https://doi.org/10.31449/inf.v45i2.3192 Informatica 45 (2021) 213–222 213 Method for Estimating Tensiomyography Parameters from Motion Capture Data Dino Vlahek, Tadej Stoši´ c and Tamara Golob Institute of Computer Science Faculty of Electrical Engineering and Computer Science at the University of Maribor, Maribor, Slovenia E-mail: dino.vlahek1@um.si, tadej.stosic1@um.si, t.golob@um.si Miloš Kalc, Teja Liˇ cen and Matjaž V ogrin Institute of Sports Medicine, Faculty of Medicine at the University of Maribor, Maribor, Slovenia E-mail: milos.kalc@ism-mb.si, teja.licen@um.si, matjaz.vogrin@um.si Domen Mongus Institute of Computer Science Faculty of Electrical Engineering and Computer Science at the University of Maribor, Maribor, Slovenia E-mail: domen.mongus@um.si Keywords: tensiomyography, marker-based motion capture, 3D points, geometric transformation Received: June 05, 2020 Tensiomyography is a muscle performance assessment technique that measures its mechanical responses. In this study, we explored the possibility of replacing traditional tensiomyography measurement systems with motion capture. The proposed method allows the measurement of multiple muscle points simultane- ously while achieving measurements during a patient’s movements. The results showed that approximately 5 mm error was achieved when estimating maximal muscle displacement, while time delay in muscle con- traction and contraction time was assessed with up to 20 ms error. As confirmed by physicians, the intro- duced errors are within the acceptable margin and, thus, the obtained results are medically valid. Povzetek: V ˇ clanku predstavimo novo metodo, ki omogoˇ ca veˇ ctoˇ ckovno merjenje tensiomiografije. Metoda temelji na snemanju mišiˇ cne kontrakcije s sistemom za zajem gibanja. Rezultati metode in pri- padajoˇ ce napake so ovrednoteni s strani zdravnikov. Le-ti ocenjujejo, ali so napake še znotraj sprejemljive meje, da so rezultati medicinsko veljavni. 1 Introduction Tensiomyography (TMG) is a non-invasive mechanomyo- graphy method that measures mechanical muscle response based on radial muscle belly displacement induced by the electrical stimulus. The measurement unit usually includes an electrical stimulator, a data acquisition subunit, a dig- ital sensor, and muscle electrodes [28]. TMG output is a displacement-time curve evaluated with the following pa- rameters: Delay time (T d ) is a time difference between the electrical impulse and 10% of the contraction, contraction time (T c ) is a time difference between 10% and 90% of the contraction, sustain time (T s ) is a time difference be- tween 50% of the contraction and 50% of the relaxation, and relaxation time (T r ) is a time difference between 90% and 50% of the relaxation and maximal displacement of the muscle contraction (D m ). TMG’s resulting parameters are usually used for the evaluation of an individual’s maximal speed, explosive- ness, endurance, and flexibility [16]. They are also applied in the training optimization process in order to prevent neg- ative effects of muscle asymmetry and asynchrony on an in- dividual’s performance [19]. Additionally, after an injury, muscle functional capacity can be assessed using TMG, so that the most effective rehabilitation treatment is adminis- tered [21], while its usage in medical research includes es- timation of muscle composition [24], evaluation of muscle atrophy [10], measuring adaptation to different pathologies [12], and for determination of muscle fiber type composi- tion [6]. However, TMG has significant drawbacks, as it is a fixed, static tool that can perform single-point measure- ments [28, 10]. Additionally, the reliability of measure- ment highly depends on the experiences of the measurer, since placements of sensors and electrodes could affect the reliability of the results [24], while measurements are