Dose-response relationship between isokinetic strength training intensity and lower limb spasticity improvement in stroke patients: a retrospective cohort study

Background Post-stroke spasticity (PSS) significantly impairs motor function recovery and quality of life in stroke survivors. While isokinetic strength training has demonstrated efficacy in neurological rehabilitation, the optimal training intensity for spasticity management remains unclear. This study aimed to investigate the dose-response relationship between different isokinetic training intensities and lower limb spasticity improvement in stroke patients. Methods This retrospective cohort study analyzed medical-record data from 392 stroke patients with lower limb spasticity who received rehabilitation therapy at our institution between January 2021 and December 2023. Patients were categorized into four groups based on isokinetic training intensity: control (standard rehabilitation only, n = 98), low-intensity (30% maximal voluntary contraction [MVC], n = 98), moderate-intensity (50% MVC, n = 98), and high-intensity (70% MVC, n = 98). The primary outcome was change in Modified Ashworth Scale (MAS) scores at 8 weeks. Secondary outcomes included Fugl-Meyer Assessment Lower Extremity (FMA-LE), Berg Balance Scale (BBS), 10-Meter Walk Test (10MWT), and isokinetic peak torque measurements. Covariate-adjusted and sensitivity analyses were performed to address confounding by indication. Results At 8 weeks, all groups demonstrated significant improvements from baseline (all P < 0.001). The high-intensity group achieved the greatest MAS reduction (1.07 ± 0.36 points), followed by moderate-intensity (1.02 ± 0.29), low-intensity (0.69 ± 0.48), and control (0.20 ± 0.45) groups (F = 95.789, P < 0.001, η 2 = 0.425). These associations remained significant after adjustment for baseline covariates (all adjusted P < 0.001). The difference in MAS reduction between the moderate- and high-intensity groups was not statistically significant (1.02 versus 1.07 points, P = 0.813). Linear dose-response relationships were observed for all outcomes (all R 2 > 0.40, P < 0.001). Between-group comparisons revealed significant differences between all training intensities for FMA-LE improvement (high: 7.23 ± 1.92; moderate: 5.64 ± 1.89; low: 3.48 ± 1.92; control: 1.27 ± 1.72 points; P < 0.001). Conclusions This study demonstrates a significant dose-response relationship between isokinetic strength training intensity and lower limb spasticity improvement in stroke patients. Higher training intensities (50%–70% MVC) were associated with superior outcomes across all measures, although no additional antispasticity benefit was demonstrated at 70% versus 50% MVC, suggesting that structured progressive resistance training may be incorporated into comprehensive post-stroke rehabilitation programs.