Determining range of motion from IMU sensors

Abstract

A method, apparatus, and computer program product for assessing a motion of a human subject, the method comprising: obtaining measurements from two or more sensor systems, wherein the sensor systems are positioned at two locations on two body parts of the subject, the two body parts capable of moving relative to each other, wherein the measurements are received in a form of quaternion elements at least for the sagittal plane of the subject; calculating from the quaternion elements, Euler angles for a first sensor system and a second sensor system of the two sensor systems, for at least one dimension in a three dimensional space; and determining an angle between the two body parts in a sagittal plane as a difference between an Euler angle of the first sensor an the second sensor system for the at least one dimension.

Description

DETERMINING RANGE OF MOTION FROM IMU SENSORSCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 712,55 Ifiled October 28, 2024, titled "Determining Range of Motion from IMU Sensors", hereby incorporated by reference in its entirety.TECHNICAL FIELD

[0002] The present disclosure relates to determining motion angles of a human subject using IMU sensors in one or more anatomical planes.BACKGROUND

[0003] Range of Motion (ROM), and in particular Cervical Range of Motion (CROM) biomechanical assessment relates to evaluating and analyzing human movement, identifying abnormalities, and making treatment, performance improvement, or other suggestions.

[0004] Current technologies for ROM assessment in clinical and academic settings include the use of a universal Goniometer (UG) which is easy to use, relatively fast and reasonably accurate. However, the use of goniometer has some significant drawbacks. One such drawback is that all measurements are performed statically, and it is impossible to dynamically track the subject’s motions. Additionally, for some measurements, such as CROM measurement, the UG has known accuracy and reproducibility limitations. For example, the subject has to be in mostly upright positions, and the subject's trunk needs to be stabilized.

[0005] A significant shift has emerged in the assessment of human motion with the advancement of optical motion capture (Mocap) systems, which may include both marker-based and marker-less technologies. These systems offer increased accuracy, speed, and intuitive capability for capturing various angles across different planes and movements, frequently yielding reliable analyses of diverse body parts, including upper limb and facial motion. However, Mocap systems are susceptible to errors, particularly in joint position and rotation, where the body's silhouette undergoes minimal change andnear the axis of rotation. Marker-based inaccuracies often arise from soft tissue artifacts, as muscle and skin move independently of the bone. Additionally, optical motion capture systems are also limited to specific laboratory-based settings, and are also highly expensive and time-intensive, thus limiting their real-world applications.BRIEF SUMMARY

[0006] One exemplary embodiment of the disclosed subject matter is a method for assessing a motion of a human subject, comprising: obtaining measurements from two or more sensor systems, wherein the sensor systems are positioned at two locations on two body parts of the subject, the two body parts capable of moving relative to each other, wherein the measurements are received in a form of quaternion elements at least for the sagittal plane of the subject; calculating from the quaternion elements, Euler angles for a first sensor system and a second sensor system of the two sensor systems, for at least one dimension in a three dimensional space; and determining an angle between the two body parts in a sagittal plane as a difference between an Euler angle of the first sensor an the second sensor system for the at least one dimension. Within the method, the sensor system is optionally an Inertial Measurement Unit (IMU sensor). Within the method, the first sensor system or the second sensor system comprise at least one accelerometer, at least one gyroscope, or at least one magnetometer. The method can further comprise repeating dynamically said obtaining, said calculating and said determining at determined intervals. The method can further comprise analyzing a series of two or more angles between the two body parts to determine a practical insight for the subject. Within the method, the first sensor system is optionally placed externally to a cervical vertebra of the subject, and the second sensor system is placed on an occipital protuberance of the subject, thereby providing indications to cervical motion. Within the method, the at least one dimension is a Y dimension. The method can further comprise calculating the quaternion elements from raw measurements of the IMUs, comprising applying a Kalman filter. Within the method, the angle is optionally calculated at least for the Sagittal plane of the subject.

