Effects Of Single Bouts Of Kilohertz- Versus Low-Frequency Electrical Stimulation Of Wrist Extensors In Stroke Patients

Purpose: To compare the effects of single bouts of 1.0 kilohertz- (50 Hz modulation frequency) versus low-frequency (50 Hz) biphasic rectangular pulsed current for electrical stimulation of the wrist extensors on stimulation efficiency, electrically-induced force (EIF), discomfort, and muscle fatigue in patients with subacute stroke with arm paresis. Methods: 21 participants with stroke [65 ± 12 years; 175 ± 11 cm; 88.5 ± 19.5 kg; 56 ± 33 days since stroke; 17 ischaemic stroke; maximal voluntary isometric contraction (MVIC) of the affected (50 ± 29 N) and unaffected hand; 99 ± 32 N; 8 female] underwent kilohertz- and low-frequency stimulation in a randomized order on separate days (48 h wash-out). Electrically induced force [N] and discomfort [numerical rating scale, 0-10] were measured as the stimulation intensity gradually increased, starting with the first measurable force, with a maximum of 12 steps (1 mA increments, 8 s stimulation,60 s rest). Muscle fatigue was measured as the decrease in force [N] during 30 repetitions at an intensity of 1.25 times the first measurable force. The primary outcome was stimulation efficiency (electrically induced force /stimulation intensity). Linear-mixed-effects models were used to analyze outcome measures. Results: Low-frequency stimulation showed significantly higher stimulation efficiency [mean difference0.14 (95 % confidence interval: 0.01 to 0.27 N/mA), p = 0.031]. However, current type did not significantly affect electrically induced force, perceived level of discomfort or muscle fatigue (p > 0.005). Conclusion: Our findings suggest that low-frequency stimulation is more efficient than Kilohertz frequency stimulation. However, both types showed similar effects on force, discomfort, and fatigue. Given the variability in individual responses and potential therapeutic benefits of each current type, therapists should consider combining both current types and make individual decisions when selecting stimulation parameters. This work was supported by the Federal Ministry for Economic Affairs and Energy (Germany; BMWi) under Grant ZF4478606TS9