Breathing: how deep is too deep? Why do I want to increase and decrease stress at the same time?

I listened to track 4, “Deep Breathing” of Relax; 6 Techniques to Lower Your Stress with Daniel Goleman to focus my morning practice today.  I felt some hesitation to use this CD in my morning practice.  I’ve been practicing for years after all- I could give meditation instruction.  Do I really need a CD?  However, I decided to be open and see what I could learn from it.    

Goleman starts by explaining that when we feel tension, we make our breathing more shallow and fast.  He provides simple instructions to put my hand on my belly, deeply breathe in relaxation and breath out tension.  I found the instruction and practice to be a helpful thing to which to return when my mind started to drift.  I started to breath deeper and longer than he was suggesting and actually found that made me winded, so I slowed it down.  I tried to keep my attention on the practice while also letting other thoughts, emotions or sensations flow through me.  I remembered I was planning to make a phone call to a government agency that I was feeling anxiety about.  I observed the desire to make my breath more shallow and used a touch of effort to deepen it.  At another point, the sun rose to a point where it was gently shining on my face.  In this case, it eased and supported my relaxation practice.   I made a phone call to a government agency.  At the end of the practice, he recommends keeping the practice throughout the day.  I kept my hand on my belly when I made the actual phone call and simply observed how shallow my breath really got.  I then deepened my breath slightly.  

      

I understand that meditation and yoga lower stress hormones like Adrenaline and Cortisol.  I also understand that psychologists differentiation between good stress (eustress) and bad stress (distress).  I enjoy what I understand to be an adrenaline rush when I go on a roller coaster or mountain bike down a hill, or face a work challenge that I consider meaningful and manageable.  Why would I seek to increase Adrenaline in some circumstances (while biking) and decrease it in others (while meditating)?  To me, biking and meditating seem to compliment each other as part of a balanced life, but are they actually working in opposition to each other?