Challenges in the application of Semmes-Weinstein monofilament testing: Practitioner-related variables

Abstract

Objectives

The Semmes-Weinstein monofilament (SWM) test is commonly used to evaluate tactile sensation in individuals with neurological or orthopedic conditions. This study aimed to examine practitioner-related factors affecting SWM testing, particularly focusing on adherence to protocol guidelines and the accuracy of force-controlled application, and to assess the intra-rater reliability of the measurements obtained.

Patients and Methods

Fifty-three inexperienced occupational therapists, trained in SWM application, participated in the study. Standardized tests were conducted using three monofilaments (4.31/2 g, 4.56/4 g, 5.07/10 g). A specialized instrument measurement system recorded maximum buckling forces (Max F), contact durations (T), and intervals between applications (L). Participants applied each filament perpendicularly to the sensor three times consecutively with 1.5-second intervals. Intrarater reliability was assessed using the intraclass correlation coefficient (ICC).

Results

None of the participants achieved the exact prescribed buckling forces. Significant differences were observed between the prescribed buckling forces, application times, and intervals (p<0.05). However, each participant showed consistency across repeated trials (p>0.05). ICCs indicated good-to-excellent reliability for Max F, T, and L.

Conclusion

Most errors in SWM testing were due to incorrect buckling force and failure to adhere to application timing. Future research should focus on improving practitioner training and minimizing variability in SWM test performance.

The somatosensory system, encompassing the sense of touch, plays a pivotal role in our ability to perceive and discern the external environment, as well as in safeguarding against potential hazards. The tactile perception of the hand is necessary for conducting daily living activities, including manipulating objects, grasping, and performing fine motor movements. Consequently, assessment of sensory function is essential following hand injury or neurological impairment that may affect tactile sensation. This evaluation is essential for creating effective intervention plans to address resulting challenges.^[1] Sensory evaluation is typically performed using standardized test kits, which are carried out following application protocols.^[2]

The Semmes-Weinstein monofilament (SWM) test is a valuable clinical tool for evaluating tactile sensation, especially in patients with neurological or orthopedic conditions. It comprises 20 monofilaments of varying weights, allowing for the precise determination of touch threshold.^[3] SWM test is reliable, standardized, and cost-effective, making it widely used in assessing sensory perception and monitoring nerve function recovery. Its significant correlations with other diagnostic methods, like nerve conduction studies, enhance its utility, particularly in conditions such as carpal tunnel syndrome.^{[4, 5, 6]}

SWM test is widely recognized as a reliable method for assessing tactile sensitivity.^{[4, 7, 8, 9, 10]} However, studies have indicated instances where the results obtained from this test may exhibit limitations in terms of reproducibility.^[2] These discrepancies in results can stem from instrument-related errors and practitioner-related errors. Despite efforts to minimize instrument-related error in the manufacturing of SWM, variability in outcomes has been observed. Instrument-related errors such as incorrect length, kinking, or fatigue of the filament after repeated use, as well as environmental factors like humidity, ambient temperature, and background noise, have been implicated in contributing to this variability.^[11] Additionally, practitioner-related errors, including the force applied on the monofilament, the positioning of the monofilament during the test, and the level of expertise of the examiner, have been identified as influential determinants of test results. To reduce these sources of error, protocols have been developed for the use of the test.^{[12, 13]} According to the defined test protocol, the test administrator is instructed to touch a monofilament to the surface of the skin from a perpendicular angle, applying pressure just until the fiber buckles, and then removing the monofilament. The filament should be moved slowly towards the skin from a height of about 1 inch, contacting the skin in approximately 1.5 seconds and remaining in place for the same duration. Subsequently, the filament should be removed to the starting position (less than 1 inch above the skin) over a period of 1.5 seconds.^[14]

SWM can be considered force-controlled if applied correctly. However, its controllability diminishes if applied too quickly and bounced against the skin. While instrument-related errors are well-documented in the literature, practitioner-related variables for the test protocol remain unexplored.^[15] Specifically, the consistency of adherence to the testing protocol, including factors such as duration of touch and interval between each application has yet to be thoroughly evaluated.

The study aims to investigate practitioner-related variables particularly focusing on the adherence to the testing protocol and generating prescribed monofilament force accurately. The primary objective is to assess the force values of the monofilament application on simulated skin surfaces. We hypothesize that practitioners may struggle to achieve the prescribed monofilament force accurately, resulting in variations between consecutive touches. Furthermore, we propose a second hypothesis suggesting deviations from the standard application guideline of 1.5 seconds for both the contact of monofilament application and the time intervals between consecutive touches. Through an assessment of these factors’ influence on the testing protocol, the study seeks to enhance the reliability of SWM test in tactile sensitivity assessment.