[0007] Another exemplary embodiment of the disclosed subject matter is an apparatus comprising: at least two sensor systems, positioned at two locations on two body parts of the subject, the two body parts capable of moving relative to each other; and a processor configured to: obtaining measurements from the at least two sensor systems, wherein the measurements are received in a form of quaternion elements at least for the sagittal plane of the subject; calculating from the quaternion elements Euler angles for a first sensor system and a second sensor system of the two sensor systems, for at least one dimension in a three dimensional space; and determining an angle between the two body parts in asagittal plane as a difference between an Euler angle of the first sensor an the second sensor system for the at least one dimension. Within the apparatus, each of the at least two sensor systems is optionally an IMU sensor. Within the apparatus, the first sensor system or the second sensor system optionally comprise at least one accelerometer, at least one gyroscope, or at least one magnetometer. Within the apparatus, the processor is optionally further adapted to repeat dynamically said obtaining, said calculating and said determining, at determined intervals, and to analyze a series of two or more angles between the two body parts to determine a practical insight for the subject. Within the apparatus, the at least one dimension is optionally a Y dimension. Within the apparatus, the processor is optionally further adapted to calculate the quaternion elements from raw measurements of the IMUs, comprising applying a Kalman filter.

[0008] Yet another exemplary embodiment of the disclosed subject matter is a computer program product comprising a computer readable storage medium retaining program instructions, which program instructions when read by a processor, cause the processor to perform a method comprising: obtaining measurements from two or more sensor systems, wherein the sensor systems are positioned at two locations on two body parts of the subject, the two body parts capable of moving relative to each other, wherein the measurements are received in a form of quaternion elements at least for the sagittal plane of the subject; calculating from the quaternion elements, Euler angles for a first sensor system and a second sensor system of the two sensor systems, for at least one dimension in a three dimensional space; and determining an angle between the two body parts in a sagittal plane as a difference between an Euler angle of the first sensor an the second sensor system for the at least one dimension. Within the computer program product, each of the at least two sensor systems is optionally an Inertial Measurement Unit (IMU sensor), or the first sensor system or the second sensor system comprise at least one accelerometer, at least one gyroscope, or at least one magnetometer. Within the computer program product, the processor may further repeat dynamically said obtaining, said calculating and said determining, at determined intervals, and further performs analysis of a series of two or more angles between the two body parts to determine a practical insight for the subject. Within the computer program product, the at least one dimension is optionally a Y dimension, the processor may calculate the quaternion elements from raw measurements of the IMUs, comprising applying a Kalman filter.THE BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0009] The present disclosed subject matter will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which corresponding or like numerals or characters indicate corresponding or like components. Unless indicated otherwise, the drawings provide exemplary embodiments or aspects of the disclosure and do not limit the scope of the disclosure. In the drawings:

[0010] Fig. 1 shows steps in a flowchart of a method for assessing and using an angle of a joint of a subject , in accordance with some exemplary embodiments of the disclosed subject matter;

[0011] Fig. 2 is a schematic block diagram of an angle assessment system for assessing motion angles and using the assessment, in accordance with some exemplary embodiments of the disclosed subject matter; and

[0012] Figs. 3A-3C show a schematic illustration of an exemplary experimental environment where a subject performs sagittal, frontal and horizontal motions, respectively, in accordance with some exemplary embodiments of the disclosed subject matter.DETAILED DESCRIPTION

[0013] Range of motion (ROM) and in particular Cervical Range of motion (CROM) biomechanical assessment is important for objectively evaluating and analyzing human movement, identifying abnormalities, suggesting treatment options and monitoring the progression. CROM is applicable to both experimental and clinical contexts, whether preoperative, athletic performance, ergonomic evaluation, pain management, or other applications.

[0014] Common techniques for assessing ROM and in particular CROM include the use of a universal Goniometer (UG) which is easy to use, fast and reasonably accurate, but on the other hand does not enable dynamic assessment, has known limitations in reproducibility and may not be accurate enough for certain needs. In addition, it may be limited in setting, for example the subject's trunk needs to be stabilized and the subject mostly has to be in upright positions.

[0015] Other common techniques for assessing ROM include optical motion capture (Mocap) systems, which offer increased accuracy, speed, and intuitive capability for capturing various angles across different planes and movements, frequently yielding reliable analyses of certain body parts. However, Mocap systems are susceptible to errors and are also limited to specific laboratory-based settings, are highly expensive and labor- intensive , thus limiting their real-world applications.

[0016] Over the past years, sensors have been used to monitor physical parameters with a wide range of precision with regard to CROM measurements, but no dynamic and accurate method for estimating the ROM has been determined.

