Discussion
This study investigated the reliability of easy-to-implement upper limb assessments for muscle mechanical properties, manual dexterity, pressure pain thresholds, active range of motion, and maximal isometric strength, considering both absolute values and asymmetries between sides, as well as correlations between tests to determine their interrelationship. The results indicated ‘good’ to ‘excellent’ reliability for absolute values and ‘moderate’ to ‘good’ reliability for asymmetries. Although some intra-test correlations were observed, no inter-tests ‘strong’ correlations were found consistently. These findings indicate that a multimodal sensorimotor assessment test battery could provide rehabilitation professionals with valuable information to guide their monitoring of subjects with MSD in the upper extremities.

Previous research has investigated intra-limb reliability in healthy adults across various parameters of the forearm and hand. Concerning myotonometry variables ( i.e ., oscillation frequency, dynamic stiffness, and logarithmic decrement), consistent ‘excellent’ reliability values were observed for forearm muscles, and specifically for the extensor carpi radialis brevis muscle ( Çevik Saldıran, Kara & Kutlutürk Yıkılmaz, 2022 ). Similar reliability was also observed for the completion time of the Nine Hole Peg test, which has previously demonstrated ‘good’ to ‘moderate’ reliability and presenting faster performance on the second day compared to the first day ( Temporiti et al., 2022 ), probably due to a learning effect. Moreover, the dominant hand performed faster than the non-dominant hand ( Bachman et al., 2023 ). Therefore, to employ the Nine Hole Peg test effectively, it may be advisable for subjects to undergo a habituation session, or alternatively, consider discarding the first trials altogether.

Equally, pressure pain thresholds in healthy adults exhibited similar ‘good’ to ‘excellent’ reliability as in previous studies ( Pedersini et al., 2020 ). With regards to active range of motion, previous studies showed ‘excellent’ reliability when assessing wrist extension and flexion ( Hanks & Myers, 2023 ) as was found in this study. However, this study revealed higher ICC values for maximal isometric strength of the wrist extensors compared to previous studies ( Romero-Franco et al., 2019 ). This discrepancy could be attributed to the stabilization of test performance using a strap, a unique approach in this study that has been shown to enhance measurement repeatability ( Custódio et al., 2023 ).

Numerous studies have evaluated asymmetries as an outcome measure ( Baldursdottir et al., 2020 ; Gutiérrez-Espinoza et al., 2022 ; Jiménez-Del-Barrio et al., 2022 ; Burdukiewicz et al., 2020 ; Pradas et al., 2022 ; Bravo-Sánchez et al., 2019 ), although the calculation methods employed sometimes deviate from current recommendations ( Parkinson et al., 2021 ), potentially introducing biases ( Bailey, Sato & McInnis, 2021 ). However, only few studies have explored the reliability of asymmetry assessments ( Howe et al., 2020 ; Pérez-Castilla et al., 2021 ), but none have done so specifically for the hand, forearm, or upper limb. When assessing changes over time, interventional or prospective studies frequently rely solely on interpreting p -values ( Andrade, 2019 ), overlooking the necessity of contextualizing the magnitude of these changes by comparing them to reference values such as SEM or MDC ( Furlan & Sterr, 2018 ). Determining whether the progression over time exceeds the measurement error values would aid in evaluating the clinical relevance of the recovery process and treatments used.

While certain variables, like the active range of motion, possess raw or absolute reference values approximating normality ( Soucie et al., 2011 ), these values may not apply to individuals with physical-anatomical variations. For instance, for strength assessment, normalizing values by weight or body mass index ( McGee et al., 2020 ) could complicate its interpretation and practical application. In this context, a notable advantage of employing asymmetry assessments is the practical relevance in offering clinically significant insights into a patient’s or worker’s functional status, without requiring a previous reference measurement for comparison. However, in athletes, where reference and follow-up measurements are common throughout the season, asymmetries can be considered adaptive in unilateral sports ( Ellenbecker et al., 2002 ). Therefore, asymmetries should not be assessed in isolation but considered within a multidimensional context and considering the characteristics of the study population. For example, this study demonstrates that in a healthy population, the dominant side tends to outperform the non-dominant side in terms of strength and speed during fine motor skills.

The lower ICC values obtained for asymmetry assessments compared to raw values for both the non-dominant and dominant sides were to be expected as the asymmetry index includes the variance across time of two measurements instead of one. On the contrary, considering their acceptable reliability, asymmetry values should be interpreted with a conservative clinical perspective. In other words, this indicates that more substantial variations would be required to attribute the observed changes to factors other than measurement error, potentially indicating genuine improvement over time. In addition, it is worth noting the absence of systematic error between sessions for the values of the asymmetries. Consequently, rehabilitation professionals are advised not to limit their assessments and recordings to the affected side alone but to conduct a bilateral assessment, thereby obtaining a more comprehensive understanding of their clients’ condition and progression.

The present study revealed ‘strong’ to ‘moderate’ positive intra-variable correlations like pressure pain thresholds, myotonometry parameters of frequency and stiffness, as well as the total active range of motion, active extension, and flexion range of motion. Nonetheless, consistent inter-variable correlations were largely absent among the multimodal variables, indicating each variable offers independent information, and potentially advocating for their inclusion in a comprehensive assessment of upper limb MSDs. An exception to this pattern was observed anecdotally on the dominant side, where ‘moderate’ positive correlations consistently emerged between myotonometry parameters of decrement and the active flexion range of motion. This hints at a potential relationship between increased elasticity and enhanced flexibility, suggesting that greater elasticity may contribute to improved flexibility and vice versa ( Miyamoto & Hirata, 2019 ). Interestingly, ‘moderate’ negative correlations were identified between the maximal isometric strength of wrist extensors and the active total and flexion range of motion. This finding indicates that individuals with higher strength in the wrist extensors tend to exhibit reduced active range of motion in flexion, possibly due to heightened passive resistance from antagonist muscles ( Nagano, Uoya & Nagano, 2019 ). Overall, the intra-variable correlations and the lack of inter-variable correlations advocate for a streamlined sensorimotor assessment protocol, potentially involving a single parameter from each variable ( e.g ., pressure pain threshold, maximal isometric strength, active range of motion and manual dexterity). Such an approach could prove sufficient to evaluate the clinical progression of the sensorimotor profile over time while minimizing assessment duration.

The main strength of this study is the implementation of a systematic assessment protocol to minimize the influence of confounding factors, controlling room conditions, and maintaining consistency in the timing of assessments. Additionally, providing MDC values at both 95% and 90% for both raw values and asymmetries offers greater utility to researchers and clinicians for monitoring improvements and calculating sample sizes. However, a primary limitation of this study is the utilization of data from a healthy volunteer cohort. Nonetheless, it can still establish reference values for assessing a normal range of asymmetries in clinical research or practice. Future research should apply this test battery to patient populations with MSD in the upper extremity to assess its responsiveness, accounting also for contextual and psychosocial factors, to evaluate its clinical feasibility.