Preliminary validation of a mobile force Sensing device for clinical and telerehabilitation

Abstract

Muscle strength and force production are important measures of patient progress during physical rehabilitation. Reliable and objective measurements are important to ascertain throughout rehabilitation. Current methods—manual muscle testing, electromechanical dynamometer, and hand-held dynamometer—are accurate and reliable, but have limitations that prevent wide implementation. As healthcare systems adapt to more patient-centered outcome models, changes to the delivery of rehabilitation, whether at-home or in the clinic, must also change to become more cost effective and accessible and provide quantifiable information regarding patient progress.

We developed a novel Force Sensing (FoSe) device to quantify either tensile or compressive isometric muscle strength. The device was tested in a laboratory setting with healthy participants (n = 32) and compared to the commonly used hand-held dynamometer (HHD). Participants used both devices to perform several common isometric muscle tests including: hip abduction, knee extension, knee flexion, shoulder external rotation, and shoulder internal rotation.

Compared to the HHD, FoSe was found to be an accurate and reliable measurement of force production. Intraclass Correlation Coefficients ranged from 0.58 to 0.89 without a magnitude dependent variation in force measurement. A second round of clinical testing with a patient population is warranted to determine FoSe’s ability to measure clinically relevant asymmetry and progress over time. Further usability testing also needs to be conducted to determine the adequacy of FoSe for at-home use by both patients and clinicians.

Introduction

Muscle strength and force production are important measures of patient progress during physical rehabilitation. Objective and reliable measurement of strength is critical to quantify strength improvement over the course of treatment to document progress, justify continued treatment, and indicate preparedness for progression of activities (Ellenbecker and Davies, 2000, Thomee et al., 2011).

Manual muscle testing (MMT) is commonly used in the clinic, however has poor inter-rater reliability (Frese et al., 1987) and low diagnostic accuracy compared to dynamometry (Bohannon, 2005). The hand-held dynamometer (HHD) is used to measure muscle strength during MMT. Testing with an HHD presents limb stabilization issues but can be managed though the use of strapping and other strategies (Laprade and Wijdicks, 2012, Sinacore et al., 2017). The HHD measures the compressive force applied by the participant and displays force on the device’s screen, however currently available devices are limited by design features, data storage, and analysis issues.

The FoSe (Force Sensor, Fig. 1) is a novel device designed to measure either tensile or compressive isometric muscle contraction. Consisting of a commercial force sensor, FoSe is anchored at one end to an immobile surface (e.g. wall, door anchor, table leg) with the other end attached to the patient with either a Velcro cuff or standard hand grip. The tester then instructs the patient to perform an isometric contraction with the desired muscle. FoSe measures the force applied by the participant over time, including maximum force of contraction, contraction duration, and work of contraction. The device is coupled via Bluetooth to an Android device, where data can be displayed graphically and stored for recall. While other alternative devices are available, none have been validated against HHD or electromechanical dynamometry.

The purpose of this study was to determine FoSe’s accuracy and compare its reliability to an HHD for measuring maximum force production in healthy individuals. We hypothesized that the two devices will demonstrate consistent results for absolute strength measurements.