gen- erally performed in a static and relaxed position [28]. In order to address the above-mentioned drawbacks, we propose a method that generates output similar to TMG using marker-based motion capture. The proposed ap- proach allows for measuring multiple points simultane- ously, thus reducing the effort required in order to measure muscle contractions. In addition, the measurements can be achieved not only in the relaxed positions but also while moving, as control markers are used in order to stabilize 214 Informatica 45 (2021) 213–222 D. Vlahek et al. natural limb movement in markers. Accordingly, related work in motion capture is described in Section 2. Section 3 introduces a new method that estimates TMG output from motion capture. The proposed method validation results are presented and discussed in Section 4, while section 5 concludes the paper. 2 Related work Motion capture allows for recording the movement of ob- jects or people. Various motion capturing systems were in- troduced recently, including acoustical, mechanical, mag- netic, and optical ones. The most widely used systems are optical. They use a camera for recording the motions of markers attached to an object [18]. Two types of markers are used for this purpose, namely, passive and active ones. Passive markers reflect light generated by a near camera lens, while the active ones use their own light source. In any case, 3D positions of markers over time can be recon- structed using optical triangulation, and the estimated tra- jectories can be used for pinpointing positions of displace- ments for analysis, visualization, and simulation purposes [11]. Both motion capture systems have been used in the entertainment industry for years as well, where its success- ful implementation ranges from famous films like Avatar and Lord of the rings [1] to the gaming industry [20]. Opti- cal motion tracking usage, with the support of virtual real- ity, was also demonstrated for tracking and reconstruction of hand movements for sign language interpretation and dance coaching [26]. Furthermore, optical motion capture technology is today an emerging technology in sports and medicine. For instance, its usage was examined for the pur- poses of facial performance acquisition [13], animation of the natural bending, bulging, and jiggling [4], reconstruc- tion of three-dimensional rotations of human joints [7], and gait analysis [3]. Within this context, the efficiency com- parison of marker-less and marker-based motion capture for gait analysis was conducted, where the authors con- cluded that maker-based motion capture is more suitable for clinical use. A more recent study, however, has shown that motion capture, in general, can introduce errors due to linear scaling and technology imperfection [14]. Here, the musculoskeletal models of different centers of joints, ob- tained from marker-based motion capture, were scaled and compared with measurements obtained from MRI images that are today believed to be the gold standard. Nevertheless, optical motion capture is still widely used in sport gesture analysis that ranges from repetitive stresses and movements on the shoulder [23] to underwater body motions [2]. Moreover, efficient utilization of motion cap- ture technology for medical uses was proposed in [22, 25]. In addition, motion capture technology was successfully used for the rehabilitation of patients with spastic hemi- plegic cerebral palsy [15] and Duchenne muscular dys- trophy [9]. Thus, as marker-based motion capture is frequently used for gait and skeleton analysis in sports medicine and animating 3D objects in the entertainment in- dustry, it provides a solid technological foundation for our study. 