Katz 2019.

Study characteristics
Methods	Study design: multicentre 2‐year RCT comparing LVR (breathstacking exercises) as an add‐on to conventional treatment and conventional treatment alone* Study grouping: parallel‐group assignment 'Rescue' vs maintenance therapy: maintenance Ethics: no information regarding ethical review or informed consent was provided.
Participants	Baseline characteristics (entire sample, n = 67) Sample size, n: 67 Age in years, median: 11.4 Gender (male/female), n: 67/0 Diagnosis, n (%): DMD 67 (100) Baseline FVC (% predicted), median: 85.5% Percentage ambulatory: 31.9% Conventional treatment + LVR No separate group data were presented Conventional treatment No separate group data were presented Inclusion criteria Boys aged 6–16 years Diagnosed with DMD: confirmed by any of the following: muscle biopsy showing complete dystrophin deficiency; genetic test positive for deletion or duplication in the dystrophin gene resulting in an 'out‐of‐frame' mutation; or dystrophin gene sequencing showing a mutation associated with DMD. FVC ≥ 30% predicted A caregiver willing to provide the therapy Fluency in English or French Exclusion criteria Unable to perform pulmonary function tests or LVR manoeuvre, or both Presence of an endotracheal or tracheostomy tube Already using LVR or the Respironics in‐exsufflator between and during respiratory infections, or both Known susceptibility to pneumothorax or pneumomediastinum Uncontrolled asthma or other obstructive lung disease Symptomatic cardiomyopathy (ejection fraction < 50%)
Interventions	Conventional treatment This could have included: physiotherapy, consisting of percussion, active cycle of breathing, postural drainage, or a combination; nutritional support, consisting of oral or tube‐fed dietary supplements; antibiotics (oral or intravenous), if there was evidence of respiratory infection; NIPPV, if there was evidence of nocturnal hypoventilation or sleep‐disordered breathing; systemic steroids. LVR (breathstacking) Participants were instructed to use LVR (breathstacking) twice per day, using an inexpensive, portable self‐inflating resuscitation bag containing a 1‐way valve and mouthpiece. Details regarding the number of repetitions/sets per session were not provided. Duration: 2 years
Outcomes	Primary outcome measures Relative decline in FVC (% predicted) over 2 years, measured according to American Thoracic Society standards, using the Stanojevic normative equations (time frame 2 years) Secondary outcome measures Time to FVC decline of 10% of predicted (time frame 2 years) Total number and duration of outpatient oral antibiotic courses, hospital and ICU admissions for respiratory exacerbations over 2 years Health‐related quality of life over 2 years: measured biannually with Pediatric Quality of Life Inventory 4.0 Change in unassisted PCF over 2 years Change in MIC over 2 years Change in MIP over 2 years Change in Pe max over 2 years Other outcome measures Maximal and mean pressure achieved with LVR (cmH2O) (time frame 2 years) Respiratory symptoms: assessed every 3 months by telephone and personnel interview at clinic visits. A self‐report usage diary was given to participants to record daily activities to help with recall at the telephone follow‐ups Satisfaction with LVR, as assessed every 3 months by telephone Adverse events: not listed as a primary or secondary outcome in the published protocol, but were reported in the abstract. It is unclear what adverse events were monitored or recorded.
Identification	Funding source: Children's Hospital of Eastern Ontario Conflict of interest: Craig Campbell declared a "Scientific Medical Advisor relationship with Biogen, Genzyme, PTC Therapeutics" and Sherri Katz disclosed a financial speaker relationship with Biogen. Unclear how declared interests may have influenced the study. Country: Canada Setting: participants were recruited from 9 tertiary care paediatric hospitals across Canada. Interventions were conducted at the participants' homes. Comments: none First author name: Sherri Katz Institutions: Canadian study sites listed on the protocol: Alberta Children's Hospital; Stollery Children's Hospital; BC Children's Hospital; McMaster University; London Health Sciences; Children's Hospital of Eastern Ontario; Holland Bloorview Kids Rehabilitation Hospital; SickKids Hospital; Hôpital Ste. Justine Email: not provided Address: not provided
Notes	*Information was sourced from a published abstract of findings as well as from ClinicalTrials.org. Adherence to all aspects of the published protocol could not be assessed based on the published abstract. No contact information was available on either the abstract or protocol; however, a current email address of the corresponding author was identified using "Google" search and she was contacted (unsuccessfully) for additional information.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "multi‐centre randomized controlled trial." Quote: "Participants were allocated with a minimisation procedure to receive conventional treatment or conventional treatment plus twice daily lung volume recruitment exercises." Comment: unclear whether the minimisation procedure biased the randomisation procedure, as there was insufficient methodological information.
Allocation concealment (selection bias)	Unclear risk	Comment: no information provided on allocation concealment
Blinding of participants and personnel (performance bias) All outcomes	High risk	Quote: "Single (Investigator) blinding." Comment: no information provided regarding participant blinding; however, considering they were randomised to receiving breathstacking with standard care or standard care alone, blinding of participants seems unlikely to have been achievable.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Comment: study was described as single blinded, but there was no description provided of how blinding was maintained.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Quote: "Primary analysis was by intention to treat." Quote: "Multiple imputation was used to account for longitudinal missing data." Comment: there was no indication of dropout numbers or reasons for loss to follow‐up.
Selective reporting (reporting bias)	High risk	Comment: published protocol listed numerous outcome measures. Only FVC, time to 10% decline in FVC, and adverse events (adverse events was not an a priori listed outcome measure) were reported in the published abstract.
Other bias	Unclear risk	Comment: insufficient detail provided in the description of interventions.