PATIENTS AND METHODS

Although this was a cross-sectional study, intra-rater reliability was assessed by requiring participants to perform multiple SWM applications within a single session. All research procedures were approved by the Ethics Committee of Hacettepe University (approval no: SBA 23/432, date: 06.02.2024). The procedures followed were consistent with the revised Helsinki Declaration of 2000. All the data for the study were collected between March 2024 and May 2024. All participants provided informed consent, understood the risks and benefits of participating in the study, and were aware that participation was voluntary. They were also assured that their identities would remain confidential.

The study was conducted among recently graduated, inexperienced occupational therapists with no prior professional experience. All participants had received theoretical and practical training in the SWM test during their undergraduate education and had completed a hand rehabilitation course focused on SWM application. At the time of data collection, none had prior routine SWM experience, and their clinical exposure to SWM was limited to training contexts.

All participants had graduated from the same university, approximately two months prior to data collection. Because they were trained within the same undergraduate program, their undergraduate coursework was identical. Instruction on the SWM test was delivered as part of the hand rehabilitation course in the third year of the program; by the time of testing, approximately 1.5 years had elapsed since completion of that course. Following graduation, participants were invited to take part in the study, and data were collected from those who volunteered to participate.

Pre-test protocol

Three different sizes of new SWMs made of nylon (North Coast Medical, Inc., Gilroy, CA) were employed in the study: 4.31 (2 g), 4.56 (4 g), and 5.07 (10 g). These SWMs, selected from the “small handset” of this manufacturer, are widely used to assess whether there is a decrease (Diminished Protective Sensation) or loss (Loss of Protective Sensation) in hand protective sensation. Singh et al.^[16] demonstrated that the inability to perceive the 5.07 (10 g) SWM is linked to clinically significant large-fiber neuropathy. Kamei et al.^[17] suggested that the use of 4.31 (2 g) SWMs is an advantageous clinical test for screening diabetic peripheral neuropathy, providing a rapid and cost-effective screening approach.

Instrument measurement system

The study employed a specialized measurement system to assess the time and buckling force of each filament used in the research. Monofilament buckling force is measured using a single-axis force sensor. The force sensor collected data at a rate of 1000 samples per second (accuracy: 5 mg, signal bandwidth: 0-250 Hz, measurement noise-rms: 2 uV) during each task. The sensor measuring system used in this study was calibrated to ensure that the monofilaments produced the prescribed forces of 2 g, 4 g, and 10 g (e.g., 4.31, 4.56, and 5.07 monofilaments, respectively). Traceable standard weights corresponding to the prescribed monofilament forces (2 g, 4 g, and 10 g) were used. The sensor was placed on a stable, vibration-free surface in a controlled environment to minimize external interference, and the weights were applied incrementally. The outputs were recorded and compared against the expected values. The calibration process also verified that a force of 4.31 generates 2 g, 4.56 generates 4 g, and 5.07 generates 10 g, which aligns with the specifications of the monofilaments used. This calibration was confirmed by an independent expert specializing in sensory measurement devices, who used a calibrated force gauge to verify the forces applied by the monofilaments. The system’s reliability and accuracy were verified prior to testing, ensuring precise force measurements as per the SWM testing protocol. Measurement site is covered with a silicone gel layer (2.2 mm thickness) to decrease initial touch response noise also. Throughout the article, this measuring instrument will be referred to as a sensor.

Test protocol

The participants were questioned about their age and gender. Subsequently, the standard SWM test protocol was reiterated to them. They were instructed to advance one filament at a time perpendicularly to the sensor three times consecutively until they were seen to buckle, with a 1.5-second interval between each application.^[18] The monofilament to be tested was randomly assigned to participants by the researchers. Participants applied it to the sensor three times consecutively upon the “Ready now” command. Then, the test moved on to the next monofilament. A one-minute rest period was provided between each monofilament application. Participants did not have visual access to the computer screen. The highest buckling force during the three consecutive applications of the monofilaments were recorded. Additionally, the duration of monofilament contact time to the sensor and the interval between consecutive touches were documented. Measurements were conducted with participants seated in a comfortable upright position in a quiet room at an approximate temperature of 22 °C. All monofilaments were inspected to ensure standard length.