3 Method In this section, a method for estimating TMG parameters from 3D motion capture data is presented. The proposed method uses a set of markers in order to trace muscle con- traction using motion capture, while TMG parameters are estimated during the following steps: – Point stabilization is achieved first in order to com- pensate for natural limb movements and preserve only those movements that result from muscle contractions. – Construction of displacement-time curves is achieved next by estimating displacement distances from stabilized 3D marker positions. – Extraction of TMG parameters is finally achieved based on the estimated displacement-time curve. Following the description of the mathematical framework, these steps are described in detail. 3.1 Theoretical background The implementation of the proposed mathematical frame- work is given in the homogeneous coordinate system. This allows for implementing all the used geometric transforma- tions, including translation, by matrix multiplication and, thus, enables efficient utilization of a graphic processing unit [8]. Let a set of markers M = f t m i g, where t m i = [ t x i ; t y i ; t z i ; 1], whilei is a markers index andt is the time t of its capture. A vector between points t m i and t m j is de- noted as t ~ v i;j = t m i t m j , while its projections toXY andXZ planes are denoted as t u i;j = ( t x i;j ; t y i;j ; 1) and t w i = ( t x i;j ; t z i;j ; 1), respectively. A translation for an ar- bitrary vector t ~ v i;j = ( t x i;j ; t y i;j ; t z i;j ) is then given by a translation matrixM T , defined as M T (~ v T ) = 2 6 6 4 1 0 0 t x i;j 0 1 0 t y i;j 0 0 1 t z i;j 0 0 0 1 3 7 7 5 : (1) In addition, rotation matricesM Ry ( y ) andM Rz ( z ) that define rotation aroundY andZ axis for given angles y and z , respectively, are denoted by M Ry ( y ) = 2 6 6 4 cos y 0 sin y 0 0 1 0 0 sin y 0 cos y 0 0 0 0 1 3 7 7 5 ; M Rz ( z ) = 2 6 6 4 cos z sin z 0 0 sin z cos z 0 0 0 0 1 0 0 0 0 1 3 7 7 5 (2) Method for Estimating Tensiomyography Parameters from. . . Informatica 45 (2021) 213–222 215 [27]. 3.2 Point stabilization In order to account for the natural movement of a limb, two control markers were placed on the limb joints in such a way that they were not affected by muscle contractions. They are denoted by the indices i = 1 and i = 2, while the corresponding vector t ~ v 1;2 was used to stabilize the set of markers M (see Figure 1). In order to achieve stabi- lization, the origin of coordinate system was shifted to the control markeri = 1, while theX axis was aligned with t ~ v 1;2 . Note that the latter only requires rotation aroundY andZ axis, while the rotation aroundX axis can be ne- glected due to the nature of measurement that limits such limb movements. Thus, rotations aroundY andZ axis were denoted by rotation angles y and z , defined as angles between projected vectors t ~ u 1;2 and t ~ w 1;2 and the X axis, respectively [27]. This stabilization, denoted as M S , is formally defined as M S =M T ( t m 1 ) M Ry ( y ) M Rz ( z ) = 2 6 6 4 cos t y cos t z sin t z cos t y sin t y t x 1 sin t z 0 0 t y 1 sin t y cos t z sin t y sin t z cos t y t z 1 0 0 0 1 3 7 7 5 ; (3) where M T ( t m 1 ) denotes translation of the origin of co- ordinate system to control markeri = 1, whileM Ry ( y ) andM Rz ( z ) rotations by y and z , respectively. More- over, stabilized set of markers S = f t s i g, where t s i = ( t x 0 i ; t y 0 i ; t z 0 i ) is, thus, given as: t s i =M S t m i : (4) 3.3 Construction of displacement-time curves and TMG parameters extraction This step aims to construct a displacement time curves fromS and extract the required TMG parameters. As mus- cle contraction is captured by the movement of stabilized markers, a displacement curve for each marker t s i 2 S is generated by measuring its distance t d i in time t > 0 from its starting point, given at t = 0. Formally, a dis- placement curve is given by a discrete mapping function D : (t;i)!R defined by: D(t;i) = p ( 0 s i