM: 11.70 Nm [8.38%]; MDC: 32.43 Nm [23.24%]) 또한 모두 우수하였다.
연구 2에는 39명의 건강한 성인(평균 연령: 29.5 ± 4.0세; 남성 17명, 여성 22명)이 참여하였으며, 39명 모두 검사-재검사 평가를 완료하였다. WDS는 무릎 신전(ICC: 0.893; SEM: 17.12 Nm [9.85%]; MDC: 47.47 Nm [27.31%])과 굴곡(ICC: 0.857; SEM: 9.31 Nm [11.93%]; MDC: 25.81 Nm [33.07%]) 모두에서 IKD와 좋은 일치도를 보였다.
이러한 결과는 PADS와 WDS가 표준 장비인 IKD에 상응하는 측정 정확도와 신뢰도를 가진 무릎 근력 정량적 평가를 위한 휴대형 및 웨어러블 대안을 제공함을 검증한다. 본 논문은 차세대 웨어러블 다이나모미터 장치의 개발과 검증을 입증하며, 재활의학, 스포츠 과학, 노인 보건의료를 개선하기 위한 임상적 및 공학적 잠재력에 초점을 맞춘다.

다국어 초록 (Multilingual Abstract)

Knee muscle strength is an essential clinical parameter in rehabilitation medicine, sports science, and geriatric healthcare, playing a central role in activities of daily living, balance maintenance, and fall prevention. However, conventional assessment techniques have important limitations. Manual muscle testing, though widely used, provides only qualitative grading and is examiner-dependent. Hand-held dynamometers (HHD) offer quantitative measurements but have low reproducibility when measuring strong muscle groups due to examiner strength limitations. Isokinetic dynamometers (IKD), while considered the gold standard with high accuracy and reliability, are expensive, bulky, and require dedicated facilities, limiting their accessibility for routine clinical monitoring and field based assessments.
This dissertation aimed to develop and validate two novel dynamometry systems, a portable articulated dynamometry system (PADS) and a wearable dynamometry system (WDS), and to evaluate their measurement performance against an IKD reference standard. The research comprised two sequential studies. Study 1 developed the PADS using a load cell mounted on a foldable aluminum frame and evaluated its performance against the IKD operating in isokinetic mode to assess clinical feasibility. Study 2 developed the WDS with an improved wearable design for consistent positioning and validated its performance against the IKD in isometric mode for both knee extension and flexion.
Study 1 included 72 healthy adults (mean age: 29.3 ± 4.6 years; 36 males, 36 females), with 40 participants completing test–retest evaluations. The PADS demonstrated strong agreement with the IKD (intraclass correlation coefficient [ICC]: 0.935; standard error of measurement [SEM]: 13.96 Nm [9.75%]; minimal detectable change [MDC]: 38.70 Nm [26.66%]). Interrater reliability was excellent (ICC: 0.979; SEM: 7.94 Nm [5.51%]; MDC: 22.01 Nm [15.25%]), as was test–retest reliability (ICC: 0.954; SEM: 11.70 Nm [8.38%]; MDC: 32.43 Nm [23.24%]).
Study 2 involved 39 healthy adults (mean age: 29.5 ± 4.0 years; 17 males, 22 females), all of whom successfully completed test–retest evaluations. The WDS demonstrated good agreement with the IKD for both knee extension (ICC: 0.893; SEM: 17.12 Nm [9.85%]; MDC: 47.47 Nm [27.31%]) and knee flexion (ICC: 0.857; SEM: 9.31 Nm [11.93%]; MDC: 25.81 Nm [33.07%]).
These findings validate that PADS and WDS provide portable and wearable alternatives for quantitative knee strength assessment with measurement accuracy and reliability comparable to the gold standard IKD. This dissertation demonstrates the development and validation of next-generation wearable dynamometry devices, focusing its clinical and engineering potential for improving rehabilitation medicine, sports science, and geriatric healthcare.