The variables Maximum buckling forces (Max F) 1, Max F2, and Max F3 represent the Max F of consecutive touches, while T1, T2, and T3 denote the durations of these touches. Additionally, L1 and L2 signify the time intervals between consecutive applications of the monofilament. Figure 1 illustrates the distribution of Max F across trials for each monofilament size. The discrepancies highlight the challenges participants faced in achieving consistent force application.

Figure 1.

Touch duration and buckling force variation over consecutive applications.

Max F: Maximum buckling forces.

Statistical analysis

Data analysis was conducted using IBM SPSS Statistics (version 29), with a significance level set at 0.05. The Shapiro-Wilk test was performed to assess the normality of the data. The results indicated that the majority of the variables followed a normal distribution. The mean and standard deviation (SD) of Max F1, Max F2, and Max F3; T1, T2, and T3; L1 and L2 were provided. One-sample t-tests were conducted to determine the deviation amount from the prescribed monofilament buckling force for each filament. The difference between the Max F and the monofilament touch duration was evaluated using repeated measures analysis, while the time difference between two touches was analyzed using the paired t-test. Intrarater reliability of the maximum forces of each monofilament and touch durations on the sensor was assessed using the intraclass correlation coefficient (ICC). A higher ICC value suggests that the monofilament measurements are not influenced by the specific raters involved. The standard error of measurement (SEM) was calculated to evaluate the stability of each participant’s touch on the monofilament sensor, and the minimal detectable change (MDC) was estimated to determine the smallest amount of detectable change. Based on the 95% confidence interval, an ICC value of <0.5 indicates poor reliability, 0.5 to 0.75 indicates moderate reliability, 0.75 to 0.9 indicates good reliability, and >0.90 indicates excellent reliability.^[19] An a priori power analysis was conducted in G*Power 3.1 for a within-subjects repeated-measures design with three measurements (trials) on the primary outcomes (buckling force and timing variables). Assuming a moderate effect size (Cohen’s f=0.25), α=0.05, power (1-β)=0.80, three repeated measures, and a conservative correlation among repeated measures of 0.50, the minimum required sample size was 43 participants. To ensure adequate precision for reliability estimates, we additionally set a precision-based target for the intra-rater ICC, aiming at a 95% confidence interval half-width ≤0.10 (k=3 repeated measurements per parameter). Under these combined criteria, a total sample of 53 participants was recruited, which exceeds the minimum requirement and provides sufficient power for detecting within-subject effects and for estimating ICCs with acceptable precision.^{[20, 21]}

RESULTS

A total of 53 occupational therapists participated in this study, 5 males and 48 females, with a mean age of 21.73 years (range: 21-29 years, SD: 2.17 years). Forty-six were right-hand dominant, and 7 were left-hand dominant.

Figure 2 presents the mean Max F and T values across repeated trials.

Figure 2.

Mean Max F, T, L values across repeated trials. A) Mean maximum buckling force across three consecutive applications for each monofilament. B) Mean touch duration (T) across three consecutive applications for each monofilament. C) Mean intervals between consecutive applications (L) for each monofilament.

SD: Standard deviation.

Table 1 provides the mean Max F1, Max F2, and Max F3 for each trial. It was observed that none of the participants could achieve the prescribed buckling force for each trial. Although the Max F for each trial were found to be statistically different from the prescribed buckling force for 4.31/2 g (Max F1: p=0.017; Max F2: p=0.054; Max F3: p=0.027), there was no statistical difference between consecutive touches for Max F buckling force for 4.31/2 g (p=0.53). Similarly, for 4.56/4 g, although the Max F for each trial were statistically different from the prescribed buckling force (Max F1: p<0.001; Max F2: p<0.001; Max F3: p<0.001), there was no statistical difference between consecutive touches for Max F buckling force for 4.56/4 g (p=0.352). Likewise, for 5.07/10 g, although the Max F for each trial were statistically different from the prescribed buckling force (Max F1: p<0.001; Max F2: p<0.001; Max F3: p<0.001), there was no statistical difference between consecutive touches for Max F buckling force (p=0.300) (Table 1).

TABLE 1. The results of the maximum buckling force for each trial of SWMs.