t s i ) 2 : (5) As Eq. 5 cannot produce negative values, it is critical that the initial measurement given at time t = 0 is mea- sured in the relaxing (non-contracted) state of the mus- cle. D(t;i), thus, provides a set of control points based on which a polynomial interpolation is achieved in order to increase the precision of the estimated TMG parame- ters. As polynomial interpolation is a well-know problem, it is not further discussed here. Its efficient implementa- tion is described in [5]. Moreover, as explained in Section 1, five parameters can be extracted from a displacement curve, where most of the medically relevant information is contained in maximal contractionD m , delay timeT d , and contraction time T c . Given an interpolated displacement curved i (t), definitions are as follows: D m (i) = max t d i (t); T d (i) = arg min t (t;d i (t) 0:1 D m (i)); T c (i) =T d (i) arg min t (t;d i (t) 0:9 D m (i)): (6) 4 Results and discussion The proposed method’s implementation was done using C++, and experiments were conducted on a workstation with Intel ® Core TM i5 CPU and 16 GB of main mem- ory. Experimental data about twelve different participants were collected using a 4 5 matrix of reflective markers that were placed on the quadriceps femoris of participants’ left leg, while two control markers were placed over the trochanter head and lateral condyle (see Fig. 1). The par- ticipants were instructed to lie supine on a therapeutic ta- ble where each placed its left leg on a triangular cushion that provided approximately 30 knee angle support. Then, Rectus Femoris (RF - the upper central part of the thigh) and Vastus Medialis (VM - lower internal part of the thigh) muscles were stimulated with a single electrical impulse provided by a high voltage constant current electrical stim- ulator, while control measurements were obtained using a traditional TMG sensor (TMG-BMC Ltd, Ljubljana, Slove- nia). One series of these measurements consisted of five consecutive muscle stimulation with a 5 s interstimulus in- tervals in order to prevent post-activation potentiating. For each muscle, six different sets of stimulations were admin- istrated, starting with the stimulation intensity of 30 mA, increasing the power in each measurement by 10 mA, un- til a maximum of 80 mA was reached. Thus, a total of 30 stimuli for each muscle were measured. At the same time, the same muscle contractions were captured from reflective markers with a Smart-D, BTS s.p.a. motion capture sys- tem. The system consisted of eight infrared cameras with 800 600 spatial and 60 Hz temporal resolution, while their position at the therapeutic table is shown in Figure 2. At each marker, the measured motion capture data was used in order to reconstruct the displacement-time curves, while their agreement with the control TMG curve was es- timated in terms of Pearson correlation coefficient [17]. The obtained results are shown in Table 1. Obviously, the displacement-time curves showed a different agreement level with the control TMG measurements, depending on the markers’ proximities to the TMG sensor. On average, VM measurements displayed lower correlations with con- trol ones than those performed on RF due to the dilated oscillations of the muscular surface, while those markers 216 Informatica 45 (2021) 213–222 D. Vlahek et al. Figure 1: The placement of twenty markers and two control markers on the subject’s leg. The Violet area represents the placement of the TMG sensor during measurement, while red circles indicate control markers. Figure 2: Position of cameras where measurements were performed. placed near the TMG sensor displayed better correlation in both cases. As follows from Table 1, in the case of VM, the highest correlations with control TMG were mea- sured atm5 andm9, whilem15 displayed best results in case of RF stimulation. In