# MScope: A Reliable Battery for Functional Status Assessment in Multiple Sclerosis
## 4 Discussion
However, similarly to MVICSQ and UMVICEXT_L, handgrip strength demonstrated statistically significant inter-day differences, being the only neuromuscular variable to show such significant variations (Figure 4). Nevertheless, no significant differences were observed in heteroscedasticity tests (Supplementary File S2), and although the bias identified in the Bland-Altman analysis was statistically significant, it is not clinically relevant (1.34 kg). The observed variability in these neuromuscular tests may be attributed to learning effects given the absence of familiarization with the tests. Alternatively, it may be attributed to daily fluctuations such as fatigue and motivation, which are specific characteristics of the MS population. Additionally, slight variations in the technique may also influence force production. It is worth noting that, although the test battery includes the measurement of both GRF and MVIC in the squat exercise, GRF can be measured for each leg individually, enabling reliable asymmetry analysis without requiring a separate unilateral test for each leg. A unilateral test, while validated [49], demands higher balance and may require extensive familiarization, potentially reducing its reliability. However, GRF measurement requires complex and less-accessible equipment. Therefore, measuring GRF is not essential for future test application, as inter-leg asymmetry can also be assessed using a unilateral leg extension exercise, which is safer and simpler for PwMS. Future research should focus on the reliability of unilateral strength assessments in PwMS, particularly about measuring inter-limb asymmetries. Evaluating asymmetrical force output may provide valuable insights into neuromuscular dysfunctions and compensatory strategies within this population [3]. As inter-limb strength disparities are associated with increased injury risk and reduced functional capacity, understanding the reliability of unilateral strength measures could enhance the utility of these tests in both clinical and research settings [50]. Furthermore, establishing robust protocols for assessing unilateral strength could aid in developing targeted rehabilitation strategies that address specific functional deficits in PwMS. The use of ultrasound imaging as a structural assessment tool for PwMS has recently been proposed by [PERSON] et al. [9], offering a practical alternative to MRI or DXA for regularly monitoring muscle health. This method is promising for tracking sarcopenia, a concern in MS due to inactivity, neurogenic atrophy, and metabolic changes [51,52]. Muscle thickness and cross-sectional area measurements obtained via ultrasound serve as reliable indicators of muscle mass and functional decline [52,53]. Reviews have shown ultrasound's reliability in muscle size assessment across various health conditions, especially in the VL and RF muscles with ICCs ranging from 0.72 to 1.00 in older adults [53]. Similarly, [PERSON] et al. [54] reported excellent inter- and intra-rater reliabilities for muscle thickness in younger populations (ICCs: 0.91-0.99), supporting ultrasound's applicability across different age groups. In this study, the muscle thickness of the VL and RF was assessed through ultrasound in MS patients, marking the first analysis of its reliability within this population. The results showed excellent intra-day reliability (ICCs: 0.978-0.998), indicating minimal measurement error, and strong test-retest reliability (ICCs: 0.933-0.973). This positions ultrasound as a robust tool for tracking muscle health, especially important for PwMS facing sarcopenia and dynapenia as contributing factors to frailty. The primary limitation of this study lies in the narrow disability range of the participants, as all patients presented with relatively low levels of disability (EDSS score \(<\) 4). This restricts the applicability of our findings to patients with moderate-to-severe disability levels.