-	Max F1 X ± SD	Max F2 X ± SD	Max F3 X ± SD	Max F1 pa	Max F2 pa	Max F3 pa	Max F1-Max F2-Max F3 pb
4.31 (2 g)	1.89±0.29	1.91±0.29	1.89±0.31	0.017*	0.054	0.027*	0.531
4.56 (4 g)	3.72±0.35	3.68±0.30	3.67±0.34	<0.001*	<0.001*	<0.001*	0.352
5.07 (10 g)	9.28±0.73	9.16±0.81	9.09±0.80	<0.001*	<0.001*	<0.001*	0.300

*p<0.05; ^aOne-Sample t-test; ^bRepeated Measure ANOVA.

X: Mean; SD: Standard deviation; SWM: Semmes-Weinstein monofilament; Max F: Maximum buckling force.

Table 2 presents the duration of each application on the sensor (T) and the intervals between applications (L). The results indicate that the application times of all tested monofilaments deviated from the recommended guideline. Both T and L were statistically different from the prescribed time (1500 milliseconds) (p<0.001). The application times (T) showed consistency for 4.31/2 g (p=0.519) and 5.07/10 g (p=0.212), indicating no significant differences between consecutive applications, whereas for 4.56/4 g (p=0.042), a significant difference was found between applications, suggesting a lack of consistency. Similarly, no statistically significant differences were found in the intervals between applications (L) for 4.31/2 g (p=0.112), 4.56/4 g (p=0.151), and 5.07/10 g (p=0.718) (Table 2).

TABLE 2. The results of duration and interval of each application for each trial of SWMs.

-	T1 (ms) X ± SD	T2 (ms) X ± SD	T3 (ms) X ± SD	T1 pa	T2 pa	T3 pa	T1-T2-T3 pb
4.31 (2 g)	673.02±343.96	681.14±355.24	701.73±402.22	<0.001*	<0.001*	<0.001*	0.519
4.56 (4 g)	732.60±416.54	675.96±358.41	695.43±381.03	<0.001*	<0.001*	<0.001*	0.042*
5.07 (10 g)	706.15±399.45	673.05±384.84	683.53±399.43	<0.001*	<0.001*	<0.001*	0.212
-		L1 (ms) X ± SD	L2 (ms) X ± SD	L1 pa	L2 pa	L1-L2 pc
4.31 (2 g)		872.11±364.48	837.64±339.46	<0.001*	<0.001*	0.112
4.56 (4 g)		932.41±551.96	840.22±418.59	<0.001*	<0.001*	0.151
5.07 (10 g)		855.23±368.48	847.89±403.38	<0.001*	<0.001*	0.718

*p<0.05; ^aOne-sample t-test; ^bRepeated measure ANOVA; ^cPaired sample t-test.

X: Mean; SD: Standard deviation; ms: Milliseconds; SWM: Semmes-Weinstein monofilament.

Intra-rater reliability of Max F, T and L

The ICCs and their 95% confidence intervals as well as SEMs and MDCs are presented in Table 3. For Max F values, the ICCs ranged between 0.643 and 0.938, the SEMs between 0.074 g and 0.466 g, and the MDCs between 0.205 g and 1.292 g. These findings indicate moderate to excellent intra-rater reliability, with lower reliability observed for the heaviest monofilament (5.07/10 g) compared to the lighter ones. For T values, the ICC was above 0.9 for all monofilaments, demonstrating excellent reliability and a high level of measurement stability. The corresponding SEM and MDC values were within narrow limits, suggesting minimal measurement error. For L values, the ICCs ranged from 0.716 to 0.961, SEM values ranged from 76.215 to 258.611 ms, and MDC values ranged from 211.257 to 716.833 ms. These results indicate good to excellent reliability, though slightly greater variability was observed for the 4.56/4 g filament. Overall, the results confirm that the measurement parameters of Max F, T, and L demonstrated consistent and reproducible intra-rater reliability across repeated applications. These results are also illustrated in Figure 3, which presents the ICC values (±95% CI) for Max F, T, and L across different monofilament sizes.

TABLE 3. Intra-rater reliability of the SWMs.