목차 (Table of Contents)

• Abstract i
• Table of Contents iv
• List of Tables ix
• List of Figures x
• List of Abbreviations xiv
• Chapter 1. Introduction １５
• 1.1. Clinical Importance of Muscle Strength Assessment １５
• 1.2. Measurement and Training Modalities １９
• 1.2.1. Isometric Contraction １９
• 1.2.2. Isokinetic Contraction ２０
• 1.2.3. Isotonic Contraction ２１
• 1.3. Sensor Technologies for Strength Assessment ２３
• 1.3.1. Dynamometer-Based Measurement ２３
• 1.3.2. Surface Electromyography ３１
• 1.3.3. Ultrasound–Based Muscle Thickness Estimation ３２
• 1.4. Clinical Needs and Limitations of Current Systems ３４
• 1.5. Backgrounds and Need for New Devices ３６
• 1.6. Research Objectives ４０
• 1.6.1. Overall Objectives ４０
• 1.6.2. Study 1: PADS vs. IKD in Isokinetic Mode ４０
• 1.6.3. Study 2: WDS vs. IKD in Isometric Mode ４１
• 1.7. Dissertation Outline ４２
• 1.8. Ethical Review and Regulatory Considerations ４６
• Chapter 2. Materials and Methods ４８
• 2.1. Participants ４９
• 2.2. Measurement Devices ５０
• 2.2.1. Portable Articulated Dynamometry System ５０
• 2.2.2. Wearable Dynamometry System ５７
• 2.2.3. Isokinetic Dynamometer ６２
• 2.3. Measurement Principle and Biomechanical Model ６７
• 2.3.1. Components of Biomechanical Torque ６８
• 2.3.2. Modeling of Gravitational Torque with Joint Angle ６９
• 2.3.3. Torque Equilibrium in PADS during Extension ７１
• 2.3.4. Torque Equilibrium in WDS during Extension ７３
• 2.3.5. Torque Equilibrium in WDS during Flexion ７５
• 2.3.6. Resistive Torque at the Anchor Point ７７
• 2.3.7. Gravity Compensation Procedure ７８
• 2.4. Finite Element Analysis Framework for WDS ８０
• 2.4.1. Geometry and Mesh Generation ８０
• 2.4.2. Boundary Conditions and Material Properties ８３
• 2.5. Calibration Protocols ８５
• 2.5.1. Calibration of PADS ８５
• 2.5.2. Calibration of WDS ８６
• 2.6. Crosstalk Validation Framework for WDS ８９
• 2.7. Experimental Procedure ９２
• 2.7.1. General Protocol for Strength Measurement ９２
• 2.7.2. Specific Conditions for PADS vs. IKD ９５
• 2.7.3. Specific Conditions for WDS vs. IKD ９６
• 2.8. Statistical Analyses ９８
• Chapter 3. Study 1: PADS vs. IKD １００
• 3.1. Participants １００
• 3.2. Calibration Results for PADS １０１
• 3.3. Agreement Between PADS and IKD １０４
• 3.4. Reliability of PADS １０７
• 3.4.1. Interrater Reliability １０７
• 3.4.2. Test-retest Reliability １１１
• 3.5. User Experience Evaluation １１６
• Chapter 4. Study 2: WDS vs. IKD １１９
• 4.1. Finite Element Analysis of WDS １１９
• 4.1.1. Von Mises Stress Distribution １１９
• 4.1.2. Deformation of the Frame １２０
• 4.1.3. Reaction Moments at the Torque Sensor Interface １２４
• 4.2. Results of Calibration (WDS) １２７
• 4.3. Crosstalk Validation of WDS １２９
• 4.3.1. Axial Force Sensitivity １２９
• 4.3.2. Bending Moment Sensitivity １２９
• 4.3.3. Transverse/Shear Load Sensitivity １３１
• 4.4. Participants １３２
• 4.5. Agreement Between WDS and IKD １３４
• 4.6. Reliability of WDS １３８
• 4.6.1. Interrater Reliability １３８
• 4.6.2. Test-retest Reliability １４２
• 4.7. User Experience Evaluation １４７
• Chapter 5. Discussion １５０
• 5.1. Overview and Significance １５０
• 5.2. Comparison with Existing Studies １５１
• 5.2.1. Trends in Portable and Wearable Muscle Strength Measurement Devices １５１
• 5.2.2. Validation Approach Compared to Reference Standards １５３
• 5.2.3. Measurement Reliability and Error Analysis １５４
• 5.3. Clinical Implications １５８
• 5.4. Limitations １６０
• 5.5. Future Directions １６１
• Chapter 6. Conclusions １６４
• Acknowledgments １６６
• Funding １６７
• References １６８
• Abstract in Korean １８８
• 감사의 글 (Special Acknowledgments) １９０