Table 1 Inclusion and exclusion criteria

 ≥ 18 and ≤ 65 years old

Results of the trial should be generalizable to the working age population. Furthermore, there can be numerous reasons for sleep disorders in older patients [68]

 Primary diagnosis of depression (F32, F33) without psychotic episode according to ICD-10

Mental disorder used to define the sample

 Regular use of hypnotic agents* (patients are included if no hypnotic agents were taken two weeks before study participation)

Use of hypnotic agents might mask the effect of aerobic exercise on sleep

 Factors precluding exercise testing or training

For safety reasons, patients who have any condition which precludes exercise testing or training are excluded. Absolute and relative contraindications are based on ACSM’s Guidelines for Exercise Testing and Prescription [69]

 Use of beta-blockers (except carvedilol and nebivolol)

Except for carvedilol and nebivolol [70, 71], beta-blockers have been shown to reduce nocturnal melatonin levels [70, 72, 73]

 Use of opioids

Opioids affect sleep architecture [74]

 History of epilepsy

Epilepsy is associated with quantitative and qualitative alterations of sleep [75] and might, therefore, mask the intervention effects

 Restless legs syndrome defined by ≥ 7 points on the restless legs screening questionnaire [76]

Can also cause sleep disturbance, but the etiology is distinct from depression [77]

 Moderate or severe sleep apnea defined by an oxygen desaturation index (ODI) ≥ 15 in the first polysomnography

Sleep apnea is a distinct sleep disorder with clearly delineated etiology. ODI has been shown to be highly correlated with the apnea-hypopnea index and to detect sleep apnea with high sensitivity and specificity [78,79,80]

 Morbid adiposity with BMI > 40

These patients might suffer from hypoventilation syndrome which affects sleep