[0017] Thus, one technical problem addressed by the disclosure is the need to measure the ROM of a joint or a series of joints (hereinafter collectively referred to as "joint") using sensors. The measurement should be dynamic and provided in high frequency, such that continuous monitoring may be performed when the subject is in motion. The cervical spine is one of the most complex systems in terms of articular motion. It includes seven cervical vertebrae and the skull, containing 37 separate joints that function simultaneously, allowing for small amounts of sliding and tilting between each joint. Due to this multi-joint structure, measuring the cervical spine's range of motion is highly complex and remains an ongoing challenge.

[0018] The measurement should also be suitable for laboratory settings as well as for outdoor and free motion settings, to provide for measuring subjects under different conditions and activities, which may not be enabled in a laboratory.

[0019] The sensors should be comfortable, lightweight and un-disturbing to the subject, and user-friendly for the installer.

[0020] One technical solution of the disclosure relates to measuring a ROM and in particular CROM using two or more IMU sensor systems (hereinafter also referred to as "sensor system"). In some exemplary embodiments, each IMU sensor system may combine one or more accelerometers, one or more gyroscopes and one or more magnetometers, each providing measurements in three dimensions, such that the sensor system provides a total of nine (9) measurements. In some exemplary embodiments, one or more sensors may also comprise an Electromyography (EMG) sensor, and / or an Electrocardiography (ECG) sensor which may be used for examining neck muscles and heart rate in concert with the cervical movement.

[0021] At least one sensor system may be attached to the subject on each of the body parts connected by the joint. For example, when assessing the CROM, one sensor system may be attached to a cervical vertebra of the subject, for example T1 vertebra, and the other to the subject’s head, for example over the Occipital Protuberance.

[0022] Each of the sensor systems may fuse the readings provided by its various sensors to provide the sensor system output in the form of quaternion elements for each plane, being the sagittal, frontal and horizontal planes, wherein a quaternion is a fourdimensional number system that extends complex numbers, consisting of one real part and three imaginary parts (i, j, k), commonly used to represent 3D rotations and orientations of in space. A quaternion may be represented by a four-tuple comprising a scalar and a three-dimensional vector.

[0023] Alternatively, each sensor system may output raw data by the various sensors, or a combination thereof, and the quaternion elements for each plane may be calculated, for example by applying a Kalman filter.

[0024] The quaternion elements for the sagittal plane and optionally also for the frontal plane may then be converted to obtain the Euler angles0Z) representing the position and angle of the respective sensor system in the respective plane. For example, the Euler angles may be calculated using the segment (XYZ, ZYZ, ZYX).

[0025] The angle over the sagittal plane and optionally over the frontal plane may then be obtained by subtracting the corresponding Euler angles associated with the two sensor systems.

[0026] As for the horizontal plane, the quaternion elements may be converted into Cartesian coordinates in two dimensions (2D), using a rotation matrix according to a chosen segment.

[0027] After adjusting the offsets for each sensor system, the angle of the joint in the horizontal plane may be calculated as the normalized product of the two vectors.

[0028] It is appreciated that the measurements and angle calculations for all planes may be repeated dynamically and continuously throughout the activity or part thereof, for example every 0.1 second, every 0.5 second, every 1 second, or the like.

[0029] The sequence of angles in each plane or combination of planes may then be analyzed, optionally in accordance with a required application, for example guiding thesubject how to correct the subject’s posture, how to eliminate pain, adjusting equipment such as bike, or the like.

[0030] In some embodiments, the series of angles may be automatically analyzed, for example using a dedicated application and / or an Artificial Intelligence (Al) engine, and a recommendation may be automatically provided, such as a recommendation how to change one’s posture. In some embodiments, a hybrid system, comprising a combination of automatic analysis and a human may be obtained and provided to the subject.

[0031] One technical effect of the disclosure is the provisioning of a systematic method for assessing the angle at a joint of a subject, at least in the sagittal plane.

[0032] Another technical effect of the disclosure is that the method is fast and therefore dynamic, since it enables to repeatedly measure the angle at small time intervals, for example every 0.1 seconds, and thus assess the angles generated by the subject’s motion. The angles assessment may then be used for improving ergonomic evaluation, pain management, athletic equipment and performance, or any other elated application.

[0033] Yet another technical effect of the disclosure is that the method can be used indoors or outdoors, in all kinds of activities and by any human subject, and is therefore not limited to laboratory-condition testing.

[0034] Yet another technical effect of the disclosure is that the method utilizes output from small and light-weight sensor systems, and is thus comfortable and un-hindering to the subject and user-friendly to an operator, such as a laboratorian, a physician, or the like.

