Effects of Holding Breath?

End of class Oshima Sensei would have us go through exertional stuff and then line up in seiza and start kokyuho, always challenging us to regain breath under voluntary control (involved holding breath if one could not inhale or exhale slow enough to his clappers pace). Pranayama in yoga does not introduce breath retention (in combo w/ locks, chin and anus) till a more advanced stage. Both have the same goal, what is commonly considered an autonomic function is brought under mental control, breath being the easiest starting place...then heart rat, BP and so on. Effects of breath practice (Pranayama) esp retention w/o an Experienced Guru according to the tenants of yoga can be dangerous. Gurudev Amrit Desai has helped me along my path. Note books on Pranayama by Iengyar.

I have also been introduced to breath control/holding breath exercises (chi gung and also yoga - related but different techniques). There can be positive benefits with stamina, speed, coordination, focus etc.. I wouldn't experiment on my own with it (waste of time), you need a skilled teacher to get any benefit IMO. I've also heard it could be dangerous if not done right (maybe, but I never heard of anyone die from breathing exercises or even holding their breath).

What do you mean? Elvis Lives!

Elvis died holding his breath to strain for a BM (breath hold and increased abdominal pressure is called the valsalva maneuver and is the first method by ER Docs to convert ventricular tachycardia, the valsalva stimulates the vagus nerve to slow heart rate) as his HR was already slow due to barbiturate use, he became bradycardic and died...on the Throne. Jim Morrison Lives, we hang out at times.
Qi Gong is an amazing thing, prior to Ba Gua, Master Huang would always spend 1-2 hrs as prep for internal work. Amazing how seemingly simple movements or postures w/ breath training will heat up the body.

Note, question to all at asterisks please reply.
I think the posts on holding breath (from possible improvement or lack thereof of physiologic increase of lung capacity/oxygen exchange at the alveolar level to the possible/definitive dangers esp without a very experienced Teacher) have all been straight on target.
***To Joe7987 and any interested to comment. I love Qi Gong now that I've experienced this internal energy/healing style in the presence of Master Wei Lun Huang (huangtaichi.com) the variety and intensity w/ explanation of proper breathing and visualization of energy movement, so like Yoga (in movement one is still and in stillness exists movement). Gurudev Amrit is less and less available personally as he prepares to enter a final seclusion of meditation in preparation for "that journey from which no man hath returned".
*** Is just me?? I can only seem to truly enjoy and feel benefit from Qi Gong practice if Master Huang is physically present (its not just that trying to do Incense Chi Kung is so complex,and it is full) and as in the practice of Zen Buddhism I feel a total difference alone vs. having been part of the Sangha at Mountian and Rivers order in the catskills. I just wonder if I have not practiced enough and like a child need the Parent and Family??? Long time w/ Gurudev and solitary practice was what I wanted. any thoughts????

OK, maybe my last post didnt deserve response.
Chi Kung_ In the variety of chi kung w/ Master Huang I have not encountered holding the breath unless one counts either the obligatory exaggerated swallowing of saliva collected during practice (tip of tongue to palate) or the momentary hold at peak inspiration and expiration during preparation for chi kung (and same prep prior to Ba Gua) where visualization of movement of energy is raising and lowering through energy channels and looking within for imbalances(Inhale palms rise up,exhale as palms face down,inhale and expand, exhale and compress)...otherwise breathing was to be in through nostrils out through mouth, and even with a static pose like (Love these names) "Monkey awaits Peach" or end of lion chi kung ("lion shakes his mane") where the simple direction to keep hands in lion claw tight and "just relax and shake" if you dont breath like a bellows you wont last to the next.
Yoga_ Yoga Pranayama practice begins without breath hold, as student learns to move energy through the energy channels in the spine and using nostril closing balance the Ida and Pingale (Yn/and yang) channels of spine (a familiar autonomic function one has probably already noticed, the cycle of one nostril dominant (more open) the other passive less open or even clogged. Breath holding is practiced w/ energy locks (Physical restrictions on primary areas of body where energy is lost) to build internal energy in preparation to awaken kundalini shakti and begin to raise to the crown chakra, Not unlike chi kung and the jade nectar mentioned above. Yoginda back to time immemorial have cautioned the unwary (read, no teacher, not ready, not practicing ridding excess energy after practice, abusing the accumulated energy) that headaches, illness, insanity and even death are possible.
Buddhism_ Other than development of internal energy, control of the breath is the first control of a generally autonomic function, control of the breath requires focus, focus is required for meditation and the transformation of the Mind. This part is outrageous, His Holiness the Dalai Lama has written that meditation can begin when one can focus "vividly and continuously for Four hours,stability can be said to be achieved" paraphrase from "How to Practice" HH the 14th Dalai Lama pg127, there is no mention of breath holding.