## 4 Discussion
### Clinical Measurement Instruments  
The following clinical assessment instruments were used in the studies: the Modified Ashworth Scale (MAS) [17; 20; 29; 31; 33], the Modified Modified Ashworth Scale (MMAS) [28; 29; 30], the combination of the MMAS with BioTone(tm) [17; 20], the Montreal Spasticity Measurement (MSM) [32], and the Tone Evaluation Scale [31]. The MAS or its modification was the main clinical measure of spasticity used in the studies assessed, with the exception of the studies by [PERSON] et al. [31] and [PERSON] et al. [20], which claimed to assess muscle tone with the same tool. Its application involves assessing the resistance, felt by the examiner, of a distal segment, which is passively moved from an initial position to a final position [18; 32]. The MMAS was later published in 2006 and aimed to improve the reliability of the MAS [30]. Both are practical and easy to apply; however, despite the proposed modification [33], it is still described as a subjective scale [17]. [PERSON] et al. [22] defined spasticity as involuntary muscle activity induced by stretching velocity as part of the neural contributions to increased resistance perceived during passive muscle stretching. In the studies by [PERSON] et al. [28], [PERSON] et al. [29], [PERSON] et al. [30], and [PERSON] et al. [33], the proposed scales, which have already been identified, do not consider the speed factor, as they only assess the component of muscle tension in response to passive movement, thus not discriminating between the known neural and non-neural contributions of tone [22]. Furthermore, it is known that this component of muscle tension to passive stretching is solely related to the non-neural mechanical response [6]. There is also the fact that the identified scales indicate a result recorded by the examiner based on subjective perception [6; 38] with information about the properties of muscle tissue [22]. These scales therefore seem to have limitations in terms of construct, reliability, sensitivity, quantification, and objectivity. This information could serve as the basis for the development of measurement tools with better defined psychometric properties and objectivity. Given the specificity of the [PERSON] et al. [31] study that applied botulinum toxin to the lower limbs, they considered it relevant to add a specific scale that could measure the results of their intervention to provide more information. They complemented the MAS evaluation of spasticity with the Tone Evaluation Scale in the hip adductors to accomplish their study aim. To reduce potential subjectivity and improve the objectivity of the assessment, [PERSON] et al. [17] and [PERSON] et al. [20] used a sensor system concomitantly with the evaluation by passive stretching of muscle structures to quantify passive muscle resistance more objectively in a clinical context. Thus, the BioTone(tm) system, that incorporates a two-channel EMG system and a single degree of freedom fibre-optic goniometer, was used in combination with kinematic and electromyographic evaluations [17]; the system was demonstrated to be a reliable and valid method for enhancing the information obtained about neural contributions and non-neural characteristics that define muscle tone [22]. However, its large-scale use in clinical practice is limited due to the need for continuous technical training and maintenance and specific equipment that could be expensive [17]. A potential solution is the development of simple and less expensive methods that retain the reliability and validity of these instruments while making them more accessible. In line with that described, [PERSON] et al. [33] proposed a low-cost instrument to quantify spasticity using inertial data collected with a portable device equipped with sensors, a three-axis accelerometer, a three-axis gyroscope, and a three-axis magnetometer, and this system exhibited characteristics compatible with the MAS. This form of assessment, in addition to being less expensive, is also simpler and more accessible [33].