[0035] Referring now to Fig. 1, showing a flowchart of steps in a method for assessing and using an angle of a joint of a subject, in accordance with some exemplary embodiments of the disclosure.

[0036] The method makes use of measurements from two or more sensor systems, such as IMU sensors. Each sensor system may comprise one or more 3D-accelerometer, one or more 3D gyroscopes, and one or more 3D-magnetometers. In some embodiments, the sensor system may also comprise an Electromyography (EMG) sensor, and / or an Electrocardiography (ECG) sensor.

[0037] In some embodiments, two-surface wireless 3D Delsys Trigno® Avanti sensors, available from Delsys Inc. of Natick, MA may be used as the IMU sensor, comprising an accelerometer, a gyroscope, a magnetometer and an EMG.

[0038] Within the specific sensor, the accelerometer offers a range of ±16g with a bandwidth of 24Hz - 473Hz and a resolution of 16 bits; the gyroscope features a range of ±2000 dps, a bandwidth of 24 Hz - 360 Hz, and a resolution of 16 bits; and the magnetometer has a range of ±4900 pT and a bandwidth of 50 Hz. Sampling rates for the sensors include an EMG sampling rate of 1259 S / s, and an accelerometer and gyroscope sampling rate of 74 S / s. The orientation data can be recorded at a corresponding sampling rate, for example, at a sampling rate of 74 Hz.

[0039] The sensor system may output quaternion elements describing the orientation of the sensor in space, by applying a Kalman filter to the fusion of the magnetometer, accelerometer and gyroscope data for each plane.

[0040] Thus, at step 104, measurements may be obtained from two or more sensor systems, wherein the sensor systems may be positioned at two locations on two body parts of the subject, the two body parts connected by a joint or a series of joint, and capable of moving relative to each other, wherein the measurements are received in a form of quaternion elements at least for the sagittal plane of the subject.

[0041] At step 108, the quaternion elements may be converted into absolute Euler angles (0X> &Y> ®Z) foreach sensor and each of the sagittal and optionally the frontal planes. The angles may be wrapped to 360°, using a chosen segment (XYZ, ZYZ, ZYX). It is appreciated that the offset of the angles may be calibrated prior to the subject starting the motion, by setting a baseline angle measured between the two sensor systems at the initial position of the subject to be zero.

[0042] The quaternion data for the horizontal plane may be converted into cartesian coordinates in 2D using the rotation matrix described in Equations ( 1 )-(3) below for the chosen segment XYZ, ZYX, and ZYZ, respectively:(Equation 1). Segment XYZ: -1 i- x V2— y 172dy2(xy + wz(Equation2(xy — wz)2(xz + wy)(Equation 3). Segment ZYZ:='2(wy + xz) 2(wz — xy)where the output quaternion for the horizontal plane is represented as w + xi + yj + zk.

[0043] At step 112, the angle between the two sensor systems for the sagittal and optionally the frontal planes may be calculated based upon the Euler angles associated with the two sensor systems. Thus, the angle for the sagittal plane may be calculated as the difference between the 0Yassociated with one sensor system, and the 0Yassociated with the other sensor system. Optionally, the angle for the frontal plane may be calculated as the difference between the 0Zassociated with one sensor system, and the 0Zassociated with the other sensor system.

[0044] Additionally, the angle between the two sensor systems for the horizontal plane may be calculated based upon the Cartesian coordinates. The offset of the Cartesian coordinates for a first sensor system may be adjusted relative to a baseline where the subject is assuming a neutral position, setting it to (1,0). Similarly, the coordinates for second sensor system may be aligned with the baseline, and set to (0,0). Then the angle between the vectors associated with the two sensor systems may be calculated according to Equation 4 below, which represents the neck’s angle:where SI and S2 are the cartesian coordinates of the first and the second sensor systems, respectively.

[0045] Steps 104, 108 and 112 may be repeated during the motion, and at a frequency determined in accordance with the measurement rate of the sensor system, the processing resources and the application.

[0046] In some embodiments, the assessed angles may be averaged over time periods such as 0.5 second, 1 second, or the like. In further embodiments, the time periods may be averaged over a sliding time window which enhances the continuity of the measurements.

