Zanotti 2003.

Methods	Randomised controlled trial
Participants	24 participants were enrolled. All participants had chronic hypercapnic respiratory failure due to COPD, needed mechanical ventilation via a tracheostomy and had marked muscle atrophy. They had been referred to a high dependency unit from an ICU and had been confined to bed for ≥ 30 days. However, they were clinically stable. 12 were allocated to the intervention group (9 men, mean age = 66 (SD 8) yr). 12 were allocated to the control group (8 men, mean age = 64 (SD 4) yr).
Interventions	All participants received rehabilitation, which comprised active limb exercises 5 days per week, twice per day for 4 weeks. Each session was conducted for the maximum time that could be tolerated, up to a maximum of 30 minutes. Intervention: rehabilitation + bilateral electrical stimulation of the quadriceps and vastus glutei for 30 min using a bipolar, biphasic, asymmetric, rectangular pulse. Each session comprised 5 min at frequency of 8 Hz, and a pulse width of 250 µs. This was followed by 25 min of stimulation at 35 Hz for 350 µs. Control: rehabilitation without any stimulation
Outcomes	Quadriceps strength measured via manual muscle testing Cardiorespiratory variables such as heart rate and arterial oxygen saturation at the beginning and end of treatment Functional outcomes such as the number of days needed to transfer from bed to chair
Notes	Funding support not stated
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "The patients were randomly assigned…" Details pertaining to the development of the randomisation sequence were not reported.
Allocation concealment (selection bias)	Unclear risk	No details given
Blinding of participants and personnel (performance bias) All outcomes	High risk	Although the rehabilitation (provided to both groups) was overseen by a therapist who was unaware of the aim of the study, there was no mention of any attempt to blind participants or other study personnel. The control group did not receive a sham intervention. Unlikely that the investigators administering the electrical stimulation were blinded to group allocation, but the risk of bias from this was low.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	No mention of blinding for outcome assessors. A lack of blinding of the outcome assessors was unlikely to have affected outcomes related to cardiorespiratory function collected at the beginning and the end of treatment, but may have affected outcomes such as muscle strength and attainment of functional milestones.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Insufficient details on attrition to comment on whether this was a source of bias.
Selective reporting (reporting bias)	Unclear risk	No protocol available
Other bias	Low risk	Study appeared free from other sources of bias.