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Background Transcutaneous electrical stimulation (TES) has been explored as a potential non-CPAP therapy for patients with obstructive sleep apnoea (OSA). However, limited data exist regarding its effects on upper airway muscle function and fatigue. This study used the tibialis anterior (TA) as a surrogate muscle to investigate the impact of TES on skeletal muscle fatigue.Methods Ethical approval was obtained from King’s College London Research Ethics Committee (Ref: HR/DP-24/25–46029). TA isometric maximum voluntary contraction (MVC) force was measured before and after fatigue using a forceplate attached to the foot. Fatigue was induced by 15 minutes of continuous TES from a constant-current stimulator at 30 Hz, 250 μs pulse width via 4×4 cm surface electrodes. Stimulation intensity (1–100 mA) was titrated to visible contraction. The TA force-frequency relationship was assessed pre- and post-fatigue via one-second trains of stimuli (1, 5, 10, 20, 30, 50, 80, 100 Hz). Protocol repeatability was evaluated using intraclass correlation coefficients (ICC) with a two-way random effects model.Results Eleven healthy participants (7 males, 4 females; mean age 35 ± 10 years; BMI 22 ± 4 kg/m 2) were studied. MVC fell from 276 ± 166 N at baseline to 253 ± 160 N post-TES (p = 0.095). The force-frequency curve showed a characteristic sigmoidal shape (figure 1). At 100 Hz, mean (SD) evoked force decreased from 60 ± 46 to 40 ± 27 N (−34%), and at 30 Hz from 47 ± 36 to 22 ± 14 N (−54%). The mean (SD) tetanic force across all frequencies decreased from 38 ± 29 N pre-fatigue to 20 ± 13 N post-fatigue, corresponding to an absolute reduction of -17 ± 18 N and a relative reduction of -46 ± 31%. Stimulation threshold to elicit visible contraction was 7 ± 2 mA. Protocol repeatability was excellent (ICC = 0.86, 95% CI: 0.73–0.93; p < 0.001).Abstract S77 Figure 1Conclusion Fifteen minutes of continuous electrical stimulation applied to the TA led to consistent, measurable reductions in evoked muscle force, supporting the feasibility of using this protocol to model muscle fatigue in a controlled setting with implications for clinical applicability.