Q: What are the psychological benefits of exercise, and how much exercise at what intensity is needed to reap those benefits?

A: That's a great question, and one which is very personal. You need to become the expert on yourself. Become the scientist and do the research. How much exercise do you need, and to what intensity, to feel the benefits?

A good way to explore this is to keep a mood journal. Before you exercise, pick up your mood journal and describe the mood you are in at that very moment. Then, after your exercise, describe the mood you are in. Vary your exercise time and the intensity to see the impacts.

The science of exercise, mood and stress teaches us two main things: at a certain level of intensity (varying for each of us), our bodies produce mood-elevating endorphins. So exercise provides a "natural high" that combats depression and actually reduces our perception of pain.

Also, exercise "uses up" a lot of the chemicals that we produce in the "fight or flight" stress response. After all, the function of fight or flight is to optimize our ability to — drum roll - fight or run away. If we don't get active, but just let our minds "run away with us," we fill our bodies with toxic substances that hang around and drag us down.

One variable that clearly affects how exercise impacts your moods is what you focus on during the exercise. Are you on stairmaster watching news about a recent terrorist bombing? You might leave your exercise in a worse mood. Are you walking for 10 minutes in nature listening to the birds sing and the wind rustle through the treets? That might affect your mood quite quickly, even at much lower intensity.

By the way, your mood is deeply affected by what you eat as well. Too much sugar can decimate the mood impact of a hearty walk along the beach. When it comes to the psycological impact of health, it's critical to focus on the whole picture of the mood, not just the isolated exercise segment.

Research has shown that people are fueled not just by food and exercise but by challenge, relationships, and other factors. Being able to complete a challenging jog that was too hard for you a month ago can do wonders for your mood. Likewise, taking a walk with a friend — or even holding a "walking meeting" at work — can lift your spirits and reduce stress.

So go out there, play with the variables, discover new ones (and post them on this board), and see what works best for you. Share your studies!