 blood flow reduces the amount of oxygen carried to muscle cells in the chronically tense areas, thus causing a reduction in energy in those constricted areas. Tense muscles also squeeze nerves, and affect the smooth flow of bioelectrical signals along neural pathways, leading to an additional reduction in the overall energy of the tensed area and an overall state of lowered energies which can eventually lead to depression.
In summary, while in a chronically tense condition we feel less than we could be feeling, and we block the energizing functions of our body and hence live at a lowered energy state which then just slowly deteriorates into the state called depression.
Keeping muscles chronically tense is the work of our subconscious mind. That's why we're not even aware we're doing it. Basically, our subconscious is doing its best to protect us from difficult feelings, and it often started doing it when we were pre-rational.
That's the problem; because the chronic tension was invoked at a pre-rational level, it doesn't respond to reason. That's why talk therapies don't completely solve the problem. We can completely understand why we feel the way we do, but we are powerless to overcome the fear-based defence mechanism, chronic muscular tension, used by our subconscious mind.
Bioenergetic therapy (http://www.Bioenergetic-Therapy.com), a mind/body psychotherapy that aims at helping us discover our own tenseness, is an effective tool in overcoming the issue of chronic tension. Once we can feel our tense muscles, we can start the process of releasing them. Once they're loose, energy flow increases and depression disappears.
In summary, suppressed emotions often cause depression, and, vice versa, the expression of emotions can help prevent depression from occurring.
A medical intuitive and distance healer (http://www.CoherentHealing.com) whose more that 20 years experience in the field has convinced him that not only depression, but also many of the physical pathologies he encounters are the body's physical response to suppressed emotions.