addition, the results obtained atm11,m16,m19, andm20 were also statistically signifi- cant in both cases. Such results are expected as these mark- ers were located in anatomical regions of measured mus- cles. Displacement-time curves from markers that show the highest agreement with corresponding control TMG curves are further presented in Figure 3, while TMG parameters were extracted from these particular markers and further examined. In order to assess the accuracy of the extracted TMG pa- rameter, their values were estimated from displacement- time curves generated from markers. Moreover, param- eters error rates represent differences between their val- ues and the parameters’ values from corresponding control TMG. The results are shown in the appendix (Tables 2 7). When consideringT c andT d for VM, the lowest error rates were observed in case of m5 at 50 mA and m20 at 50 mA with 0:2% and 0%, respectively, while error rates between 1:1 25:3% in case ofT c and 3 30:4% in case T d were observed in other cases. On the other hand, no er- ror was observed forD m atm20 at 60 mA, while the error rates in other cases ranged between 1:7 61:7%. In the case of RF,T c error rates were in the range of 0:9 33:7%, with the smallest related tom20 at 30 mA. However,T d in- troduced inconsistent error rates, from 1:8% in case ofm16 at 30 mA, up to 75:7% in case ofm11 at 60 mA.D m error rates were between 6:4 33:7%, where the lowest one is associated withm19 at 80 mA. According to the evaluation provided by the medical ex- perts, the obtained error rates were within the acceptable ranges and can be considered as medically irrelevant. The error of D m can be explained by the fact that the TMG sensor is slightly pressed into the soft tissue, resulting in a small depression at a baseline level, causing a higher value ofD m when a traditional TMG is measured. As expected, there were high errors in theT d parameter since the signals from motion capture and TMG were not properly synchro- nized. Additionally, obtained errors could be explained by Method for Estimating Tensiomyography Parameters from. . . Informatica 45 (2021) 213–222 217 Table 1: Pearson correlation coefficients between the displacement-time curves of markers and control TMG measure- ments together with average result according to each marker. 30mA 40mA 50mA 60mA 70mA 80mA Average VM RF VM RF VM RF VM RF VM RF VM RF VM RF m3 0.652 0.774 0.527 0.803 0.497 0.81 0.514 0.716 0.607 0.701 0.657 0.628 0.575 0.738 m4 0.696 0.745 0.543 0.721 0.504 0.672 0.529 0.557 0.604 0.583 0.698 0.512 0.595 0.632 m5 0.74 0.837 0.606 0.842 0.581 0.839 0.569 0.75 0.637 0.747 0.729 0.672 0.644 0.781 m6 0.604 0.77 0.508 0.76 0.584 0.785 0.538 0.699 0.647 0.732 0.681 0.638 0.594 0.731 m7 0.575 0.735 0.393 0.779 0.352 0.767 0.386 0.677 0.478 0.756 0.515 0.664 0.45 0.73 m8 0.745 0.766 0.578 0.725 0.559 0.686 0.529 0.625 0.63 0.691 0.584 0.644 0.604 0.689 m9 0.73 0.818 0.578 0.825 0.629 0.809 0.621 0.699 0.628 0.723 0.681 0.666 0.644 0.757 m10 0.734 0.732 0.596 0.789 0.578 0.761 0.555 0.767 0.646 0.801 0.718 0.697 0.638 0.757 m11 0.746 0.761 0.573 0.839 0.607 0.845 0.659 0.743 0.652 0.829 0.666 0.644 0.65 0.777 m12 0.531 0.748 0.374 0.796 0.35 0.825 0.365 0.724 0.425 0.79 0.453 0.65 0.417 0.755 m13 0.612 0.738 0.482 0.759 0.431 0.717 0.423 0.656 0.567 0.613 0.55 0.593 0.511 0.679 m14 0.647 0.732 0.525 0.727 0.516 0.668 0.494 0.626 0.605 0.635 0.607 0.654 0.566 0.674 m15 0.729 0.878 0.562 0.846 0.537 0.858 0.6 0.758 0.665 0.81 0.638 0.718 0.622 0.811 m16 0.731 0.789 0.574 0.797 0.589 0.826 0.632 0.724 0.631 0.758 0.669 0.679 0.637 0.762 m17 0.528 0.816 0.45 0.813 0.422 0.801 0.412 0.758 0.408 0.776 0.43 0.693 0.441 0.776 m18 0.567 0.558 0.427 0.603 0.381 0.639 0.406 0.558 0.536 0.535 0.523 0.496 0.473 0.565 m19 0.712 0.795 0.661 0.761 0.62 0.817 0.53 0.714 0.668 0.785 0.647 