The RESISTANT study (Respiratory Muscle Training in Patients with Spinal Muscular Atrophy): results of a randomized controlled trial

Objectives: To investigate the efficacy and feasibility of respiratory muscle training (RMT) in patients with spinal muscular atrophy (SMA) and respiratory muscle weakness. Design: A 4-month, single-blinded RCT, followed by an 8-month extension phase. Setting: The outpatient clinic of the Neurology department and the Child Development and Exercise Center at the University Medical Center Utrecht, The Netherlands. Participants: 30 participants, ≥eight years, SMA type 1 to 4, and respiratory muscle weakness. Interventions: The training group started RMT at 30% of their maximum inspiratory (PImax) and expiratory pressure (PEmax) and adjusted their training intensity based on perceived exertion. The control group started and continued RMT at 10% of PImax and PEmax. After four months, the control group received the same RMT as the training group. Main outcome measures: The primary outcome was the between-group difference in PImax after the RCT phase. Additionally, we explored the association between training volume (i.e., number of training sessions x training intensity) and increase in PImax over 1 year. Results: 25 participants completed the study. Mean PImax after four months (corrected for baseline value) training group: 61.1 cmH₂O, control group: 54.3 cmH₂O, mean difference in PImax: 6.8 cmH₂O [95% CI: −2.0 to 15.6]. Despite the study being underpowered, we did find an association between training volume and increase in PImax (R² = 0.531). Conclusion: There was a small between-group difference in PImax after the RCT phase. The training was safe, but the feasibility of the training needs further improvement. Clinical Trial Registration Number: NL73280.041.20. Contribution of the Paper: • There was a small difference in PImax improvement between training at different intensities (10% vs 30% of PImax). • Higher training volume (frequency times intensity) is associated with improvement of inspiratory muscle strength. • Supervision (by physiotherapists) might contribute to better adherence to respiratory muscle training.