Acute aerobic exercise improves affective stats in patients with mental illnesses. Brain derived neurotropic factor (BDNF) may be a biological mechanism that contributes to the affective benefits. The magnitude of the increase of serum BDNF might be exercise intensity dependent, but no study has compared low high-aerobic-intensity training at 90-95 % of the maximal heart rate (HRmax) with long-slow-distance training at 70 % of the HRmax in patients with depression.