0.703 0.639 0.763 m20 0.61 0.789 0.632 0.837 0.613 0.819 0.561 0.788 0.698 0.71 0.665 0.691 0.63 0.772 m21 0.641 0.824 0.527 0.796 0.53 0.795 0.484 0.727 0.609 0.761 0.617 0.589 0.563 0.749 m22 0.483 0.76 0.439 0.801 0.542 0.774 0.504 0.688 0.617 0.801 0.576 0.67 0.527 0.749 0 0:2 0:4 0:6 0:8 1 0 2 4 6 8 10 12 s mm m5 at40 mA m9 at30 mA m11 at30 mA TMG at30 mA TMG at40 mA (a) 0 0:2 0:4 0:6 0:8 1 0 2 4 6 8 s mm m15 at30 mA m16 at50 mA m19 at30 mA m20 at40 mA TMG at30 mA TMG at40 mA TMG at50 mA (b) Figure 3: Displacement-time curves from traditional TMG (dashed lines) and corresponding markers (solid lines) that produced the highest level of agreement with traditional TMG for muscle a) VM and b) RF. On thex axis, there is time in s, while they axis represents displacement in mm. the fact that the TMG measurement unit provides more pre- cise measurements because of its 1000 Hz temporal reso- lution when comparing it with 60 Hz of the motion capture system. On the other hand, markers m19 and m11 reg- istered significant movements, even though they were not placed in the anatomical regions, where contraction of RF and VM was expected. Such an outcome might have dif- ferent explanations: – strong electrical stimulation can cause the propagation of the electrical stimuli in deeper tissues, causing mus- cle contraction of adjacent muscles, – the passive mass, represented by inactivated muscles and adipose tissue near the stimulated region, can vi- brate, causing errors in measurements. 218 Informatica 45 (2021) 213–222 D. Vlahek et al. 5 Conclusion A new method for estimating TMG parameters from 3D motion capture, proposed in this paper, allows for mea- surement of TMG parameters at multiple points simulta- neously, while measurements can be obtained during the patient’s movement. With the error rates of 5 mm when estimating maximal muscle displacement and up to 20 ms when estimating delay time and contraction time, the pro- vided results proved to be medically relevant. Nevertheless, selection and proper placement of markers are required. One of the future tasks is a synchronization of the TMG and motion capture signals that would allow us to obtain the exact starting time of muscle contraction and, thus, fur- ther improved contraction and delay time assessment. In addition, improved point stabilization with compensating for rotations along theX-axis will be considered. 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Vastus medialis Rectus femoris Tc(ms) T d (ms) Dm(mm) Tc(ms) T d (ms) Dm(mm) m5 39 ( 15.95) 27.2 ( 11.43) 6.5 ( 3.58) 47.2 ( 7.14) 36.7 ( 8.21) 3.4 ( 1.16) m9 41.8 ( 17.95) 19.4 ( 3.23) 9 ( 5.08) 55.1 ( 7.56) 28.3 ( 9.84) 3 ( 1.43) m11 43.5 ( 19.18) 21.6 ( 5.48) 5.3 ( 3.31) 59.2 ( 15.13) 27.6 ( 11.02) 2.9 ( 1.8) m15 44.8 ( 20.08) 21.9 ( 4.64) 7.4 ( 4.74) 49.4 ( 6.01) 33.8 ( 6.75) 4.9 ( 1.8) m16 45.3 ( 17.85) 22 ( 4.47) 5.2 ( 3.28) 50.5 ( 10.46) 26.1 ( 10.68) 3.5 ( 1.11) m19 45.7 ( 18.22) 25.4 ( 9.35) 5 ( 3.62) 50.4 ( 6.9) 34.8 ( 11.04) 2.8 ( 1.35) m20 41.9 ( 17.6) 29.1 ( 10.43) 4.8 ( 3.42) 51 ( 4.5) 29.8 ( 7.58) 3.3 ( 1.33) TMG 36.5 ( 14.11) 24.2 ( 2.93) 4.9 ( 1.31) 51.5 ( 20.1) 25.6 ( 3.37) 4.3 ( 1.4) Error(Tc) Error(T d ) Error(Dm) Error(Tc) Error(T d ) Error(Dm) m5 2.5 (6.9 %) 3.0 ( 12.4 %) 1.6 ( 33.7%) 4.3 ( 8.4%) 11.1 ( 43.2%) 0.9 (20.4%) m9 5.4 (14.7 %) 4.8 ( 19.8 %) 4.1 ( 83.7%) 3.6 ( 6.9%) 2.7 ( 10.4%) 1.3 (30.9%) m11 7.1 (19.4 %) 2.6 ( 10.8 %) 0.4 ( 8.7%) 7.7 ( 14.9%) 2.0 ( 8.0%) 1.5 (33.8%) m15 8.3 (22.9 %) 2.3 ( 9.3 %) 2.5 ( 51.1%) 2.1 ( 4.1%) 8.2 ( 32.2%) 0.5 (12.5%) m16 8.8 (24.2 %) 2.2 ( 9.0 %) 0.3 ( 6.8%) 1.0 ( 1.9%) 0.5 ( 1.8%) 0.8 (18.8%) m19 9.2 (25.3 %) 1.2 ( 5.0 %) 0.2 ( 3.2%) 1.1 ( 2.2%) 9.2 ( 36.0%) 1.5 (33.8%) m20 5.4 (14.9 %) 4.9 ( 20.4 %) 0.1 ( 1.9%) 0.5 ( 0.9%) 4.2 ( 16.4%) 1.0 (22.9%) Table 3: The table shows average values and associated standard deviation for