Efficacy of functional electrical stimulation at different frequencies for post-stroke foot drop: a retrospective cohort study

Objective To compare the efficacy and safety of low, medium, and high-frequency functional electrical stimulation (FES) in post-stroke foot drop (FD), aiming to identify optimal frequency parameters for clinical practice. Methods In this retrospective cohort study, 90 patients with post-stroke FD admitted between January 2021–December 2023 were grouped based on received FES frequency: low-frequency (20–30 Hz, n = 30), medium-frequency (31–40 Hz, n = 30), and high-frequency (41–50 Hz, n = 30). All patients received conventional rehabilitation combined with FES. The primary efficacy outcome was the improvement in 10-meter maximum walking speed (10MWS). Secondary outcomes included Fugl-Meyer Assessment for Lower Extremity (FMA-LE) scores and Functional Ambulation Category (FAC), and ankle dorsiflexor muscle strength. Results Baseline characteristics were comparable (all p > 0.05). The medium-frequency group showed significantly greater improvement in 10MWS (0.246 ± 0.095 m/s) versus low (0.154 ± 0.063 m/s) and high-frequency groups (0.145 ± 0.050 m/s) ( p < 0.001). FMA-LE improvement was also superior in the medium-frequency group (8.60 ± 1.99 points; p < 0.001). Ankle dorsi-flexor strength improvement was significantly greater in the medium-frequency group (1.93 ± 0.25 grade) compared to both low (0.97 ± 0.18 grade) and high-frequency groups (1.03 ± 0.18 grade) ( p < 0.001), with a favorable trend also observed in FAC. Adverse event incidence was low (3.3%) and similar across groups ( p = 0.355). Subgroup analysis indicated consistent medium-frequency efficacy across stroke types. Conclusion In this retrospective comparative study, medium-frequency (31–40 Hz) FES was associated with optimal efficacy and safety outcomes for post-stroke FD, showing significantly greater improvement in walking speed and lower limb function without added risk. These findings suggest it as a promising parameter for clinical evaluation, though verification by prospective trials is warranted.