Abstract Background Disorders of airway protection, including impaired cough and swallowing, are clinically important complications of Parkinson’s disease. Expiratory muscle strength training (EMST) is an established non-pharmacological intervention targeting these deficits. The aim of this study was to evaluate the acute effect of visual feedback provided by the SpiroGym mHealth app on expiratory muscle activation during EMST in people with Parkinson’s disease. Methods We conducted a single-center, randomised, two-period crossover trial in people with Parkinson’s disease. Participants performed EMST under two conditions, in randomised order: conventional EMST without visual feedback and EMST with real-time visual feedback provided by the SpiroGym app. Expiratory muscle activation was measured using surface electromyography of the abdominal muscles. The primary outcome was the within-participant difference in mean peak normalised internal oblique activity between conditions. Secondary outcomes included external oblique and rectus abdominis activity, associations with neuropsychiatric symptoms, and participant-reported usability ratings. Results Twenty participants were randomised, and 19 completed the study and were included in the final analysis. No study-related adverse events occurred. Visual feedback significantly increased mean peak normalised internal oblique activity compared with no feedback (118.2 ± 36.4% vs. 90.5 ± 23.0% of reference voluntary contraction; p < 0.001; Cohen d = 0.95). Without feedback, internal oblique activation significantly declined from 100.1 ± 22.2% in the first set to 84.4 ± 25.5% in the fifth set, whereas it remained stable with feedback (120.3 ± 29.4% to 119.9 ± 40.6%). External oblique activation was also significantly higher with feedback (122.2 ± 38.1% vs. 100.9 ± 32.4%; p = 0.002; Cohen d = 0.66), while rectus abdominis activation did not differ significantly between conditions (105.2 ± 41.3% vs. 90.2 ± 36.1%; p = 0.06; Cohen d = 0.43). No significant associations between feedback responsiveness and depression, apathy, or anxiety were detected. Participants rated the visual feedback as easy to understand and helpful for EMST performance. Conclusions Real-time visual feedback delivered by the SpiroGym app acutely increased and stabilized expiratory muscle activation during EMST in people with Parkinson’s disease. Trial registration ClinicalTrials.gov NCT06942533, 1 May 2025.
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