[0047] At step 116, the series of angles, at least in the sagittal plane may be analyzed to determine practical insights. The analysis may be automatic, made by a human or a combination thereof. The insights may relate to suggesting to the subject to correct theposture, adapting assistive equipment for the subject, adapting sports equipment to the subject, or the like.

[0048] Referring now to Fig. 2, showing a block diagram of an angle assessment system for assessing motion angles and using the assessment, in accordance with some exemplary embodiments of the disclosed subject matter.

[0049] The system may comprise a first sensor system 204 and a second sensor system 208, for example IMU sensors as described above. Each of first sensor system 204 and second sensor system 208 may comprise an accelerometer, a gyroscope and a magnetometer. In some embodiments, first sensor system 204 or second sensor system 208 may comprise one or more additional sensors, such as ECG, EMG, or the like.

[0050] Each of first sensor system 204 and second sensor system 208 is to be attached to a different body part of the subject, wherein the body parts are connected by a joint or a series of joints, can move relative to each other and form an angle therebetween.

[0051] The system may further comprise a computing platform 212. It will be appreciated that one or more of the components detailed below may be executed by a remote processor communicating with computing platform 212, such as a remote server. The remote server may receive information and provide results to one or more instances of computing platforms 212, providing services to multiple users such as physicians, physiotherapists or others, treating multiple subjects. In some embodiments, a hybrid approach may be taken, in which some of the calculations are performed in real time by a computing platform 212 and other calculations are performed remotely.

[0052] In some exemplary embodiments computing platform 212 may comprise a processor 216, which may be a Central Processing Unit (CPU), a microprocessor, an electronic circuit, an Integrated Circuit (IC) or the like. Processor 216 may be utilized to perform computations required by computing platform 212 or any of its subcomponents. Processor 216 may be configured to execute computer programs useful in performing the method of Fig. 1 above.

[0053] In some exemplary embodiments, computing platform 212 may comprise one or more I / O devices 220 which may be configured to receive input from and provide output to a user. In some exemplary embodiments, I / O devices 220 may be utilized to present to the user a user interface, obtain user definitions, or the like. I / O devices 220may comprise a display, a keyboard, a mouse, a touch screen or another pointing or tracking device, a voice activated device, or the like.

[0054] In some exemplary embodiments computing platform 212 may comprise one or more communication devices 224 for obtaining measures from one or more first sensor system 204 or second sensor system 208, to communicate with additional computing platforms, or the like.

[0055] In some exemplary embodiments computing platform 212 may comprise a memory unit 228. Memory unit 228 may be a short-term storage device or long-term storage device. Memory unit 228 may be a persistent storage or volatile storage. Memory unit 228 may be a disk drive, a Flash disk, a Random Access Memory (RAM), a memory chip, or the like. Memory unit 228 may be a single memory device, or multiple interconnected memory devices which may be co-located or located in different locations and communicating via any communication channel.

[0056] In some exemplary embodiments, memory unit 228 may retain program code operative to cause processor 216 to perform acts associated with any of the subcomponents of computing platform 212. In some exemplary embodiments, memory unit 228 may retain program code operative to cause processor 216 to perform acts associated with any of the steps shown in Figs 1 above.

[0057] The components detailed below may be implemented as one or more sets of interrelated computer instructions, executed for example by processor 216 or by another processor. The components may be arranged as one or more executable files, dynamic libraries, static libraries, methods, functions, services, or the like, programmed in any programming language and under any computing environment.

[0058] Memory unit 228 may retain measurement obtaining module 232 for obtaining measurements from sensor system 204 or sensor system 208. In some embodiments, In some embodiments may comprise internally a Kalman filter application module, for providing the measures in quaternion elements. In further embodiments, measurement obtaining module 232 may also comprise internally the Kalman filter application module. In yet further embodiments, a separate Kalman filter application module, or another module for converting the measurements to quaternions may be retained in Memory unit 228.

[0059] Memory unit 228 may retain Euler angle calculation module 236 for calculating Euler angles from the quaternion elements for the sagittal and optionally the frontal planes, and Cartesian coordinates calculation module 240 for calculating the coordinates for the horizontal plane.

[0060] Memory unit 228 may retain angle determination module 244 for determining the angle between sensor system 204 and sensor system 208 upon the Euler angles. In some embodiments, Euler angle calculation module 236 and / or Cartesian coordinates calculation module 240 may be implemented as part of angle determination module 244. In further embodiments, Euler angle calculation module 236 and / or Cartesian coordinates calculation module 240 may comprise separate modules and calculations which may be invoked by angle determination module 244.

