35 participants diagnosed with major depressive disorder were randomized in 3 intervention groups: (1) aerobic exercise (AE) ; (2) placebo (stretching) exercise (ST); and (3) no intervention (control group; NI). The intervention length was 10 consecutive days. In groups 1 (aerobic exercise) and 2 (sham exercise), participants exercised for 30 minutes each day. Depressive symptoms were assessed the day before the beginning of intervention and the day after the end of intervention for participants of both groups.

In the aerobic exercise (AE) group, the intervention consisted of 30 minutes of daily brisk walking or jogging. This was done individually and supervised. Participants who missed > 2 training sessions were considered as non-completers. Exercise intensity had to be maintained within 65%-75% of age-predicted maximal heart rate, as commonly prescribed in studies using aerobic exercise to alleviate depression. Heart rate monitoring devices were used.

Participants in the stretching (ST) group also performed a daily 30 minutes exercise program but this was "sham" exercise, consisting of stretching exercises. Several muscle groups (thighs, calves, gluteal, shoulders, back) were stretched for 60 seconds, with equivalent resting intervals between stretching series. These activities were also individual and supervised. As was the case for the AE intervention, participants who missed > 2 training sessions were considered as non-completers.

Participants in the control (NI) group received no intervention other than prescribed medication.

All participants started antidepressants within less than 2 weeks before study entry.

Inclusion Criteria:

• diagnosis of major depressive disorder (MDD)
• antidepressant drug therapy initiated for less than 2 weeks
• score of 29 or more on the Beck depression inventory

Exclusion Criteria:

• medical contraindication for exercise practice
• inability to understand written French
• beta-blocking drugs or another forms of antidepressant therapy (sleep deprivation, electroconvulsive therapy)