parameters extracted from markers at a stimulation intensity of 40 mA. Associated errors were placed below the results. The lowest errors are highlighted. Vastus medialis Rectus femoris Tc(ms) T d (ms) Dm(mm) Tc(ms) T d (ms) Dm(mm) m5 30.9 ( 11.9) 29.1 ( 16.9) 6.9 ( 3.7) 47 ( 10.8) 35.4 ( 13.7) 4 ( 1) m9 33.1 ( 14.5) 24 ( 14.1) 6.9 ( 5.6) 50.9 ( 7.8) 33.7 ( 10.6) 3.8 ( 1.7) m11 35.3 ( 16) 24.8 ( 12.7) 5.5 ( 2.6) 55.3 ( 14.5) 30.3 ( 9.9) 3.8 ( 2.1) m15 33.6 ( 15.1) 26.2 ( 13.7) 7.8 ( 4.7) 50.2 ( 7.3) 33.9 ( 7.2) 6.2 ( 1.7) m16 36.2 ( 14) 25.9 ( 13.8) 5.3 ( 3) 54.3 ( 10) 29.1 ( 10.1) 4.3 ( 2) m19 35.3 ( 13.4) 28.7 ( 15.5) 5.4 ( 4.1) 49.3 ( 6.1) 34.9 ( 10.8) 3.2 ( 0.8) m20 35.6 ( 12.5) 28 ( 13.8) 5.1 ( 3.8) 49.9 ( 6.8) 32 ( 11) 4.3 ( 1.4) TMG 31.3 ( 10.9) 23.1 ( 2.5) 5.7 ( 1.8) 45.1 ( 18.3) 24.8 ( 3.1) 4.9 ( 1.6) Error(Tc) Error(T d ) Error(Dm) Error(Tc) Error(T d ) Error(Dm) m5 0.3 (1.1 %) 6 ( 25.8 %) 1.2 ( 20.3%) 1.9 ( 4.2%) 10.7 ( 43%) 0.9 (18.2%) m9 1.8 (5.7 %) 0.9 ( 3.8 %) 1.2 ( 21.0%) 5.8 ( 12.9%) 8.9 ( 36%) 1 (21.4%) m11 4.1 (13 %) 1.6 ( 7.1 %) 0.2 ( 3.5%) 10.2 ( 22.7%) 5.5 ( 22.3%) 1.1 (21.7%) m15 2.3 (7.4 %) 3.1 ( 13.2 %) 2.1 ( 36.3%) 5.1 ( 11.3%) 9.1 ( 36.9%) 1.3 (26.9%) m16 4.9 (15.8 %) 2.8 ( 12.1 %) 0.4 ( 6.2%) 9.2 ( 20.5%) 4.3 ( 17.6%) 0.6 (11.8%) m19 4 (12.8 %) 5.6 ( 24.1 %) 0.4 ( 6.2%) 4.2 ( 9.4%) 10.1 ( 40.8%) 1.6 (33.9%) m20 4.3 (13.7 %) 4.8 ( 20.9 %) 0.6 ( 10.8%) 4.9 ( 10.8%) 7.2 ( 29.3%) 0.6 (11.9%) Method for Estimating Tensiomyography Parameters from. . . Informatica 45 (2021) 213–222 221 Table 4: The table shows average values and associated standard deviation for parameters extracted from markers at a stimulation intensity of 50 mA. Associated errors were placed below the results. The lowest errors are highlighted. Vastus medialis Rectus femoris Tc(ms) T d (ms) Dm(mm) Tc(ms) T d (ms) Dm(mm) m5 28.93 ( 11.01) 23.89 ( 8.60) 7.35 ( 3.76) 48.14 ( 4.01) 38.70 ( 13.90) 12.86 ( 1.29) m9 31.41 ( 12.99) 19.56 ( 4.33) 10.07 ( 5.65) 49.42 ( 4.20) 39.29 ( 16.25) 6.19 ( 2.01) m11 33.45 ( 15.45) 19.91 ( 3.23) 6.62 ( 2.65) 46.98 ( 4.67) 39.21 ( 17.36) 9.83 ( 1.75) m15 30.44 ( 14.53) 20.99 ( 5.26) 9.08 ( 4.76) 50.57 ( 6.98) 36.57 ( 9.64) 8.00 ( 1.73) m16 33.12 ( 14.47) 21.45 ( 6.30) 6.50 ( 2.92) 48.79 ( 4.89) 39.78 ( 13.43) 4.56 ( 1.72) m19 31.90 ( 13.95) 23.77 ( 8.49) 6.14 ( 4.32) 49.07 ( 3.34) 37.13 ( 11.97) 4.31 ( 0.78) m20 31.93 ( 14.84) 23.11 ( 7.21) 6.09 ( 3.83) 53.01 ( 4.79) 29.9 ( 11.49) 9.15 ( 1.21) TMG 28.86 ( 9.14) 23.08 ( 2.24) 6.31 ( 1.88) 42.04 ( 5.22) 24.44 ( 2.98) 18.97 ( 1.66) Error(Tc) Error(T d ) Error(Dm) Error(Tc) Error(T d ) Error(Dm) m5 0.1 (0.2 %) 0.8 ( 3.5 %) 1.0 ( 16.5%) 6.1 ( 14.5%) 14.3 ( 58.3%) 1.2 (23.1%) m9 2.5 (8.8 %) 3.5 ( 15.3 %) 3.8 ( 59.5%) 7.4 ( 17.6%) 14.8 ( 60.5%) 1.0 (19.5%) m11 4.6 (15.9 %) 3.2 ( 13.7 %) 0.3 ( 4.8%) 4.9 ( 11.8%) 14.8 ( 60.5%) 0.6 (10.6%) m15 1.6 (5.5 %) 2.1 ( 9.0 %) 2.8 ( 43.9%) 8.5 ( 20.3%) 12.1 ( 49.6%) 1.8 (33.6%) m16 4.3 (14.7 %) 1.6 ( 7.0 %) 0.2 ( 3.0%) 6.7 ( 16.0%) 15.3 ( 62.7%) 0.3 (6.4%) m19 3.0 (10.5 %) 0.7 ( 3.0 %) 0.2 ( 3.0%) 7.0 ( 16.7%) 12.7 ( 51.9%) 1.9 (36.0%) m20 3.1 (10.6 %) 0.0 ( 0.0 %) 0.2 ( 3.0%) 11.0 ( 26.1%) 5.5 ( 22.5%) 0.4 (8.3%) Table 5: The table shows average values and associated standard deviation for parameters extracted from markers at a stimulation intensity of 60 mA. Associated errors were placed below the results. The lowest errors are highlighted. Vastus medialis Rectus femoris Tc(ms) T d (ms) Dm(mm) Tc(ms) T d (ms) Dm(mm) m5 29.5 ( 9) 25.4 ( 10.5) 7.6 ( 3.8) 47.3 ( 13.2) 35.2 ( 10.9) 4 ( 1.7) m9 30.2 ( 12.2) 21.6 ( 8.9) 10.8 ( 5.6) 45.7 ( 4.3) 39 ( 19.2) 4.5 ( 2.4) m11 32.8 ( 12.3) 20.7 ( 5.3) 7.6 ( 2.9) 40.9 ( 10.4) 43 ( 24.3) 5 ( 2.4) m15 31.1 ( 14.1) 22 ( 7.1) 10.3 ( 4.8) 51.1 ( 11.7) 32 ( 6.4) 7.3 ( 3) m16 33.6 ( 15.6) 22.8 ( 8.6) 7.5 ( 3) 45.1 ( 3) 38.8 ( 17.5) 5.1 ( 2.4) m19 32.8 ( 13.4) 25 ( 10) 