This section should specify the details about types of participants considered for the review, for example, age; gender; ethnicity; diagnosis; diagnostic criteria; stage or severity of the disease; co-existing diseases. What are the most important characteristics of the population? (e.g., age, disease/condition, severity of illness, setting, gender, etc.).

Consider the following example regarding COPD, describe the population (patients with COPD), the severity of illness (moderate-to-severe), trajectory of the disease (stable), with a specific setting (community dwelling). Diagnostic criteria should be made clear to allow inclusion and exclusion; if reviewers anticipate subgroup analysis related to population characteristics, these subgroups should be reflected in the population inclusion criteria. For example, ‘COPD includes patients with chronic bronchitis and emphysema but not asthma (fixed airway obstruction with forced expiratory volume in one second [FEV1] less than <80% of predicted). According to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) and the American Thoracic/European Respiratory Society Guidelines (ATS/ERS), the description of the severity of disease is as follows: stage II or moderate disease is an FEV1 of 50-80% predicted; stage III or severe is an FEV1 of 30-50% predicted and stage IV or very severe is an FEV1 <30% predicted. Patients with reversible airway disease (improvement in FEV1 >20% with fast acting bronchodilator) will be excluded because their response to training may relate more to changes in their airway obstruction than a training effect.’ Specific reference to population characteristics, either for inclusion or exclusion should be based on a clear, scientific justification rather than based on unsubstantiated clinical, theoretical or personal reasoning.