-	Max F1 X ± SD	Max F2 X ± SD	Max F3 X ± SD	ICC (95% CI)	SEM (g)	MDC95
4.31 (2 g)	1.89±0.29	1.91±0.29	1.89±0.31	0.938 (0.901-0.963)	0.074	0.205
4.56 (4 g)	3.72±0.35	3.68±0.30	3.67±0.34	0.84 (0.832-0.935)	0.132	0.366
5.07 (10 g)	9.28±0.73	9.16±0.81	9.09±0.80	0.643 (0.442-0.780)	0.466	1.292
-	T1 (ms) X ± SD	T2 (ms) X ± SD	T3 (ms) X ± SD	ICC (95% CI)	SEM (ms)	MDC95
4.31 (2 g)	673.02±343.96	681.14±355.24	701.73±402.22	0.955 (0.928-0.973)	77.882	215.878
4.56 (4 g)	732.60±416.54	675.96±358.41	695.43±381.03	0.968 (0.949-0.980)	68.929	191.062
5.07 (10 g)	706.15±399.45	673.05±384.84	683.53±399.43	0.978 (0.965-0.986)	58.524	162.221
-	L1 (ms) X ± SD	L2 (ms) X ± SD		ICC (95% CI)	SEM (ms)	MDC95
4.31 (2 g)	872.11±364.48	837.64±339.46		0.951 (0.914-0.972)	77.912	215.961
4.56 (4 g)	932.41±551.96	840.22±418.59		0.716 (0.508-0.836)	258.611	716.833
5.07 (10 g)	855.23±368.48	847.89±403.38		0.961 (0.933-0.977)	76.215	211.257

SEM=SD x √ (1-ICC); MDC₉₅ =1.96 x (SEM x √ 2).

X: Mean; SD: Standard deviation; ms: Millisecond; ICC: Intraclass correlation coefficient; SEM: Standard error of measurement; MDC: Minimal detectable change; CI: Confidence interval; SWM: Semmes-Weinstein monofilament.

Figure 3.

ICC with 95% confidence intervals for maximum buckling force (Max F), touch duration (T), and intervals between applications (L) across the three monofilament sizes [4.31 (2 g), 4.56 (4 g), 5.07 (10 g)]. Dots represent ICC estimates and horizontal lines indicate 95% confidence intervals (CIs). Vertical dashed lines mark conventional thresholds for poor-moderate (ICC: 0.50), moderate-good (ICC: 0.75), and good-excellent (ICC: 0.90) reliability.

DISCUSSION

The present findings, in agreement with previous literature, demonstrate that the monofilament application force does not align with the prescribed buckling force. In addition to these results, the findings also revealed that participants did not adhere to the prescribed application time (T) and the interval between applications (L). On the other hand, each practitioner has been able to obtain consistent results from consecutive three trials not only for buckling force but also for application time and interval between applications. We believe that a significant reason for the force being different from the prescribed buckle force is due to this temporal inconsistency.

The results showed that the forces generated consecutively for each of the three monofilaments were statistically different from the prescribed buckling forces. Moreover, the findings indicate that although participants did not produce a statistically significant difference across consecutive applications, they tended to apply less force and deviated from the target values. n the study by Bell-Krotoski and Tomancik^[22], it was demonstrated that the 4.31, 4.56, and 5.07 monofilaments generated forces of 2.062, 3.63, and 11.7 grams, respectively. However, present study’s findings indicate that subjects fell below the desired threshold level of force generation.^[22] Similar to our findings Bell-Krotoski and Buford^[23] found that light filaments may occasionally fail to exceed the desired threshold- sometimes being too light- thus requiring multiple applications. On the other hand, in Chikai and Ino^[24] study, where he tested ten consecutive applications of the 5.07 monofilament, it was noted that the buckling force decreased by more than 10% over the ten compressions, with a statistically significant difference between the first and tenth application. It has been found in instrument tests that while the lightest monofilaments may not always exceed the required threshold, one out of three applications consistently reaches the intended threshold. However, it is also clearly stated that consecutive stimulus applications significantly alter the tests detection threshold.^[18] Furthermore, it is evident from our study that all three applications are inadequate in achieving the desired force and are not statistically different from each other. Additionally, we are aware that monofilaments provide constant forces from the moment they are bent until they are released from the skin.^[18]

As stated in the study by Bell-Krotoski and Buford^[23], when applied for approximately 1.5 seconds as prescribed in clinical testing, the application force signal shows an immediate smooth increase in force upon the application of the monofilament, a relatively consistent force with minimal or no vibration while the monofilament is held, and an immediate smooth termination of force upon lifting of the monofilament. When applied for approximately 1.5 seconds, held for approximately 1.5 seconds, and lifted within 1.5 seconds, the monofilaments produce repeatable forces within a relatively small range in milligrams for the smallest filaments. However, the results showed that all holding (T) and lifting (L) durations specified in the standard protocol differed from the prescribed times for all monofilaments. As mentioned by Bell-Krotoski^[25], if applied too quickly less than 1.5 seconds and “bounced” against the skin, the force can increase beyond the desired stimulus. The monofilament force of application will spike and overshoot. These findings do not confirm this claim. The average contact times for all monofilaments were below 1.5 seconds, yet the applied forces remained below the prescribed buckling force. Furthermore, although deviations in T and L from the prescribed times were observed, they were consistent within themselves, showing no differences across repeated measurements. This suggests that each tester applied the procedure at their own pace.