6.8 ( 4.3) 46.7 ( 4.9) 38.1 ( 18) 3.4 ( 1.3) m20 32.8 ( 13.2) 25 ( 9.5) 7 ( 3.8) 51 ( 9) 31.9 ( 10.6) 4.7 ( 1.7) TMG 28.2 ( 9.2) 23 ( 2.1) 6.9 ( 1.7) 41.5 ( 19.4) 24.5 ( 2.8) 5.7 ( 1.9) Error(Tc) Error(T d ) Error(Dm) Error(Tc) Error(T d ) Error(Dm) m5 1.3 (4.7 %) 2.4 ( 10.4 %) 0.6 ( 9.1%) 5.8 ( 13.9%) 10.8 ( 44.1%) 1.7 (29.3%) m9 2.1 (7.4 %) 1.4 ( 6.2 %) 3.9 ( 55.8%) 4.1 ( 10%) 14.6 ( 59.5%) 1.2 (21.4%) m11 4.6 (16.5 %) 2.3 ( 9.8 %) 0.7 ( 10%) 0.6 ( 1.4%) 18.5 ( 75.7%) 0.7 (11.8%) m15 3 (10.5 %) 1 ( 4.5 %) 3.3 ( 48.2%) 9.6 ( 23%) 7.5 ( 30.7%) 1.6 (27.7%) m16 5.4 (19.2 %) 0.2 ( 0.9 %) 0.6 ( 8.2%) 3.6 ( 8.6%) 14.4 ( 58.8%) 0.6 (10.8%) m19 4.7 (16.6 %) 2 ( 8.8 %) 0.1 ( 1.7%) 5.2 ( 12.4%) 13.6 ( 55.8%) 2.3 (41%) m20 4.7 (16.6 %) 1.9 ( 8.4 %) 0 ( 0.0%) 9.5 ( 22.8%) 7.5 ( 30.6%) 1 (17.3%) 222 Informatica 45 (2021) 213–222 D. Vlahek et al. Table 6: The table shows average values and associated standard deviation for parameters extracted from markers at a stimulation intensity of 70 mA. Associated errors were placed below the results. The lowest errors are highlighted. Vastus medialis Rectus femoris Tc(ms) T d (ms) Dm(mm) Tc(ms) T d (ms) Dm(mm) m5 31.3 ( 11.7) 26.5 ( 24.9) 8 ( 3.7) 50.3 ( 19.2) 23.2 ( 7.1) 4.5 ( 1.4) m9 37.6 ( 23.8) 21.4 ( 6.6) 12 ( 5.2) 51.3 ( 10.1) 25.9 ( 6.5) 5.3 ( 1.8) m11 38.1 ( 23.7) 22 ( 7.5) 8.4 ( 2.7) 45.2 ( 5.6) 33.8 ( 12.8) 5.6 ( 1.9) m15 33.3 ( 16.8) 26.1 ( 17.3) 11.4 ( 4.4) 46.1 ( 5.4) 31.8 ( 9.1) 8.4 ( 2) m16 39.8 ( 24) 22.6 ( 8.5) 8.3 ( 2.8) 45.5 ( 3.1) 32.8 ( 13.1) 5.9 ( 1.7) m19 34.8 ( 14.1) 30 ( 23.2) 7.6 ( 4.2) 53 ( 8.3) 23.3 ( 3.3) 3.9 ( 0.9) m20 34.5 ( 12) 30.4 ( 25.3) 7.6 ( 3.6) 46.8 ( 3.4) 27.2 ( 8.5) 5.9 ( 1) TMG 32 ( 19.5) 23.3 ( 2.7) 7.4 ( 2) 48.2 ( 24.4) 24.7 ( 3.1) 6.4 ( 2.3) Error(Tc) Error(T d ) Error(Dm) Error(Tc) Error(T d ) Error(Dm) m5 0.7 (2.2 %) 3.2 ( 13.7 %) 0.6 ( 7.7%) 2.1 ( 4.4%) 1.5 ( 6.1%) 1.9 (30.2%) m9 5.6 (17.5 %) 2 ( 8.5 %) 4.6 ( 61.7%) 3.1 ( 6.4%) 1.2 ( 4.7%) 1.1 (16.5%) m11 6.1 (19.1 %) 1.3 ( 5.8 %) 1 ( 13.6%) 3 ( 6.1%) 9 ( 36.5%) 0.8 (12.7%) m15 1.3 (3.9 %) 2.8 ( 11.9 %) 4 ( 53.3%) 2.1 ( 4.3%) 7 ( 28.4%) 2 (30.9%) m16 7.8 (24.4 %) 0.8 ( 3.2 %) 0.9 ( 11.5%) 2.8 ( 5.7%) 8.1 ( 32.6%) 0.5 (7.4%) m19 2.8 (8.6 %) 6.7 ( 28.6 %) 0.1 ( 1.7%) 4.8 ( 9.9%) 1.4 ( 5.8%) 2.5 (39.2%) m20 2.5 (7.7 %) 7.1 ( 30.4 %) 0.2 ( 2.6%) 1.4 ( 3%) 2.5 ( 10%) 0.5 (7.5%) Table 7: The table shows average values and associated standard deviation for parameters extracted from markers at a stimulation intensity of 80 mA. Associated errors were placed below the results. The lowest errors are highlighted. Vastus medialis Rectus femoris Tc(ms) T d (ms) Dm(mm) Tc(ms) T d (ms) Dm(mm) m5 26.8 ( 7.6) 21.1 ( 13.3) 8.5 ( 3.4) 39.4 ( 12.7) 20.9 ( 10.0) 4.1 ( 1.3) m9 29.7 ( 15.3) 15.2 ( 1.7) 13.1 ( 4.6) 36.8 ( 9.4) 25.2 ( 12.7) 5.7 ( 1.4) m11 32.8 ( 17.2) 15.8 ( 2.3) 9.3 ( 2.3) 35.2 ( 9.1) 24.4 ( 13.2) 4.8 ( 1.8) m15 29.0 ( 14.0) 17.6 ( 6.2) 12.5 ( 3.8) 31.3 ( 9.4) 31.4 ( 11.8) 7.1 ( 2.4) m16 32.2 ( 18.4) 16.2 ( 2.9) 9.2 ( 2.5) 31.5 ( 4.5) 31.5 ( 13.5) 4.9 ( 1.3) m19 30.3 ( 10.7) 20.1 ( 10.9) 8.1 ( 4.0) 35.2 ( 7.7) 25.1 ( 14.6) 3.4 ( 1.3) m20 28.5 ( 10.9) 20.5 ( 11.7) 8.3 ( 3.3) 33.9 ( 5.8) 26.1 ( 13.5) 5.2 ( 1.1) TMG 31.4 ( 19.5) 23.8 ( 3.6) 7.6 ( 2.3) 47.6 ( 24.3) 24.8 ( 3.3) 6.7 ( 2.7) Error(Tc) Error(T d ) Error(Dm) Error(Tc) Error(T d ) Error(Dm) m5 4.6 (14.6 %) 2.7 ( 11.3 %) 0.9 ( 11.7%) 8.2 ( 17.1%) 3.9 ( 15.6%) 2.6 (39.1%) m9 1.7 (5.4 %) 8.6 ( 36 %) 5.4 ( 71%) 10.7 ( 22.6%) 0.4 ( 1.6%) 1 (15.0%) m11 1.4 (4.5 %) 8 ( 33.8 %) 1.7 ( 22%) 12.4 ( 26.1%) 0.4 ( 1.6%) 1.9 (28.8%) m15 2.4 (7.7 %) 6.2 ( 26.1 %) 4.9 ( 64.1%) 16.2 ( 34.1%) 6.6 ( 26.8%) 0.5 (7.1%) m16 0.8 (2.4 %) 7.6 ( 32.1 %) 1.6 ( 20.9%) 16 ( 33.7%) 6.7 ( 27.1%) 1.8 (26.7%) m19 1.1 (3.5 %) 3.7 ( 15.5 %) 0.5 ( 6.4%) 2.4 ( 26%) 0.3 ( 1.4%) 3.3 (48.8%) m20 2.9 (9.2 %) 3.3 ( 14 %) 0.6 ( 8.2%) 13.6 ( 28.6%) 1.3 ( 5.2%) 1.4 (21.4%)