[0061] Memory unit 228 may retain angle analysis module 248 for optionally collecting the angles over a period of time, analyzing the angles, for example averaging, comparing to thresholds, or the like, and making suggestions, related for example to the posture, to assistive equipment, to equipment associated with the activity the user is performing, or the like. In some embodiments, angle analysis module 248 may utilize an Al engine, trained upon collections of angles or collections of sets of angles, optional activity and associated recommendations. Then, when the engine is given a set of angles and optional activity, it may output corresponding recommendations. In some embodiments, the recommendations may be suggested in a hybrid manner, based on collaboration between a human and an automatic analysis module.

[0062] Memory unit 228 may retain user interface 252 for receiving input from a user such as an operator, for example activity type, sensor system locations, or the like. User interface 252 may also provide output to the user information such as measured angles, analysis thereof such as a sliding window average, recommendations, tracking a subject’s angles over time, or the like .

[0063] Experimental Results

[0064] An experiment has been conducted in order to measure the motion of the cervical spine of subjects, wherein the cervical spine is one of the most complex systems in terms of articular motion. The cervical spine includes seven cervical vertebrae and the skull, containing 37 separate joints that function simultaneously, allowing for small amounts of sliding and tilting between each joint. Due to this multi -joint structure, measuring thecervical spine's range of motion is highly complex. Therefore, the cervical angle has been assessed by measuring the angles rather than intersegmental or inter-joint calculations.

[0065] The angles have been assessed according to the above method, and compared to measurements taken using a conventional UG.

[0066] The subjects have been selected to be of various ages, weights, heights and genders.

[0067] The subj ects have been instructed to sit straight and upright (vertically) in a chair equipped with back support and armrests, while ensuring both feet were firmly and flat on the floor. The subjects were also guided to position themselves as far back in the chair as possible while maintaining a neutral sitting position with thoracic and lumbar spine well supported by the chair back (baseline) with their arms remaining rested on the armrests throughout the protocol. The chair remained consistent throughout with consistent placement in the room. Electromagnetic field (EMF) was also tested prior to beginning the study with minimal EMF determining chair and SRM placement.

[0068] Referring now to Figs. 3A-3C showing schematic illustrations of an exemplary experimental environment where a subject performs sagittal, frontal and horizontal motions, respectively, in accordance with some exemplary embodiments of the disclosed subject matter.

[0069] Subject 300, sitting in an upright position as described above, has a first sensor system 304 attached to the subject’s skin over the T1 vertebra, for example using a double-sided adhesive tape. Subject 300 also has a second sensor system 308 attached to a tightly fitted headband placed around the subject's head, over the Occipital Protuberance and the Glabella, wherein second sensor system 308 is attached to the Occipital Protuberance.

[0070] The locations of first sensor system 304 and second sensor system 308 have been selected to comply with the UG protocol bony surface anatomical landmarks, and this compliance has been maintained throughout the experiment for a methodical approach of sensor placement and minimal soft tissue artifacts.

[0071] In the stage of the experiment shown in Fig. 3 A, subject 300 was instructed to perform flexion / extension motions in the sagittal plane, as shown by arrows 205 and 206.The motion is thus around the Y axis, as shown in coordinate systems 320 centered at sensor 304.

[0072] In the stage of the experiment shown in Fig. 3B, subject 300 was instructed to perform left / right side flexion motions in the frontal plane, as shown by arrows 309 and 310. The motion is thus around the Z axis, as shown in coordinate systems 324 centered at sensor 304.

[0073] In the stage of the experiment shown in Fig. 3C, the subject was instructed to perform rotation to the left / right in the horizontal plane, as shown in arrows 313 and 314. The motion is thus around the X axis, as shown in coordinate systems 328 centered at sensor 304.

[0074] In all three stage of the experiment, the assessed angles were compared to the angles as measured by goniometer 316, located at each stage so as to measure the expected motion.

[0075] The subjects were instructed to perform each movement to the full extent of their range of motion and then return to baseline. Each movement has been repeated three times. Prior to each trial, a baseline measurement has been performed in which the operator aligned the Goniometer, and the Goniometer has been read for each movement.

