I'm seconding Dave Bacon's post. Your diaphragm is an involuntary muscle and it relaxes on exhale whether another trumpet player says it does or not. If you don't believe me, ask a doctor or anyone who has taken physiology. Read 'Song and Wind' by Jacobs, or 'Teaching Brass' by Kristian Steenstrup. They've done their homework about how the body actually functions in general and then how that applies to playing an instrument. If you have tension in your system your tone, range and speed will suffer for it.