METROLOGY APPLIED TO THE PRODUCTION OF ISOMETRIC TORQUE OF THE KNEE FLEXOR-EXTENSORS: REPRODUCIBILITY AND RESPONSIVENESS USING A PORTABLE TRACTION DYNAMOMETER
Description
Introduction: Measures of muscle strength and/or torque, limb symmetry (SI) and the ischium/quadriceps ratio (R-I/Q) are widely used in clinical and sports settings. It is crucial to ensure their reproducibility. Objective: To determine reproducibility and responsiveness, using the Dinabang, for aspects of knee flexor-extensor muscle function measured isometrically. Methods: An observational test-retest study with 20 volunteers aged 18 to 59. A Dinabang portable traction dynamometer was used to obtain maximum isometric torque (MIT) measurements. The volunteers were assessed bilaterally for the MITflexors and MITextensors outcomes using the test-retest approach, and the SI and R-I/Q were then calculated. There was a total of one test and two retest measurements, and the assessment procedures were identical for all tests. Relative reproducibility was assessed using the intraclass correlation coefficient (ICC) and absolute reproducibility using the standard error of measurement (SEM). Responsiveness was assessed by the minimum detectable change (MDC). Results: No differences were observed between MIT at different times, neither for MITextensors nor for MITflexors. The SI ICCs of the extensors were moderate and those of the flexors poor; the SEM values indicated high variability (around 85%) and low responsiveness (high MDC values). For R-I/Q, although the ICC was moderate, the SEM was low (with variability of 10.8%) and the responsiveness was acceptable. Conclusions: The MITextensors and R-I/Q measurements showed better reproducibility and responsiveness than those measured by MITflexors and SI, especially for the SI of the flexors
Files
Steps to reproduce
Muscle function was assessed using the Dinabang® portable traction dynamometer (Movi, Montevideo, Uruguay), equipped with an inertial sensor and a smartphone-based digital interface compatible with Android and iOS. The system captured force signals at 200 Hz and transmitted them via Bluetooth to the Dinabang app, where all measurements were stored automatically with the participant’s identification, date, and time. The app displayed data in kgf, N, or N∙m, depending on user selection. To calculate torque, the lever arm—the distance between the knee joint line and the attachment point near the malleoli—was entered manually. The inertial sensor continuously corrected the angle of force application relative to the lever arm during each test, ensuring that any minor posture variation was automatically compensated. This allowed the device to provide tangential force values precisely aligned with the true mechanical moment produced by the participant. All measurements were performed by four trained and calibrated undergraduate physiotherapy students, ensuring methodological consistency and reliability. Before testing, participants completed a 5-minute warm-up on a cycle ergometer at low intensity. Measurements of maximum isometric torque (MIT) were then performed for both the knee extensors and flexors using a PHYSIOLAB ONE® stretcher (Cascavel, Brazil), designed specifically for dynamometric evaluation of different muscle groups. For knee extensors, participants sat with the hip flexed at approximately 90°, the trunk supported, and the thighs stabilized with Velcro straps to minimize compensatory movements. The knee angle was set to 65° ± 5°, monitored in real time by the inertial sensor. The Dinabang was secured with a non-elastic chain attached behind the stretcher to the ankle anklet. Participants performed three maximal voluntary contractions, each lasting 5 seconds, with 120-second rest intervals. For knee flexors, the setup remained identical except that the chain was fixed to a point in front of the stretcher, allowing resistance to knee flexion. The same number of trials, contraction duration, and rest intervals were applied. All force data were automatically converted into torque values by the app using the equation: Torque = Force × Lever Arm. Additionally, two key derived metrics were obtained automatically: Symmetry Index (SI): the percentage difference in MIT between the dominant and non-dominant limbs. For this study, SI values below 15% were considered symmetrical. Ischiocrural-to-Quadriceps Ratio (R-I/Q): the ratio between flexor and extensor torque, with normality values between 0.5 and 0.7. This protocol ensured precise, repeatable, and fully digital acquisition of muscle torque, combining mechanical dynamometry with inertial sensing and app-based computation. The use of standardized positioning, trained assessors, and automatic correction of force vectors enhanced both data reproducibility and biomechanical validity.
Institutions
- Universidade Estadual do Oeste do Parana - Campus de Cascavel