[0076] Following the movements as shown in Figs. 3A-3C, the subjects also performed the same movements while leaning forward, in order to assess the reliability of the results. In this part, subjects were instructed to maintain a horizontal state achieved by being statically seated on an Schoberer Rad Messtechnik (SRM) ergometer bike with the handlebars dropped as they leaned forward on their forearms to perform the neck movements, thus achieving a horizontal state. This part of the experiment also included movements on the three anatomical planes.

[0077] Data Analysis

[0078] The assessed angles have been compared to gold standard noninvasive UG to obtain their validity. Results have been analyzed by SPSS 27 and Python. Following the D'Agostino & Pearson test for normality, all but one set of results proved normally distributed. Validity was assessed using the Pearson correlation between the UG and assessed results. Additionally, modified Bland-Altman analyses, incorporating random effects models for enhanced precision in estimating within-subject variance (WSV), wereconducted to assess agreement between the assessment and the UG measurements, with repeated measures

[0079] Power analysis was conducted using G*Power 3.1 (Faul et al. 2007, 2009). For correlation analysis of both test parts, with the minimum acceptable power level of 0.80, and N = 14, the minimum required correlation coefficient is 0.67. Correlation coefficients that are between 0.62 and 0.67 achieve an accepted level of power of 0.70 to 0.80. All coefficients that are below 0.62 demonstrate low power.

[0080] As for reliability, the relative reliability was assessed using inter-class correlation (ICC- Two-way random effect, absolute agreement, single rater). Pearson and ICC effect values were interpreted in accordance with the Davis' (1971) Guidelines for the Interpretation of Effect Size for Correlations; as such, r>0.7 was regarded as a very strong association; 0.69 < r >0.5 was regarded as a substantial level; 0.49 < r >0.3 was regarded as moderate; 0.29 < r >0.1 was regarded as low; and r<0.1 was regarded as negligible.

[0081] Table 1 below shows the validity of CROM for each cervical movement in accordance with the description above, both Flexion / Extension (Sagittal plane), Side flexion Left / Right (frontal plane) and rotation left / right (horizontal plane). Table indicates the Pearson r score for the ROM between the UG and the assessed measurement for each cervical movement. Validation is provided for each repetition, as well as averaged over the repetitionsTable 1

[0082] Table 2 below shows the reliability, also referred to as repeatability, of the measurements. The table shows the Interclass Correlation Coefficient scores (ICC) and individual mean and SD scores for each pair of test-retest sensor system measurements, related to each cervical movement. The data is divided by repetition.Table 2

[0083] Table 3 below shows the mean and standard deviation of the range of motion analysis for each cervical movement, compared to past studies conducted using theUniversal Goniometer or a similar device.Table 3

[0084] The present invention may be a system, a method, and / or a computer program product. The computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present invention.

[0085] The computer readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. A non- exhaustive list of more specific examples of the computer readable storage medium includes the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanically encoded device such as punch-cards or raised structures in a groove having instructions recorded thereon, and any suitable combination of the foregoing. A computer readable storage medium, as used herein, is not to be construed as being transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission media (e.g., light pulses passing through a fiber-optic cable), or electrical signals transmitted through a wire.

[0086] Computer readable program instructions described herein can be downloaded to respective computing / processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and / or a wireless network. The network may comprise copper transmission cables, optical transmission fibers, wireless transmission, routers, firewalls, switches, gateway computers and / or edge servers. A network adapter card or network interface in each computing / processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium within the respective computing / processing device.

[0087] Computer readable program instructions for carrying out operations of the present invention may be assembler instructions, instruction-set-architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, or either source code or object code written in any combination of one or more programming languages, including an object orientedprogramming language such as Smalltalk, C++ or the like, and conventional procedural programming languages, such as Python, MATLAB, the "C" programming language or similar programming languages. The computer readable program instructions may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) may execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present invention.

[0088] Aspects of the present invention are described herein with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer readable program instructions.

[0089] These computer readable program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions / acts specified in the flowchart and / or block diagram block or blocks. These computer readable program instructions may also be stored in a computer readable storage medium that can direct a computer, a programmable data processing apparatus, and / or other devices to function in a particular manner, such that the computer readable storage medium having instructions stored therein comprises an article of manufacture including instructions which implement aspects of the function / act specified in the flowchart and / or block diagram block or blocks.

[0090] The computer readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus or other device to produce a computer implemented process, such that the instructions which execute on the computer, other programmable apparatus, or other device implement the functions / acts specified in the flowchart and / or block diagram block or blocks.

