Is improved fitness following a 12-week exercise program associated with decreased symptom severity, better wellbeing, and fewer sleep complaints in patients with major depressive disorders? A secondary analysis of a randomized controlled trial.

Major depressive disorder (MDD) is one of the most burdensome disorders worldwide. While exercise training in patients with MDD contributes to clinically relevant improvements in cardiorespiratory fitness, whether and to what degree changes in cardiorespiratory fitness impact depressive symptom severity has not yet been addressed systematically in prior research. The purpose of our study was threefold. Firstly, to examine whether baseline levels and improvements in objectively assessed VOmax and subjectively perceived fitness predicted endpoint levels and change in depressive symptoms, wellbeing and sleep. Secondly, to determine whether exercise modality (sprint interval training [SIT]) versus continuous aerobic exercise training [CAT]) predicted depressive symptoms, wellbeing and sleep. Thirdly, whether the affective responses during and following exercise predicted depressive symptoms, wellbeing and sleep. All measurements were taken in a sample of inpatients diagnosed with MDD. The sample consisted of 53 participants (41 women and 12 men, M = 36.3 years, SD = 11.3) with unipolar depression who were randomly assigned to SIT and CAT. Data were assessed at baseline and after four weeks of exercise training (including three weekly 35 min sessions). Multiple linear regression analyses showed that improvements in VOmax were associated with fewer depressive symptoms, better mental wellbeing, and better sleep after completion of the intervention. Additionally, improvements in perceived fitness were associated with fewer dysfunctional sleep-related cognitions and higher mental toughness post-intervention. Improvements in VO2max and perceived fitness were also associated with favorable changes in depressive symptoms, mental wellbeing, and sleep. More research is needed to find out which fitness tests are most time- and cost-efficient in a clinical setting and most acceptable for psychiatric patients.