This study investigates the dose-response effectiveness of focused ESWT on post-stroke ankle plantar flexor spasticity. Our within-group analysis revealed significant improvements in key clinical measures, such as the MAS, PROM, TUG test, and Barthel Index, in the double ESWT group throughout the follow-up period. The between-group analysis highlighted the superior performance of the double ESWT group, especially in reducing TUG Test times, improving the Barthel Index at the 24-week mark, and demonstrating an early reduction in muscle stiffness as shown by strain elastography. The GEE analysis further confirmed the superiority of the double-dose group in the TUG test, Barthel index, and strain elastography, suggesting a potential dose-response relationship. To our knowledge, this is the first prospective, randomized, double-blinded clinical trial to explore the optimal dosing and dose-response effectiveness of ESWT on post-stroke ankle plantar flexor spasticity.

Our study unveiled a significant improvement in MAS in the double ESWT group over the study period. The MAS did not significantly change after treatment in the control ESWT group (Table 2). In previous studies, the MAS has been a primary tool for assessing lower limb spasticity, with ESWT treatments leading to significant reductions in MAS scores. The MTS and Tardieu angles are utilized to evaluate spasticity changes [19,20,21, 28, 29, 37]. Notably, Wu et al. reported a 35% improvement in the Tardieu angle [29], while Aslan et al. observed a 29.8% improvement in the spasticity angle as measured by the Tardieu scale [28]. In our research, a significant decrease in spasticity was evident in the double-dose group, which aligned with the marked reduction in MAS reported in earlier studies [19,20,21, 28, 29, 37]. There was no significant change observed when employing the MTS in our study. This may be due to the lack of standardized protocols regarding test position, speed of stretch, number of stretch repetitions, and testing time [33, 38]. Variations in the stretch velocity and frequency, patient posture, and the nature of the reflexes measured by MAS and MTS could lead to these differences in results observed in our study [33].

The treatment and total number of sessions varied widely in previous research, including a single application, weekly sessions spanning three weeks, and twice-weekly sessions over two weeks [19, 21, 28, 29, 37]. The dose-dependent effectiveness observed in our study aimed to reinforce the association between higher energy flux densities in ESWT and more favorable therapeutic outcomes. It also highlighted the potential for optimizing ESWT parameters to improve the management of lower limb post-stroke flexor spasticity.

Our study demonstrates that ESWT has a beneficial impact on the TUG test outcomes. Within the double-dose ESWT group, there was a marked and statistically significant enhancement in TUG test performance. This group also outperformed the control group at all follow-up intervals, with the GEE analysis validating better results in those who received the double dose. The TUG test is a widely recognized measure for evaluating functional mobility and balance abilities [39]. Our consistent findings across different analyses highlight the efficacy of ESWT in improving mobility as measured by the TUG test and suggest the benefits of double-dose ESWT over 24 weeks. This sustained effect contrasted with the findings of Radinmehr et al., who reported a minimal, clinically insignificant 9.6% improvement after ESWT [21]. In comparison, our study revealed long-term improvements beyond an immediate response. Other research demonstrated significant increases in walking speed post-ESWT, as measured by the 10-meter walk test [40]. Conversely, Wu et al. found no improvement in the 10-meter walk test after an 8-week follow-up [29]. These differences could be attributed to stroke-related gait disturbances, often caused by spasticity and restricted ankle dorsiflexion [41].

Our research documented a significant increase in ankle dorsiflexion among those in the double-dose ESWT group, as measured by PROM, which likely contributed to their improved mobility. Our PROM of ankle dorsiflexion results were similar to other studies assessing ROM alterations post-ESWT [21, 42]. The observed decrease in intrinsic muscle stiffness and increased tissue extensibility due to ESWT might facilitate an improved PROM [29]. However, the divergent assessment tools and protocols across various studies lead to inconsistent results concerning the effect of ESWT on the gait pattern of people who have experienced stroke [19, 21, 29]. Therefore, future research should employ standardized methods and assessment instruments for a definitive evaluation of ESWT’s effects on gait performance among stroke survivors.

In our study, both groups showed notable improvements in the Barthel Index, highlighting ESWT’s potential to significantly enhance ADLs. This aligned with Taheri et al.’s findings of significant enhancements in the lower extremities functional scale [19]. Additionally, Aslan et al. discovered that while increased lower extremity function scores of the Modified Barthel Index were not initially evident, they became significant by the sixth week [28]. Furthermore, our between-group comparisons revealed pronounced improvements in the Barthel Index for the double-dose ESWT group throughout the follow-up period compared to the control ESWT group. The GEE analysis confirmed the superior performance of the double-dose ESWT group in the Barthel Index, indicating the benefits of ESWT on ADL functions over the whole follow-up period. Our findings suggested a dose-response relationship between ESWT and ADLs. Such outcomes could provide stroke survivors with improved functional independence and enhanced overall quality of life [28].