[0091] The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and / or flowchart illustration, and combinations of blocks in the block diagrams and / or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions.

[0092] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0093] The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elementsas specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.

Claims

CLAIMSWhat is claimed is:

1. A method for assessing a motion of a human subject, comprising: obtaining measurements from two or more sensor systems, wherein the sensor systems are positioned at two locations on two body parts of the subject, the two body parts capable of moving relative to each other, wherein the measurements are received in a form of quaternion elements at least for the sagittal plane of the subject; calculating from the quaternion elements, Euler angles for a first sensor system and a second sensor system of the two sensor systems, for at least one dimension in a three dimensional space; and determining an angle between the two body parts in a sagittal plane as a difference between an Euler angle of the first sensor an the second sensor system for the at least one dimension.

2. The method of Claim 1, wherein the sensor system is an Inertial Measurement Unit (IMU sensor).

3. The method of Claim 1, wherein the first sensor system or the second sensor system comprise at least one accelerometer, at least one gyroscope, or at least one magnetometer.

4. The method of Claim 1, further comprising repeating dynamically said obtaining, said calculating and said determining at determined intervals.

5. The method of Claim 1, further comprising analyzing a series of two or more angles between the two body parts to determine a practical insight for the subject.

6. The method of Claim 1, wherein the first sensor system is placed externally to a cervical vertebra of the subject, and the second sensor system is placed on an occipital protuberance of the subject, thereby providing indications to cervical motion.

7. The method of Claim 1, wherein the at least one dimension is a Y dimension.

8. The method of Claim 1, further comprising calculating the quaternion elements from raw measurements of the IMUs, comprising applying a Kalman filter.

9. The method of Claim 1, wherein the angle is calculated at least for the Sagittal plane of the subject.

10. An apparatus comprising: at least two sensor systems, positioned at two locations on two body parts of the subject, the two body parts capable of moving relative to each other; and a processor configured to: obtaining measurements from the at least two sensor systems, wherein the measurements are received in a form of quaternion elements at least for the sagittal plane of the subject; calculating from the quaternion elements Euler angles for a first sensor system and a second sensor system of the two sensor systems, for at least one dimension in a three dimensional space; and determining an angle between the two body parts in a sagittal plane as a difference between an Euler angle of the first sensor an the second sensor system for the at least one dimension.

11. The apparatus of Claim 10, wherein each of the at least two sensor systems is an IMU sensor.

12. The apparatus of Claim 10, wherein the first sensor system or the second sensor system comprise at least one accelerometer, at least one gyroscope, or at least one magnetometer.

13. The apparatus of Claim 10, wherein the processor is further adapted to repeat dynamically said obtaining, said calculating and said determining, at determined intervals, and wherein the processor is further adapted to analyze a series of two or more angles between the two body parts to determine a practical insight for the subject.

14. The apparatus of Claim 10, wherein the at least one dimension is a Y dimension.

15. The apparatus of Claim 10, wherein the processor is further adapted to calculate the quaternion elements from raw measurements of the IMUs, comprising applying a Kalman filter.

16. A computer program product comprising a computer readable storage medium retaining program instructions, which program instructions when read by a processor, cause the processor to perform a method comprising: obtaining measurements from two or more sensor systems, wherein the sensor systems are positioned at two locations on two body parts of the subject, the two body parts capable of moving relative to each other, wherein the measurements are received in a form of quaternion elements at least for the sagittal plane of the subject; calculating from the quaternion elements, Euler angles for a first sensor system and a second sensor system of the two sensor systems, for at least one dimension in a three dimensional space; and determining an angle between the two body parts in a sagittal plane as a difference between an Euler angle of the first sensor an the second sensor system for the at least one dimension.

17. The computer program product of Claim 16, wherein each of the at least two sensor systems is an IMU sensor, or wherein the first sensor system or the second sensor system comprise at least one accelerometer, at least one gyroscope, or at least one magnetometer.

18. The computer program product of Claim 16, wherein the processor further repeats dynamically said obtaining, said calculating and said determining, at determined intervals, and further performs analysis of a series of two or more angles between the two body parts to determine a practical insight for the subject.

19. The computer program product of Claim 16, wherein the at least one dimension is a Y dimension.

20. The computer program product of Claim 16, wherein the processor calculates the quaternion elements from raw measurements of the IMUs, comprising applying a Kalman filter.

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