It is evident from the literature that hand-held testing instruments, such as SWM rely on manual application of touch stimuli. This manual application introduces significant variability in the force exerted by different examiners, thereby resulting in restricted repeatability and consequently limited reliability of the stimulus.^[26] The reproducibility of successive continuous stimuli is at the mercy of the concentration and manual dexterity of the clinician.^[27] In her study, Tena et al.^[28] reported fair intra-observer reliability for von Frey monofilaments; however, electronic von Frey demonstrated good intra-observer and interobserver reliability. On the other hand, Vora’s review indicated that SWM 5-piece sets have low interrater reliability in Charcot-Marie-Tooth patients, whereas the 20-piece set showed moderate reliability in individuals with spinal cord injury and neuropathic pain.^[29] Novak et al.^[9] also demonstrated inter-rater reliability of ICC 0.965 in 30 subjects, including those with peripheral nerve injury, blind Braille readers, and healthy controls. However, it’s important to note that all these studies relied on measurements based on patient self-perception. Although all reliability studies in the literature have been conducted on the subject, present study carries the unique feature of presenting measurement results obtained from a sensor independent of interpretation. The findings showed excellent interrater reliability for the 4.31 monofilament, good reliability for the 4.56, and moderate reliability for the 5.07.

The strict adherence to the 1.5-second application and interval rule in SWM testing, while emphasized in the protocol, may not hold substantial clinical significance. We believe this duration, specified in the SWM application manual, could potentially be reconsidered or even excluded from future guidelines. The application of SWM testing at precise 1.5-second intervals requires the use of tools like a timer, which may not be practical in most clinical settings. Despite deviations from the 1.5-second rule, our findings demonstrate that even inexperienced therapists achieved acceptable inter- and intra-rater reliability, with ICCs consistently greater than 0.64. This suggests that minor variations in the application and interval times may not significantly compromise test reliability or sensory threshold detection. These results provide evidence that the clinical outcomes of SWM testing may not be heavily influenced by strict adherence to the 1.5-second timing, particularly in practical, real-world scenarios.

The first limitation of this study was that it included recently graduated, inexperienced occupational therapists. This restricts the generalizability of the findings to more experienced clinicians. The second limitation concerns the potential influence of application distance on stimulus control. Although previous studies have suggested that distance may affect the precision of the applied stimulus,^[23] the SWM application distance was not measured in this study. The third limitation is that all measurements were obtained during a single session, preventing an evaluation of long-term reliability. Finally, the force measurements were conducted on a simulated skin surface. Although this surface closely resembled the mechanical properties of real skin, some differences from actual patient applications may exist.

The strength of our study lies in its ability to provide valuable insight into the practitioner-related challenges encountered during the SWM test. By focusing on inexperienced therapists, it highlights how clinical experience influences test accuracy and adherence to standardized protocols. The use of a sensor-based, objective measurement system under controlled conditions allowed precise quantification of application force and timing, minimizing subjective bias. Furthermore, the study emphasizes the importance of integrating structured SWM training particularly regarding contact duration and force control into undergraduate education. These methodological and educational aspects enhance the rigor of the study and contribute meaningful evidence toward improving training strategies and the reliability of SWM testing in clinical practice.

In conclusion, the present study highlights the importance of protocol adherence and precise force application in SWM testing for tactile sensitivity assessment. Despite efforts to standardize testing procedures, our findings reveal deviations from prescribed application times and force levels among study participants, potentially impacting the reliability of results. While consistency within study participants was observed, deviations from standard protocols were evident. These deviations highlight the need for ongoing training and vigilance in adhering to established testing guidelines. Moreover, the findings highlight the need for further research to develop strategies for improving the reliability and accuracy of SWM testing, particularly through addressing practitioner-related variables. Additionally, future studies involving experienced hand therapists may provide valuable insights into the practical implementation of SWM testing in clinical settings, thereby advancing the effectiveness of sensory evaluation and intervention planning for patients with neurological or orthopedic conditions.