The muscle tested softer based on strain elastography after double-dose ESWT treatment compared to the control ESWT treatment in the early stage, but this difference was not observed in the long-term follow-up. This provides insight into ESWT’s physiological impact on muscle properties. Lee et al.‘s research employed ultrasound methods to track post-ESWT alterations, uncovering reductions in Achilles tendon length, muscle thickness, and pennation angle and an increase in muscle fascicle length. These changes were most significant at the four-week follow-up [37]. Similarly, Aslan et al. observed improvements in the muscle elasticity of the plantar flexor muscles in both the ESWT and control groups, but a marked improvement in clinical spasticity measures solely in the ESWT group [28]. Our previous review unveiled the commendable reliability of elastography to evaluate PSS, validated through its correlation with clinical measurements, and monitor the therapeutic response and efficacy of targeted muscles [43]. Our results underscored ESWT’s effect on the early decrease of muscle stiffness and muscle mechanics, leading to benefits in both clinical and elastographic evaluations. The consistency of our elastography findings with previous research highlights the importance of imaging techniques in assessing the impact of ESWT on muscle characteristics. This elucidates areas for further investigation, such as how ESWT may alter muscle structure and function, particularly post-stroke.

In our study, the primary outcome, MAS, showed significant improvement within the double-dose ESWT group but not between the groups, while secondary outcomes like the TUG test showed significant improvements both within and between groups. One possible explanation for this discrepancy is the effects of traditional rehabilitation, which both groups received, potentially masking the specific effects of ESWT and leading to non-significant differences in MAS between groups. The essential therapies to reduce PSS were traditional rehabilitations including range of motion exercises, muscle stretching and strengthening, stance and balance training, core stability exercises, gait training, functional training, the use of physical modalities, and orthoses [31]. Additionally, MAS, despite being widely used, has limitations due to its six-level ordinal scale, which might lack sensitivity to detect subtle changes in spasticity [44]. Furthermore, MAS cannot distinguish between dynamic shortening (exaggerated reflexes or clonus) and fixed shortening (stiffness or contracture) of a muscle [45]. In contrast, the TUG test provides a continuous measure, making it more sensitive and robust against masking effects from co-interventions. It detects smaller changes in functional mobility and provides a more reliable assessment of functional gains [46].

The strengths of this study include its double-blind design and comprehensive 24-week follow-up period. Previous studies typically have had a 12-week follow-up period. An extended follow-up allows for the assessment of ESWT’s long-term effects and sustained impacts. Our variety of assessment tools, including the MAS and Tardieu Scale for spasticity, the TUG Test for functional mobility, the Barthel Index for ADL, and elastography for examining muscle properties, further enriched our findings. The use of elastography added a novel dimension by evaluating the intrinsic and elastic structures of spastic muscles, offering a comprehensive understanding of ESWT.

This study had some limitations. First, extended treatment regimens may yield greater or more durable outcomes. Future studies should explore the effects of various numbers of ESWT sessions to identify optimal treatment strategies for sustained therapeutic results. Second, the study’s sample size, while adequate for preliminary exploration, could be increased in future research to improve applicability and provide further insight into ESWT’s effectiveness across diverse patient populations. Third, the variation in participants’ post-stroke phases was complex, suggesting the need to stratify participants based on their post-stroke timing for customized treatment protocols. Fourth, traditional rehabilitation may have masked the effects of ESWT, leading to non-significant differences in the primary outcome. Addressing these limitations is essential to advancing our comprehension of ESWT’s role in post-stroke rehabilitation and optimizing its clinical application.

The findings of our study indicate that double-dose ESWT provides better functional improvements compared to the standard single-dose ESWT, although both doses resulted in similar reductions in spasticity. Therefore, double-dose ESWT could be a potential choice for clinicians aiming to achieve better functional outcomes in patients with post-stroke ankle plantar flexor spasticity. Future research should explore varying frequencies, durations, and intensities of ESWT to determine the most effective parameters for treating post-stroke spasticity. Additionally, investigating the molecular mechanisms underlying the observed improvements could provide deeper insights into the treatment’s efficacy. Comparative analyses with other modalities such as botulinum toxin injections, physical therapy, or emerging technologies like repetitive transcranial magnetic stimulation could offer a comprehensive perspective on integrating ESWT into broader therapeutic practices. Developing an innovative artificial intelligence tool using ultrasound imaging for assessing spasticity, ROI identification, and 3D visualization holds promising potential to guide anti-spastic treatments and enable precise analysis of treatment effectiveness.